diff -r 4e648a2d8480 -r 7893d1012580 src/hotspot/share/gc/cms/concurrentMarkSweepGeneration.cpp --- a/src/hotspot/share/gc/cms/concurrentMarkSweepGeneration.cpp Thu Nov 14 12:38:31 2019 +0000 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,8145 +0,0 @@ -/* - * Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved. - * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. - * - * This code is free software; you can redistribute it and/or modify it - * under the terms of the GNU General Public License version 2 only, as - * published by the Free Software Foundation. - * - * This code is distributed in the hope that it will be useful, but WITHOUT - * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or - * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License - * version 2 for more details (a copy is included in the LICENSE file that - * accompanied this code). - * - * You should have received a copy of the GNU General Public License version - * 2 along with this work; if not, write to the Free Software Foundation, - * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. - * - * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA - * or visit www.oracle.com if you need additional information or have any - * questions. - * - */ - -#include "precompiled.hpp" -#include "classfile/classLoaderDataGraph.hpp" -#include "classfile/systemDictionary.hpp" -#include "code/codeCache.hpp" -#include "gc/cms/cmsGCStats.hpp" -#include "gc/cms/cmsHeap.hpp" -#include "gc/cms/cmsOopClosures.inline.hpp" -#include "gc/cms/cmsVMOperations.hpp" -#include "gc/cms/compactibleFreeListSpace.hpp" -#include "gc/cms/concurrentMarkSweepGeneration.inline.hpp" -#include "gc/cms/concurrentMarkSweepThread.hpp" -#include "gc/cms/parNewGeneration.hpp" -#include "gc/cms/promotionInfo.inline.hpp" -#include "gc/serial/genMarkSweep.hpp" -#include "gc/serial/tenuredGeneration.hpp" -#include "gc/shared/adaptiveSizePolicy.hpp" -#include "gc/shared/cardGeneration.inline.hpp" -#include "gc/shared/cardTableRS.hpp" -#include "gc/shared/collectedHeap.inline.hpp" -#include "gc/shared/collectorCounters.hpp" -#include "gc/shared/gcLocker.hpp" -#include "gc/shared/gcPolicyCounters.hpp" -#include "gc/shared/gcTimer.hpp" -#include "gc/shared/gcTrace.hpp" -#include "gc/shared/gcTraceTime.inline.hpp" -#include "gc/shared/genCollectedHeap.hpp" -#include "gc/shared/genOopClosures.inline.hpp" -#include "gc/shared/isGCActiveMark.hpp" -#include "gc/shared/owstTaskTerminator.hpp" -#include "gc/shared/referencePolicy.hpp" -#include "gc/shared/referenceProcessorPhaseTimes.hpp" -#include "gc/shared/space.inline.hpp" -#include "gc/shared/strongRootsScope.hpp" -#include "gc/shared/taskqueue.inline.hpp" -#include "gc/shared/weakProcessor.hpp" -#include "gc/shared/workerPolicy.hpp" -#include "logging/log.hpp" -#include "logging/logStream.hpp" -#include "memory/allocation.hpp" -#include "memory/binaryTreeDictionary.inline.hpp" -#include "memory/iterator.inline.hpp" -#include "memory/padded.hpp" -#include "memory/resourceArea.hpp" -#include "memory/universe.hpp" -#include "oops/access.inline.hpp" -#include "oops/oop.inline.hpp" -#include "prims/jvmtiExport.hpp" -#include "runtime/atomic.hpp" -#include "runtime/flags/flagSetting.hpp" -#include "runtime/globals_extension.hpp" -#include "runtime/handles.inline.hpp" -#include "runtime/java.hpp" -#include "runtime/orderAccess.hpp" -#include "runtime/timer.hpp" -#include "runtime/vmThread.hpp" -#include "services/memoryService.hpp" -#include "services/runtimeService.hpp" -#include "utilities/align.hpp" -#include "utilities/stack.inline.hpp" -#if INCLUDE_JVMCI -#include "jvmci/jvmci.hpp" -#endif - -// statics -CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL; -bool CMSCollector::_full_gc_requested = false; -GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc; - -////////////////////////////////////////////////////////////////// -// In support of CMS/VM thread synchronization -////////////////////////////////////////////////////////////////// -// We split use of the CGC_lock into 2 "levels". -// The low-level locking is of the usual CGC_lock monitor. We introduce -// a higher level "token" (hereafter "CMS token") built on top of the -// low level monitor (hereafter "CGC lock"). -// The token-passing protocol gives priority to the VM thread. The -// CMS-lock doesn't provide any fairness guarantees, but clients -// should ensure that it is only held for very short, bounded -// durations. -// -// When either of the CMS thread or the VM thread is involved in -// collection operations during which it does not want the other -// thread to interfere, it obtains the CMS token. -// -// If either thread tries to get the token while the other has -// it, that thread waits. However, if the VM thread and CMS thread -// both want the token, then the VM thread gets priority while the -// CMS thread waits. This ensures, for instance, that the "concurrent" -// phases of the CMS thread's work do not block out the VM thread -// for long periods of time as the CMS thread continues to hog -// the token. (See bug 4616232). -// -// The baton-passing functions are, however, controlled by the -// flags _foregroundGCShouldWait and _foregroundGCIsActive, -// and here the low-level CMS lock, not the high level token, -// ensures mutual exclusion. -// -// Two important conditions that we have to satisfy: -// 1. if a thread does a low-level wait on the CMS lock, then it -// relinquishes the CMS token if it were holding that token -// when it acquired the low-level CMS lock. -// 2. any low-level notifications on the low-level lock -// should only be sent when a thread has relinquished the token. -// -// In the absence of either property, we'd have potential deadlock. -// -// We protect each of the CMS (concurrent and sequential) phases -// with the CMS _token_, not the CMS _lock_. -// -// The only code protected by CMS lock is the token acquisition code -// itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the -// baton-passing code. -// -// Unfortunately, i couldn't come up with a good abstraction to factor and -// hide the naked CGC_lock manipulation in the baton-passing code -// further below. That's something we should try to do. Also, the proof -// of correctness of this 2-level locking scheme is far from obvious, -// and potentially quite slippery. We have an uneasy suspicion, for instance, -// that there may be a theoretical possibility of delay/starvation in the -// low-level lock/wait/notify scheme used for the baton-passing because of -// potential interference with the priority scheme embodied in the -// CMS-token-passing protocol. See related comments at a CGC_lock->wait() -// invocation further below and marked with "XXX 20011219YSR". -// Indeed, as we note elsewhere, this may become yet more slippery -// in the presence of multiple CMS and/or multiple VM threads. XXX - -class CMSTokenSync: public StackObj { - private: - bool _is_cms_thread; - public: - CMSTokenSync(bool is_cms_thread): - _is_cms_thread(is_cms_thread) { - assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(), - "Incorrect argument to constructor"); - ConcurrentMarkSweepThread::synchronize(_is_cms_thread); - } - - ~CMSTokenSync() { - assert(_is_cms_thread ? - ConcurrentMarkSweepThread::cms_thread_has_cms_token() : - ConcurrentMarkSweepThread::vm_thread_has_cms_token(), - "Incorrect state"); - ConcurrentMarkSweepThread::desynchronize(_is_cms_thread); - } -}; - -// Convenience class that does a CMSTokenSync, and then acquires -// upto three locks. -class CMSTokenSyncWithLocks: public CMSTokenSync { - private: - // Note: locks are acquired in textual declaration order - // and released in the opposite order - MutexLocker _locker1, _locker2, _locker3; - public: - CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1, - Mutex* mutex2 = NULL, Mutex* mutex3 = NULL): - CMSTokenSync(is_cms_thread), - _locker1(mutex1, Mutex::_no_safepoint_check_flag), - _locker2(mutex2, Mutex::_no_safepoint_check_flag), - _locker3(mutex3, Mutex::_no_safepoint_check_flag) - { } -}; - - -////////////////////////////////////////////////////////////////// -// Concurrent Mark-Sweep Generation ///////////////////////////// -////////////////////////////////////////////////////////////////// - -NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;) - -// This struct contains per-thread things necessary to support parallel -// young-gen collection. -class CMSParGCThreadState: public CHeapObj { - public: - CompactibleFreeListSpaceLAB lab; - PromotionInfo promo; - - // Constructor. - CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) { - promo.setSpace(cfls); - } -}; - -ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration( - ReservedSpace rs, - size_t initial_byte_size, - size_t min_byte_size, - size_t max_byte_size, - CardTableRS* ct) : - CardGeneration(rs, initial_byte_size, ct), - _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))), - _did_compact(false) -{ - HeapWord* bottom = (HeapWord*) _virtual_space.low(); - HeapWord* end = (HeapWord*) _virtual_space.high(); - - _direct_allocated_words = 0; - NOT_PRODUCT( - _numObjectsPromoted = 0; - _numWordsPromoted = 0; - _numObjectsAllocated = 0; - _numWordsAllocated = 0; - ) - - _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end)); - NOT_PRODUCT(debug_cms_space = _cmsSpace;) - _cmsSpace->_old_gen = this; - - _gc_stats = new CMSGCStats(); - - // Verify the assumption that FreeChunk::_prev and OopDesc::_klass - // offsets match. The ability to tell free chunks from objects - // depends on this property. - debug_only( - FreeChunk* junk = NULL; - assert(UseCompressedClassPointers || - junk->prev_addr() == (void*)(oop(junk)->klass_addr()), - "Offset of FreeChunk::_prev within FreeChunk must match" - " that of OopDesc::_klass within OopDesc"); - ) - - _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC); - for (uint i = 0; i < ParallelGCThreads; i++) { - _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace()); - } - - _incremental_collection_failed = false; - // The "dilatation_factor" is the expansion that can occur on - // account of the fact that the minimum object size in the CMS - // generation may be larger than that in, say, a contiguous young - // generation. - // Ideally, in the calculation below, we'd compute the dilatation - // factor as: MinChunkSize/(promoting_gen's min object size) - // Since we do not have such a general query interface for the - // promoting generation, we'll instead just use the minimum - // object size (which today is a header's worth of space); - // note that all arithmetic is in units of HeapWords. - assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking"); - assert(_dilatation_factor >= 1.0, "from previous assert"); - - initialize_performance_counters(min_byte_size, max_byte_size); -} - - -// The field "_initiating_occupancy" represents the occupancy percentage -// at which we trigger a new collection cycle. Unless explicitly specified -// via CMSInitiatingOccupancyFraction (argument "io" below), it -// is calculated by: -// -// Let "f" be MinHeapFreeRatio in -// -// _initiating_occupancy = 100-f + -// f * (CMSTriggerRatio/100) -// where CMSTriggerRatio is the argument "tr" below. -// -// That is, if we assume the heap is at its desired maximum occupancy at the -// end of a collection, we let CMSTriggerRatio of the (purported) free -// space be allocated before initiating a new collection cycle. -// -void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) { - assert(io <= 100 && tr <= 100, "Check the arguments"); - if (io >= 0) { - _initiating_occupancy = (double)io / 100.0; - } else { - _initiating_occupancy = ((100 - MinHeapFreeRatio) + - (double)(tr * MinHeapFreeRatio) / 100.0) - / 100.0; - } -} - -void ConcurrentMarkSweepGeneration::ref_processor_init() { - assert(collector() != NULL, "no collector"); - collector()->ref_processor_init(); -} - -void CMSCollector::ref_processor_init() { - if (_ref_processor == NULL) { - // Allocate and initialize a reference processor - _ref_processor = - new ReferenceProcessor(&_span_based_discoverer, - (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing - ParallelGCThreads, // mt processing degree - _cmsGen->refs_discovery_is_mt(), // mt discovery - MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree - _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic - &_is_alive_closure, // closure for liveness info - false); // disable adjusting number of processing threads - // Initialize the _ref_processor field of CMSGen - _cmsGen->set_ref_processor(_ref_processor); - - } -} - -AdaptiveSizePolicy* CMSCollector::size_policy() { - return CMSHeap::heap()->size_policy(); -} - -void ConcurrentMarkSweepGeneration::initialize_performance_counters(size_t min_old_size, - size_t max_old_size) { - - const char* gen_name = "old"; - // Generation Counters - generation 1, 1 subspace - _gen_counters = new GenerationCounters(gen_name, 1, 1, - min_old_size, max_old_size, &_virtual_space); - - _space_counters = new GSpaceCounters(gen_name, 0, - _virtual_space.reserved_size(), - this, _gen_counters); -} - -CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha): - _cms_gen(cms_gen) -{ - assert(alpha <= 100, "bad value"); - _saved_alpha = alpha; - - // Initialize the alphas to the bootstrap value of 100. - _gc0_alpha = _cms_alpha = 100; - - _cms_begin_time.update(); - _cms_end_time.update(); - - _gc0_duration = 0.0; - _gc0_period = 0.0; - _gc0_promoted = 0; - - _cms_duration = 0.0; - _cms_period = 0.0; - _cms_allocated = 0; - - _cms_used_at_gc0_begin = 0; - _cms_used_at_gc0_end = 0; - _allow_duty_cycle_reduction = false; - _valid_bits = 0; -} - -double CMSStats::cms_free_adjustment_factor(size_t free) const { - // TBD: CR 6909490 - return 1.0; -} - -void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) { -} - -// If promotion failure handling is on use -// the padded average size of the promotion for each -// young generation collection. -double CMSStats::time_until_cms_gen_full() const { - size_t cms_free = _cms_gen->cmsSpace()->free(); - CMSHeap* heap = CMSHeap::heap(); - size_t expected_promotion = MIN2(heap->young_gen()->capacity(), - (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average()); - if (cms_free > expected_promotion) { - // Start a cms collection if there isn't enough space to promote - // for the next young collection. Use the padded average as - // a safety factor. - cms_free -= expected_promotion; - - // Adjust by the safety factor. - double cms_free_dbl = (double)cms_free; - double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0; - // Apply a further correction factor which tries to adjust - // for recent occurance of concurrent mode failures. - cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free); - cms_free_dbl = cms_free_dbl * cms_adjustment; - - log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT, - cms_free, expected_promotion); - log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0); - // Add 1 in case the consumption rate goes to zero. - return cms_free_dbl / (cms_consumption_rate() + 1.0); - } - return 0.0; -} - -// Compare the duration of the cms collection to the -// time remaining before the cms generation is empty. -// Note that the time from the start of the cms collection -// to the start of the cms sweep (less than the total -// duration of the cms collection) can be used. This -// has been tried and some applications experienced -// promotion failures early in execution. This was -// possibly because the averages were not accurate -// enough at the beginning. -double CMSStats::time_until_cms_start() const { - // We add "gc0_period" to the "work" calculation - // below because this query is done (mostly) at the - // end of a scavenge, so we need to conservatively - // account for that much possible delay - // in the query so as to avoid concurrent mode failures - // due to starting the collection just a wee bit too - // late. - double work = cms_duration() + gc0_period(); - double deadline = time_until_cms_gen_full(); - // If a concurrent mode failure occurred recently, we want to be - // more conservative and halve our expected time_until_cms_gen_full() - if (work > deadline) { - log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ", - cms_duration(), gc0_period(), time_until_cms_gen_full()); - return 0.0; - } - return work - deadline; -} - -#ifndef PRODUCT -void CMSStats::print_on(outputStream *st) const { - st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha); - st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT, - gc0_duration(), gc0_period(), gc0_promoted()); - st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT, - cms_duration(), cms_period(), cms_allocated()); - st->print(",cms_since_beg=%g,cms_since_end=%g", - cms_time_since_begin(), cms_time_since_end()); - st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT, - _cms_used_at_gc0_begin, _cms_used_at_gc0_end); - - if (valid()) { - st->print(",promo_rate=%g,cms_alloc_rate=%g", - promotion_rate(), cms_allocation_rate()); - st->print(",cms_consumption_rate=%g,time_until_full=%g", - cms_consumption_rate(), time_until_cms_gen_full()); - } - st->cr(); -} -#endif // #ifndef PRODUCT - -CMSCollector::CollectorState CMSCollector::_collectorState = - CMSCollector::Idling; -bool CMSCollector::_foregroundGCIsActive = false; -bool CMSCollector::_foregroundGCShouldWait = false; - -CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen, - CardTableRS* ct): - _overflow_list(NULL), - _conc_workers(NULL), // may be set later - _completed_initialization(false), - _collection_count_start(0), - _should_unload_classes(CMSClassUnloadingEnabled), - _concurrent_cycles_since_last_unload(0), - _roots_scanning_options(GenCollectedHeap::SO_None), - _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"), - _verifying(false), - _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding), - _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding), - _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()), - _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()), - _cms_start_registered(false), - _cmsGen(cmsGen), - // Adjust span to cover old (cms) gen - _span(cmsGen->reserved()), - _ct(ct), - _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"), - _modUnionTable((CardTable::card_shift - LogHeapWordSize), - -1 /* lock-free */, "No_lock" /* dummy */), - _restart_addr(NULL), - _ser_pmc_preclean_ovflw(0), - _ser_pmc_remark_ovflw(0), - _par_pmc_remark_ovflw(0), - _ser_kac_preclean_ovflw(0), - _ser_kac_ovflw(0), - _par_kac_ovflw(0), -#ifndef PRODUCT - _num_par_pushes(0), -#endif - _span_based_discoverer(_span), - _ref_processor(NULL), // will be set later - // Construct the is_alive_closure with _span & markBitMap - _is_alive_closure(_span, &_markBitMap), - _modUnionClosurePar(&_modUnionTable), - _between_prologue_and_epilogue(false), - _abort_preclean(false), - _start_sampling(false), - _stats(cmsGen), - _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true, - //verify that this lock should be acquired with safepoint check. - Monitor::_safepoint_check_never)), - _eden_chunk_array(NULL), // may be set in ctor body - _eden_chunk_index(0), // -- ditto -- - _eden_chunk_capacity(0), // -- ditto -- - _survivor_chunk_array(NULL), // -- ditto -- - _survivor_chunk_index(0), // -- ditto -- - _survivor_chunk_capacity(0), // -- ditto -- - _survivor_plab_array(NULL) // -- ditto -- -{ - // Now expand the span and allocate the collection support structures - // (MUT, marking bit map etc.) to cover both generations subject to - // collection. - - // For use by dirty card to oop closures. - _cmsGen->cmsSpace()->set_collector(this); - - // Allocate MUT and marking bit map - { - MutexLocker x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag); - if (!_markBitMap.allocate(_span)) { - log_warning(gc)("Failed to allocate CMS Bit Map"); - return; - } - assert(_markBitMap.covers(_span), "_markBitMap inconsistency?"); - } - { - _modUnionTable.allocate(_span); - assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?"); - } - - if (!_markStack.allocate(MarkStackSize)) { - log_warning(gc)("Failed to allocate CMS Marking Stack"); - return; - } - - // Support for multi-threaded concurrent phases - if (CMSConcurrentMTEnabled) { - if (FLAG_IS_DEFAULT(ConcGCThreads)) { - // just for now - FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4); - } - if (ConcGCThreads > 1) { - _conc_workers = new YieldingFlexibleWorkGang("CMS Thread", - ConcGCThreads, true); - if (_conc_workers == NULL) { - log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled"); - CMSConcurrentMTEnabled = false; - } else { - _conc_workers->initialize_workers(); - } - } else { - CMSConcurrentMTEnabled = false; - } - } - if (!CMSConcurrentMTEnabled) { - ConcGCThreads = 0; - } else { - // Turn off CMSCleanOnEnter optimization temporarily for - // the MT case where it's not fixed yet; see 6178663. - CMSCleanOnEnter = false; - } - assert((_conc_workers != NULL) == (ConcGCThreads > 1), - "Inconsistency"); - log_debug(gc)("ConcGCThreads: %u", ConcGCThreads); - log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads); - - // Parallel task queues; these are shared for the - // concurrent and stop-world phases of CMS, but - // are not shared with parallel scavenge (ParNew). - { - uint i; - uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads); - - if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled - || ParallelRefProcEnabled) - && num_queues > 0) { - _task_queues = new OopTaskQueueSet(num_queues); - if (_task_queues == NULL) { - log_warning(gc)("task_queues allocation failure."); - return; - } - typedef Padded PaddedOopTaskQueue; - for (i = 0; i < num_queues; i++) { - PaddedOopTaskQueue *q = new PaddedOopTaskQueue(); - if (q == NULL) { - log_warning(gc)("work_queue allocation failure."); - return; - } - _task_queues->register_queue(i, q); - } - for (i = 0; i < num_queues; i++) { - _task_queues->queue(i)->initialize(); - } - } - } - - _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio); - - // Clip CMSBootstrapOccupancy between 0 and 100. - _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0; - - // Now tell CMS generations the identity of their collector - ConcurrentMarkSweepGeneration::set_collector(this); - - // Create & start a CMS thread for this CMS collector - _cmsThread = ConcurrentMarkSweepThread::start(this); - assert(cmsThread() != NULL, "CMS Thread should have been created"); - assert(cmsThread()->collector() == this, - "CMS Thread should refer to this gen"); - assert(CGC_lock != NULL, "Where's the CGC_lock?"); - - // Support for parallelizing young gen rescan - CMSHeap* heap = CMSHeap::heap(); - _young_gen = heap->young_gen(); - if (heap->supports_inline_contig_alloc()) { - _top_addr = heap->top_addr(); - _end_addr = heap->end_addr(); - assert(_young_gen != NULL, "no _young_gen"); - _eden_chunk_index = 0; - _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain; - _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC); - } - - // Support for parallelizing survivor space rescan - if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) { - const size_t max_plab_samples = - _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize); - - _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC); - _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC); - _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC); - _survivor_chunk_capacity = max_plab_samples; - for (uint i = 0; i < ParallelGCThreads; i++) { - HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC); - ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples); - assert(cur->end() == 0, "Should be 0"); - assert(cur->array() == vec, "Should be vec"); - assert(cur->capacity() == max_plab_samples, "Error"); - } - } - - NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;) - _gc_counters = new CollectorCounters("CMS full collection pauses", 1); - _cgc_counters = new CollectorCounters("CMS concurrent cycle pauses", 2); - _completed_initialization = true; - _inter_sweep_timer.start(); // start of time -} - -const char* ConcurrentMarkSweepGeneration::name() const { - return "concurrent mark-sweep generation"; -} -void ConcurrentMarkSweepGeneration::update_counters() { - if (UsePerfData) { - _space_counters->update_all(); - _gen_counters->update_all(); - } -} - -// this is an optimized version of update_counters(). it takes the -// used value as a parameter rather than computing it. -// -void ConcurrentMarkSweepGeneration::update_counters(size_t used) { - if (UsePerfData) { - _space_counters->update_used(used); - _space_counters->update_capacity(); - _gen_counters->update_all(); - } -} - -void ConcurrentMarkSweepGeneration::print() const { - Generation::print(); - cmsSpace()->print(); -} - -#ifndef PRODUCT -void ConcurrentMarkSweepGeneration::print_statistics() { - cmsSpace()->printFLCensus(0); -} -#endif - -size_t -ConcurrentMarkSweepGeneration::contiguous_available() const { - // dld proposes an improvement in precision here. If the committed - // part of the space ends in a free block we should add that to - // uncommitted size in the calculation below. Will make this - // change later, staying with the approximation below for the - // time being. -- ysr. - return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc()); -} - -size_t -ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const { - return _cmsSpace->max_alloc_in_words() * HeapWordSize; -} - -size_t ConcurrentMarkSweepGeneration::used_stable() const { - return cmsSpace()->used_stable(); -} - -size_t ConcurrentMarkSweepGeneration::max_available() const { - return free() + _virtual_space.uncommitted_size(); -} - -bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const { - size_t available = max_available(); - size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average(); - bool res = (available >= av_promo) || (available >= max_promotion_in_bytes); - log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")", - res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes); - return res; -} - -// At a promotion failure dump information on block layout in heap -// (cms old generation). -void ConcurrentMarkSweepGeneration::promotion_failure_occurred() { - Log(gc, promotion) log; - if (log.is_trace()) { - LogStream ls(log.trace()); - cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls); - } -} - -void ConcurrentMarkSweepGeneration::reset_after_compaction() { - // Clear the promotion information. These pointers can be adjusted - // along with all the other pointers into the heap but - // compaction is expected to be a rare event with - // a heap using cms so don't do it without seeing the need. - for (uint i = 0; i < ParallelGCThreads; i++) { - _par_gc_thread_states[i]->promo.reset(); - } -} - -void ConcurrentMarkSweepGeneration::compute_new_size() { - assert_locked_or_safepoint(Heap_lock); - - // If incremental collection failed, we just want to expand - // to the limit. - if (incremental_collection_failed()) { - clear_incremental_collection_failed(); - grow_to_reserved(); - return; - } - - // The heap has been compacted but not reset yet. - // Any metric such as free() or used() will be incorrect. - - CardGeneration::compute_new_size(); - - // Reset again after a possible resizing - if (did_compact()) { - cmsSpace()->reset_after_compaction(); - } -} - -void ConcurrentMarkSweepGeneration::compute_new_size_free_list() { - assert_locked_or_safepoint(Heap_lock); - - // If incremental collection failed, we just want to expand - // to the limit. - if (incremental_collection_failed()) { - clear_incremental_collection_failed(); - grow_to_reserved(); - return; - } - - double free_percentage = ((double) free()) / capacity(); - double desired_free_percentage = (double) MinHeapFreeRatio / 100; - double maximum_free_percentage = (double) MaxHeapFreeRatio / 100; - - // compute expansion delta needed for reaching desired free percentage - if (free_percentage < desired_free_percentage) { - size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); - assert(desired_capacity >= capacity(), "invalid expansion size"); - size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes); - Log(gc) log; - if (log.is_trace()) { - size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); - log.trace("From compute_new_size: "); - log.trace(" Free fraction %f", free_percentage); - log.trace(" Desired free fraction %f", desired_free_percentage); - log.trace(" Maximum free fraction %f", maximum_free_percentage); - log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000); - log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000); - CMSHeap* heap = CMSHeap::heap(); - size_t young_size = heap->young_gen()->capacity(); - log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000); - log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000); - log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000); - log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes); - } - // safe if expansion fails - expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio); - log.trace(" Expanded free fraction %f", ((double) free()) / capacity()); - } else { - size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); - assert(desired_capacity <= capacity(), "invalid expansion size"); - size_t shrink_bytes = capacity() - desired_capacity; - // Don't shrink unless the delta is greater than the minimum shrink we want - if (shrink_bytes >= MinHeapDeltaBytes) { - shrink_free_list_by(shrink_bytes); - } - } -} - -Mutex* ConcurrentMarkSweepGeneration::freelistLock() const { - return cmsSpace()->freelistLock(); -} - -HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) { - CMSSynchronousYieldRequest yr; - MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag); - return have_lock_and_allocate(size, tlab); -} - -HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size, - bool tlab /* ignored */) { - assert_lock_strong(freelistLock()); - size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size); - HeapWord* res = cmsSpace()->allocate(adjustedSize); - // Allocate the object live (grey) if the background collector has - // started marking. This is necessary because the marker may - // have passed this address and consequently this object will - // not otherwise be greyed and would be incorrectly swept up. - // Note that if this object contains references, the writing - // of those references will dirty the card containing this object - // allowing the object to be blackened (and its references scanned) - // either during a preclean phase or at the final checkpoint. - if (res != NULL) { - // We may block here with an uninitialized object with - // its mark-bit or P-bits not yet set. Such objects need - // to be safely navigable by block_start(). - assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here."); - assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size"); - collector()->direct_allocated(res, adjustedSize); - _direct_allocated_words += adjustedSize; - // allocation counters - NOT_PRODUCT( - _numObjectsAllocated++; - _numWordsAllocated += (int)adjustedSize; - ) - } - return res; -} - -// In the case of direct allocation by mutators in a generation that -// is being concurrently collected, the object must be allocated -// live (grey) if the background collector has started marking. -// This is necessary because the marker may -// have passed this address and consequently this object will -// not otherwise be greyed and would be incorrectly swept up. -// Note that if this object contains references, the writing -// of those references will dirty the card containing this object -// allowing the object to be blackened (and its references scanned) -// either during a preclean phase or at the final checkpoint. -void CMSCollector::direct_allocated(HeapWord* start, size_t size) { - assert(_markBitMap.covers(start, size), "Out of bounds"); - if (_collectorState >= Marking) { - MutexLocker y(_markBitMap.lock(), - Mutex::_no_safepoint_check_flag); - // [see comments preceding SweepClosure::do_blk() below for details] - // - // Can the P-bits be deleted now? JJJ - // - // 1. need to mark the object as live so it isn't collected - // 2. need to mark the 2nd bit to indicate the object may be uninitialized - // 3. need to mark the end of the object so marking, precleaning or sweeping - // can skip over uninitialized or unparsable objects. An allocated - // object is considered uninitialized for our purposes as long as - // its klass word is NULL. All old gen objects are parsable - // as soon as they are initialized.) - _markBitMap.mark(start); // object is live - _markBitMap.mark(start + 1); // object is potentially uninitialized? - _markBitMap.mark(start + size - 1); - // mark end of object - } - // check that oop looks uninitialized - assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL"); -} - -void CMSCollector::promoted(bool par, HeapWord* start, - bool is_obj_array, size_t obj_size) { - assert(_markBitMap.covers(start), "Out of bounds"); - // See comment in direct_allocated() about when objects should - // be allocated live. - if (_collectorState >= Marking) { - // we already hold the marking bit map lock, taken in - // the prologue - if (par) { - _markBitMap.par_mark(start); - } else { - _markBitMap.mark(start); - } - // We don't need to mark the object as uninitialized (as - // in direct_allocated above) because this is being done with the - // world stopped and the object will be initialized by the - // time the marking, precleaning or sweeping get to look at it. - // But see the code for copying objects into the CMS generation, - // where we need to ensure that concurrent readers of the - // block offset table are able to safely navigate a block that - // is in flux from being free to being allocated (and in - // transition while being copied into) and subsequently - // becoming a bona-fide object when the copy/promotion is complete. - assert(SafepointSynchronize::is_at_safepoint(), - "expect promotion only at safepoints"); - - if (_collectorState < Sweeping) { - // Mark the appropriate cards in the modUnionTable, so that - // this object gets scanned before the sweep. If this is - // not done, CMS generation references in the object might - // not get marked. - // For the case of arrays, which are otherwise precisely - // marked, we need to dirty the entire array, not just its head. - if (is_obj_array) { - // The [par_]mark_range() method expects mr.end() below to - // be aligned to the granularity of a bit's representation - // in the heap. In the case of the MUT below, that's a - // card size. - MemRegion mr(start, - align_up(start + obj_size, - CardTable::card_size /* bytes */)); - if (par) { - _modUnionTable.par_mark_range(mr); - } else { - _modUnionTable.mark_range(mr); - } - } else { // not an obj array; we can just mark the head - if (par) { - _modUnionTable.par_mark(start); - } else { - _modUnionTable.mark(start); - } - } - } - } -} - -oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) { - assert(obj_size == (size_t)obj->size(), "bad obj_size passed in"); - // allocate, copy and if necessary update promoinfo -- - // delegate to underlying space. - assert_lock_strong(freelistLock()); - -#ifndef PRODUCT - if (CMSHeap::heap()->promotion_should_fail()) { - return NULL; - } -#endif // #ifndef PRODUCT - - oop res = _cmsSpace->promote(obj, obj_size); - if (res == NULL) { - // expand and retry - size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords - expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion); - // Since this is the old generation, we don't try to promote - // into a more senior generation. - res = _cmsSpace->promote(obj, obj_size); - } - if (res != NULL) { - // See comment in allocate() about when objects should - // be allocated live. - assert(oopDesc::is_oop(obj), "Will dereference klass pointer below"); - collector()->promoted(false, // Not parallel - (HeapWord*)res, obj->is_objArray(), obj_size); - // promotion counters - NOT_PRODUCT( - _numObjectsPromoted++; - _numWordsPromoted += - (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size())); - ) - } - return res; -} - - -// IMPORTANT: Notes on object size recognition in CMS. -// --------------------------------------------------- -// A block of storage in the CMS generation is always in -// one of three states. A free block (FREE), an allocated -// object (OBJECT) whose size() method reports the correct size, -// and an intermediate state (TRANSIENT) in which its size cannot -// be accurately determined. -// STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS) -// ----------------------------------------------------- -// FREE: klass_word & 1 == 1; mark_word holds block size -// -// OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0; -// obj->size() computes correct size -// -// TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT -// -// STATE IDENTIFICATION: (64 bit+COOPS) -// ------------------------------------ -// FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size -// -// OBJECT: klass_word installed; klass_word != 0; -// obj->size() computes correct size -// -// TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT -// -// -// STATE TRANSITION DIAGRAM -// -// mut / parnew mut / parnew -// FREE --------------------> TRANSIENT ---------------------> OBJECT --| -// ^ | -// |------------------------ DEAD <------------------------------------| -// sweep mut -// -// While a block is in TRANSIENT state its size cannot be determined -// so readers will either need to come back later or stall until -// the size can be determined. Note that for the case of direct -// allocation, P-bits, when available, may be used to determine the -// size of an object that may not yet have been initialized. - -// Things to support parallel young-gen collection. -oop -ConcurrentMarkSweepGeneration::par_promote(int thread_num, - oop old, markWord m, - size_t word_sz) { -#ifndef PRODUCT - if (CMSHeap::heap()->promotion_should_fail()) { - return NULL; - } -#endif // #ifndef PRODUCT - - CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; - PromotionInfo* promoInfo = &ps->promo; - // if we are tracking promotions, then first ensure space for - // promotion (including spooling space for saving header if necessary). - // then allocate and copy, then track promoted info if needed. - // When tracking (see PromotionInfo::track()), the mark word may - // be displaced and in this case restoration of the mark word - // occurs in the (oop_since_save_marks_)iterate phase. - if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) { - // Out of space for allocating spooling buffers; - // try expanding and allocating spooling buffers. - if (!expand_and_ensure_spooling_space(promoInfo)) { - return NULL; - } - } - assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant"); - const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz); - HeapWord* obj_ptr = ps->lab.alloc(alloc_sz); - if (obj_ptr == NULL) { - obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz); - if (obj_ptr == NULL) { - return NULL; - } - } - oop obj = oop(obj_ptr); - OrderAccess::storestore(); - assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); - assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); - // IMPORTANT: See note on object initialization for CMS above. - // Otherwise, copy the object. Here we must be careful to insert the - // klass pointer last, since this marks the block as an allocated object. - // Except with compressed oops it's the mark word. - HeapWord* old_ptr = (HeapWord*)old; - // Restore the mark word copied above. - obj->set_mark_raw(m); - assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); - assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); - OrderAccess::storestore(); - - if (UseCompressedClassPointers) { - // Copy gap missed by (aligned) header size calculation below - obj->set_klass_gap(old->klass_gap()); - } - if (word_sz > (size_t)oopDesc::header_size()) { - Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(), - obj_ptr + oopDesc::header_size(), - word_sz - oopDesc::header_size()); - } - - // Now we can track the promoted object, if necessary. We take care - // to delay the transition from uninitialized to full object - // (i.e., insertion of klass pointer) until after, so that it - // atomically becomes a promoted object. - if (promoInfo->tracking()) { - promoInfo->track((PromotedObject*)obj, old->klass()); - } - assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); - assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); - assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below"); - - // Finally, install the klass pointer (this should be volatile). - OrderAccess::storestore(); - obj->set_klass(old->klass()); - // We should now be able to calculate the right size for this object - assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object"); - - collector()->promoted(true, // parallel - obj_ptr, old->is_objArray(), word_sz); - - NOT_PRODUCT( - Atomic::inc(&_numObjectsPromoted); - Atomic::add(alloc_sz, &_numWordsPromoted); - ) - - return obj; -} - -void -ConcurrentMarkSweepGeneration:: -par_promote_alloc_done(int thread_num) { - CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; - ps->lab.retire(thread_num); -} - -void -ConcurrentMarkSweepGeneration:: -par_oop_since_save_marks_iterate_done(int thread_num) { - CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; - ParScanWithoutBarrierClosure* dummy_cl = NULL; - ps->promo.promoted_oops_iterate(dummy_cl); - - // Because card-scanning has been completed, subsequent phases - // (e.g., reference processing) will not need to recognize which - // objects have been promoted during this GC. So, we can now disable - // promotion tracking. - ps->promo.stopTrackingPromotions(); -} - -bool ConcurrentMarkSweepGeneration::should_collect(bool full, - size_t size, - bool tlab) -{ - // We allow a STW collection only if a full - // collection was requested. - return full || should_allocate(size, tlab); // FIX ME !!! - // This and promotion failure handling are connected at the - // hip and should be fixed by untying them. -} - -bool CMSCollector::shouldConcurrentCollect() { - LogTarget(Trace, gc) log; - - if (_full_gc_requested) { - log.print("CMSCollector: collect because of explicit gc request (or GCLocker)"); - return true; - } - - FreelistLocker x(this); - // ------------------------------------------------------------------ - // Print out lots of information which affects the initiation of - // a collection. - if (log.is_enabled() && stats().valid()) { - log.print("CMSCollector shouldConcurrentCollect: "); - - LogStream out(log); - stats().print_on(&out); - - log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full()); - log.print("free=" SIZE_FORMAT, _cmsGen->free()); - log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available()); - log.print("promotion_rate=%g", stats().promotion_rate()); - log.print("cms_allocation_rate=%g", stats().cms_allocation_rate()); - log.print("occupancy=%3.7f", _cmsGen->occupancy()); - log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy()); - log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin()); - log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end()); - log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect()); - } - // ------------------------------------------------------------------ - - // If the estimated time to complete a cms collection (cms_duration()) - // is less than the estimated time remaining until the cms generation - // is full, start a collection. - if (!UseCMSInitiatingOccupancyOnly) { - if (stats().valid()) { - if (stats().time_until_cms_start() == 0.0) { - return true; - } - } else { - // We want to conservatively collect somewhat early in order - // to try and "bootstrap" our CMS/promotion statistics; - // this branch will not fire after the first successful CMS - // collection because the stats should then be valid. - if (_cmsGen->occupancy() >= _bootstrap_occupancy) { - log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f", - _cmsGen->occupancy(), _bootstrap_occupancy); - return true; - } - } - } - - // Otherwise, we start a collection cycle if - // old gen want a collection cycle started. Each may use - // an appropriate criterion for making this decision. - // XXX We need to make sure that the gen expansion - // criterion dovetails well with this. XXX NEED TO FIX THIS - if (_cmsGen->should_concurrent_collect()) { - log.print("CMS old gen initiated"); - return true; - } - - // We start a collection if we believe an incremental collection may fail; - // this is not likely to be productive in practice because it's probably too - // late anyway. - CMSHeap* heap = CMSHeap::heap(); - if (heap->incremental_collection_will_fail(true /* consult_young */)) { - log.print("CMSCollector: collect because incremental collection will fail "); - return true; - } - - if (MetaspaceGC::should_concurrent_collect()) { - log.print("CMSCollector: collect for metadata allocation "); - return true; - } - - // CMSTriggerInterval starts a CMS cycle if enough time has passed. - if (CMSTriggerInterval >= 0) { - if (CMSTriggerInterval == 0) { - // Trigger always - return true; - } - - // Check the CMS time since begin (we do not check the stats validity - // as we want to be able to trigger the first CMS cycle as well) - if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) { - if (stats().valid()) { - log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)", - stats().cms_time_since_begin()); - } else { - log.print("CMSCollector: collect because of trigger interval (first collection)"); - } - return true; - } - } - - return false; -} - -void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); } - -// Clear _expansion_cause fields of constituent generations -void CMSCollector::clear_expansion_cause() { - _cmsGen->clear_expansion_cause(); -} - -// We should be conservative in starting a collection cycle. To -// start too eagerly runs the risk of collecting too often in the -// extreme. To collect too rarely falls back on full collections, -// which works, even if not optimum in terms of concurrent work. -// As a work around for too eagerly collecting, use the flag -// UseCMSInitiatingOccupancyOnly. This also has the advantage of -// giving the user an easily understandable way of controlling the -// collections. -// We want to start a new collection cycle if any of the following -// conditions hold: -// . our current occupancy exceeds the configured initiating occupancy -// for this generation, or -// . we recently needed to expand this space and have not, since that -// expansion, done a collection of this generation, or -// . the underlying space believes that it may be a good idea to initiate -// a concurrent collection (this may be based on criteria such as the -// following: the space uses linear allocation and linear allocation is -// going to fail, or there is believed to be excessive fragmentation in -// the generation, etc... or ... -// [.(currently done by CMSCollector::shouldConcurrentCollect() only for -// the case of the old generation; see CR 6543076): -// we may be approaching a point at which allocation requests may fail because -// we will be out of sufficient free space given allocation rate estimates.] -bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const { - - assert_lock_strong(freelistLock()); - if (occupancy() > initiating_occupancy()) { - log_trace(gc)(" %s: collect because of occupancy %f / %f ", - short_name(), occupancy(), initiating_occupancy()); - return true; - } - if (UseCMSInitiatingOccupancyOnly) { - return false; - } - if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) { - log_trace(gc)(" %s: collect because expanded for allocation ", short_name()); - return true; - } - return false; -} - -void ConcurrentMarkSweepGeneration::collect(bool full, - bool clear_all_soft_refs, - size_t size, - bool tlab) -{ - collector()->collect(full, clear_all_soft_refs, size, tlab); -} - -void CMSCollector::collect(bool full, - bool clear_all_soft_refs, - size_t size, - bool tlab) -{ - // The following "if" branch is present for defensive reasons. - // In the current uses of this interface, it can be replaced with: - // assert(!GCLocker.is_active(), "Can't be called otherwise"); - // But I am not placing that assert here to allow future - // generality in invoking this interface. - if (GCLocker::is_active()) { - // A consistency test for GCLocker - assert(GCLocker::needs_gc(), "Should have been set already"); - // Skip this foreground collection, instead - // expanding the heap if necessary. - // Need the free list locks for the call to free() in compute_new_size() - compute_new_size(); - return; - } - acquire_control_and_collect(full, clear_all_soft_refs); -} - -void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) { - CMSHeap* heap = CMSHeap::heap(); - unsigned int gc_count = heap->total_full_collections(); - if (gc_count == full_gc_count) { - MutexLocker y(CGC_lock, Mutex::_no_safepoint_check_flag); - _full_gc_requested = true; - _full_gc_cause = cause; - CGC_lock->notify(); // nudge CMS thread - } else { - assert(gc_count > full_gc_count, "Error: causal loop"); - } -} - -bool CMSCollector::is_external_interruption() { - GCCause::Cause cause = CMSHeap::heap()->gc_cause(); - return GCCause::is_user_requested_gc(cause) || - GCCause::is_serviceability_requested_gc(cause); -} - -void CMSCollector::report_concurrent_mode_interruption() { - if (is_external_interruption()) { - log_debug(gc)("Concurrent mode interrupted"); - } else { - log_debug(gc)("Concurrent mode failure"); - _gc_tracer_cm->report_concurrent_mode_failure(); - } -} - - -// The foreground and background collectors need to coordinate in order -// to make sure that they do not mutually interfere with CMS collections. -// When a background collection is active, -// the foreground collector may need to take over (preempt) and -// synchronously complete an ongoing collection. Depending on the -// frequency of the background collections and the heap usage -// of the application, this preemption can be seldom or frequent. -// There are only certain -// points in the background collection that the "collection-baton" -// can be passed to the foreground collector. -// -// The foreground collector will wait for the baton before -// starting any part of the collection. The foreground collector -// will only wait at one location. -// -// The background collector will yield the baton before starting a new -// phase of the collection (e.g., before initial marking, marking from roots, -// precleaning, final re-mark, sweep etc.) This is normally done at the head -// of the loop which switches the phases. The background collector does some -// of the phases (initial mark, final re-mark) with the world stopped. -// Because of locking involved in stopping the world, -// the foreground collector should not block waiting for the background -// collector when it is doing a stop-the-world phase. The background -// collector will yield the baton at an additional point just before -// it enters a stop-the-world phase. Once the world is stopped, the -// background collector checks the phase of the collection. If the -// phase has not changed, it proceeds with the collection. If the -// phase has changed, it skips that phase of the collection. See -// the comments on the use of the Heap_lock in collect_in_background(). -// -// Variable used in baton passing. -// _foregroundGCIsActive - Set to true by the foreground collector when -// it wants the baton. The foreground clears it when it has finished -// the collection. -// _foregroundGCShouldWait - Set to true by the background collector -// when it is running. The foreground collector waits while -// _foregroundGCShouldWait is true. -// CGC_lock - monitor used to protect access to the above variables -// and to notify the foreground and background collectors. -// _collectorState - current state of the CMS collection. -// -// The foreground collector -// acquires the CGC_lock -// sets _foregroundGCIsActive -// waits on the CGC_lock for _foregroundGCShouldWait to be false -// various locks acquired in preparation for the collection -// are released so as not to block the background collector -// that is in the midst of a collection -// proceeds with the collection -// clears _foregroundGCIsActive -// returns -// -// The background collector in a loop iterating on the phases of the -// collection -// acquires the CGC_lock -// sets _foregroundGCShouldWait -// if _foregroundGCIsActive is set -// clears _foregroundGCShouldWait, notifies _CGC_lock -// waits on _CGC_lock for _foregroundGCIsActive to become false -// and exits the loop. -// otherwise -// proceed with that phase of the collection -// if the phase is a stop-the-world phase, -// yield the baton once more just before enqueueing -// the stop-world CMS operation (executed by the VM thread). -// returns after all phases of the collection are done -// - -void CMSCollector::acquire_control_and_collect(bool full, - bool clear_all_soft_refs) { - assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint"); - assert(!Thread::current()->is_ConcurrentGC_thread(), - "shouldn't try to acquire control from self!"); - - // Start the protocol for acquiring control of the - // collection from the background collector (aka CMS thread). - assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), - "VM thread should have CMS token"); - // Remember the possibly interrupted state of an ongoing - // concurrent collection - CollectorState first_state = _collectorState; - - // Signal to a possibly ongoing concurrent collection that - // we want to do a foreground collection. - _foregroundGCIsActive = true; - - // release locks and wait for a notify from the background collector - // releasing the locks in only necessary for phases which - // do yields to improve the granularity of the collection. - assert_lock_strong(bitMapLock()); - // We need to lock the Free list lock for the space that we are - // currently collecting. - assert(haveFreelistLocks(), "Must be holding free list locks"); - bitMapLock()->unlock(); - releaseFreelistLocks(); - { - MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag); - if (_foregroundGCShouldWait) { - // We are going to be waiting for action for the CMS thread; - // it had better not be gone (for instance at shutdown)! - assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(), - "CMS thread must be running"); - // Wait here until the background collector gives us the go-ahead - ConcurrentMarkSweepThread::clear_CMS_flag( - ConcurrentMarkSweepThread::CMS_vm_has_token); // release token - // Get a possibly blocked CMS thread going: - // Note that we set _foregroundGCIsActive true above, - // without protection of the CGC_lock. - CGC_lock->notify(); - assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(), - "Possible deadlock"); - while (_foregroundGCShouldWait) { - // wait for notification - CGC_lock->wait_without_safepoint_check(); - // Possibility of delay/starvation here, since CMS token does - // not know to give priority to VM thread? Actually, i think - // there wouldn't be any delay/starvation, but the proof of - // that "fact" (?) appears non-trivial. XXX 20011219YSR - } - ConcurrentMarkSweepThread::set_CMS_flag( - ConcurrentMarkSweepThread::CMS_vm_has_token); - } - } - // The CMS_token is already held. Get back the other locks. - assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), - "VM thread should have CMS token"); - getFreelistLocks(); - bitMapLock()->lock_without_safepoint_check(); - log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d", - p2i(Thread::current()), first_state); - log_debug(gc, state)(" gets control with state %d", _collectorState); - - // Inform cms gen if this was due to partial collection failing. - // The CMS gen may use this fact to determine its expansion policy. - CMSHeap* heap = CMSHeap::heap(); - if (heap->incremental_collection_will_fail(false /* don't consult_young */)) { - assert(!_cmsGen->incremental_collection_failed(), - "Should have been noticed, reacted to and cleared"); - _cmsGen->set_incremental_collection_failed(); - } - - if (first_state > Idling) { - report_concurrent_mode_interruption(); - } - - set_did_compact(true); - - // If the collection is being acquired from the background - // collector, there may be references on the discovered - // references lists. Abandon those references, since some - // of them may have become unreachable after concurrent - // discovery; the STW compacting collector will redo discovery - // more precisely, without being subject to floating garbage. - // Leaving otherwise unreachable references in the discovered - // lists would require special handling. - ref_processor()->disable_discovery(); - ref_processor()->abandon_partial_discovery(); - ref_processor()->verify_no_references_recorded(); - - if (first_state > Idling) { - save_heap_summary(); - } - - do_compaction_work(clear_all_soft_refs); - - // Has the GC time limit been exceeded? - size_t max_eden_size = _young_gen->max_eden_size(); - GCCause::Cause gc_cause = heap->gc_cause(); - size_policy()->check_gc_overhead_limit(_young_gen->eden()->used(), - _cmsGen->max_capacity(), - max_eden_size, - full, - gc_cause, - heap->soft_ref_policy()); - - // Reset the expansion cause, now that we just completed - // a collection cycle. - clear_expansion_cause(); - _foregroundGCIsActive = false; - return; -} - -// Resize the tenured generation -// after obtaining the free list locks for the -// two generations. -void CMSCollector::compute_new_size() { - assert_locked_or_safepoint(Heap_lock); - FreelistLocker z(this); - MetaspaceGC::compute_new_size(); - _cmsGen->compute_new_size_free_list(); - // recalculate CMS used space after CMS collection - _cmsGen->cmsSpace()->recalculate_used_stable(); -} - -// A work method used by the foreground collector to do -// a mark-sweep-compact. -void CMSCollector::do_compaction_work(bool clear_all_soft_refs) { - CMSHeap* heap = CMSHeap::heap(); - - STWGCTimer* gc_timer = GenMarkSweep::gc_timer(); - gc_timer->register_gc_start(); - - SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer(); - gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start()); - - heap->pre_full_gc_dump(gc_timer); - - GCTraceTime(Trace, gc, phases) t("CMS:MSC"); - - // Temporarily widen the span of the weak reference processing to - // the entire heap. - MemRegion new_span(CMSHeap::heap()->reserved_region()); - ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span); - // Temporarily, clear the "is_alive_non_header" field of the - // reference processor. - ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL); - // Temporarily make reference _processing_ single threaded (non-MT). - ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false); - // Temporarily make refs discovery atomic - ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true); - // Temporarily make reference _discovery_ single threaded (non-MT) - ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false); - - ref_processor()->set_enqueuing_is_done(false); - ref_processor()->enable_discovery(); - ref_processor()->setup_policy(clear_all_soft_refs); - // If an asynchronous collection finishes, the _modUnionTable is - // all clear. If we are assuming the collection from an asynchronous - // collection, clear the _modUnionTable. - assert(_collectorState != Idling || _modUnionTable.isAllClear(), - "_modUnionTable should be clear if the baton was not passed"); - _modUnionTable.clear_all(); - assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(), - "mod union for klasses should be clear if the baton was passed"); - _ct->cld_rem_set()->clear_mod_union(); - - - // We must adjust the allocation statistics being maintained - // in the free list space. We do so by reading and clearing - // the sweep timer and updating the block flux rate estimates below. - assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive"); - if (_inter_sweep_timer.is_active()) { - _inter_sweep_timer.stop(); - // Note that we do not use this sample to update the _inter_sweep_estimate. - _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), - _inter_sweep_estimate.padded_average(), - _intra_sweep_estimate.padded_average()); - } - - GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs); - #ifdef ASSERT - CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); - size_t free_size = cms_space->free(); - assert(free_size == - pointer_delta(cms_space->end(), cms_space->compaction_top()) - * HeapWordSize, - "All the free space should be compacted into one chunk at top"); - assert(cms_space->dictionary()->total_chunk_size( - debug_only(cms_space->freelistLock())) == 0 || - cms_space->totalSizeInIndexedFreeLists() == 0, - "All the free space should be in a single chunk"); - size_t num = cms_space->totalCount(); - assert((free_size == 0 && num == 0) || - (free_size > 0 && (num == 1 || num == 2)), - "There should be at most 2 free chunks after compaction"); - #endif // ASSERT - _collectorState = Resetting; - assert(_restart_addr == NULL, - "Should have been NULL'd before baton was passed"); - reset_stw(); - _cmsGen->reset_after_compaction(); - _concurrent_cycles_since_last_unload = 0; - - // Clear any data recorded in the PLAB chunk arrays. - if (_survivor_plab_array != NULL) { - reset_survivor_plab_arrays(); - } - - // Adjust the per-size allocation stats for the next epoch. - _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */); - // Restart the "inter sweep timer" for the next epoch. - _inter_sweep_timer.reset(); - _inter_sweep_timer.start(); - - // No longer a need to do a concurrent collection for Metaspace. - MetaspaceGC::set_should_concurrent_collect(false); - - heap->post_full_gc_dump(gc_timer); - - gc_timer->register_gc_end(); - - gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions()); - - // For a mark-sweep-compact, compute_new_size() will be called - // in the heap's do_collection() method. -} - -void CMSCollector::print_eden_and_survivor_chunk_arrays() { - Log(gc, heap) log; - if (!log.is_trace()) { - return; - } - - ContiguousSpace* eden_space = _young_gen->eden(); - ContiguousSpace* from_space = _young_gen->from(); - ContiguousSpace* to_space = _young_gen->to(); - // Eden - if (_eden_chunk_array != NULL) { - log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")", - p2i(eden_space->bottom()), p2i(eden_space->top()), - p2i(eden_space->end()), eden_space->capacity()); - log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT, - _eden_chunk_index, _eden_chunk_capacity); - for (size_t i = 0; i < _eden_chunk_index; i++) { - log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i])); - } - } - // Survivor - if (_survivor_chunk_array != NULL) { - log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")", - p2i(from_space->bottom()), p2i(from_space->top()), - p2i(from_space->end()), from_space->capacity()); - log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT, - _survivor_chunk_index, _survivor_chunk_capacity); - for (size_t i = 0; i < _survivor_chunk_index; i++) { - log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i])); - } - } -} - -void CMSCollector::getFreelistLocks() const { - // Get locks for all free lists in all generations that this - // collector is responsible for - _cmsGen->freelistLock()->lock_without_safepoint_check(); -} - -void CMSCollector::releaseFreelistLocks() const { - // Release locks for all free lists in all generations that this - // collector is responsible for - _cmsGen->freelistLock()->unlock(); -} - -bool CMSCollector::haveFreelistLocks() const { - // Check locks for all free lists in all generations that this - // collector is responsible for - assert_lock_strong(_cmsGen->freelistLock()); - PRODUCT_ONLY(ShouldNotReachHere()); - return true; -} - -// A utility class that is used by the CMS collector to -// temporarily "release" the foreground collector from its -// usual obligation to wait for the background collector to -// complete an ongoing phase before proceeding. -class ReleaseForegroundGC: public StackObj { - private: - CMSCollector* _c; - public: - ReleaseForegroundGC(CMSCollector* c) : _c(c) { - assert(_c->_foregroundGCShouldWait, "Else should not need to call"); - MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag); - // allow a potentially blocked foreground collector to proceed - _c->_foregroundGCShouldWait = false; - if (_c->_foregroundGCIsActive) { - CGC_lock->notify(); - } - assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "Possible deadlock"); - } - - ~ReleaseForegroundGC() { - assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?"); - MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag); - _c->_foregroundGCShouldWait = true; - } -}; - -void CMSCollector::collect_in_background(GCCause::Cause cause) { - assert(Thread::current()->is_ConcurrentGC_thread(), - "A CMS asynchronous collection is only allowed on a CMS thread."); - - CMSHeap* heap = CMSHeap::heap(); - { - MutexLocker hl(Heap_lock, Mutex::_no_safepoint_check_flag); - FreelistLocker fll(this); - MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag); - if (_foregroundGCIsActive) { - // The foreground collector is. Skip this - // background collection. - assert(!_foregroundGCShouldWait, "Should be clear"); - return; - } else { - assert(_collectorState == Idling, "Should be idling before start."); - _collectorState = InitialMarking; - register_gc_start(cause); - // Reset the expansion cause, now that we are about to begin - // a new cycle. - clear_expansion_cause(); - - // Clear the MetaspaceGC flag since a concurrent collection - // is starting but also clear it after the collection. - MetaspaceGC::set_should_concurrent_collect(false); - } - // Decide if we want to enable class unloading as part of the - // ensuing concurrent GC cycle. - update_should_unload_classes(); - _full_gc_requested = false; // acks all outstanding full gc requests - _full_gc_cause = GCCause::_no_gc; - // Signal that we are about to start a collection - heap->increment_total_full_collections(); // ... starting a collection cycle - _collection_count_start = heap->total_full_collections(); - } - - size_t prev_used = _cmsGen->used(); - - // The change of the collection state is normally done at this level; - // the exceptions are phases that are executed while the world is - // stopped. For those phases the change of state is done while the - // world is stopped. For baton passing purposes this allows the - // background collector to finish the phase and change state atomically. - // The foreground collector cannot wait on a phase that is done - // while the world is stopped because the foreground collector already - // has the world stopped and would deadlock. - while (_collectorState != Idling) { - log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d", - p2i(Thread::current()), _collectorState); - // The foreground collector - // holds the Heap_lock throughout its collection. - // holds the CMS token (but not the lock) - // except while it is waiting for the background collector to yield. - // - // The foreground collector should be blocked (not for long) - // if the background collector is about to start a phase - // executed with world stopped. If the background - // collector has already started such a phase, the - // foreground collector is blocked waiting for the - // Heap_lock. The stop-world phases (InitialMarking and FinalMarking) - // are executed in the VM thread. - // - // The locking order is - // PendingListLock (PLL) -- if applicable (FinalMarking) - // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue()) - // CMS token (claimed in - // stop_world_and_do() --> - // safepoint_synchronize() --> - // CMSThread::synchronize()) - - { - // Check if the FG collector wants us to yield. - CMSTokenSync x(true); // is cms thread - if (waitForForegroundGC()) { - // We yielded to a foreground GC, nothing more to be - // done this round. - assert(_foregroundGCShouldWait == false, "We set it to false in " - "waitForForegroundGC()"); - log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d", - p2i(Thread::current()), _collectorState); - return; - } else { - // The background collector can run but check to see if the - // foreground collector has done a collection while the - // background collector was waiting to get the CGC_lock - // above. If yes, break so that _foregroundGCShouldWait - // is cleared before returning. - if (_collectorState == Idling) { - break; - } - } - } - - assert(_foregroundGCShouldWait, "Foreground collector, if active, " - "should be waiting"); - - switch (_collectorState) { - case InitialMarking: - { - ReleaseForegroundGC x(this); - stats().record_cms_begin(); - VM_CMS_Initial_Mark initial_mark_op(this); - VMThread::execute(&initial_mark_op); - } - // The collector state may be any legal state at this point - // since the background collector may have yielded to the - // foreground collector. - break; - case Marking: - // initial marking in checkpointRootsInitialWork has been completed - if (markFromRoots()) { // we were successful - assert(_collectorState == Precleaning, "Collector state should " - "have changed"); - } else { - assert(_foregroundGCIsActive, "Internal state inconsistency"); - } - break; - case Precleaning: - // marking from roots in markFromRoots has been completed - preclean(); - assert(_collectorState == AbortablePreclean || - _collectorState == FinalMarking, - "Collector state should have changed"); - break; - case AbortablePreclean: - abortable_preclean(); - assert(_collectorState == FinalMarking, "Collector state should " - "have changed"); - break; - case FinalMarking: - { - ReleaseForegroundGC x(this); - - VM_CMS_Final_Remark final_remark_op(this); - VMThread::execute(&final_remark_op); - } - assert(_foregroundGCShouldWait, "block post-condition"); - break; - case Sweeping: - // final marking in checkpointRootsFinal has been completed - sweep(); - assert(_collectorState == Resizing, "Collector state change " - "to Resizing must be done under the free_list_lock"); - - case Resizing: { - // Sweeping has been completed... - // At this point the background collection has completed. - // Don't move the call to compute_new_size() down - // into code that might be executed if the background - // collection was preempted. - { - ReleaseForegroundGC x(this); // unblock FG collection - MutexLocker y(Heap_lock, Mutex::_no_safepoint_check_flag); - CMSTokenSync z(true); // not strictly needed. - if (_collectorState == Resizing) { - compute_new_size(); - save_heap_summary(); - _collectorState = Resetting; - } else { - assert(_collectorState == Idling, "The state should only change" - " because the foreground collector has finished the collection"); - } - } - break; - } - case Resetting: - // CMS heap resizing has been completed - reset_concurrent(); - assert(_collectorState == Idling, "Collector state should " - "have changed"); - - MetaspaceGC::set_should_concurrent_collect(false); - - stats().record_cms_end(); - // Don't move the concurrent_phases_end() and compute_new_size() - // calls to here because a preempted background collection - // has it's state set to "Resetting". - break; - case Idling: - default: - ShouldNotReachHere(); - break; - } - log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d", - p2i(Thread::current()), _collectorState); - assert(_foregroundGCShouldWait, "block post-condition"); - } - - // Should this be in gc_epilogue? - heap->counters()->update_counters(); - - { - // Clear _foregroundGCShouldWait and, in the event that the - // foreground collector is waiting, notify it, before - // returning. - MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag); - _foregroundGCShouldWait = false; - if (_foregroundGCIsActive) { - CGC_lock->notify(); - } - assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "Possible deadlock"); - } - log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d", - p2i(Thread::current()), _collectorState); - log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)", - prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K); -} - -void CMSCollector::register_gc_start(GCCause::Cause cause) { - _cms_start_registered = true; - _gc_timer_cm->register_gc_start(); - _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start()); -} - -void CMSCollector::register_gc_end() { - if (_cms_start_registered) { - report_heap_summary(GCWhen::AfterGC); - - _gc_timer_cm->register_gc_end(); - _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions()); - _cms_start_registered = false; - } -} - -void CMSCollector::save_heap_summary() { - CMSHeap* heap = CMSHeap::heap(); - _last_heap_summary = heap->create_heap_summary(); - _last_metaspace_summary = heap->create_metaspace_summary(); -} - -void CMSCollector::report_heap_summary(GCWhen::Type when) { - _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary); - _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary); -} - -bool CMSCollector::waitForForegroundGC() { - bool res = false; - assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "CMS thread should have CMS token"); - // Block the foreground collector until the - // background collectors decides whether to - // yield. - MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag); - _foregroundGCShouldWait = true; - if (_foregroundGCIsActive) { - // The background collector yields to the - // foreground collector and returns a value - // indicating that it has yielded. The foreground - // collector can proceed. - res = true; - _foregroundGCShouldWait = false; - ConcurrentMarkSweepThread::clear_CMS_flag( - ConcurrentMarkSweepThread::CMS_cms_has_token); - ConcurrentMarkSweepThread::set_CMS_flag( - ConcurrentMarkSweepThread::CMS_cms_wants_token); - // Get a possibly blocked foreground thread going - CGC_lock->notify(); - log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d", - p2i(Thread::current()), _collectorState); - while (_foregroundGCIsActive) { - CGC_lock->wait_without_safepoint_check(); - } - ConcurrentMarkSweepThread::set_CMS_flag( - ConcurrentMarkSweepThread::CMS_cms_has_token); - ConcurrentMarkSweepThread::clear_CMS_flag( - ConcurrentMarkSweepThread::CMS_cms_wants_token); - } - log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d", - p2i(Thread::current()), _collectorState); - return res; -} - -// Because of the need to lock the free lists and other structures in -// the collector, common to all the generations that the collector is -// collecting, we need the gc_prologues of individual CMS generations -// delegate to their collector. It may have been simpler had the -// current infrastructure allowed one to call a prologue on a -// collector. In the absence of that we have the generation's -// prologue delegate to the collector, which delegates back -// some "local" work to a worker method in the individual generations -// that it's responsible for collecting, while itself doing any -// work common to all generations it's responsible for. A similar -// comment applies to the gc_epilogue()'s. -// The role of the variable _between_prologue_and_epilogue is to -// enforce the invocation protocol. -void CMSCollector::gc_prologue(bool full) { - // Call gc_prologue_work() for the CMSGen - // we are responsible for. - - // The following locking discipline assumes that we are only called - // when the world is stopped. - assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption"); - - // The CMSCollector prologue must call the gc_prologues for the - // "generations" that it's responsible - // for. - - assert( Thread::current()->is_VM_thread() - || ( CMSScavengeBeforeRemark - && Thread::current()->is_ConcurrentGC_thread()), - "Incorrect thread type for prologue execution"); - - if (_between_prologue_and_epilogue) { - // We have already been invoked; this is a gc_prologue delegation - // from yet another CMS generation that we are responsible for, just - // ignore it since all relevant work has already been done. - return; - } - - // set a bit saying prologue has been called; cleared in epilogue - _between_prologue_and_epilogue = true; - // Claim locks for common data structures, then call gc_prologue_work() - // for each CMSGen. - - getFreelistLocks(); // gets free list locks on constituent spaces - bitMapLock()->lock_without_safepoint_check(); - - // Should call gc_prologue_work() for all cms gens we are responsible for - bool duringMarking = _collectorState >= Marking - && _collectorState < Sweeping; - - // The young collections clear the modified oops state, which tells if - // there are any modified oops in the class. The remark phase also needs - // that information. Tell the young collection to save the union of all - // modified klasses. - if (duringMarking) { - _ct->cld_rem_set()->set_accumulate_modified_oops(true); - } - - bool registerClosure = duringMarking; - - _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar); - - if (!full) { - stats().record_gc0_begin(); - } -} - -void ConcurrentMarkSweepGeneration::gc_prologue(bool full) { - - _capacity_at_prologue = capacity(); - _used_at_prologue = used(); - _cmsSpace->recalculate_used_stable(); - - // We enable promotion tracking so that card-scanning can recognize - // which objects have been promoted during this GC and skip them. - for (uint i = 0; i < ParallelGCThreads; i++) { - _par_gc_thread_states[i]->promo.startTrackingPromotions(); - } - - // Delegate to CMScollector which knows how to coordinate between - // this and any other CMS generations that it is responsible for - // collecting. - collector()->gc_prologue(full); -} - -// This is a "private" interface for use by this generation's CMSCollector. -// Not to be called directly by any other entity (for instance, -// GenCollectedHeap, which calls the "public" gc_prologue method above). -void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full, - bool registerClosure, ModUnionClosure* modUnionClosure) { - assert(!incremental_collection_failed(), "Shouldn't be set yet"); - assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL, - "Should be NULL"); - if (registerClosure) { - cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure); - } - cmsSpace()->gc_prologue(); - // Clear stat counters - NOT_PRODUCT( - assert(_numObjectsPromoted == 0, "check"); - assert(_numWordsPromoted == 0, "check"); - log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently", - _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord)); - _numObjectsAllocated = 0; - _numWordsAllocated = 0; - ) -} - -void CMSCollector::gc_epilogue(bool full) { - // The following locking discipline assumes that we are only called - // when the world is stopped. - assert(SafepointSynchronize::is_at_safepoint(), - "world is stopped assumption"); - - // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks - // if linear allocation blocks need to be appropriately marked to allow the - // the blocks to be parsable. We also check here whether we need to nudge the - // CMS collector thread to start a new cycle (if it's not already active). - assert( Thread::current()->is_VM_thread() - || ( CMSScavengeBeforeRemark - && Thread::current()->is_ConcurrentGC_thread()), - "Incorrect thread type for epilogue execution"); - - if (!_between_prologue_and_epilogue) { - // We have already been invoked; this is a gc_epilogue delegation - // from yet another CMS generation that we are responsible for, just - // ignore it since all relevant work has already been done. - return; - } - assert(haveFreelistLocks(), "must have freelist locks"); - assert_lock_strong(bitMapLock()); - - _ct->cld_rem_set()->set_accumulate_modified_oops(false); - - _cmsGen->gc_epilogue_work(full); - - if (_collectorState == AbortablePreclean || _collectorState == Precleaning) { - // in case sampling was not already enabled, enable it - _start_sampling = true; - } - // reset _eden_chunk_array so sampling starts afresh - _eden_chunk_index = 0; - - size_t cms_used = _cmsGen->cmsSpace()->used(); - _cmsGen->cmsSpace()->recalculate_used_stable(); - - // update performance counters - this uses a special version of - // update_counters() that allows the utilization to be passed as a - // parameter, avoiding multiple calls to used(). - // - _cmsGen->update_counters(cms_used); - - bitMapLock()->unlock(); - releaseFreelistLocks(); - - if (!CleanChunkPoolAsync) { - Chunk::clean_chunk_pool(); - } - - set_did_compact(false); - _between_prologue_and_epilogue = false; // ready for next cycle -} - -void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) { - collector()->gc_epilogue(full); - - // When using ParNew, promotion tracking should have already been - // disabled. However, the prologue (which enables promotion - // tracking) and epilogue are called irrespective of the type of - // GC. So they will also be called before and after Full GCs, during - // which promotion tracking will not be explicitly disabled. So, - // it's safer to also disable it here too (to be symmetric with - // enabling it in the prologue). - for (uint i = 0; i < ParallelGCThreads; i++) { - _par_gc_thread_states[i]->promo.stopTrackingPromotions(); - } -} - -void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) { - assert(!incremental_collection_failed(), "Should have been cleared"); - cmsSpace()->setPreconsumptionDirtyCardClosure(NULL); - cmsSpace()->gc_epilogue(); - // Print stat counters - NOT_PRODUCT( - assert(_numObjectsAllocated == 0, "check"); - assert(_numWordsAllocated == 0, "check"); - log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes", - _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord)); - _numObjectsPromoted = 0; - _numWordsPromoted = 0; - ) - - // Call down the chain in contiguous_available needs the freelistLock - // so print this out before releasing the freeListLock. - log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available()); -} - -#ifndef PRODUCT -bool CMSCollector::have_cms_token() { - Thread* thr = Thread::current(); - if (thr->is_VM_thread()) { - return ConcurrentMarkSweepThread::vm_thread_has_cms_token(); - } else if (thr->is_ConcurrentGC_thread()) { - return ConcurrentMarkSweepThread::cms_thread_has_cms_token(); - } else if (thr->is_GC_task_thread()) { - return ConcurrentMarkSweepThread::vm_thread_has_cms_token() && - ParGCRareEvent_lock->owned_by_self(); - } - return false; -} - -// Check reachability of the given heap address in CMS generation, -// treating all other generations as roots. -bool CMSCollector::is_cms_reachable(HeapWord* addr) { - // We could "guarantee" below, rather than assert, but I'll - // leave these as "asserts" so that an adventurous debugger - // could try this in the product build provided some subset of - // the conditions were met, provided they were interested in the - // results and knew that the computation below wouldn't interfere - // with other concurrent computations mutating the structures - // being read or written. - assert(SafepointSynchronize::is_at_safepoint(), - "Else mutations in object graph will make answer suspect"); - assert(have_cms_token(), "Should hold cms token"); - assert(haveFreelistLocks(), "must hold free list locks"); - assert_lock_strong(bitMapLock()); - - // Clear the marking bit map array before starting, but, just - // for kicks, first report if the given address is already marked - tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr), - _markBitMap.isMarked(addr) ? "" : " not"); - - if (verify_after_remark()) { - MutexLocker x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); - bool result = verification_mark_bm()->isMarked(addr); - tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr), - result ? "IS" : "is NOT"); - return result; - } else { - tty->print_cr("Could not compute result"); - return false; - } -} -#endif - -void -CMSCollector::print_on_error(outputStream* st) { - CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector; - if (collector != NULL) { - CMSBitMap* bitmap = &collector->_markBitMap; - st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap)); - bitmap->print_on_error(st, " Bits: "); - - st->cr(); - - CMSBitMap* mut_bitmap = &collector->_modUnionTable; - st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap)); - mut_bitmap->print_on_error(st, " Bits: "); - } -} - -//////////////////////////////////////////////////////// -// CMS Verification Support -//////////////////////////////////////////////////////// -// Following the remark phase, the following invariant -// should hold -- each object in the CMS heap which is -// marked in markBitMap() should be marked in the verification_mark_bm(). - -class VerifyMarkedClosure: public BitMapClosure { - CMSBitMap* _marks; - bool _failed; - - public: - VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {} - - bool do_bit(size_t offset) { - HeapWord* addr = _marks->offsetToHeapWord(offset); - if (!_marks->isMarked(addr)) { - Log(gc, verify) log; - ResourceMark rm; - LogStream ls(log.error()); - oop(addr)->print_on(&ls); - log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr)); - _failed = true; - } - return true; - } - - bool failed() { return _failed; } -}; - -bool CMSCollector::verify_after_remark() { - GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking."); - MutexLocker ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); - static bool init = false; - - assert(SafepointSynchronize::is_at_safepoint(), - "Else mutations in object graph will make answer suspect"); - assert(have_cms_token(), - "Else there may be mutual interference in use of " - " verification data structures"); - assert(_collectorState > Marking && _collectorState <= Sweeping, - "Else marking info checked here may be obsolete"); - assert(haveFreelistLocks(), "must hold free list locks"); - assert_lock_strong(bitMapLock()); - - - // Allocate marking bit map if not already allocated - if (!init) { // first time - if (!verification_mark_bm()->allocate(_span)) { - return false; - } - init = true; - } - - assert(verification_mark_stack()->isEmpty(), "Should be empty"); - - // Turn off refs discovery -- so we will be tracing through refs. - // This is as intended, because by this time - // GC must already have cleared any refs that need to be cleared, - // and traced those that need to be marked; moreover, - // the marking done here is not going to interfere in any - // way with the marking information used by GC. - NoRefDiscovery no_discovery(ref_processor()); - -#if COMPILER2_OR_JVMCI - DerivedPointerTableDeactivate dpt_deact; -#endif - - // Clear any marks from a previous round - verification_mark_bm()->clear_all(); - assert(verification_mark_stack()->isEmpty(), "markStack should be empty"); - verify_work_stacks_empty(); - - CMSHeap* heap = CMSHeap::heap(); - heap->ensure_parsability(false); // fill TLABs, but no need to retire them - // Update the saved marks which may affect the root scans. - heap->save_marks(); - - if (CMSRemarkVerifyVariant == 1) { - // In this first variant of verification, we complete - // all marking, then check if the new marks-vector is - // a subset of the CMS marks-vector. - verify_after_remark_work_1(); - } else { - guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2"); - // In this second variant of verification, we flag an error - // (i.e. an object reachable in the new marks-vector not reachable - // in the CMS marks-vector) immediately, also indicating the - // identify of an object (A) that references the unmarked object (B) -- - // presumably, a mutation to A failed to be picked up by preclean/remark? - verify_after_remark_work_2(); - } - - return true; -} - -void CMSCollector::verify_after_remark_work_1() { - ResourceMark rm; - HandleMark hm; - CMSHeap* heap = CMSHeap::heap(); - - // Get a clear set of claim bits for the roots processing to work with. - ClassLoaderDataGraph::clear_claimed_marks(); - - // Mark from roots one level into CMS - MarkRefsIntoClosure notOlder(_span, verification_mark_bm()); - heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. - - { - StrongRootsScope srs(1); - - heap->cms_process_roots(&srs, - true, // young gen as roots - GenCollectedHeap::ScanningOption(roots_scanning_options()), - should_unload_classes(), - ¬Older, - NULL); - } - - // Now mark from the roots - MarkFromRootsClosure markFromRootsClosure(this, _span, - verification_mark_bm(), verification_mark_stack(), - false /* don't yield */, true /* verifying */); - assert(_restart_addr == NULL, "Expected pre-condition"); - verification_mark_bm()->iterate(&markFromRootsClosure); - while (_restart_addr != NULL) { - // Deal with stack overflow: by restarting at the indicated - // address. - HeapWord* ra = _restart_addr; - markFromRootsClosure.reset(ra); - _restart_addr = NULL; - verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); - } - assert(verification_mark_stack()->isEmpty(), "Should have been drained"); - verify_work_stacks_empty(); - - // Marking completed -- now verify that each bit marked in - // verification_mark_bm() is also marked in markBitMap(); flag all - // errors by printing corresponding objects. - VerifyMarkedClosure vcl(markBitMap()); - verification_mark_bm()->iterate(&vcl); - if (vcl.failed()) { - Log(gc, verify) log; - log.error("Failed marking verification after remark"); - ResourceMark rm; - LogStream ls(log.error()); - heap->print_on(&ls); - fatal("CMS: failed marking verification after remark"); - } -} - -class VerifyCLDOopsCLDClosure : public CLDClosure { - class VerifyCLDOopsClosure : public OopClosure { - CMSBitMap* _bitmap; - public: - VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { } - void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); } - void do_oop(narrowOop* p) { ShouldNotReachHere(); } - } _oop_closure; - public: - VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {} - void do_cld(ClassLoaderData* cld) { - cld->oops_do(&_oop_closure, ClassLoaderData::_claim_none, false); - } -}; - -void CMSCollector::verify_after_remark_work_2() { - ResourceMark rm; - HandleMark hm; - CMSHeap* heap = CMSHeap::heap(); - - // Get a clear set of claim bits for the roots processing to work with. - ClassLoaderDataGraph::clear_claimed_marks(); - - // Mark from roots one level into CMS - MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(), - markBitMap()); - CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong); - - heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. - - { - StrongRootsScope srs(1); - - heap->cms_process_roots(&srs, - true, // young gen as roots - GenCollectedHeap::ScanningOption(roots_scanning_options()), - should_unload_classes(), - ¬Older, - &cld_closure); - } - - // Now mark from the roots - MarkFromRootsVerifyClosure markFromRootsClosure(this, _span, - verification_mark_bm(), markBitMap(), verification_mark_stack()); - assert(_restart_addr == NULL, "Expected pre-condition"); - verification_mark_bm()->iterate(&markFromRootsClosure); - while (_restart_addr != NULL) { - // Deal with stack overflow: by restarting at the indicated - // address. - HeapWord* ra = _restart_addr; - markFromRootsClosure.reset(ra); - _restart_addr = NULL; - verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); - } - assert(verification_mark_stack()->isEmpty(), "Should have been drained"); - verify_work_stacks_empty(); - - VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm()); - ClassLoaderDataGraph::cld_do(&verify_cld_oops); - - // Marking completed -- now verify that each bit marked in - // verification_mark_bm() is also marked in markBitMap(); flag all - // errors by printing corresponding objects. - VerifyMarkedClosure vcl(markBitMap()); - verification_mark_bm()->iterate(&vcl); - assert(!vcl.failed(), "Else verification above should not have succeeded"); -} - -void ConcurrentMarkSweepGeneration::save_marks() { - // delegate to CMS space - cmsSpace()->save_marks(); -} - -bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() { - return cmsSpace()->no_allocs_since_save_marks(); -} - -void -ConcurrentMarkSweepGeneration::oop_iterate(OopIterateClosure* cl) { - if (freelistLock()->owned_by_self()) { - Generation::oop_iterate(cl); - } else { - MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag); - Generation::oop_iterate(cl); - } -} - -void -ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) { - if (freelistLock()->owned_by_self()) { - Generation::object_iterate(cl); - } else { - MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag); - Generation::object_iterate(cl); - } -} - -void -ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) { - if (freelistLock()->owned_by_self()) { - Generation::safe_object_iterate(cl); - } else { - MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag); - Generation::safe_object_iterate(cl); - } -} - -void -ConcurrentMarkSweepGeneration::post_compact() { -} - -void -ConcurrentMarkSweepGeneration::prepare_for_verify() { - // Fix the linear allocation blocks to look like free blocks. - - // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those - // are not called when the heap is verified during universe initialization and - // at vm shutdown. - if (freelistLock()->owned_by_self()) { - cmsSpace()->prepare_for_verify(); - } else { - MutexLocker fll(freelistLock(), Mutex::_no_safepoint_check_flag); - cmsSpace()->prepare_for_verify(); - } -} - -void -ConcurrentMarkSweepGeneration::verify() { - // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those - // are not called when the heap is verified during universe initialization and - // at vm shutdown. - if (freelistLock()->owned_by_self()) { - cmsSpace()->verify(); - } else { - MutexLocker fll(freelistLock(), Mutex::_no_safepoint_check_flag); - cmsSpace()->verify(); - } -} - -void CMSCollector::verify() { - _cmsGen->verify(); -} - -#ifndef PRODUCT -bool CMSCollector::overflow_list_is_empty() const { - assert(_num_par_pushes >= 0, "Inconsistency"); - if (_overflow_list == NULL) { - assert(_num_par_pushes == 0, "Inconsistency"); - } - return _overflow_list == NULL; -} - -// The methods verify_work_stacks_empty() and verify_overflow_empty() -// merely consolidate assertion checks that appear to occur together frequently. -void CMSCollector::verify_work_stacks_empty() const { - assert(_markStack.isEmpty(), "Marking stack should be empty"); - assert(overflow_list_is_empty(), "Overflow list should be empty"); -} - -void CMSCollector::verify_overflow_empty() const { - assert(overflow_list_is_empty(), "Overflow list should be empty"); - assert(no_preserved_marks(), "No preserved marks"); -} -#endif // PRODUCT - -// Decide if we want to enable class unloading as part of the -// ensuing concurrent GC cycle. We will collect and -// unload classes if it's the case that: -// (a) class unloading is enabled at the command line, and -// (b) old gen is getting really full -// NOTE: Provided there is no change in the state of the heap between -// calls to this method, it should have idempotent results. Moreover, -// its results should be monotonically increasing (i.e. going from 0 to 1, -// but not 1 to 0) between successive calls between which the heap was -// not collected. For the implementation below, it must thus rely on -// the property that concurrent_cycles_since_last_unload() -// will not decrease unless a collection cycle happened and that -// _cmsGen->is_too_full() are -// themselves also monotonic in that sense. See check_monotonicity() -// below. -void CMSCollector::update_should_unload_classes() { - _should_unload_classes = false; - if (CMSClassUnloadingEnabled) { - _should_unload_classes = (concurrent_cycles_since_last_unload() >= - CMSClassUnloadingMaxInterval) - || _cmsGen->is_too_full(); - } -} - -bool ConcurrentMarkSweepGeneration::is_too_full() const { - bool res = should_concurrent_collect(); - res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0); - return res; -} - -void CMSCollector::setup_cms_unloading_and_verification_state() { - const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC - || VerifyBeforeExit; - const int rso = GenCollectedHeap::SO_AllCodeCache; - - // We set the proper root for this CMS cycle here. - if (should_unload_classes()) { // Should unload classes this cycle - remove_root_scanning_option(rso); // Shrink the root set appropriately - set_verifying(should_verify); // Set verification state for this cycle - return; // Nothing else needs to be done at this time - } - - // Not unloading classes this cycle - assert(!should_unload_classes(), "Inconsistency!"); - - // If we are not unloading classes then add SO_AllCodeCache to root - // scanning options. - add_root_scanning_option(rso); - - if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) { - set_verifying(true); - } else if (verifying() && !should_verify) { - // We were verifying, but some verification flags got disabled. - set_verifying(false); - // Exclude symbols, strings and code cache elements from root scanning to - // reduce IM and RM pauses. - remove_root_scanning_option(rso); - } -} - - -#ifndef PRODUCT -HeapWord* CMSCollector::block_start(const void* p) const { - const HeapWord* addr = (HeapWord*)p; - if (_span.contains(p)) { - if (_cmsGen->cmsSpace()->is_in_reserved(addr)) { - return _cmsGen->cmsSpace()->block_start(p); - } - } - return NULL; -} -#endif - -HeapWord* -ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size, - bool tlab, - bool parallel) { - CMSSynchronousYieldRequest yr; - assert(!tlab, "Can't deal with TLAB allocation"); - MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag); - expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation); - if (GCExpandToAllocateDelayMillis > 0) { - os::naked_sleep(GCExpandToAllocateDelayMillis); - } - return have_lock_and_allocate(word_size, tlab); -} - -void ConcurrentMarkSweepGeneration::expand_for_gc_cause( - size_t bytes, - size_t expand_bytes, - CMSExpansionCause::Cause cause) -{ - - bool success = expand(bytes, expand_bytes); - - // remember why we expanded; this information is used - // by shouldConcurrentCollect() when making decisions on whether to start - // a new CMS cycle. - if (success) { - set_expansion_cause(cause); - log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause)); - } -} - -HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) { - HeapWord* res = NULL; - MutexLocker x(ParGCRareEvent_lock); - while (true) { - // Expansion by some other thread might make alloc OK now: - res = ps->lab.alloc(word_sz); - if (res != NULL) return res; - // If there's not enough expansion space available, give up. - if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) { - return NULL; - } - // Otherwise, we try expansion. - expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab); - // Now go around the loop and try alloc again; - // A competing par_promote might beat us to the expansion space, - // so we may go around the loop again if promotion fails again. - if (GCExpandToAllocateDelayMillis > 0) { - os::naked_sleep(GCExpandToAllocateDelayMillis); - } - } -} - - -bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space( - PromotionInfo* promo) { - MutexLocker x(ParGCRareEvent_lock); - size_t refill_size_bytes = promo->refillSize() * HeapWordSize; - while (true) { - // Expansion by some other thread might make alloc OK now: - if (promo->ensure_spooling_space()) { - assert(promo->has_spooling_space(), - "Post-condition of successful ensure_spooling_space()"); - return true; - } - // If there's not enough expansion space available, give up. - if (_virtual_space.uncommitted_size() < refill_size_bytes) { - return false; - } - // Otherwise, we try expansion. - expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space); - // Now go around the loop and try alloc again; - // A competing allocation might beat us to the expansion space, - // so we may go around the loop again if allocation fails again. - if (GCExpandToAllocateDelayMillis > 0) { - os::naked_sleep(GCExpandToAllocateDelayMillis); - } - } -} - -void ConcurrentMarkSweepGeneration::shrink(size_t bytes) { - // Only shrink if a compaction was done so that all the free space - // in the generation is in a contiguous block at the end. - if (did_compact()) { - CardGeneration::shrink(bytes); - } -} - -void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() { - assert_locked_or_safepoint(Heap_lock); -} - -void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) { - assert_locked_or_safepoint(Heap_lock); - assert_lock_strong(freelistLock()); - log_trace(gc)("Shrinking of CMS not yet implemented"); - return; -} - - -// Simple ctor/dtor wrapper for accounting & timer chores around concurrent -// phases. -class CMSPhaseAccounting: public StackObj { - public: - CMSPhaseAccounting(CMSCollector *collector, - const char *title); - ~CMSPhaseAccounting(); - - private: - CMSCollector *_collector; - const char *_title; - GCTraceConcTime(Info, gc) _trace_time; - - public: - // Not MT-safe; so do not pass around these StackObj's - // where they may be accessed by other threads. - double wallclock_millis() { - return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time()); - } -}; - -CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector, - const char *title) : - _collector(collector), _title(title), _trace_time(title) { - - _collector->resetYields(); - _collector->resetTimer(); - _collector->startTimer(); - _collector->gc_timer_cm()->register_gc_concurrent_start(title); -} - -CMSPhaseAccounting::~CMSPhaseAccounting() { - _collector->gc_timer_cm()->register_gc_concurrent_end(); - _collector->stopTimer(); - log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_millis(_collector->timerTicks())); - log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields()); -} - -// CMS work - -// The common parts of CMSParInitialMarkTask and CMSParRemarkTask. -class CMSParMarkTask : public AbstractGangTask { - protected: - CMSCollector* _collector; - uint _n_workers; - CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) : - AbstractGangTask(name), - _collector(collector), - _n_workers(n_workers) {} - // Work method in support of parallel rescan ... of young gen spaces - void do_young_space_rescan(OopsInGenClosure* cl, - ContiguousSpace* space, - HeapWord** chunk_array, size_t chunk_top); - void work_on_young_gen_roots(OopsInGenClosure* cl); -}; - -// Parallel initial mark task -class CMSParInitialMarkTask: public CMSParMarkTask { - StrongRootsScope* _strong_roots_scope; - public: - CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) : - CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers), - _strong_roots_scope(strong_roots_scope) {} - void work(uint worker_id); -}; - -// Checkpoint the roots into this generation from outside -// this generation. [Note this initial checkpoint need only -// be approximate -- we'll do a catch up phase subsequently.] -void CMSCollector::checkpointRootsInitial() { - assert(_collectorState == InitialMarking, "Wrong collector state"); - check_correct_thread_executing(); - TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause()); - - save_heap_summary(); - report_heap_summary(GCWhen::BeforeGC); - - ReferenceProcessor* rp = ref_processor(); - assert(_restart_addr == NULL, "Control point invariant"); - { - // acquire locks for subsequent manipulations - MutexLocker x(bitMapLock(), - Mutex::_no_safepoint_check_flag); - checkpointRootsInitialWork(); - // enable ("weak") refs discovery - rp->enable_discovery(); - _collectorState = Marking; - } - - _cmsGen->cmsSpace()->recalculate_used_stable(); -} - -void CMSCollector::checkpointRootsInitialWork() { - assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped"); - assert(_collectorState == InitialMarking, "just checking"); - - // Already have locks. - assert_lock_strong(bitMapLock()); - assert(_markBitMap.isAllClear(), "was reset at end of previous cycle"); - - // Setup the verification and class unloading state for this - // CMS collection cycle. - setup_cms_unloading_and_verification_state(); - - GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm); - - // Reset all the PLAB chunk arrays if necessary. - if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) { - reset_survivor_plab_arrays(); - } - - ResourceMark rm; - HandleMark hm; - - MarkRefsIntoClosure notOlder(_span, &_markBitMap); - CMSHeap* heap = CMSHeap::heap(); - - verify_work_stacks_empty(); - verify_overflow_empty(); - - heap->ensure_parsability(false); // fill TLABs, but no need to retire them - // Update the saved marks which may affect the root scans. - heap->save_marks(); - - // weak reference processing has not started yet. - ref_processor()->set_enqueuing_is_done(false); - - // Need to remember all newly created CLDs, - // so that we can guarantee that the remark finds them. - ClassLoaderDataGraph::remember_new_clds(true); - - // Whenever a CLD is found, it will be claimed before proceeding to mark - // the klasses. The claimed marks need to be cleared before marking starts. - ClassLoaderDataGraph::clear_claimed_marks(); - - print_eden_and_survivor_chunk_arrays(); - - { -#if COMPILER2_OR_JVMCI - DerivedPointerTableDeactivate dpt_deact; -#endif - if (CMSParallelInitialMarkEnabled) { - // The parallel version. - WorkGang* workers = heap->workers(); - assert(workers != NULL, "Need parallel worker threads."); - uint n_workers = workers->active_workers(); - - StrongRootsScope srs(n_workers); - - CMSParInitialMarkTask tsk(this, &srs, n_workers); - initialize_sequential_subtasks_for_young_gen_rescan(n_workers); - // If the total workers is greater than 1, then multiple workers - // may be used at some time and the initialization has been set - // such that the single threaded path cannot be used. - if (workers->total_workers() > 1) { - workers->run_task(&tsk); - } else { - tsk.work(0); - } - } else { - // The serial version. - CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong); - heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. - - StrongRootsScope srs(1); - - heap->cms_process_roots(&srs, - true, // young gen as roots - GenCollectedHeap::ScanningOption(roots_scanning_options()), - should_unload_classes(), - ¬Older, - &cld_closure); - } - } - - // Clear mod-union table; it will be dirtied in the prologue of - // CMS generation per each young generation collection. - - assert(_modUnionTable.isAllClear(), - "Was cleared in most recent final checkpoint phase" - " or no bits are set in the gc_prologue before the start of the next " - "subsequent marking phase."); - - assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be"); - - // Save the end of the used_region of the constituent generations - // to be used to limit the extent of sweep in each generation. - save_sweep_limits(); - verify_overflow_empty(); -} - -bool CMSCollector::markFromRoots() { - // we might be tempted to assert that: - // assert(!SafepointSynchronize::is_at_safepoint(), - // "inconsistent argument?"); - // However that wouldn't be right, because it's possible that - // a safepoint is indeed in progress as a young generation - // stop-the-world GC happens even as we mark in this generation. - assert(_collectorState == Marking, "inconsistent state?"); - check_correct_thread_executing(); - verify_overflow_empty(); - - // Weak ref discovery note: We may be discovering weak - // refs in this generation concurrent (but interleaved) with - // weak ref discovery by the young generation collector. - - CMSTokenSyncWithLocks ts(true, bitMapLock()); - GCTraceCPUTime tcpu; - CMSPhaseAccounting pa(this, "Concurrent Mark"); - bool res = markFromRootsWork(); - if (res) { - _collectorState = Precleaning; - } else { // We failed and a foreground collection wants to take over - assert(_foregroundGCIsActive, "internal state inconsistency"); - assert(_restart_addr == NULL, "foreground will restart from scratch"); - log_debug(gc)("bailing out to foreground collection"); - } - verify_overflow_empty(); - return res; -} - -bool CMSCollector::markFromRootsWork() { - // iterate over marked bits in bit map, doing a full scan and mark - // from these roots using the following algorithm: - // . if oop is to the right of the current scan pointer, - // mark corresponding bit (we'll process it later) - // . else (oop is to left of current scan pointer) - // push oop on marking stack - // . drain the marking stack - - // Note that when we do a marking step we need to hold the - // bit map lock -- recall that direct allocation (by mutators) - // and promotion (by the young generation collector) is also - // marking the bit map. [the so-called allocate live policy.] - // Because the implementation of bit map marking is not - // robust wrt simultaneous marking of bits in the same word, - // we need to make sure that there is no such interference - // between concurrent such updates. - - // already have locks - assert_lock_strong(bitMapLock()); - - verify_work_stacks_empty(); - verify_overflow_empty(); - bool result = false; - if (CMSConcurrentMTEnabled && ConcGCThreads > 0) { - result = do_marking_mt(); - } else { - result = do_marking_st(); - } - return result; -} - -// Forward decl -class CMSConcMarkingTask; - -class CMSConcMarkingParallelTerminator: public ParallelTaskTerminator { - CMSCollector* _collector; - CMSConcMarkingTask* _task; - public: - virtual void yield(); - - // "n_threads" is the number of threads to be terminated. - // "queue_set" is a set of work queues of other threads. - // "collector" is the CMS collector associated with this task terminator. - // "yield" indicates whether we need the gang as a whole to yield. - CMSConcMarkingParallelTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) : - ParallelTaskTerminator(n_threads, queue_set), - _collector(collector) { } - - void set_task(CMSConcMarkingTask* task) { - _task = task; - } -}; - -class CMSConcMarkingOWSTTerminator: public OWSTTaskTerminator { - CMSCollector* _collector; - CMSConcMarkingTask* _task; - public: - virtual void yield(); - - // "n_threads" is the number of threads to be terminated. - // "queue_set" is a set of work queues of other threads. - // "collector" is the CMS collector associated with this task terminator. - // "yield" indicates whether we need the gang as a whole to yield. - CMSConcMarkingOWSTTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) : - OWSTTaskTerminator(n_threads, queue_set), - _collector(collector) { } - - void set_task(CMSConcMarkingTask* task) { - _task = task; - } -}; - -class CMSConcMarkingTaskTerminator { - private: - ParallelTaskTerminator* _term; - public: - CMSConcMarkingTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) { - if (UseOWSTTaskTerminator) { - _term = new CMSConcMarkingOWSTTerminator(n_threads, queue_set, collector); - } else { - _term = new CMSConcMarkingParallelTerminator(n_threads, queue_set, collector); - } - } - ~CMSConcMarkingTaskTerminator() { - assert(_term != NULL, "Must not be NULL"); - delete _term; - } - - void set_task(CMSConcMarkingTask* task); - ParallelTaskTerminator* terminator() const { return _term; } -}; - -class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator { - CMSConcMarkingTask* _task; - public: - bool should_exit_termination(); - void set_task(CMSConcMarkingTask* task) { - _task = task; - } -}; - -// MT Concurrent Marking Task -class CMSConcMarkingTask: public YieldingFlexibleGangTask { - CMSCollector* _collector; - uint _n_workers; // requested/desired # workers - bool _result; - CompactibleFreeListSpace* _cms_space; - char _pad_front[64]; // padding to ... - HeapWord* volatile _global_finger; // ... avoid sharing cache line - char _pad_back[64]; - HeapWord* _restart_addr; - - // Exposed here for yielding support - Mutex* const _bit_map_lock; - - // The per thread work queues, available here for stealing - OopTaskQueueSet* _task_queues; - - // Termination (and yielding) support - CMSConcMarkingTaskTerminator _term; - CMSConcMarkingTerminatorTerminator _term_term; - - public: - CMSConcMarkingTask(CMSCollector* collector, - CompactibleFreeListSpace* cms_space, - YieldingFlexibleWorkGang* workers, - OopTaskQueueSet* task_queues): - YieldingFlexibleGangTask("Concurrent marking done multi-threaded"), - _collector(collector), - _n_workers(0), - _result(true), - _cms_space(cms_space), - _bit_map_lock(collector->bitMapLock()), - _task_queues(task_queues), - _term(_n_workers, task_queues, _collector) - { - _requested_size = _n_workers; - _term.set_task(this); - _term_term.set_task(this); - _restart_addr = _global_finger = _cms_space->bottom(); - } - - - OopTaskQueueSet* task_queues() { return _task_queues; } - - OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } - - HeapWord* volatile* global_finger_addr() { return &_global_finger; } - - ParallelTaskTerminator* terminator() { return _term.terminator(); } - - virtual void set_for_termination(uint active_workers) { - terminator()->reset_for_reuse(active_workers); - } - - void work(uint worker_id); - bool should_yield() { - return ConcurrentMarkSweepThread::should_yield() - && !_collector->foregroundGCIsActive(); - } - - virtual void coordinator_yield(); // stuff done by coordinator - bool result() { return _result; } - - void reset(HeapWord* ra) { - assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)"); - _restart_addr = _global_finger = ra; - _term.terminator()->reset_for_reuse(); - } - - static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, - OopTaskQueue* work_q); - - private: - void do_scan_and_mark(int i, CompactibleFreeListSpace* sp); - void do_work_steal(int i); - void bump_global_finger(HeapWord* f); -}; - -bool CMSConcMarkingTerminatorTerminator::should_exit_termination() { - assert(_task != NULL, "Error"); - return _task->yielding(); - // Note that we do not need the disjunct || _task->should_yield() above - // because we want terminating threads to yield only if the task - // is already in the midst of yielding, which happens only after at least one - // thread has yielded. -} - -void CMSConcMarkingParallelTerminator::yield() { - if (_task->should_yield()) { - _task->yield(); - } else { - ParallelTaskTerminator::yield(); - } -} - -void CMSConcMarkingOWSTTerminator::yield() { - if (_task->should_yield()) { - _task->yield(); - } else { - OWSTTaskTerminator::yield(); - } -} - -void CMSConcMarkingTaskTerminator::set_task(CMSConcMarkingTask* task) { - if (UseOWSTTaskTerminator) { - ((CMSConcMarkingOWSTTerminator*)_term)->set_task(task); - } else { - ((CMSConcMarkingParallelTerminator*)_term)->set_task(task); - } -} - -//////////////////////////////////////////////////////////////// -// Concurrent Marking Algorithm Sketch -//////////////////////////////////////////////////////////////// -// Until all tasks exhausted (both spaces): -// -- claim next available chunk -// -- bump global finger via CAS -// -- find first object that starts in this chunk -// and start scanning bitmap from that position -// -- scan marked objects for oops -// -- CAS-mark target, and if successful: -// . if target oop is above global finger (volatile read) -// nothing to do -// . if target oop is in chunk and above local finger -// then nothing to do -// . else push on work-queue -// -- Deal with possible overflow issues: -// . local work-queue overflow causes stuff to be pushed on -// global (common) overflow queue -// . always first empty local work queue -// . then get a batch of oops from global work queue if any -// . then do work stealing -// -- When all tasks claimed (both spaces) -// and local work queue empty, -// then in a loop do: -// . check global overflow stack; steal a batch of oops and trace -// . try to steal from other threads oif GOS is empty -// . if neither is available, offer termination -// -- Terminate and return result -// -void CMSConcMarkingTask::work(uint worker_id) { - elapsedTimer _timer; - ResourceMark rm; - HandleMark hm; - - DEBUG_ONLY(_collector->verify_overflow_empty();) - - // Before we begin work, our work queue should be empty - assert(work_queue(worker_id)->size() == 0, "Expected to be empty"); - // Scan the bitmap covering _cms_space, tracing through grey objects. - _timer.start(); - do_scan_and_mark(worker_id, _cms_space); - _timer.stop(); - log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds()); - - // ... do work stealing - _timer.reset(); - _timer.start(); - do_work_steal(worker_id); - _timer.stop(); - log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds()); - assert(_collector->_markStack.isEmpty(), "Should have been emptied"); - assert(work_queue(worker_id)->size() == 0, "Should have been emptied"); - // Note that under the current task protocol, the - // following assertion is true even of the spaces - // expanded since the completion of the concurrent - // marking. XXX This will likely change under a strict - // ABORT semantics. - // After perm removal the comparison was changed to - // greater than or equal to from strictly greater than. - // Before perm removal the highest address sweep would - // have been at the end of perm gen but now is at the - // end of the tenured gen. - assert(_global_finger >= _cms_space->end(), - "All tasks have been completed"); - DEBUG_ONLY(_collector->verify_overflow_empty();) -} - -void CMSConcMarkingTask::bump_global_finger(HeapWord* f) { - HeapWord* read = _global_finger; - HeapWord* cur = read; - while (f > read) { - cur = read; - read = Atomic::cmpxchg(f, &_global_finger, cur); - if (cur == read) { - // our cas succeeded - assert(_global_finger >= f, "protocol consistency"); - break; - } - } -} - -// This is really inefficient, and should be redone by -// using (not yet available) block-read and -write interfaces to the -// stack and the work_queue. XXX FIX ME !!! -bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, - OopTaskQueue* work_q) { - // Fast lock-free check - if (ovflw_stk->length() == 0) { - return false; - } - assert(work_q->size() == 0, "Shouldn't steal"); - MutexLocker ml(ovflw_stk->par_lock(), - Mutex::_no_safepoint_check_flag); - // Grab up to 1/4 the size of the work queue - size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, - (size_t)ParGCDesiredObjsFromOverflowList); - num = MIN2(num, ovflw_stk->length()); - for (int i = (int) num; i > 0; i--) { - oop cur = ovflw_stk->pop(); - assert(cur != NULL, "Counted wrong?"); - work_q->push(cur); - } - return num > 0; -} - -void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) { - SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); - int n_tasks = pst->n_tasks(); - // We allow that there may be no tasks to do here because - // we are restarting after a stack overflow. - assert(pst->valid() || n_tasks == 0, "Uninitialized use?"); - uint nth_task = 0; - - HeapWord* aligned_start = sp->bottom(); - if (sp->used_region().contains(_restart_addr)) { - // Align down to a card boundary for the start of 0th task - // for this space. - aligned_start = align_down(_restart_addr, CardTable::card_size); - } - - size_t chunk_size = sp->marking_task_size(); - while (pst->try_claim_task(/* reference */ nth_task)) { - // Having claimed the nth task in this space, - // compute the chunk that it corresponds to: - MemRegion span = MemRegion(aligned_start + nth_task*chunk_size, - aligned_start + (nth_task+1)*chunk_size); - // Try and bump the global finger via a CAS; - // note that we need to do the global finger bump - // _before_ taking the intersection below, because - // the task corresponding to that region will be - // deemed done even if the used_region() expands - // because of allocation -- as it almost certainly will - // during start-up while the threads yield in the - // closure below. - HeapWord* finger = span.end(); - bump_global_finger(finger); // atomically - // There are null tasks here corresponding to chunks - // beyond the "top" address of the space. - span = span.intersection(sp->used_region()); - if (!span.is_empty()) { // Non-null task - HeapWord* prev_obj; - assert(!span.contains(_restart_addr) || nth_task == 0, - "Inconsistency"); - if (nth_task == 0) { - // For the 0th task, we'll not need to compute a block_start. - if (span.contains(_restart_addr)) { - // In the case of a restart because of stack overflow, - // we might additionally skip a chunk prefix. - prev_obj = _restart_addr; - } else { - prev_obj = span.start(); - } - } else { - // We want to skip the first object because - // the protocol is to scan any object in its entirety - // that _starts_ in this span; a fortiori, any - // object starting in an earlier span is scanned - // as part of an earlier claimed task. - // Below we use the "careful" version of block_start - // so we do not try to navigate uninitialized objects. - prev_obj = sp->block_start_careful(span.start()); - // Below we use a variant of block_size that uses the - // Printezis bits to avoid waiting for allocated - // objects to become initialized/parsable. - while (prev_obj < span.start()) { - size_t sz = sp->block_size_no_stall(prev_obj, _collector); - if (sz > 0) { - prev_obj += sz; - } else { - // In this case we may end up doing a bit of redundant - // scanning, but that appears unavoidable, short of - // locking the free list locks; see bug 6324141. - break; - } - } - } - if (prev_obj < span.end()) { - MemRegion my_span = MemRegion(prev_obj, span.end()); - // Do the marking work within a non-empty span -- - // the last argument to the constructor indicates whether the - // iteration should be incremental with periodic yields. - ParMarkFromRootsClosure cl(this, _collector, my_span, - &_collector->_markBitMap, - work_queue(i), - &_collector->_markStack); - _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end()); - } // else nothing to do for this task - } // else nothing to do for this task - } - // We'd be tempted to assert here that since there are no - // more tasks left to claim in this space, the global_finger - // must exceed space->top() and a fortiori space->end(). However, - // that would not quite be correct because the bumping of - // global_finger occurs strictly after the claiming of a task, - // so by the time we reach here the global finger may not yet - // have been bumped up by the thread that claimed the last - // task. - pst->all_tasks_completed(); -} - -class ParConcMarkingClosure: public MetadataVisitingOopIterateClosure { - private: - CMSCollector* _collector; - CMSConcMarkingTask* _task; - MemRegion _span; - CMSBitMap* _bit_map; - CMSMarkStack* _overflow_stack; - OopTaskQueue* _work_queue; - protected: - DO_OOP_WORK_DEFN - public: - ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue, - CMSBitMap* bit_map, CMSMarkStack* overflow_stack): - MetadataVisitingOopIterateClosure(collector->ref_processor()), - _collector(collector), - _task(task), - _span(collector->_span), - _bit_map(bit_map), - _overflow_stack(overflow_stack), - _work_queue(work_queue) - { } - virtual void do_oop(oop* p); - virtual void do_oop(narrowOop* p); - - void trim_queue(size_t max); - void handle_stack_overflow(HeapWord* lost); - void do_yield_check() { - if (_task->should_yield()) { - _task->yield(); - } - } -}; - -DO_OOP_WORK_IMPL(ParConcMarkingClosure) - -// Grey object scanning during work stealing phase -- -// the salient assumption here is that any references -// that are in these stolen objects being scanned must -// already have been initialized (else they would not have -// been published), so we do not need to check for -// uninitialized objects before pushing here. -void ParConcMarkingClosure::do_oop(oop obj) { - assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); - HeapWord* addr = (HeapWord*)obj; - // Check if oop points into the CMS generation - // and is not marked - if (_span.contains(addr) && !_bit_map->isMarked(addr)) { - // a white object ... - // If we manage to "claim" the object, by being the - // first thread to mark it, then we push it on our - // marking stack - if (_bit_map->par_mark(addr)) { // ... now grey - // push on work queue (grey set) - bool simulate_overflow = false; - NOT_PRODUCT( - if (CMSMarkStackOverflowALot && - _collector->simulate_overflow()) { - // simulate a stack overflow - simulate_overflow = true; - } - ) - if (simulate_overflow || - !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) { - // stack overflow - log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity()); - // We cannot assert that the overflow stack is full because - // it may have been emptied since. - assert(simulate_overflow || - _work_queue->size() == _work_queue->max_elems(), - "Else push should have succeeded"); - handle_stack_overflow(addr); - } - } // Else, some other thread got there first - do_yield_check(); - } -} - -void ParConcMarkingClosure::trim_queue(size_t max) { - while (_work_queue->size() > max) { - oop new_oop; - if (_work_queue->pop_local(new_oop)) { - assert(oopDesc::is_oop(new_oop), "Should be an oop"); - assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object"); - assert(_span.contains((HeapWord*)new_oop), "Not in span"); - new_oop->oop_iterate(this); // do_oop() above - do_yield_check(); - } - } -} - -// Upon stack overflow, we discard (part of) the stack, -// remembering the least address amongst those discarded -// in CMSCollector's _restart_address. -void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) { - // We need to do this under a mutex to prevent other - // workers from interfering with the work done below. - MutexLocker ml(_overflow_stack->par_lock(), - Mutex::_no_safepoint_check_flag); - // Remember the least grey address discarded - HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); - _collector->lower_restart_addr(ra); - _overflow_stack->reset(); // discard stack contents - _overflow_stack->expand(); // expand the stack if possible -} - - -void CMSConcMarkingTask::do_work_steal(int i) { - OopTaskQueue* work_q = work_queue(i); - oop obj_to_scan; - CMSBitMap* bm = &(_collector->_markBitMap); - CMSMarkStack* ovflw = &(_collector->_markStack); - ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw); - while (true) { - cl.trim_queue(0); - assert(work_q->size() == 0, "Should have been emptied above"); - if (get_work_from_overflow_stack(ovflw, work_q)) { - // Can't assert below because the work obtained from the - // overflow stack may already have been stolen from us. - // assert(work_q->size() > 0, "Work from overflow stack"); - continue; - } else if (task_queues()->steal(i, /* reference */ obj_to_scan)) { - assert(oopDesc::is_oop(obj_to_scan), "Should be an oop"); - assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object"); - obj_to_scan->oop_iterate(&cl); - } else if (terminator()->offer_termination(&_term_term)) { - assert(work_q->size() == 0, "Impossible!"); - break; - } else if (yielding() || should_yield()) { - yield(); - } - } -} - -// This is run by the CMS (coordinator) thread. -void CMSConcMarkingTask::coordinator_yield() { - assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "CMS thread should hold CMS token"); - // First give up the locks, then yield, then re-lock - // We should probably use a constructor/destructor idiom to - // do this unlock/lock or modify the MutexUnlocker class to - // serve our purpose. XXX - assert_lock_strong(_bit_map_lock); - _bit_map_lock->unlock(); - ConcurrentMarkSweepThread::desynchronize(true); - _collector->stopTimer(); - _collector->incrementYields(); - - // It is possible for whichever thread initiated the yield request - // not to get a chance to wake up and take the bitmap lock between - // this thread releasing it and reacquiring it. So, while the - // should_yield() flag is on, let's sleep for a bit to give the - // other thread a chance to wake up. The limit imposed on the number - // of iterations is defensive, to avoid any unforseen circumstances - // putting us into an infinite loop. Since it's always been this - // (coordinator_yield()) method that was observed to cause the - // problem, we are using a parameter (CMSCoordinatorYieldSleepCount) - // which is by default non-zero. For the other seven methods that - // also perform the yield operation, as are using a different - // parameter (CMSYieldSleepCount) which is by default zero. This way we - // can enable the sleeping for those methods too, if necessary. - // See 6442774. - // - // We really need to reconsider the synchronization between the GC - // thread and the yield-requesting threads in the future and we - // should really use wait/notify, which is the recommended - // way of doing this type of interaction. Additionally, we should - // consolidate the eight methods that do the yield operation and they - // are almost identical into one for better maintainability and - // readability. See 6445193. - // - // Tony 2006.06.29 - for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount && - ConcurrentMarkSweepThread::should_yield() && - !CMSCollector::foregroundGCIsActive(); ++i) { - os::naked_short_sleep(1); - } - - ConcurrentMarkSweepThread::synchronize(true); - _bit_map_lock->lock_without_safepoint_check(); - _collector->startTimer(); -} - -bool CMSCollector::do_marking_mt() { - assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition"); - uint num_workers = WorkerPolicy::calc_active_conc_workers(conc_workers()->total_workers(), - conc_workers()->active_workers(), - Threads::number_of_non_daemon_threads()); - num_workers = conc_workers()->update_active_workers(num_workers); - log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers()); - - CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); - - CMSConcMarkingTask tsk(this, - cms_space, - conc_workers(), - task_queues()); - - // Since the actual number of workers we get may be different - // from the number we requested above, do we need to do anything different - // below? In particular, may be we need to subclass the SequantialSubTasksDone - // class?? XXX - cms_space ->initialize_sequential_subtasks_for_marking(num_workers); - - // Refs discovery is already non-atomic. - assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic"); - assert(ref_processor()->discovery_is_mt(), "Discovery should be MT"); - conc_workers()->start_task(&tsk); - while (tsk.yielded()) { - tsk.coordinator_yield(); - conc_workers()->continue_task(&tsk); - } - // If the task was aborted, _restart_addr will be non-NULL - assert(tsk.completed() || _restart_addr != NULL, "Inconsistency"); - while (_restart_addr != NULL) { - // XXX For now we do not make use of ABORTED state and have not - // yet implemented the right abort semantics (even in the original - // single-threaded CMS case). That needs some more investigation - // and is deferred for now; see CR# TBF. 07252005YSR. XXX - assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency"); - // If _restart_addr is non-NULL, a marking stack overflow - // occurred; we need to do a fresh marking iteration from the - // indicated restart address. - if (_foregroundGCIsActive) { - // We may be running into repeated stack overflows, having - // reached the limit of the stack size, while making very - // slow forward progress. It may be best to bail out and - // let the foreground collector do its job. - // Clear _restart_addr, so that foreground GC - // works from scratch. This avoids the headache of - // a "rescan" which would otherwise be needed because - // of the dirty mod union table & card table. - _restart_addr = NULL; - return false; - } - // Adjust the task to restart from _restart_addr - tsk.reset(_restart_addr); - cms_space ->initialize_sequential_subtasks_for_marking(num_workers, - _restart_addr); - _restart_addr = NULL; - // Get the workers going again - conc_workers()->start_task(&tsk); - while (tsk.yielded()) { - tsk.coordinator_yield(); - conc_workers()->continue_task(&tsk); - } - } - assert(tsk.completed(), "Inconsistency"); - assert(tsk.result() == true, "Inconsistency"); - return true; -} - -bool CMSCollector::do_marking_st() { - ResourceMark rm; - HandleMark hm; - - // Temporarily make refs discovery single threaded (non-MT) - ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false); - MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap, - &_markStack, CMSYield); - // the last argument to iterate indicates whether the iteration - // should be incremental with periodic yields. - _markBitMap.iterate(&markFromRootsClosure); - // If _restart_addr is non-NULL, a marking stack overflow - // occurred; we need to do a fresh iteration from the - // indicated restart address. - while (_restart_addr != NULL) { - if (_foregroundGCIsActive) { - // We may be running into repeated stack overflows, having - // reached the limit of the stack size, while making very - // slow forward progress. It may be best to bail out and - // let the foreground collector do its job. - // Clear _restart_addr, so that foreground GC - // works from scratch. This avoids the headache of - // a "rescan" which would otherwise be needed because - // of the dirty mod union table & card table. - _restart_addr = NULL; - return false; // indicating failure to complete marking - } - // Deal with stack overflow: - // we restart marking from _restart_addr - HeapWord* ra = _restart_addr; - markFromRootsClosure.reset(ra); - _restart_addr = NULL; - _markBitMap.iterate(&markFromRootsClosure, ra, _span.end()); - } - return true; -} - -void CMSCollector::preclean() { - check_correct_thread_executing(); - assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread"); - verify_work_stacks_empty(); - verify_overflow_empty(); - _abort_preclean = false; - if (CMSPrecleaningEnabled) { - if (!CMSEdenChunksRecordAlways) { - _eden_chunk_index = 0; - } - size_t used = get_eden_used(); - size_t capacity = get_eden_capacity(); - // Don't start sampling unless we will get sufficiently - // many samples. - if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100) - * CMSScheduleRemarkEdenPenetration)) { - _start_sampling = true; - } else { - _start_sampling = false; - } - GCTraceCPUTime tcpu; - CMSPhaseAccounting pa(this, "Concurrent Preclean"); - preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1); - } - CMSTokenSync x(true); // is cms thread - if (CMSPrecleaningEnabled) { - sample_eden(); - _collectorState = AbortablePreclean; - } else { - _collectorState = FinalMarking; - } - verify_work_stacks_empty(); - verify_overflow_empty(); -} - -// Try and schedule the remark such that young gen -// occupancy is CMSScheduleRemarkEdenPenetration %. -void CMSCollector::abortable_preclean() { - check_correct_thread_executing(); - assert(CMSPrecleaningEnabled, "Inconsistent control state"); - assert(_collectorState == AbortablePreclean, "Inconsistent control state"); - - // If Eden's current occupancy is below this threshold, - // immediately schedule the remark; else preclean - // past the next scavenge in an effort to - // schedule the pause as described above. By choosing - // CMSScheduleRemarkEdenSizeThreshold >= max eden size - // we will never do an actual abortable preclean cycle. - if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) { - GCTraceCPUTime tcpu; - CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean"); - // We need more smarts in the abortable preclean - // loop below to deal with cases where allocation - // in young gen is very very slow, and our precleaning - // is running a losing race against a horde of - // mutators intent on flooding us with CMS updates - // (dirty cards). - // One, admittedly dumb, strategy is to give up - // after a certain number of abortable precleaning loops - // or after a certain maximum time. We want to make - // this smarter in the next iteration. - // XXX FIX ME!!! YSR - size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0; - while (!(should_abort_preclean() || - ConcurrentMarkSweepThread::cmst()->should_terminate())) { - workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2); - cumworkdone += workdone; - loops++; - // Voluntarily terminate abortable preclean phase if we have - // been at it for too long. - if ((CMSMaxAbortablePrecleanLoops != 0) && - loops >= CMSMaxAbortablePrecleanLoops) { - log_debug(gc)(" CMS: abort preclean due to loops "); - break; - } - if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) { - log_debug(gc)(" CMS: abort preclean due to time "); - break; - } - // If we are doing little work each iteration, we should - // take a short break. - if (workdone < CMSAbortablePrecleanMinWorkPerIteration) { - // Sleep for some time, waiting for work to accumulate - stopTimer(); - cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis); - startTimer(); - waited++; - } - } - log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ", - loops, waited, cumworkdone); - } - CMSTokenSync x(true); // is cms thread - if (_collectorState != Idling) { - assert(_collectorState == AbortablePreclean, - "Spontaneous state transition?"); - _collectorState = FinalMarking; - } // Else, a foreground collection completed this CMS cycle. - return; -} - -// Respond to an Eden sampling opportunity -void CMSCollector::sample_eden() { - // Make sure a young gc cannot sneak in between our - // reading and recording of a sample. - assert(Thread::current()->is_ConcurrentGC_thread(), - "Only the cms thread may collect Eden samples"); - assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "Should collect samples while holding CMS token"); - if (!_start_sampling) { - return; - } - // When CMSEdenChunksRecordAlways is true, the eden chunk array - // is populated by the young generation. - if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) { - if (_eden_chunk_index < _eden_chunk_capacity) { - _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample - assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr, - "Unexpected state of Eden"); - // We'd like to check that what we just sampled is an oop-start address; - // however, we cannot do that here since the object may not yet have been - // initialized. So we'll instead do the check when we _use_ this sample - // later. - if (_eden_chunk_index == 0 || - (pointer_delta(_eden_chunk_array[_eden_chunk_index], - _eden_chunk_array[_eden_chunk_index-1]) - >= CMSSamplingGrain)) { - _eden_chunk_index++; // commit sample - } - } - } - if ((_collectorState == AbortablePreclean) && !_abort_preclean) { - size_t used = get_eden_used(); - size_t capacity = get_eden_capacity(); - assert(used <= capacity, "Unexpected state of Eden"); - if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) { - _abort_preclean = true; - } - } -} - -size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) { - assert(_collectorState == Precleaning || - _collectorState == AbortablePreclean, "incorrect state"); - ResourceMark rm; - HandleMark hm; - - // Precleaning is currently not MT but the reference processor - // may be set for MT. Disable it temporarily here. - ReferenceProcessor* rp = ref_processor(); - ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false); - - // Do one pass of scrubbing the discovered reference lists - // to remove any reference objects with strongly-reachable - // referents. - if (clean_refs) { - CMSPrecleanRefsYieldClosure yield_cl(this); - assert(_span_based_discoverer.span().equals(_span), "Spans should be equal"); - CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap, - &_markStack, true /* preclean */); - CMSDrainMarkingStackClosure complete_trace(this, - _span, &_markBitMap, &_markStack, - &keep_alive, true /* preclean */); - - // We don't want this step to interfere with a young - // collection because we don't want to take CPU - // or memory bandwidth away from the young GC threads - // (which may be as many as there are CPUs). - // Note that we don't need to protect ourselves from - // interference with mutators because they can't - // manipulate the discovered reference lists nor affect - // the computed reachability of the referents, the - // only properties manipulated by the precleaning - // of these reference lists. - stopTimer(); - CMSTokenSyncWithLocks x(true /* is cms thread */, - bitMapLock()); - startTimer(); - sample_eden(); - - // The following will yield to allow foreground - // collection to proceed promptly. XXX YSR: - // The code in this method may need further - // tweaking for better performance and some restructuring - // for cleaner interfaces. - GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases - rp->preclean_discovered_references( - rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl, - gc_timer); - } - - if (clean_survivor) { // preclean the active survivor space(s) - PushAndMarkClosure pam_cl(this, _span, ref_processor(), - &_markBitMap, &_modUnionTable, - &_markStack, true /* precleaning phase */); - stopTimer(); - CMSTokenSyncWithLocks ts(true /* is cms thread */, - bitMapLock()); - startTimer(); - unsigned int before_count = - CMSHeap::heap()->total_collections(); - SurvivorSpacePrecleanClosure - sss_cl(this, _span, &_markBitMap, &_markStack, - &pam_cl, before_count, CMSYield); - _young_gen->from()->object_iterate_careful(&sss_cl); - _young_gen->to()->object_iterate_careful(&sss_cl); - } - MarkRefsIntoAndScanClosure - mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable, - &_markStack, this, CMSYield, - true /* precleaning phase */); - // CAUTION: The following closure has persistent state that may need to - // be reset upon a decrease in the sequence of addresses it - // processes. - ScanMarkedObjectsAgainCarefullyClosure - smoac_cl(this, _span, - &_markBitMap, &_markStack, &mrias_cl, CMSYield); - - // Preclean dirty cards in ModUnionTable and CardTable using - // appropriate convergence criterion; - // repeat CMSPrecleanIter times unless we find that - // we are losing. - assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large"); - assert(CMSPrecleanNumerator < CMSPrecleanDenominator, - "Bad convergence multiplier"); - assert(CMSPrecleanThreshold >= 100, - "Unreasonably low CMSPrecleanThreshold"); - - size_t numIter, cumNumCards, lastNumCards, curNumCards; - for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0; - numIter < CMSPrecleanIter; - numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) { - curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl); - log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards); - // Either there are very few dirty cards, so re-mark - // pause will be small anyway, or our pre-cleaning isn't - // that much faster than the rate at which cards are being - // dirtied, so we might as well stop and re-mark since - // precleaning won't improve our re-mark time by much. - if (curNumCards <= CMSPrecleanThreshold || - (numIter > 0 && - (curNumCards * CMSPrecleanDenominator > - lastNumCards * CMSPrecleanNumerator))) { - numIter++; - cumNumCards += curNumCards; - break; - } - } - - preclean_cld(&mrias_cl, _cmsGen->freelistLock()); - - curNumCards = preclean_card_table(_cmsGen, &smoac_cl); - cumNumCards += curNumCards; - log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)", - curNumCards, cumNumCards, numIter); - return cumNumCards; // as a measure of useful work done -} - -// PRECLEANING NOTES: -// Precleaning involves: -// . reading the bits of the modUnionTable and clearing the set bits. -// . For the cards corresponding to the set bits, we scan the -// objects on those cards. This means we need the free_list_lock -// so that we can safely iterate over the CMS space when scanning -// for oops. -// . When we scan the objects, we'll be both reading and setting -// marks in the marking bit map, so we'll need the marking bit map. -// . For protecting _collector_state transitions, we take the CGC_lock. -// Note that any races in the reading of of card table entries by the -// CMS thread on the one hand and the clearing of those entries by the -// VM thread or the setting of those entries by the mutator threads on the -// other are quite benign. However, for efficiency it makes sense to keep -// the VM thread from racing with the CMS thread while the latter is -// dirty card info to the modUnionTable. We therefore also use the -// CGC_lock to protect the reading of the card table and the mod union -// table by the CM thread. -// . We run concurrently with mutator updates, so scanning -// needs to be done carefully -- we should not try to scan -// potentially uninitialized objects. -// -// Locking strategy: While holding the CGC_lock, we scan over and -// reset a maximal dirty range of the mod union / card tables, then lock -// the free_list_lock and bitmap lock to do a full marking, then -// release these locks; and repeat the cycle. This allows for a -// certain amount of fairness in the sharing of these locks between -// the CMS collector on the one hand, and the VM thread and the -// mutators on the other. - -// NOTE: preclean_mod_union_table() and preclean_card_table() -// further below are largely identical; if you need to modify -// one of these methods, please check the other method too. - -size_t CMSCollector::preclean_mod_union_table( - ConcurrentMarkSweepGeneration* old_gen, - ScanMarkedObjectsAgainCarefullyClosure* cl) { - verify_work_stacks_empty(); - verify_overflow_empty(); - - // strategy: starting with the first card, accumulate contiguous - // ranges of dirty cards; clear these cards, then scan the region - // covered by these cards. - - // Since all of the MUT is committed ahead, we can just use - // that, in case the generations expand while we are precleaning. - // It might also be fine to just use the committed part of the - // generation, but we might potentially miss cards when the - // generation is rapidly expanding while we are in the midst - // of precleaning. - HeapWord* startAddr = old_gen->reserved().start(); - HeapWord* endAddr = old_gen->reserved().end(); - - cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding - - size_t numDirtyCards, cumNumDirtyCards; - HeapWord *nextAddr, *lastAddr; - for (cumNumDirtyCards = numDirtyCards = 0, - nextAddr = lastAddr = startAddr; - nextAddr < endAddr; - nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { - - ResourceMark rm; - HandleMark hm; - - MemRegion dirtyRegion; - { - stopTimer(); - // Potential yield point - CMSTokenSync ts(true); - startTimer(); - sample_eden(); - // Get dirty region starting at nextOffset (inclusive), - // simultaneously clearing it. - dirtyRegion = - _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr); - assert(dirtyRegion.start() >= nextAddr, - "returned region inconsistent?"); - } - // Remember where the next search should begin. - // The returned region (if non-empty) is a right open interval, - // so lastOffset is obtained from the right end of that - // interval. - lastAddr = dirtyRegion.end(); - // Should do something more transparent and less hacky XXX - numDirtyCards = - _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size()); - - // We'll scan the cards in the dirty region (with periodic - // yields for foreground GC as needed). - if (!dirtyRegion.is_empty()) { - assert(numDirtyCards > 0, "consistency check"); - HeapWord* stop_point = NULL; - stopTimer(); - // Potential yield point - CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), - bitMapLock()); - startTimer(); - { - verify_work_stacks_empty(); - verify_overflow_empty(); - sample_eden(); - stop_point = - old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); - } - if (stop_point != NULL) { - // The careful iteration stopped early either because it found an - // uninitialized object, or because we were in the midst of an - // "abortable preclean", which should now be aborted. Redirty - // the bits corresponding to the partially-scanned or unscanned - // cards. We'll either restart at the next block boundary or - // abort the preclean. - assert((_collectorState == AbortablePreclean && should_abort_preclean()), - "Should only be AbortablePreclean."); - _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end())); - if (should_abort_preclean()) { - break; // out of preclean loop - } else { - // Compute the next address at which preclean should pick up; - // might need bitMapLock in order to read P-bits. - lastAddr = next_card_start_after_block(stop_point); - } - } - } else { - assert(lastAddr == endAddr, "consistency check"); - assert(numDirtyCards == 0, "consistency check"); - break; - } - } - verify_work_stacks_empty(); - verify_overflow_empty(); - return cumNumDirtyCards; -} - -// NOTE: preclean_mod_union_table() above and preclean_card_table() -// below are largely identical; if you need to modify -// one of these methods, please check the other method too. - -size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen, - ScanMarkedObjectsAgainCarefullyClosure* cl) { - // strategy: it's similar to precleamModUnionTable above, in that - // we accumulate contiguous ranges of dirty cards, mark these cards - // precleaned, then scan the region covered by these cards. - HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high()); - HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low()); - - cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding - - size_t numDirtyCards, cumNumDirtyCards; - HeapWord *lastAddr, *nextAddr; - - for (cumNumDirtyCards = numDirtyCards = 0, - nextAddr = lastAddr = startAddr; - nextAddr < endAddr; - nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { - - ResourceMark rm; - HandleMark hm; - - MemRegion dirtyRegion; - { - // See comments in "Precleaning notes" above on why we - // do this locking. XXX Could the locking overheads be - // too high when dirty cards are sparse? [I don't think so.] - stopTimer(); - CMSTokenSync x(true); // is cms thread - startTimer(); - sample_eden(); - // Get and clear dirty region from card table - dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr), - true, - CardTable::precleaned_card_val()); - - assert(dirtyRegion.start() >= nextAddr, - "returned region inconsistent?"); - } - lastAddr = dirtyRegion.end(); - numDirtyCards = - dirtyRegion.word_size()/CardTable::card_size_in_words; - - if (!dirtyRegion.is_empty()) { - stopTimer(); - CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock()); - startTimer(); - sample_eden(); - verify_work_stacks_empty(); - verify_overflow_empty(); - HeapWord* stop_point = - old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); - if (stop_point != NULL) { - assert((_collectorState == AbortablePreclean && should_abort_preclean()), - "Should only be AbortablePreclean."); - _ct->invalidate(MemRegion(stop_point, dirtyRegion.end())); - if (should_abort_preclean()) { - break; // out of preclean loop - } else { - // Compute the next address at which preclean should pick up. - lastAddr = next_card_start_after_block(stop_point); - } - } - } else { - break; - } - } - verify_work_stacks_empty(); - verify_overflow_empty(); - return cumNumDirtyCards; -} - -class PrecleanCLDClosure : public CLDClosure { - MetadataVisitingOopsInGenClosure* _cm_closure; - public: - PrecleanCLDClosure(MetadataVisitingOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {} - void do_cld(ClassLoaderData* cld) { - if (cld->has_accumulated_modified_oops()) { - cld->clear_accumulated_modified_oops(); - - _cm_closure->do_cld(cld); - } - } -}; - -// The freelist lock is needed to prevent asserts, is it really needed? -void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) { - // Needed to walk CLDG - MutexLocker ml(ClassLoaderDataGraph_lock); - - cl->set_freelistLock(freelistLock); - - CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock()); - - // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean? - // SSS: We should probably check if precleaning should be aborted, at suitable intervals? - PrecleanCLDClosure preclean_closure(cl); - ClassLoaderDataGraph::cld_do(&preclean_closure); - - verify_work_stacks_empty(); - verify_overflow_empty(); -} - -void CMSCollector::checkpointRootsFinal() { - assert(_collectorState == FinalMarking, "incorrect state transition?"); - check_correct_thread_executing(); - // world is stopped at this checkpoint - assert(SafepointSynchronize::is_at_safepoint(), - "world should be stopped"); - TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause()); - - verify_work_stacks_empty(); - verify_overflow_empty(); - - log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)", - _young_gen->used() / K, _young_gen->capacity() / K); - { - if (CMSScavengeBeforeRemark) { - CMSHeap* heap = CMSHeap::heap(); - // Temporarily set flag to false, GCH->do_collection will - // expect it to be false and set to true - FlagSetting fl(heap->_is_gc_active, false); - - heap->do_collection(true, // full (i.e. force, see below) - false, // !clear_all_soft_refs - 0, // size - false, // is_tlab - GenCollectedHeap::YoungGen // type - ); - } - FreelistLocker x(this); - MutexLocker y(bitMapLock(), - Mutex::_no_safepoint_check_flag); - checkpointRootsFinalWork(); - _cmsGen->cmsSpace()->recalculate_used_stable(); - } - verify_work_stacks_empty(); - verify_overflow_empty(); -} - -void CMSCollector::checkpointRootsFinalWork() { - GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm); - - assert(haveFreelistLocks(), "must have free list locks"); - assert_lock_strong(bitMapLock()); - - ResourceMark rm; - HandleMark hm; - - CMSHeap* heap = CMSHeap::heap(); - - assert(haveFreelistLocks(), "must have free list locks"); - assert_lock_strong(bitMapLock()); - - // We might assume that we need not fill TLAB's when - // CMSScavengeBeforeRemark is set, because we may have just done - // a scavenge which would have filled all TLAB's -- and besides - // Eden would be empty. This however may not always be the case -- - // for instance although we asked for a scavenge, it may not have - // happened because of a JNI critical section. We probably need - // a policy for deciding whether we can in that case wait until - // the critical section releases and then do the remark following - // the scavenge, and skip it here. In the absence of that policy, - // or of an indication of whether the scavenge did indeed occur, - // we cannot rely on TLAB's having been filled and must do - // so here just in case a scavenge did not happen. - heap->ensure_parsability(false); // fill TLAB's, but no need to retire them - // Update the saved marks which may affect the root scans. - heap->save_marks(); - - print_eden_and_survivor_chunk_arrays(); - - { -#if COMPILER2_OR_JVMCI - DerivedPointerTableDeactivate dpt_deact; -#endif - - // Note on the role of the mod union table: - // Since the marker in "markFromRoots" marks concurrently with - // mutators, it is possible for some reachable objects not to have been - // scanned. For instance, an only reference to an object A was - // placed in object B after the marker scanned B. Unless B is rescanned, - // A would be collected. Such updates to references in marked objects - // are detected via the mod union table which is the set of all cards - // dirtied since the first checkpoint in this GC cycle and prior to - // the most recent young generation GC, minus those cleaned up by the - // concurrent precleaning. - if (CMSParallelRemarkEnabled) { - GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm); - do_remark_parallel(); - } else { - GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm); - do_remark_non_parallel(); - } - } - verify_work_stacks_empty(); - verify_overflow_empty(); - - { - GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm); - refProcessingWork(); - } - verify_work_stacks_empty(); - verify_overflow_empty(); - - if (should_unload_classes()) { - heap->prune_scavengable_nmethods(); - } - - // If we encountered any (marking stack / work queue) overflow - // events during the current CMS cycle, take appropriate - // remedial measures, where possible, so as to try and avoid - // recurrence of that condition. - assert(_markStack.isEmpty(), "No grey objects"); - size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw + - _ser_kac_ovflw + _ser_kac_preclean_ovflw; - if (ser_ovflw > 0) { - log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")", - _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw); - _markStack.expand(); - _ser_pmc_remark_ovflw = 0; - _ser_pmc_preclean_ovflw = 0; - _ser_kac_preclean_ovflw = 0; - _ser_kac_ovflw = 0; - } - if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) { - log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")", - _par_pmc_remark_ovflw, _par_kac_ovflw); - _par_pmc_remark_ovflw = 0; - _par_kac_ovflw = 0; - } - if (_markStack._hit_limit > 0) { - log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")", - _markStack._hit_limit); - } - if (_markStack._failed_double > 0) { - log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT, - _markStack._failed_double, _markStack.capacity()); - } - _markStack._hit_limit = 0; - _markStack._failed_double = 0; - - if ((VerifyAfterGC || VerifyDuringGC) && - CMSHeap::heap()->total_collections() >= VerifyGCStartAt) { - verify_after_remark(); - } - - _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure); - - // Change under the freelistLocks. - _collectorState = Sweeping; - // Call isAllClear() under bitMapLock - assert(_modUnionTable.isAllClear(), - "Should be clear by end of the final marking"); - assert(_ct->cld_rem_set()->mod_union_is_clear(), - "Should be clear by end of the final marking"); -} - -void CMSParInitialMarkTask::work(uint worker_id) { - elapsedTimer _timer; - ResourceMark rm; - HandleMark hm; - - // ---------- scan from roots -------------- - _timer.start(); - CMSHeap* heap = CMSHeap::heap(); - ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap)); - - // ---------- young gen roots -------------- - { - work_on_young_gen_roots(&par_mri_cl); - _timer.stop(); - log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); - } - - // ---------- remaining roots -------------- - _timer.reset(); - _timer.start(); - - CLDToOopClosure cld_closure(&par_mri_cl, ClassLoaderData::_claim_strong); - - heap->cms_process_roots(_strong_roots_scope, - false, // yg was scanned above - GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), - _collector->should_unload_classes(), - &par_mri_cl, - &cld_closure); - - assert(_collector->should_unload_classes() - || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache), - "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); - _timer.stop(); - log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); -} - -// Parallel remark task -class CMSParRemarkTask: public CMSParMarkTask { - CompactibleFreeListSpace* _cms_space; - - // The per-thread work queues, available here for stealing. - OopTaskQueueSet* _task_queues; - TaskTerminator _term; - StrongRootsScope* _strong_roots_scope; - - public: - // A value of 0 passed to n_workers will cause the number of - // workers to be taken from the active workers in the work gang. - CMSParRemarkTask(CMSCollector* collector, - CompactibleFreeListSpace* cms_space, - uint n_workers, WorkGang* workers, - OopTaskQueueSet* task_queues, - StrongRootsScope* strong_roots_scope): - CMSParMarkTask("Rescan roots and grey objects in parallel", - collector, n_workers), - _cms_space(cms_space), - _task_queues(task_queues), - _term(n_workers, task_queues), - _strong_roots_scope(strong_roots_scope) { } - - OopTaskQueueSet* task_queues() { return _task_queues; } - - OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } - - ParallelTaskTerminator* terminator() { return _term.terminator(); } - uint n_workers() { return _n_workers; } - - void work(uint worker_id); - - private: - // ... of dirty cards in old space - void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i, - ParMarkRefsIntoAndScanClosure* cl); - - // ... work stealing for the above - void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl); -}; - -class RemarkCLDClosure : public CLDClosure { - CLDToOopClosure _cm_closure; - public: - RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure, ClassLoaderData::_claim_strong) {} - void do_cld(ClassLoaderData* cld) { - // Check if we have modified any oops in the CLD during the concurrent marking. - if (cld->has_accumulated_modified_oops()) { - cld->clear_accumulated_modified_oops(); - - // We could have transfered the current modified marks to the accumulated marks, - // like we do with the Card Table to Mod Union Table. But it's not really necessary. - } else if (cld->has_modified_oops()) { - // Don't clear anything, this info is needed by the next young collection. - } else { - // No modified oops in the ClassLoaderData. - return; - } - - // The klass has modified fields, need to scan the klass. - _cm_closure.do_cld(cld); - } -}; - -void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) { - ParNewGeneration* young_gen = _collector->_young_gen; - ContiguousSpace* eden_space = young_gen->eden(); - ContiguousSpace* from_space = young_gen->from(); - ContiguousSpace* to_space = young_gen->to(); - - HeapWord** eca = _collector->_eden_chunk_array; - size_t ect = _collector->_eden_chunk_index; - HeapWord** sca = _collector->_survivor_chunk_array; - size_t sct = _collector->_survivor_chunk_index; - - assert(ect <= _collector->_eden_chunk_capacity, "out of bounds"); - assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds"); - - do_young_space_rescan(cl, to_space, NULL, 0); - do_young_space_rescan(cl, from_space, sca, sct); - do_young_space_rescan(cl, eden_space, eca, ect); -} - -// work_queue(i) is passed to the closure -// ParMarkRefsIntoAndScanClosure. The "i" parameter -// also is passed to do_dirty_card_rescan_tasks() and to -// do_work_steal() to select the i-th task_queue. - -void CMSParRemarkTask::work(uint worker_id) { - elapsedTimer _timer; - ResourceMark rm; - HandleMark hm; - - // ---------- rescan from roots -------------- - _timer.start(); - CMSHeap* heap = CMSHeap::heap(); - ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector, - _collector->_span, _collector->ref_processor(), - &(_collector->_markBitMap), - work_queue(worker_id)); - - // Rescan young gen roots first since these are likely - // coarsely partitioned and may, on that account, constitute - // the critical path; thus, it's best to start off that - // work first. - // ---------- young gen roots -------------- - { - work_on_young_gen_roots(&par_mrias_cl); - _timer.stop(); - log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); - } - - // ---------- remaining roots -------------- - _timer.reset(); - _timer.start(); - heap->cms_process_roots(_strong_roots_scope, - false, // yg was scanned above - GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), - _collector->should_unload_classes(), - &par_mrias_cl, - NULL); // The dirty klasses will be handled below - - assert(_collector->should_unload_classes() - || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache), - "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); - _timer.stop(); - log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); - - // ---------- unhandled CLD scanning ---------- - if (worker_id == 0) { // Single threaded at the moment. - _timer.reset(); - _timer.start(); - - // Scan all new class loader data objects and new dependencies that were - // introduced during concurrent marking. - ResourceMark rm; - GrowableArray* array = ClassLoaderDataGraph::new_clds(); - for (int i = 0; i < array->length(); i++) { - Devirtualizer::do_cld(&par_mrias_cl, array->at(i)); - } - - // We don't need to keep track of new CLDs anymore. - ClassLoaderDataGraph::remember_new_clds(false); - - _timer.stop(); - log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); - } - - // We might have added oops to ClassLoaderData::_handles during the - // concurrent marking phase. These oops do not always point to newly allocated objects - // that are guaranteed to be kept alive. Hence, - // we do have to revisit the _handles block during the remark phase. - - // ---------- dirty CLD scanning ---------- - if (worker_id == 0) { // Single threaded at the moment. - _timer.reset(); - _timer.start(); - - // Scan all classes that was dirtied during the concurrent marking phase. - RemarkCLDClosure remark_closure(&par_mrias_cl); - ClassLoaderDataGraph::cld_do(&remark_closure); - - _timer.stop(); - log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); - } - - - // ---------- rescan dirty cards ------------ - _timer.reset(); - _timer.start(); - - // Do the rescan tasks for each of the two spaces - // (cms_space) in turn. - // "worker_id" is passed to select the task_queue for "worker_id" - do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl); - _timer.stop(); - log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); - - // ---------- steal work from other threads ... - // ---------- ... and drain overflow list. - _timer.reset(); - _timer.start(); - do_work_steal(worker_id, &par_mrias_cl); - _timer.stop(); - log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds()); -} - -void -CMSParMarkTask::do_young_space_rescan( - OopsInGenClosure* cl, ContiguousSpace* space, - HeapWord** chunk_array, size_t chunk_top) { - // Until all tasks completed: - // . claim an unclaimed task - // . compute region boundaries corresponding to task claimed - // using chunk_array - // . par_oop_iterate(cl) over that region - - ResourceMark rm; - HandleMark hm; - - SequentialSubTasksDone* pst = space->par_seq_tasks(); - - uint nth_task = 0; - uint n_tasks = pst->n_tasks(); - - if (n_tasks > 0) { - assert(pst->valid(), "Uninitialized use?"); - HeapWord *start, *end; - while (pst->try_claim_task(/* reference */ nth_task)) { - // We claimed task # nth_task; compute its boundaries. - if (chunk_top == 0) { // no samples were taken - assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task"); - start = space->bottom(); - end = space->top(); - } else if (nth_task == 0) { - start = space->bottom(); - end = chunk_array[nth_task]; - } else if (nth_task < (uint)chunk_top) { - assert(nth_task >= 1, "Control point invariant"); - start = chunk_array[nth_task - 1]; - end = chunk_array[nth_task]; - } else { - assert(nth_task == (uint)chunk_top, "Control point invariant"); - start = chunk_array[chunk_top - 1]; - end = space->top(); - } - MemRegion mr(start, end); - // Verify that mr is in space - assert(mr.is_empty() || space->used_region().contains(mr), - "Should be in space"); - // Verify that "start" is an object boundary - assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())), - "Should be an oop"); - space->par_oop_iterate(mr, cl); - } - pst->all_tasks_completed(); - } -} - -void -CMSParRemarkTask::do_dirty_card_rescan_tasks( - CompactibleFreeListSpace* sp, int i, - ParMarkRefsIntoAndScanClosure* cl) { - // Until all tasks completed: - // . claim an unclaimed task - // . compute region boundaries corresponding to task claimed - // . transfer dirty bits ct->mut for that region - // . apply rescanclosure to dirty mut bits for that region - - ResourceMark rm; - HandleMark hm; - - OopTaskQueue* work_q = work_queue(i); - ModUnionClosure modUnionClosure(&(_collector->_modUnionTable)); - // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! - // CAUTION: This closure has state that persists across calls to - // the work method dirty_range_iterate_clear() in that it has - // embedded in it a (subtype of) UpwardsObjectClosure. The - // use of that state in the embedded UpwardsObjectClosure instance - // assumes that the cards are always iterated (even if in parallel - // by several threads) in monotonically increasing order per each - // thread. This is true of the implementation below which picks - // card ranges (chunks) in monotonically increasing order globally - // and, a-fortiori, in monotonically increasing order per thread - // (the latter order being a subsequence of the former). - // If the work code below is ever reorganized into a more chaotic - // work-partitioning form than the current "sequential tasks" - // paradigm, the use of that persistent state will have to be - // revisited and modified appropriately. See also related - // bug 4756801 work on which should examine this code to make - // sure that the changes there do not run counter to the - // assumptions made here and necessary for correctness and - // efficiency. Note also that this code might yield inefficient - // behavior in the case of very large objects that span one or - // more work chunks. Such objects would potentially be scanned - // several times redundantly. Work on 4756801 should try and - // address that performance anomaly if at all possible. XXX - MemRegion full_span = _collector->_span; - CMSBitMap* bm = &(_collector->_markBitMap); // shared - MarkFromDirtyCardsClosure - greyRescanClosure(_collector, full_span, // entire span of interest - sp, bm, work_q, cl); - - SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); - assert(pst->valid(), "Uninitialized use?"); - uint nth_task = 0; - const int alignment = CardTable::card_size * BitsPerWord; - MemRegion span = sp->used_region(); - HeapWord* start_addr = span.start(); - HeapWord* end_addr = align_up(span.end(), alignment); - const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units - assert(is_aligned(start_addr, alignment), "Check alignment"); - assert(is_aligned(chunk_size, alignment), "Check alignment"); - - while (pst->try_claim_task(/* reference */ nth_task)) { - // Having claimed the nth_task, compute corresponding mem-region, - // which is a-fortiori aligned correctly (i.e. at a MUT boundary). - // The alignment restriction ensures that we do not need any - // synchronization with other gang-workers while setting or - // clearing bits in thus chunk of the MUT. - MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size, - start_addr + (nth_task+1)*chunk_size); - // The last chunk's end might be way beyond end of the - // used region. In that case pull back appropriately. - if (this_span.end() > end_addr) { - this_span.set_end(end_addr); - assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)"); - } - // Iterate over the dirty cards covering this chunk, marking them - // precleaned, and setting the corresponding bits in the mod union - // table. Since we have been careful to partition at Card and MUT-word - // boundaries no synchronization is needed between parallel threads. - _collector->_ct->dirty_card_iterate(this_span, - &modUnionClosure); - - // Having transferred these marks into the modUnionTable, - // rescan the marked objects on the dirty cards in the modUnionTable. - // Even if this is at a synchronous collection, the initial marking - // may have been done during an asynchronous collection so there - // may be dirty bits in the mod-union table. - _collector->_modUnionTable.dirty_range_iterate_clear( - this_span, &greyRescanClosure); - _collector->_modUnionTable.verifyNoOneBitsInRange( - this_span.start(), - this_span.end()); - } - pst->all_tasks_completed(); // declare that i am done -} - -// . see if we can share work_queues with ParNew? XXX -void -CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl) { - OopTaskQueue* work_q = work_queue(i); - NOT_PRODUCT(int num_steals = 0;) - oop obj_to_scan; - CMSBitMap* bm = &(_collector->_markBitMap); - - while (true) { - // Completely finish any left over work from (an) earlier round(s) - cl->trim_queue(0); - size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, - (size_t)ParGCDesiredObjsFromOverflowList); - // Now check if there's any work in the overflow list - // Passing ParallelGCThreads as the third parameter, no_of_gc_threads, - // only affects the number of attempts made to get work from the - // overflow list and does not affect the number of workers. Just - // pass ParallelGCThreads so this behavior is unchanged. - if (_collector->par_take_from_overflow_list(num_from_overflow_list, - work_q, - ParallelGCThreads)) { - // found something in global overflow list; - // not yet ready to go stealing work from others. - // We'd like to assert(work_q->size() != 0, ...) - // because we just took work from the overflow list, - // but of course we can't since all of that could have - // been already stolen from us. - // "He giveth and He taketh away." - continue; - } - // Verify that we have no work before we resort to stealing - assert(work_q->size() == 0, "Have work, shouldn't steal"); - // Try to steal from other queues that have work - if (task_queues()->steal(i, /* reference */ obj_to_scan)) { - NOT_PRODUCT(num_steals++;) - assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!"); - assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); - // Do scanning work - obj_to_scan->oop_iterate(cl); - // Loop around, finish this work, and try to steal some more - } else if (terminator()->offer_termination()) { - break; // nirvana from the infinite cycle - } - } - log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals); - assert(work_q->size() == 0 && _collector->overflow_list_is_empty(), - "Else our work is not yet done"); -} - -// Record object boundaries in _eden_chunk_array by sampling the eden -// top in the slow-path eden object allocation code path and record -// the boundaries, if CMSEdenChunksRecordAlways is true. If -// CMSEdenChunksRecordAlways is false, we use the other asynchronous -// sampling in sample_eden() that activates during the part of the -// preclean phase. -void CMSCollector::sample_eden_chunk() { - if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) { - if (_eden_chunk_lock->try_lock()) { - // Record a sample. This is the critical section. The contents - // of the _eden_chunk_array have to be non-decreasing in the - // address order. - _eden_chunk_array[_eden_chunk_index] = *_top_addr; - assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr, - "Unexpected state of Eden"); - if (_eden_chunk_index == 0 || - ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) && - (pointer_delta(_eden_chunk_array[_eden_chunk_index], - _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) { - _eden_chunk_index++; // commit sample - } - _eden_chunk_lock->unlock(); - } - } -} - -// Return a thread-local PLAB recording array, as appropriate. -void* CMSCollector::get_data_recorder(int thr_num) { - if (_survivor_plab_array != NULL && - (CMSPLABRecordAlways || - (_collectorState > Marking && _collectorState < FinalMarking))) { - assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds"); - ChunkArray* ca = &_survivor_plab_array[thr_num]; - ca->reset(); // clear it so that fresh data is recorded - return (void*) ca; - } else { - return NULL; - } -} - -// Reset all the thread-local PLAB recording arrays -void CMSCollector::reset_survivor_plab_arrays() { - for (uint i = 0; i < ParallelGCThreads; i++) { - _survivor_plab_array[i].reset(); - } -} - -// Merge the per-thread plab arrays into the global survivor chunk -// array which will provide the partitioning of the survivor space -// for CMS initial scan and rescan. -void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv, - int no_of_gc_threads) { - assert(_survivor_plab_array != NULL, "Error"); - assert(_survivor_chunk_array != NULL, "Error"); - assert(_collectorState == FinalMarking || - (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error"); - for (int j = 0; j < no_of_gc_threads; j++) { - _cursor[j] = 0; - } - HeapWord* top = surv->top(); - size_t i; - for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries - HeapWord* min_val = top; // Higher than any PLAB address - uint min_tid = 0; // position of min_val this round - for (int j = 0; j < no_of_gc_threads; j++) { - ChunkArray* cur_sca = &_survivor_plab_array[j]; - if (_cursor[j] == cur_sca->end()) { - continue; - } - assert(_cursor[j] < cur_sca->end(), "ctl pt invariant"); - HeapWord* cur_val = cur_sca->nth(_cursor[j]); - assert(surv->used_region().contains(cur_val), "Out of bounds value"); - if (cur_val < min_val) { - min_tid = j; - min_val = cur_val; - } else { - assert(cur_val < top, "All recorded addresses should be less"); - } - } - // At this point min_val and min_tid are respectively - // the least address in _survivor_plab_array[j]->nth(_cursor[j]) - // and the thread (j) that witnesses that address. - // We record this address in the _survivor_chunk_array[i] - // and increment _cursor[min_tid] prior to the next round i. - if (min_val == top) { - break; - } - _survivor_chunk_array[i] = min_val; - _cursor[min_tid]++; - } - // We are all done; record the size of the _survivor_chunk_array - _survivor_chunk_index = i; // exclusive: [0, i) - log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i); - // Verify that we used up all the recorded entries - #ifdef ASSERT - size_t total = 0; - for (int j = 0; j < no_of_gc_threads; j++) { - assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant"); - total += _cursor[j]; - } - assert(total == _survivor_chunk_index, "Ctl Pt Invariant"); - // Check that the merged array is in sorted order - if (total > 0) { - for (size_t i = 0; i < total - 1; i++) { - log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ", - i, p2i(_survivor_chunk_array[i])); - assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1], - "Not sorted"); - } - } - #endif // ASSERT -} - -// Set up the space's par_seq_tasks structure for work claiming -// for parallel initial scan and rescan of young gen. -// See ParRescanTask where this is currently used. -void -CMSCollector:: -initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) { - assert(n_threads > 0, "Unexpected n_threads argument"); - - // Eden space - if (!_young_gen->eden()->is_empty()) { - SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks(); - assert(!pst->valid(), "Clobbering existing data?"); - // Each valid entry in [0, _eden_chunk_index) represents a task. - size_t n_tasks = _eden_chunk_index + 1; - assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error"); - // Sets the condition for completion of the subtask (how many threads - // need to finish in order to be done). - pst->set_n_threads(n_threads); - pst->set_n_tasks((int)n_tasks); - } - - // Merge the survivor plab arrays into _survivor_chunk_array - if (_survivor_plab_array != NULL) { - merge_survivor_plab_arrays(_young_gen->from(), n_threads); - } else { - assert(_survivor_chunk_index == 0, "Error"); - } - - // To space - { - SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks(); - assert(!pst->valid(), "Clobbering existing data?"); - // Sets the condition for completion of the subtask (how many threads - // need to finish in order to be done). - pst->set_n_threads(n_threads); - pst->set_n_tasks(1); - assert(pst->valid(), "Error"); - } - - // From space - { - SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks(); - assert(!pst->valid(), "Clobbering existing data?"); - size_t n_tasks = _survivor_chunk_index + 1; - assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error"); - // Sets the condition for completion of the subtask (how many threads - // need to finish in order to be done). - pst->set_n_threads(n_threads); - pst->set_n_tasks((int)n_tasks); - assert(pst->valid(), "Error"); - } -} - -// Parallel version of remark -void CMSCollector::do_remark_parallel() { - CMSHeap* heap = CMSHeap::heap(); - WorkGang* workers = heap->workers(); - assert(workers != NULL, "Need parallel worker threads."); - // Choose to use the number of GC workers most recently set - // into "active_workers". - uint n_workers = workers->active_workers(); - - CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); - - StrongRootsScope srs(n_workers); - - CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs); - - // We won't be iterating over the cards in the card table updating - // the younger_gen cards, so we shouldn't call the following else - // the verification code as well as subsequent younger_refs_iterate - // code would get confused. XXX - // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel - - // The young gen rescan work will not be done as part of - // process_roots (which currently doesn't know how to - // parallelize such a scan), but rather will be broken up into - // a set of parallel tasks (via the sampling that the [abortable] - // preclean phase did of eden, plus the [two] tasks of - // scanning the [two] survivor spaces. Further fine-grain - // parallelization of the scanning of the survivor spaces - // themselves, and of precleaning of the young gen itself - // is deferred to the future. - initialize_sequential_subtasks_for_young_gen_rescan(n_workers); - - // The dirty card rescan work is broken up into a "sequence" - // of parallel tasks (per constituent space) that are dynamically - // claimed by the parallel threads. - cms_space->initialize_sequential_subtasks_for_rescan(n_workers); - - // It turns out that even when we're using 1 thread, doing the work in a - // separate thread causes wide variance in run times. We can't help this - // in the multi-threaded case, but we special-case n=1 here to get - // repeatable measurements of the 1-thread overhead of the parallel code. - if (n_workers > 1) { - // Make refs discovery MT-safe, if it isn't already: it may not - // necessarily be so, since it's possible that we are doing - // ST marking. - ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true); - workers->run_task(&tsk); - } else { - ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); - tsk.work(0); - } - - // restore, single-threaded for now, any preserved marks - // as a result of work_q overflow - restore_preserved_marks_if_any(); -} - -// Non-parallel version of remark -void CMSCollector::do_remark_non_parallel() { - ResourceMark rm; - HandleMark hm; - CMSHeap* heap = CMSHeap::heap(); - ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); - - MarkRefsIntoAndScanClosure - mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */, - &_markStack, this, - false /* should_yield */, false /* not precleaning */); - MarkFromDirtyCardsClosure - markFromDirtyCardsClosure(this, _span, - NULL, // space is set further below - &_markBitMap, &_markStack, &mrias_cl); - { - GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm); - // Iterate over the dirty cards, setting the corresponding bits in the - // mod union table. - { - ModUnionClosure modUnionClosure(&_modUnionTable); - _ct->dirty_card_iterate(_cmsGen->used_region(), - &modUnionClosure); - } - // Having transferred these marks into the modUnionTable, we just need - // to rescan the marked objects on the dirty cards in the modUnionTable. - // The initial marking may have been done during an asynchronous - // collection so there may be dirty bits in the mod-union table. - const int alignment = CardTable::card_size * BitsPerWord; - { - // ... First handle dirty cards in CMS gen - markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace()); - MemRegion ur = _cmsGen->used_region(); - HeapWord* lb = ur.start(); - HeapWord* ub = align_up(ur.end(), alignment); - MemRegion cms_span(lb, ub); - _modUnionTable.dirty_range_iterate_clear(cms_span, - &markFromDirtyCardsClosure); - verify_work_stacks_empty(); - log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards()); - } - } - if (VerifyDuringGC && - CMSHeap::heap()->total_collections() >= VerifyGCStartAt) { - HandleMark hm; // Discard invalid handles created during verification - Universe::verify(); - } - { - GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm); - - verify_work_stacks_empty(); - - heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. - StrongRootsScope srs(1); - - heap->cms_process_roots(&srs, - true, // young gen as roots - GenCollectedHeap::ScanningOption(roots_scanning_options()), - should_unload_classes(), - &mrias_cl, - NULL); // The dirty klasses will be handled below - - assert(should_unload_classes() - || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache), - "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); - } - - { - GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm); - - verify_work_stacks_empty(); - - // Scan all class loader data objects that might have been introduced - // during concurrent marking. - ResourceMark rm; - GrowableArray* array = ClassLoaderDataGraph::new_clds(); - for (int i = 0; i < array->length(); i++) { - Devirtualizer::do_cld(&mrias_cl, array->at(i)); - } - - // We don't need to keep track of new CLDs anymore. - ClassLoaderDataGraph::remember_new_clds(false); - - verify_work_stacks_empty(); - } - - // We might have added oops to ClassLoaderData::_handles during the - // concurrent marking phase. These oops do not point to newly allocated objects - // that are guaranteed to be kept alive. Hence, - // we do have to revisit the _handles block during the remark phase. - { - GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm); - - verify_work_stacks_empty(); - - RemarkCLDClosure remark_closure(&mrias_cl); - ClassLoaderDataGraph::cld_do(&remark_closure); - - verify_work_stacks_empty(); - } - - verify_work_stacks_empty(); - // Restore evacuated mark words, if any, used for overflow list links - restore_preserved_marks_if_any(); - - verify_overflow_empty(); -} - -//////////////////////////////////////////////////////// -// Parallel Reference Processing Task Proxy Class -//////////////////////////////////////////////////////// -class AbstractGangTaskWOopQueues : public AbstractGangTask { - OopTaskQueueSet* _queues; - TaskTerminator _terminator; - public: - AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) : - AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {} - ParallelTaskTerminator* terminator() { return _terminator.terminator(); } - OopTaskQueueSet* queues() { return _queues; } -}; - -class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues { - typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; - CMSCollector* _collector; - CMSBitMap* _mark_bit_map; - const MemRegion _span; - ProcessTask& _task; - -public: - CMSRefProcTaskProxy(ProcessTask& task, - CMSCollector* collector, - const MemRegion& span, - CMSBitMap* mark_bit_map, - AbstractWorkGang* workers, - OopTaskQueueSet* task_queues): - AbstractGangTaskWOopQueues("Process referents by policy in parallel", - task_queues, - workers->active_workers()), - _collector(collector), - _mark_bit_map(mark_bit_map), - _span(span), - _task(task) - { - assert(_collector->_span.equals(_span) && !_span.is_empty(), - "Inconsistency in _span"); - } - - OopTaskQueueSet* task_queues() { return queues(); } - - OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } - - void do_work_steal(int i, - CMSParDrainMarkingStackClosure* drain, - CMSParKeepAliveClosure* keep_alive); - - virtual void work(uint worker_id); -}; - -void CMSRefProcTaskProxy::work(uint worker_id) { - ResourceMark rm; - HandleMark hm; - assert(_collector->_span.equals(_span), "Inconsistency in _span"); - CMSParKeepAliveClosure par_keep_alive(_collector, _span, - _mark_bit_map, - work_queue(worker_id)); - CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span, - _mark_bit_map, - work_queue(worker_id)); - CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map); - _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack); - if (_task.marks_oops_alive()) { - do_work_steal(worker_id, &par_drain_stack, &par_keep_alive); - } - assert(work_queue(worker_id)->size() == 0, "work_queue should be empty"); - assert(_collector->_overflow_list == NULL, "non-empty _overflow_list"); -} - -CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector, - MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue): - _span(span), - _work_queue(work_queue), - _bit_map(bit_map), - _mark_and_push(collector, span, bit_map, work_queue), - _low_water_mark(MIN2((work_queue->max_elems()/4), - ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))) -{ } - -// . see if we can share work_queues with ParNew? XXX -void CMSRefProcTaskProxy::do_work_steal(int i, - CMSParDrainMarkingStackClosure* drain, - CMSParKeepAliveClosure* keep_alive) { - OopTaskQueue* work_q = work_queue(i); - NOT_PRODUCT(int num_steals = 0;) - oop obj_to_scan; - - while (true) { - // Completely finish any left over work from (an) earlier round(s) - drain->trim_queue(0); - size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, - (size_t)ParGCDesiredObjsFromOverflowList); - // Now check if there's any work in the overflow list - // Passing ParallelGCThreads as the third parameter, no_of_gc_threads, - // only affects the number of attempts made to get work from the - // overflow list and does not affect the number of workers. Just - // pass ParallelGCThreads so this behavior is unchanged. - if (_collector->par_take_from_overflow_list(num_from_overflow_list, - work_q, - ParallelGCThreads)) { - // Found something in global overflow list; - // not yet ready to go stealing work from others. - // We'd like to assert(work_q->size() != 0, ...) - // because we just took work from the overflow list, - // but of course we can't, since all of that might have - // been already stolen from us. - continue; - } - // Verify that we have no work before we resort to stealing - assert(work_q->size() == 0, "Have work, shouldn't steal"); - // Try to steal from other queues that have work - if (task_queues()->steal(i, /* reference */ obj_to_scan)) { - NOT_PRODUCT(num_steals++;) - assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!"); - assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); - // Do scanning work - obj_to_scan->oop_iterate(keep_alive); - // Loop around, finish this work, and try to steal some more - } else if (terminator()->offer_termination()) { - break; // nirvana from the infinite cycle - } - } - log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals); -} - -void CMSRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) { - CMSHeap* heap = CMSHeap::heap(); - WorkGang* workers = heap->workers(); - assert(workers != NULL, "Need parallel worker threads."); - assert(workers->active_workers() == ergo_workers, - "Ergonomically chosen workers (%u) must be equal to active workers (%u)", - ergo_workers, workers->active_workers()); - CMSRefProcTaskProxy rp_task(task, &_collector, - _collector.ref_processor_span(), - _collector.markBitMap(), - workers, _collector.task_queues()); - workers->run_task(&rp_task, workers->active_workers()); -} - -void CMSCollector::refProcessingWork() { - ResourceMark rm; - HandleMark hm; - - ReferenceProcessor* rp = ref_processor(); - assert(_span_based_discoverer.span().equals(_span), "Spans should be equal"); - assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete"); - // Process weak references. - rp->setup_policy(false); - verify_work_stacks_empty(); - - ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->max_num_queues()); - { - GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm); - - // Setup keep_alive and complete closures. - CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap, - &_markStack, false /* !preclean */); - CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this, - _span, &_markBitMap, &_markStack, - &cmsKeepAliveClosure, false /* !preclean */); - - ReferenceProcessorStats stats; - if (rp->processing_is_mt()) { - // Set the degree of MT here. If the discovery is done MT, there - // may have been a different number of threads doing the discovery - // and a different number of discovered lists may have Ref objects. - // That is OK as long as the Reference lists are balanced (see - // balance_all_queues() and balance_queues()). - CMSHeap* heap = CMSHeap::heap(); - uint active_workers = ParallelGCThreads; - WorkGang* workers = heap->workers(); - if (workers != NULL) { - active_workers = workers->active_workers(); - // The expectation is that active_workers will have already - // been set to a reasonable value. If it has not been set, - // investigate. - assert(active_workers > 0, "Should have been set during scavenge"); - } - rp->set_active_mt_degree(active_workers); - CMSRefProcTaskExecutor task_executor(*this); - stats = rp->process_discovered_references(&_is_alive_closure, - &cmsKeepAliveClosure, - &cmsDrainMarkingStackClosure, - &task_executor, - &pt); - } else { - stats = rp->process_discovered_references(&_is_alive_closure, - &cmsKeepAliveClosure, - &cmsDrainMarkingStackClosure, - NULL, - &pt); - } - _gc_tracer_cm->report_gc_reference_stats(stats); - pt.print_all_references(); - } - - // This is the point where the entire marking should have completed. - verify_work_stacks_empty(); - - { - GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm); - WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl); - } - - if (should_unload_classes()) { - { - GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm); - - // Unload classes and purge the SystemDictionary. - bool purged_class = SystemDictionary::do_unloading(_gc_timer_cm); - - // Unload nmethods. - CodeCache::do_unloading(&_is_alive_closure, purged_class); - - // Prune dead klasses from subklass/sibling/implementor lists. - Klass::clean_weak_klass_links(purged_class); - - // Clean JVMCI metadata handles. - JVMCI_ONLY(JVMCI::do_unloading(purged_class)); - } - } - - // Restore any preserved marks as a result of mark stack or - // work queue overflow - restore_preserved_marks_if_any(); // done single-threaded for now - - rp->set_enqueuing_is_done(true); - rp->verify_no_references_recorded(); -} - -#ifndef PRODUCT -void CMSCollector::check_correct_thread_executing() { - Thread* t = Thread::current(); - // Only the VM thread or the CMS thread should be here. - assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(), - "Unexpected thread type"); - // If this is the vm thread, the foreground process - // should not be waiting. Note that _foregroundGCIsActive is - // true while the foreground collector is waiting. - if (_foregroundGCShouldWait) { - // We cannot be the VM thread - assert(t->is_ConcurrentGC_thread(), - "Should be CMS thread"); - } else { - // We can be the CMS thread only if we are in a stop-world - // phase of CMS collection. - if (t->is_ConcurrentGC_thread()) { - assert(_collectorState == InitialMarking || - _collectorState == FinalMarking, - "Should be a stop-world phase"); - // The CMS thread should be holding the CMS_token. - assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "Potential interference with concurrently " - "executing VM thread"); - } - } -} -#endif - -void CMSCollector::sweep() { - assert(_collectorState == Sweeping, "just checking"); - check_correct_thread_executing(); - verify_work_stacks_empty(); - verify_overflow_empty(); - increment_sweep_count(); - TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause()); - - _inter_sweep_timer.stop(); - _inter_sweep_estimate.sample(_inter_sweep_timer.seconds()); - - assert(!_intra_sweep_timer.is_active(), "Should not be active"); - _intra_sweep_timer.reset(); - _intra_sweep_timer.start(); - { - GCTraceCPUTime tcpu; - CMSPhaseAccounting pa(this, "Concurrent Sweep"); - // First sweep the old gen - { - CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(), - bitMapLock()); - sweepWork(_cmsGen); - } - - // Update Universe::_heap_*_at_gc figures. - // We need all the free list locks to make the abstract state - // transition from Sweeping to Resetting. See detailed note - // further below. - { - CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock()); - - // Update heap occupancy information which is used as - // input to soft ref clearing policy at the next gc. - Universe::update_heap_info_at_gc(); - - // recalculate CMS used space after CMS collection - _cmsGen->cmsSpace()->recalculate_used_stable(); - - _collectorState = Resizing; - } - } - verify_work_stacks_empty(); - verify_overflow_empty(); - - if (should_unload_classes()) { - // Delay purge to the beginning of the next safepoint. Metaspace::contains - // requires that the virtual spaces are stable and not deleted. - ClassLoaderDataGraph::set_should_purge(true); - } - - _intra_sweep_timer.stop(); - _intra_sweep_estimate.sample(_intra_sweep_timer.seconds()); - - _inter_sweep_timer.reset(); - _inter_sweep_timer.start(); - - // We need to use a monotonically non-decreasing time in ms - // or we will see time-warp warnings and os::javaTimeMillis() - // does not guarantee monotonicity. - jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; - update_time_of_last_gc(now); - - // NOTE on abstract state transitions: - // Mutators allocate-live and/or mark the mod-union table dirty - // based on the state of the collection. The former is done in - // the interval [Marking, Sweeping] and the latter in the interval - // [Marking, Sweeping). Thus the transitions into the Marking state - // and out of the Sweeping state must be synchronously visible - // globally to the mutators. - // The transition into the Marking state happens with the world - // stopped so the mutators will globally see it. Sweeping is - // done asynchronously by the background collector so the transition - // from the Sweeping state to the Resizing state must be done - // under the freelistLock (as is the check for whether to - // allocate-live and whether to dirty the mod-union table). - assert(_collectorState == Resizing, "Change of collector state to" - " Resizing must be done under the freelistLocks (plural)"); - - // Now that sweeping has been completed, we clear - // the incremental_collection_failed flag, - // thus inviting a younger gen collection to promote into - // this generation. If such a promotion may still fail, - // the flag will be set again when a young collection is - // attempted. - CMSHeap* heap = CMSHeap::heap(); - heap->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up - heap->update_full_collections_completed(_collection_count_start); -} - -// FIX ME!!! Looks like this belongs in CFLSpace, with -// CMSGen merely delegating to it. -void ConcurrentMarkSweepGeneration::setNearLargestChunk() { - double nearLargestPercent = FLSLargestBlockCoalesceProximity; - HeapWord* minAddr = _cmsSpace->bottom(); - HeapWord* largestAddr = - (HeapWord*) _cmsSpace->dictionary()->find_largest_dict(); - if (largestAddr == NULL) { - // The dictionary appears to be empty. In this case - // try to coalesce at the end of the heap. - largestAddr = _cmsSpace->end(); - } - size_t largestOffset = pointer_delta(largestAddr, minAddr); - size_t nearLargestOffset = - (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize; - log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT, - p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset)); - _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset); -} - -bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) { - return addr >= _cmsSpace->nearLargestChunk(); -} - -FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() { - return _cmsSpace->find_chunk_at_end(); -} - -void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation, - bool full) { - // If the young generation has been collected, gather any statistics - // that are of interest at this point. - bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation); - if (!full && current_is_young) { - // Gather statistics on the young generation collection. - collector()->stats().record_gc0_end(used()); - } - _cmsSpace->recalculate_used_stable(); -} - -void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) { - // We iterate over the space(s) underlying this generation, - // checking the mark bit map to see if the bits corresponding - // to specific blocks are marked or not. Blocks that are - // marked are live and are not swept up. All remaining blocks - // are swept up, with coalescing on-the-fly as we sweep up - // contiguous free and/or garbage blocks: - // We need to ensure that the sweeper synchronizes with allocators - // and stop-the-world collectors. In particular, the following - // locks are used: - // . CMS token: if this is held, a stop the world collection cannot occur - // . freelistLock: if this is held no allocation can occur from this - // generation by another thread - // . bitMapLock: if this is held, no other thread can access or update - // - - // Note that we need to hold the freelistLock if we use - // block iterate below; else the iterator might go awry if - // a mutator (or promotion) causes block contents to change - // (for instance if the allocator divvies up a block). - // If we hold the free list lock, for all practical purposes - // young generation GC's can't occur (they'll usually need to - // promote), so we might as well prevent all young generation - // GC's while we do a sweeping step. For the same reason, we might - // as well take the bit map lock for the entire duration - - // check that we hold the requisite locks - assert(have_cms_token(), "Should hold cms token"); - assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep"); - assert_lock_strong(old_gen->freelistLock()); - assert_lock_strong(bitMapLock()); - - assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context"); - assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context"); - old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), - _inter_sweep_estimate.padded_average(), - _intra_sweep_estimate.padded_average()); - old_gen->setNearLargestChunk(); - - { - SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield); - old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure); - // We need to free-up/coalesce garbage/blocks from a - // co-terminal free run. This is done in the SweepClosure - // destructor; so, do not remove this scope, else the - // end-of-sweep-census below will be off by a little bit. - } - old_gen->cmsSpace()->sweep_completed(); - old_gen->cmsSpace()->endSweepFLCensus(sweep_count()); - if (should_unload_classes()) { // unloaded classes this cycle, - _concurrent_cycles_since_last_unload = 0; // ... reset count - } else { // did not unload classes, - _concurrent_cycles_since_last_unload++; // ... increment count - } -} - -// Reset CMS data structures (for now just the marking bit map) -// preparatory for the next cycle. -void CMSCollector::reset_concurrent() { - CMSTokenSyncWithLocks ts(true, bitMapLock()); - - // If the state is not "Resetting", the foreground thread - // has done a collection and the resetting. - if (_collectorState != Resetting) { - assert(_collectorState == Idling, "The state should only change" - " because the foreground collector has finished the collection"); - return; - } - - { - // Clear the mark bitmap (no grey objects to start with) - // for the next cycle. - GCTraceCPUTime tcpu; - CMSPhaseAccounting cmspa(this, "Concurrent Reset"); - - HeapWord* curAddr = _markBitMap.startWord(); - while (curAddr < _markBitMap.endWord()) { - size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr); - MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining)); - _markBitMap.clear_large_range(chunk); - if (ConcurrentMarkSweepThread::should_yield() && - !foregroundGCIsActive() && - CMSYield) { - assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "CMS thread should hold CMS token"); - assert_lock_strong(bitMapLock()); - bitMapLock()->unlock(); - ConcurrentMarkSweepThread::desynchronize(true); - stopTimer(); - incrementYields(); - - // See the comment in coordinator_yield() - for (unsigned i = 0; i < CMSYieldSleepCount && - ConcurrentMarkSweepThread::should_yield() && - !CMSCollector::foregroundGCIsActive(); ++i) { - os::naked_short_sleep(1); - } - - ConcurrentMarkSweepThread::synchronize(true); - bitMapLock()->lock_without_safepoint_check(); - startTimer(); - } - curAddr = chunk.end(); - } - // A successful mostly concurrent collection has been done. - // Because only the full (i.e., concurrent mode failure) collections - // are being measured for gc overhead limits, clean the "near" flag - // and count. - size_policy()->reset_gc_overhead_limit_count(); - _collectorState = Idling; - } - - register_gc_end(); -} - -// Same as above but for STW paths -void CMSCollector::reset_stw() { - // already have the lock - assert(_collectorState == Resetting, "just checking"); - assert_lock_strong(bitMapLock()); - GCIdMark gc_id_mark(_cmsThread->gc_id()); - _markBitMap.clear_all(); - _collectorState = Idling; - register_gc_end(); -} - -void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) { - GCTraceCPUTime tcpu; - TraceCollectorStats tcs_cgc(cgc_counters()); - - switch (op) { - case CMS_op_checkpointRootsInitial: { - GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true); - SvcGCMarker sgcm(SvcGCMarker::CONCURRENT); - checkpointRootsInitial(); - break; - } - case CMS_op_checkpointRootsFinal: { - GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true); - SvcGCMarker sgcm(SvcGCMarker::CONCURRENT); - checkpointRootsFinal(); - break; - } - default: - fatal("No such CMS_op"); - } -} - -#ifndef PRODUCT -size_t const CMSCollector::skip_header_HeapWords() { - return FreeChunk::header_size(); -} - -// Try and collect here conditions that should hold when -// CMS thread is exiting. The idea is that the foreground GC -// thread should not be blocked if it wants to terminate -// the CMS thread and yet continue to run the VM for a while -// after that. -void CMSCollector::verify_ok_to_terminate() const { - assert(Thread::current()->is_ConcurrentGC_thread(), - "should be called by CMS thread"); - assert(!_foregroundGCShouldWait, "should be false"); - // We could check here that all the various low-level locks - // are not held by the CMS thread, but that is overkill; see - // also CMSThread::verify_ok_to_terminate() where the CGC_lock - // is checked. -} -#endif - -size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const { - assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1), - "missing Printezis mark?"); - HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); - size_t size = pointer_delta(nextOneAddr + 1, addr); - assert(size == CompactibleFreeListSpace::adjustObjectSize(size), - "alignment problem"); - assert(size >= 3, "Necessary for Printezis marks to work"); - return size; -} - -// A variant of the above (block_size_using_printezis_bits()) except -// that we return 0 if the P-bits are not yet set. -size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const { - if (_markBitMap.isMarked(addr + 1)) { - assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects"); - HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); - size_t size = pointer_delta(nextOneAddr + 1, addr); - assert(size == CompactibleFreeListSpace::adjustObjectSize(size), - "alignment problem"); - assert(size >= 3, "Necessary for Printezis marks to work"); - return size; - } - return 0; -} - -HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const { - size_t sz = 0; - oop p = (oop)addr; - if (p->klass_or_null_acquire() != NULL) { - sz = CompactibleFreeListSpace::adjustObjectSize(p->size()); - } else { - sz = block_size_using_printezis_bits(addr); - } - assert(sz > 0, "size must be nonzero"); - HeapWord* next_block = addr + sz; - HeapWord* next_card = align_up(next_block, CardTable::card_size); - assert(align_down((uintptr_t)addr, CardTable::card_size) < - align_down((uintptr_t)next_card, CardTable::card_size), - "must be different cards"); - return next_card; -} - - -// CMS Bit Map Wrapper ///////////////////////////////////////// - -// Construct a CMS bit map infrastructure, but don't create the -// bit vector itself. That is done by a separate call CMSBitMap::allocate() -// further below. -CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name): - _shifter(shifter), - _bm(), - _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true, - Monitor::_safepoint_check_never) : NULL) -{ - _bmStartWord = 0; - _bmWordSize = 0; -} - -bool CMSBitMap::allocate(MemRegion mr) { - _bmStartWord = mr.start(); - _bmWordSize = mr.word_size(); - ReservedSpace brs(ReservedSpace::allocation_align_size_up( - (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1)); - if (!brs.is_reserved()) { - log_warning(gc)("CMS bit map allocation failure"); - return false; - } - // For now we'll just commit all of the bit map up front. - // Later on we'll try to be more parsimonious with swap. - if (!_virtual_space.initialize(brs, brs.size())) { - log_warning(gc)("CMS bit map backing store failure"); - return false; - } - assert(_virtual_space.committed_size() == brs.size(), - "didn't reserve backing store for all of CMS bit map?"); - assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >= - _bmWordSize, "inconsistency in bit map sizing"); - _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter); - - // bm.clear(); // can we rely on getting zero'd memory? verify below - assert(isAllClear(), - "Expected zero'd memory from ReservedSpace constructor"); - assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()), - "consistency check"); - return true; -} - -void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) { - HeapWord *next_addr, *end_addr, *last_addr; - assert_locked(); - assert(covers(mr), "out-of-range error"); - // XXX assert that start and end are appropriately aligned - for (next_addr = mr.start(), end_addr = mr.end(); - next_addr < end_addr; next_addr = last_addr) { - MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr); - last_addr = dirty_region.end(); - if (!dirty_region.is_empty()) { - cl->do_MemRegion(dirty_region); - } else { - assert(last_addr == end_addr, "program logic"); - return; - } - } -} - -void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const { - _bm.print_on_error(st, prefix); -} - -#ifndef PRODUCT -void CMSBitMap::assert_locked() const { - CMSLockVerifier::assert_locked(lock()); -} - -bool CMSBitMap::covers(MemRegion mr) const { - // assert(_bm.map() == _virtual_space.low(), "map inconsistency"); - assert((size_t)_bm.size() == (_bmWordSize >> _shifter), - "size inconsistency"); - return (mr.start() >= _bmStartWord) && - (mr.end() <= endWord()); -} - -bool CMSBitMap::covers(HeapWord* start, size_t size) const { - return (start >= _bmStartWord && (start + size) <= endWord()); -} - -void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) { - // verify that there are no 1 bits in the interval [left, right) - FalseBitMapClosure falseBitMapClosure; - iterate(&falseBitMapClosure, left, right); -} - -void CMSBitMap::region_invariant(MemRegion mr) -{ - assert_locked(); - // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize)); - assert(!mr.is_empty(), "unexpected empty region"); - assert(covers(mr), "mr should be covered by bit map"); - // convert address range into offset range - size_t start_ofs = heapWordToOffset(mr.start()); - // Make sure that end() is appropriately aligned - assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))), - "Misaligned mr.end()"); - size_t end_ofs = heapWordToOffset(mr.end()); - assert(end_ofs > start_ofs, "Should mark at least one bit"); -} - -#endif - -bool CMSMarkStack::allocate(size_t size) { - // allocate a stack of the requisite depth - ReservedSpace rs(ReservedSpace::allocation_align_size_up( - size * sizeof(oop))); - if (!rs.is_reserved()) { - log_warning(gc)("CMSMarkStack allocation failure"); - return false; - } - if (!_virtual_space.initialize(rs, rs.size())) { - log_warning(gc)("CMSMarkStack backing store failure"); - return false; - } - assert(_virtual_space.committed_size() == rs.size(), - "didn't reserve backing store for all of CMS stack?"); - _base = (oop*)(_virtual_space.low()); - _index = 0; - _capacity = size; - NOT_PRODUCT(_max_depth = 0); - return true; -} - -// XXX FIX ME !!! In the MT case we come in here holding a -// leaf lock. For printing we need to take a further lock -// which has lower rank. We need to recalibrate the two -// lock-ranks involved in order to be able to print the -// messages below. (Or defer the printing to the caller. -// For now we take the expedient path of just disabling the -// messages for the problematic case.) -void CMSMarkStack::expand() { - assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted"); - if (_capacity == MarkStackSizeMax) { - if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) { - // We print a warning message only once per CMS cycle. - log_debug(gc)(" (benign) Hit CMSMarkStack max size limit"); - } - return; - } - // Double capacity if possible - size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax); - // Do not give up existing stack until we have managed to - // get the double capacity that we desired. - ReservedSpace rs(ReservedSpace::allocation_align_size_up( - new_capacity * sizeof(oop))); - if (rs.is_reserved()) { - // Release the backing store associated with old stack - _virtual_space.release(); - // Reinitialize virtual space for new stack - if (!_virtual_space.initialize(rs, rs.size())) { - fatal("Not enough swap for expanded marking stack"); - } - _base = (oop*)(_virtual_space.low()); - _index = 0; - _capacity = new_capacity; - } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) { - // Failed to double capacity, continue; - // we print a detail message only once per CMS cycle. - log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K", - _capacity / K, new_capacity / K); - } -} - - -// Closures -// XXX: there seems to be a lot of code duplication here; -// should refactor and consolidate common code. - -// This closure is used to mark refs into the CMS generation in -// the CMS bit map. Called at the first checkpoint. This closure -// assumes that we do not need to re-mark dirty cards; if the CMS -// generation on which this is used is not an oldest -// generation then this will lose younger_gen cards! - -MarkRefsIntoClosure::MarkRefsIntoClosure( - MemRegion span, CMSBitMap* bitMap): - _span(span), - _bitMap(bitMap) -{ - assert(ref_discoverer() == NULL, "deliberately left NULL"); - assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); -} - -void MarkRefsIntoClosure::do_oop(oop obj) { - // if p points into _span, then mark corresponding bit in _markBitMap - assert(oopDesc::is_oop(obj), "expected an oop"); - HeapWord* addr = (HeapWord*)obj; - if (_span.contains(addr)) { - // this should be made more efficient - _bitMap->mark(addr); - } -} - -ParMarkRefsIntoClosure::ParMarkRefsIntoClosure( - MemRegion span, CMSBitMap* bitMap): - _span(span), - _bitMap(bitMap) -{ - assert(ref_discoverer() == NULL, "deliberately left NULL"); - assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); -} - -void ParMarkRefsIntoClosure::do_oop(oop obj) { - // if p points into _span, then mark corresponding bit in _markBitMap - assert(oopDesc::is_oop(obj), "expected an oop"); - HeapWord* addr = (HeapWord*)obj; - if (_span.contains(addr)) { - // this should be made more efficient - _bitMap->par_mark(addr); - } -} - -// A variant of the above, used for CMS marking verification. -MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure( - MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm): - _span(span), - _verification_bm(verification_bm), - _cms_bm(cms_bm) -{ - assert(ref_discoverer() == NULL, "deliberately left NULL"); - assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch"); -} - -void MarkRefsIntoVerifyClosure::do_oop(oop obj) { - // if p points into _span, then mark corresponding bit in _markBitMap - assert(oopDesc::is_oop(obj), "expected an oop"); - HeapWord* addr = (HeapWord*)obj; - if (_span.contains(addr)) { - _verification_bm->mark(addr); - if (!_cms_bm->isMarked(addr)) { - Log(gc, verify) log; - ResourceMark rm; - LogStream ls(log.error()); - oop(addr)->print_on(&ls); - log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr)); - fatal("... aborting"); - } - } -} - -////////////////////////////////////////////////// -// MarkRefsIntoAndScanClosure -////////////////////////////////////////////////// - -MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span, - ReferenceDiscoverer* rd, - CMSBitMap* bit_map, - CMSBitMap* mod_union_table, - CMSMarkStack* mark_stack, - CMSCollector* collector, - bool should_yield, - bool concurrent_precleaning): - _span(span), - _bit_map(bit_map), - _mark_stack(mark_stack), - _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table, - mark_stack, concurrent_precleaning), - _collector(collector), - _freelistLock(NULL), - _yield(should_yield), - _concurrent_precleaning(concurrent_precleaning) -{ - // FIXME: Should initialize in base class constructor. - assert(rd != NULL, "ref_discoverer shouldn't be NULL"); - set_ref_discoverer_internal(rd); -} - -// This closure is used to mark refs into the CMS generation at the -// second (final) checkpoint, and to scan and transitively follow -// the unmarked oops. It is also used during the concurrent precleaning -// phase while scanning objects on dirty cards in the CMS generation. -// The marks are made in the marking bit map and the marking stack is -// used for keeping the (newly) grey objects during the scan. -// The parallel version (Par_...) appears further below. -void MarkRefsIntoAndScanClosure::do_oop(oop obj) { - if (obj != NULL) { - assert(oopDesc::is_oop(obj), "expected an oop"); - HeapWord* addr = (HeapWord*)obj; - assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); - assert(_collector->overflow_list_is_empty(), - "overflow list should be empty"); - if (_span.contains(addr) && - !_bit_map->isMarked(addr)) { - // mark bit map (object is now grey) - _bit_map->mark(addr); - // push on marking stack (stack should be empty), and drain the - // stack by applying this closure to the oops in the oops popped - // from the stack (i.e. blacken the grey objects) - bool res = _mark_stack->push(obj); - assert(res, "Should have space to push on empty stack"); - do { - oop new_oop = _mark_stack->pop(); - assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop"); - assert(_bit_map->isMarked((HeapWord*)new_oop), - "only grey objects on this stack"); - // iterate over the oops in this oop, marking and pushing - // the ones in CMS heap (i.e. in _span). - new_oop->oop_iterate(&_pushAndMarkClosure); - // check if it's time to yield - do_yield_check(); - } while (!_mark_stack->isEmpty() || - (!_concurrent_precleaning && take_from_overflow_list())); - // if marking stack is empty, and we are not doing this - // during precleaning, then check the overflow list - } - assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); - assert(_collector->overflow_list_is_empty(), - "overflow list was drained above"); - - assert(_collector->no_preserved_marks(), - "All preserved marks should have been restored above"); - } -} - -void MarkRefsIntoAndScanClosure::do_yield_work() { - assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "CMS thread should hold CMS token"); - assert_lock_strong(_freelistLock); - assert_lock_strong(_bit_map->lock()); - // relinquish the free_list_lock and bitMaplock() - _bit_map->lock()->unlock(); - _freelistLock->unlock(); - ConcurrentMarkSweepThread::desynchronize(true); - _collector->stopTimer(); - _collector->incrementYields(); - - // See the comment in coordinator_yield() - for (unsigned i = 0; - i < CMSYieldSleepCount && - ConcurrentMarkSweepThread::should_yield() && - !CMSCollector::foregroundGCIsActive(); - ++i) { - os::naked_short_sleep(1); - } - - ConcurrentMarkSweepThread::synchronize(true); - _freelistLock->lock_without_safepoint_check(); - _bit_map->lock()->lock_without_safepoint_check(); - _collector->startTimer(); -} - -/////////////////////////////////////////////////////////// -// ParMarkRefsIntoAndScanClosure: a parallel version of -// MarkRefsIntoAndScanClosure -/////////////////////////////////////////////////////////// -ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure( - CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd, - CMSBitMap* bit_map, OopTaskQueue* work_queue): - _span(span), - _bit_map(bit_map), - _work_queue(work_queue), - _low_water_mark(MIN2((work_queue->max_elems()/4), - ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))), - _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue) -{ - // FIXME: Should initialize in base class constructor. - assert(rd != NULL, "ref_discoverer shouldn't be NULL"); - set_ref_discoverer_internal(rd); -} - -// This closure is used to mark refs into the CMS generation at the -// second (final) checkpoint, and to scan and transitively follow -// the unmarked oops. The marks are made in the marking bit map and -// the work_queue is used for keeping the (newly) grey objects during -// the scan phase whence they are also available for stealing by parallel -// threads. Since the marking bit map is shared, updates are -// synchronized (via CAS). -void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) { - if (obj != NULL) { - // Ignore mark word because this could be an already marked oop - // that may be chained at the end of the overflow list. - assert(oopDesc::is_oop(obj, true), "expected an oop"); - HeapWord* addr = (HeapWord*)obj; - if (_span.contains(addr) && - !_bit_map->isMarked(addr)) { - // mark bit map (object will become grey): - // It is possible for several threads to be - // trying to "claim" this object concurrently; - // the unique thread that succeeds in marking the - // object first will do the subsequent push on - // to the work queue (or overflow list). - if (_bit_map->par_mark(addr)) { - // push on work_queue (which may not be empty), and trim the - // queue to an appropriate length by applying this closure to - // the oops in the oops popped from the stack (i.e. blacken the - // grey objects) - bool res = _work_queue->push(obj); - assert(res, "Low water mark should be less than capacity?"); - trim_queue(_low_water_mark); - } // Else, another thread claimed the object - } - } -} - -// This closure is used to rescan the marked objects on the dirty cards -// in the mod union table and the card table proper. -size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m( - oop p, MemRegion mr) { - - size_t size = 0; - HeapWord* addr = (HeapWord*)p; - DEBUG_ONLY(_collector->verify_work_stacks_empty();) - assert(_span.contains(addr), "we are scanning the CMS generation"); - // check if it's time to yield - if (do_yield_check()) { - // We yielded for some foreground stop-world work, - // and we have been asked to abort this ongoing preclean cycle. - return 0; - } - if (_bitMap->isMarked(addr)) { - // it's marked; is it potentially uninitialized? - if (p->klass_or_null_acquire() != NULL) { - // an initialized object; ignore mark word in verification below - // since we are running concurrent with mutators - assert(oopDesc::is_oop(p, true), "should be an oop"); - if (p->is_objArray()) { - // objArrays are precisely marked; restrict scanning - // to dirty cards only. - size = CompactibleFreeListSpace::adjustObjectSize( - p->oop_iterate_size(_scanningClosure, mr)); - } else { - // A non-array may have been imprecisely marked; we need - // to scan object in its entirety. - size = CompactibleFreeListSpace::adjustObjectSize( - p->oop_iterate_size(_scanningClosure)); - } - #ifdef ASSERT - size_t direct_size = - CompactibleFreeListSpace::adjustObjectSize(p->size()); - assert(size == direct_size, "Inconsistency in size"); - assert(size >= 3, "Necessary for Printezis marks to work"); - HeapWord* start_pbit = addr + 1; - HeapWord* end_pbit = addr + size - 1; - assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit), - "inconsistent Printezis mark"); - // Verify inner mark bits (between Printezis bits) are clear, - // but don't repeat if there are multiple dirty regions for - // the same object, to avoid potential O(N^2) performance. - if (addr != _last_scanned_object) { - _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit); - _last_scanned_object = addr; - } - #endif // ASSERT - } else { - // An uninitialized object. - assert(_bitMap->isMarked(addr+1), "missing Printezis mark?"); - HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); - size = pointer_delta(nextOneAddr + 1, addr); - assert(size == CompactibleFreeListSpace::adjustObjectSize(size), - "alignment problem"); - // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass() - // will dirty the card when the klass pointer is installed in the - // object (signaling the completion of initialization). - } - } else { - // Either a not yet marked object or an uninitialized object - if (p->klass_or_null_acquire() == NULL) { - // An uninitialized object, skip to the next card, since - // we may not be able to read its P-bits yet. - assert(size == 0, "Initial value"); - } else { - // An object not (yet) reached by marking: we merely need to - // compute its size so as to go look at the next block. - assert(oopDesc::is_oop(p, true), "should be an oop"); - size = CompactibleFreeListSpace::adjustObjectSize(p->size()); - } - } - DEBUG_ONLY(_collector->verify_work_stacks_empty();) - return size; -} - -void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() { - assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "CMS thread should hold CMS token"); - assert_lock_strong(_freelistLock); - assert_lock_strong(_bitMap->lock()); - // relinquish the free_list_lock and bitMaplock() - _bitMap->lock()->unlock(); - _freelistLock->unlock(); - ConcurrentMarkSweepThread::desynchronize(true); - _collector->stopTimer(); - _collector->incrementYields(); - - // See the comment in coordinator_yield() - for (unsigned i = 0; i < CMSYieldSleepCount && - ConcurrentMarkSweepThread::should_yield() && - !CMSCollector::foregroundGCIsActive(); ++i) { - os::naked_short_sleep(1); - } - - ConcurrentMarkSweepThread::synchronize(true); - _freelistLock->lock_without_safepoint_check(); - _bitMap->lock()->lock_without_safepoint_check(); - _collector->startTimer(); -} - - -////////////////////////////////////////////////////////////////// -// SurvivorSpacePrecleanClosure -////////////////////////////////////////////////////////////////// -// This (single-threaded) closure is used to preclean the oops in -// the survivor spaces. -size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) { - - HeapWord* addr = (HeapWord*)p; - DEBUG_ONLY(_collector->verify_work_stacks_empty();) - assert(!_span.contains(addr), "we are scanning the survivor spaces"); - assert(p->klass_or_null() != NULL, "object should be initialized"); - // an initialized object; ignore mark word in verification below - // since we are running concurrent with mutators - assert(oopDesc::is_oop(p, true), "should be an oop"); - // Note that we do not yield while we iterate over - // the interior oops of p, pushing the relevant ones - // on our marking stack. - size_t size = p->oop_iterate_size(_scanning_closure); - do_yield_check(); - // Observe that below, we do not abandon the preclean - // phase as soon as we should; rather we empty the - // marking stack before returning. This is to satisfy - // some existing assertions. In general, it may be a - // good idea to abort immediately and complete the marking - // from the grey objects at a later time. - while (!_mark_stack->isEmpty()) { - oop new_oop = _mark_stack->pop(); - assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop"); - assert(_bit_map->isMarked((HeapWord*)new_oop), - "only grey objects on this stack"); - // iterate over the oops in this oop, marking and pushing - // the ones in CMS heap (i.e. in _span). - new_oop->oop_iterate(_scanning_closure); - // check if it's time to yield - do_yield_check(); - } - unsigned int after_count = - CMSHeap::heap()->total_collections(); - bool abort = (_before_count != after_count) || - _collector->should_abort_preclean(); - return abort ? 0 : size; -} - -void SurvivorSpacePrecleanClosure::do_yield_work() { - assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "CMS thread should hold CMS token"); - assert_lock_strong(_bit_map->lock()); - // Relinquish the bit map lock - _bit_map->lock()->unlock(); - ConcurrentMarkSweepThread::desynchronize(true); - _collector->stopTimer(); - _collector->incrementYields(); - - // See the comment in coordinator_yield() - for (unsigned i = 0; i < CMSYieldSleepCount && - ConcurrentMarkSweepThread::should_yield() && - !CMSCollector::foregroundGCIsActive(); ++i) { - os::naked_short_sleep(1); - } - - ConcurrentMarkSweepThread::synchronize(true); - _bit_map->lock()->lock_without_safepoint_check(); - _collector->startTimer(); -} - -// This closure is used to rescan the marked objects on the dirty cards -// in the mod union table and the card table proper. In the parallel -// case, although the bitMap is shared, we do a single read so the -// isMarked() query is "safe". -bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) { - // Ignore mark word because we are running concurrent with mutators - assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p)); - HeapWord* addr = (HeapWord*)p; - assert(_span.contains(addr), "we are scanning the CMS generation"); - bool is_obj_array = false; - #ifdef ASSERT - if (!_parallel) { - assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); - assert(_collector->overflow_list_is_empty(), - "overflow list should be empty"); - - } - #endif // ASSERT - if (_bit_map->isMarked(addr)) { - // Obj arrays are precisely marked, non-arrays are not; - // so we scan objArrays precisely and non-arrays in their - // entirety. - if (p->is_objArray()) { - is_obj_array = true; - if (_parallel) { - p->oop_iterate(_par_scan_closure, mr); - } else { - p->oop_iterate(_scan_closure, mr); - } - } else { - if (_parallel) { - p->oop_iterate(_par_scan_closure); - } else { - p->oop_iterate(_scan_closure); - } - } - } - #ifdef ASSERT - if (!_parallel) { - assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); - assert(_collector->overflow_list_is_empty(), - "overflow list should be empty"); - - } - #endif // ASSERT - return is_obj_array; -} - -MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector, - MemRegion span, - CMSBitMap* bitMap, CMSMarkStack* markStack, - bool should_yield, bool verifying): - _collector(collector), - _span(span), - _bitMap(bitMap), - _mut(&collector->_modUnionTable), - _markStack(markStack), - _yield(should_yield), - _skipBits(0) -{ - assert(_markStack->isEmpty(), "stack should be empty"); - _finger = _bitMap->startWord(); - _threshold = _finger; - assert(_collector->_restart_addr == NULL, "Sanity check"); - assert(_span.contains(_finger), "Out of bounds _finger?"); - DEBUG_ONLY(_verifying = verifying;) -} - -void MarkFromRootsClosure::reset(HeapWord* addr) { - assert(_markStack->isEmpty(), "would cause duplicates on stack"); - assert(_span.contains(addr), "Out of bounds _finger?"); - _finger = addr; - _threshold = align_up(_finger, CardTable::card_size); -} - -// Should revisit to see if this should be restructured for -// greater efficiency. -bool MarkFromRootsClosure::do_bit(size_t offset) { - if (_skipBits > 0) { - _skipBits--; - return true; - } - // convert offset into a HeapWord* - HeapWord* addr = _bitMap->startWord() + offset; - assert(_bitMap->endWord() && addr < _bitMap->endWord(), - "address out of range"); - assert(_bitMap->isMarked(addr), "tautology"); - if (_bitMap->isMarked(addr+1)) { - // this is an allocated but not yet initialized object - assert(_skipBits == 0, "tautology"); - _skipBits = 2; // skip next two marked bits ("Printezis-marks") - oop p = oop(addr); - if (p->klass_or_null_acquire() == NULL) { - DEBUG_ONLY(if (!_verifying) {) - // We re-dirty the cards on which this object lies and increase - // the _threshold so that we'll come back to scan this object - // during the preclean or remark phase. (CMSCleanOnEnter) - if (CMSCleanOnEnter) { - size_t sz = _collector->block_size_using_printezis_bits(addr); - HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size); - MemRegion redirty_range = MemRegion(addr, end_card_addr); - assert(!redirty_range.is_empty(), "Arithmetical tautology"); - // Bump _threshold to end_card_addr; note that - // _threshold cannot possibly exceed end_card_addr, anyhow. - // This prevents future clearing of the card as the scan proceeds - // to the right. - assert(_threshold <= end_card_addr, - "Because we are just scanning into this object"); - if (_threshold < end_card_addr) { - _threshold = end_card_addr; - } - if (p->klass_or_null_acquire() != NULL) { - // Redirty the range of cards... - _mut->mark_range(redirty_range); - } // ...else the setting of klass will dirty the card anyway. - } - DEBUG_ONLY(}) - return true; - } - } - scanOopsInOop(addr); - return true; -} - -// We take a break if we've been at this for a while, -// so as to avoid monopolizing the locks involved. -void MarkFromRootsClosure::do_yield_work() { - // First give up the locks, then yield, then re-lock - // We should probably use a constructor/destructor idiom to - // do this unlock/lock or modify the MutexUnlocker class to - // serve our purpose. XXX - assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "CMS thread should hold CMS token"); - assert_lock_strong(_bitMap->lock()); - _bitMap->lock()->unlock(); - ConcurrentMarkSweepThread::desynchronize(true); - _collector->stopTimer(); - _collector->incrementYields(); - - // See the comment in coordinator_yield() - for (unsigned i = 0; i < CMSYieldSleepCount && - ConcurrentMarkSweepThread::should_yield() && - !CMSCollector::foregroundGCIsActive(); ++i) { - os::naked_short_sleep(1); - } - - ConcurrentMarkSweepThread::synchronize(true); - _bitMap->lock()->lock_without_safepoint_check(); - _collector->startTimer(); -} - -void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) { - assert(_bitMap->isMarked(ptr), "expected bit to be set"); - assert(_markStack->isEmpty(), - "should drain stack to limit stack usage"); - // convert ptr to an oop preparatory to scanning - oop obj = oop(ptr); - // Ignore mark word in verification below, since we - // may be running concurrent with mutators. - assert(oopDesc::is_oop(obj, true), "should be an oop"); - assert(_finger <= ptr, "_finger runneth ahead"); - // advance the finger to right end of this object - _finger = ptr + obj->size(); - assert(_finger > ptr, "we just incremented it above"); - // On large heaps, it may take us some time to get through - // the marking phase. During - // this time it's possible that a lot of mutations have - // accumulated in the card table and the mod union table -- - // these mutation records are redundant until we have - // actually traced into the corresponding card. - // Here, we check whether advancing the finger would make - // us cross into a new card, and if so clear corresponding - // cards in the MUT (preclean them in the card-table in the - // future). - - DEBUG_ONLY(if (!_verifying) {) - // The clean-on-enter optimization is disabled by default, - // until we fix 6178663. - if (CMSCleanOnEnter && (_finger > _threshold)) { - // [_threshold, _finger) represents the interval - // of cards to be cleared in MUT (or precleaned in card table). - // The set of cards to be cleared is all those that overlap - // with the interval [_threshold, _finger); note that - // _threshold is always kept card-aligned but _finger isn't - // always card-aligned. - HeapWord* old_threshold = _threshold; - assert(is_aligned(old_threshold, CardTable::card_size), - "_threshold should always be card-aligned"); - _threshold = align_up(_finger, CardTable::card_size); - MemRegion mr(old_threshold, _threshold); - assert(!mr.is_empty(), "Control point invariant"); - assert(_span.contains(mr), "Should clear within span"); - _mut->clear_range(mr); - } - DEBUG_ONLY(}) - // Note: the finger doesn't advance while we drain - // the stack below. - PushOrMarkClosure pushOrMarkClosure(_collector, - _span, _bitMap, _markStack, - _finger, this); - bool res = _markStack->push(obj); - assert(res, "Empty non-zero size stack should have space for single push"); - while (!_markStack->isEmpty()) { - oop new_oop = _markStack->pop(); - // Skip verifying header mark word below because we are - // running concurrent with mutators. - assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop"); - // now scan this oop's oops - new_oop->oop_iterate(&pushOrMarkClosure); - do_yield_check(); - } - assert(_markStack->isEmpty(), "tautology, emphasizing post-condition"); -} - -ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task, - CMSCollector* collector, MemRegion span, - CMSBitMap* bit_map, - OopTaskQueue* work_queue, - CMSMarkStack* overflow_stack): - _collector(collector), - _whole_span(collector->_span), - _span(span), - _bit_map(bit_map), - _mut(&collector->_modUnionTable), - _work_queue(work_queue), - _overflow_stack(overflow_stack), - _skip_bits(0), - _task(task) -{ - assert(_work_queue->size() == 0, "work_queue should be empty"); - _finger = span.start(); - _threshold = _finger; // XXX Defer clear-on-enter optimization for now - assert(_span.contains(_finger), "Out of bounds _finger?"); -} - -// Should revisit to see if this should be restructured for -// greater efficiency. -bool ParMarkFromRootsClosure::do_bit(size_t offset) { - if (_skip_bits > 0) { - _skip_bits--; - return true; - } - // convert offset into a HeapWord* - HeapWord* addr = _bit_map->startWord() + offset; - assert(_bit_map->endWord() && addr < _bit_map->endWord(), - "address out of range"); - assert(_bit_map->isMarked(addr), "tautology"); - if (_bit_map->isMarked(addr+1)) { - // this is an allocated object that might not yet be initialized - assert(_skip_bits == 0, "tautology"); - _skip_bits = 2; // skip next two marked bits ("Printezis-marks") - oop p = oop(addr); - if (p->klass_or_null_acquire() == NULL) { - // in the case of Clean-on-Enter optimization, redirty card - // and avoid clearing card by increasing the threshold. - return true; - } - } - scan_oops_in_oop(addr); - return true; -} - -void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) { - assert(_bit_map->isMarked(ptr), "expected bit to be set"); - // Should we assert that our work queue is empty or - // below some drain limit? - assert(_work_queue->size() == 0, - "should drain stack to limit stack usage"); - // convert ptr to an oop preparatory to scanning - oop obj = oop(ptr); - // Ignore mark word in verification below, since we - // may be running concurrent with mutators. - assert(oopDesc::is_oop(obj, true), "should be an oop"); - assert(_finger <= ptr, "_finger runneth ahead"); - // advance the finger to right end of this object - _finger = ptr + obj->size(); - assert(_finger > ptr, "we just incremented it above"); - // On large heaps, it may take us some time to get through - // the marking phase. During - // this time it's possible that a lot of mutations have - // accumulated in the card table and the mod union table -- - // these mutation records are redundant until we have - // actually traced into the corresponding card. - // Here, we check whether advancing the finger would make - // us cross into a new card, and if so clear corresponding - // cards in the MUT (preclean them in the card-table in the - // future). - - // The clean-on-enter optimization is disabled by default, - // until we fix 6178663. - if (CMSCleanOnEnter && (_finger > _threshold)) { - // [_threshold, _finger) represents the interval - // of cards to be cleared in MUT (or precleaned in card table). - // The set of cards to be cleared is all those that overlap - // with the interval [_threshold, _finger); note that - // _threshold is always kept card-aligned but _finger isn't - // always card-aligned. - HeapWord* old_threshold = _threshold; - assert(is_aligned(old_threshold, CardTable::card_size), - "_threshold should always be card-aligned"); - _threshold = align_up(_finger, CardTable::card_size); - MemRegion mr(old_threshold, _threshold); - assert(!mr.is_empty(), "Control point invariant"); - assert(_span.contains(mr), "Should clear within span"); // _whole_span ?? - _mut->clear_range(mr); - } - - // Note: the local finger doesn't advance while we drain - // the stack below, but the global finger sure can and will. - HeapWord* volatile* gfa = _task->global_finger_addr(); - ParPushOrMarkClosure pushOrMarkClosure(_collector, - _span, _bit_map, - _work_queue, - _overflow_stack, - _finger, - gfa, this); - bool res = _work_queue->push(obj); // overflow could occur here - assert(res, "Will hold once we use workqueues"); - while (true) { - oop new_oop; - if (!_work_queue->pop_local(new_oop)) { - // We emptied our work_queue; check if there's stuff that can - // be gotten from the overflow stack. - if (CMSConcMarkingTask::get_work_from_overflow_stack( - _overflow_stack, _work_queue)) { - do_yield_check(); - continue; - } else { // done - break; - } - } - // Skip verifying header mark word below because we are - // running concurrent with mutators. - assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop"); - // now scan this oop's oops - new_oop->oop_iterate(&pushOrMarkClosure); - do_yield_check(); - } - assert(_work_queue->size() == 0, "tautology, emphasizing post-condition"); -} - -// Yield in response to a request from VM Thread or -// from mutators. -void ParMarkFromRootsClosure::do_yield_work() { - assert(_task != NULL, "sanity"); - _task->yield(); -} - -// A variant of the above used for verifying CMS marking work. -MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector, - MemRegion span, - CMSBitMap* verification_bm, CMSBitMap* cms_bm, - CMSMarkStack* mark_stack): - _collector(collector), - _span(span), - _verification_bm(verification_bm), - _cms_bm(cms_bm), - _mark_stack(mark_stack), - _pam_verify_closure(collector, span, verification_bm, cms_bm, - mark_stack) -{ - assert(_mark_stack->isEmpty(), "stack should be empty"); - _finger = _verification_bm->startWord(); - assert(_collector->_restart_addr == NULL, "Sanity check"); - assert(_span.contains(_finger), "Out of bounds _finger?"); -} - -void MarkFromRootsVerifyClosure::reset(HeapWord* addr) { - assert(_mark_stack->isEmpty(), "would cause duplicates on stack"); - assert(_span.contains(addr), "Out of bounds _finger?"); - _finger = addr; -} - -// Should revisit to see if this should be restructured for -// greater efficiency. -bool MarkFromRootsVerifyClosure::do_bit(size_t offset) { - // convert offset into a HeapWord* - HeapWord* addr = _verification_bm->startWord() + offset; - assert(_verification_bm->endWord() && addr < _verification_bm->endWord(), - "address out of range"); - assert(_verification_bm->isMarked(addr), "tautology"); - assert(_cms_bm->isMarked(addr), "tautology"); - - assert(_mark_stack->isEmpty(), - "should drain stack to limit stack usage"); - // convert addr to an oop preparatory to scanning - oop obj = oop(addr); - assert(oopDesc::is_oop(obj), "should be an oop"); - assert(_finger <= addr, "_finger runneth ahead"); - // advance the finger to right end of this object - _finger = addr + obj->size(); - assert(_finger > addr, "we just incremented it above"); - // Note: the finger doesn't advance while we drain - // the stack below. - bool res = _mark_stack->push(obj); - assert(res, "Empty non-zero size stack should have space for single push"); - while (!_mark_stack->isEmpty()) { - oop new_oop = _mark_stack->pop(); - assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop"); - // now scan this oop's oops - new_oop->oop_iterate(&_pam_verify_closure); - } - assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition"); - return true; -} - -PushAndMarkVerifyClosure::PushAndMarkVerifyClosure( - CMSCollector* collector, MemRegion span, - CMSBitMap* verification_bm, CMSBitMap* cms_bm, - CMSMarkStack* mark_stack): - MetadataVisitingOopIterateClosure(collector->ref_processor()), - _collector(collector), - _span(span), - _verification_bm(verification_bm), - _cms_bm(cms_bm), - _mark_stack(mark_stack) -{ } - -template void PushAndMarkVerifyClosure::do_oop_work(T *p) { - oop obj = RawAccess<>::oop_load(p); - do_oop(obj); -} - -void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); } -void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); } - -// Upon stack overflow, we discard (part of) the stack, -// remembering the least address amongst those discarded -// in CMSCollector's _restart_address. -void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) { - // Remember the least grey address discarded - HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost); - _collector->lower_restart_addr(ra); - _mark_stack->reset(); // discard stack contents - _mark_stack->expand(); // expand the stack if possible -} - -void PushAndMarkVerifyClosure::do_oop(oop obj) { - assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); - HeapWord* addr = (HeapWord*)obj; - if (_span.contains(addr) && !_verification_bm->isMarked(addr)) { - // Oop lies in _span and isn't yet grey or black - _verification_bm->mark(addr); // now grey - if (!_cms_bm->isMarked(addr)) { - Log(gc, verify) log; - ResourceMark rm; - LogStream ls(log.error()); - oop(addr)->print_on(&ls); - log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr)); - fatal("... aborting"); - } - - if (!_mark_stack->push(obj)) { // stack overflow - log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity()); - assert(_mark_stack->isFull(), "Else push should have succeeded"); - handle_stack_overflow(addr); - } - // anything including and to the right of _finger - // will be scanned as we iterate over the remainder of the - // bit map - } -} - -PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector, - MemRegion span, - CMSBitMap* bitMap, CMSMarkStack* markStack, - HeapWord* finger, MarkFromRootsClosure* parent) : - MetadataVisitingOopIterateClosure(collector->ref_processor()), - _collector(collector), - _span(span), - _bitMap(bitMap), - _markStack(markStack), - _finger(finger), - _parent(parent) -{ } - -ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector, - MemRegion span, - CMSBitMap* bit_map, - OopTaskQueue* work_queue, - CMSMarkStack* overflow_stack, - HeapWord* finger, - HeapWord* volatile* global_finger_addr, - ParMarkFromRootsClosure* parent) : - MetadataVisitingOopIterateClosure(collector->ref_processor()), - _collector(collector), - _whole_span(collector->_span), - _span(span), - _bit_map(bit_map), - _work_queue(work_queue), - _overflow_stack(overflow_stack), - _finger(finger), - _global_finger_addr(global_finger_addr), - _parent(parent) -{ } - -// Assumes thread-safe access by callers, who are -// responsible for mutual exclusion. -void CMSCollector::lower_restart_addr(HeapWord* low) { - assert(_span.contains(low), "Out of bounds addr"); - if (_restart_addr == NULL) { - _restart_addr = low; - } else { - _restart_addr = MIN2(_restart_addr, low); - } -} - -// Upon stack overflow, we discard (part of) the stack, -// remembering the least address amongst those discarded -// in CMSCollector's _restart_address. -void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { - // Remember the least grey address discarded - HeapWord* ra = (HeapWord*)_markStack->least_value(lost); - _collector->lower_restart_addr(ra); - _markStack->reset(); // discard stack contents - _markStack->expand(); // expand the stack if possible -} - -// Upon stack overflow, we discard (part of) the stack, -// remembering the least address amongst those discarded -// in CMSCollector's _restart_address. -void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { - // We need to do this under a mutex to prevent other - // workers from interfering with the work done below. - MutexLocker ml(_overflow_stack->par_lock(), - Mutex::_no_safepoint_check_flag); - // Remember the least grey address discarded - HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); - _collector->lower_restart_addr(ra); - _overflow_stack->reset(); // discard stack contents - _overflow_stack->expand(); // expand the stack if possible -} - -void PushOrMarkClosure::do_oop(oop obj) { - // Ignore mark word because we are running concurrent with mutators. - assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); - HeapWord* addr = (HeapWord*)obj; - if (_span.contains(addr) && !_bitMap->isMarked(addr)) { - // Oop lies in _span and isn't yet grey or black - _bitMap->mark(addr); // now grey - if (addr < _finger) { - // the bit map iteration has already either passed, or - // sampled, this bit in the bit map; we'll need to - // use the marking stack to scan this oop's oops. - bool simulate_overflow = false; - NOT_PRODUCT( - if (CMSMarkStackOverflowALot && - _collector->simulate_overflow()) { - // simulate a stack overflow - simulate_overflow = true; - } - ) - if (simulate_overflow || !_markStack->push(obj)) { // stack overflow - log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity()); - assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded"); - handle_stack_overflow(addr); - } - } - // anything including and to the right of _finger - // will be scanned as we iterate over the remainder of the - // bit map - do_yield_check(); - } -} - -void ParPushOrMarkClosure::do_oop(oop obj) { - // Ignore mark word because we are running concurrent with mutators. - assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); - HeapWord* addr = (HeapWord*)obj; - if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) { - // Oop lies in _span and isn't yet grey or black - // We read the global_finger (volatile read) strictly after marking oop - bool res = _bit_map->par_mark(addr); // now grey - volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr; - // Should we push this marked oop on our stack? - // -- if someone else marked it, nothing to do - // -- if target oop is above global finger nothing to do - // -- if target oop is in chunk and above local finger - // then nothing to do - // -- else push on work queue - if ( !res // someone else marked it, they will deal with it - || (addr >= *gfa) // will be scanned in a later task - || (_span.contains(addr) && addr >= _finger)) { // later in this chunk - return; - } - // the bit map iteration has already either passed, or - // sampled, this bit in the bit map; we'll need to - // use the marking stack to scan this oop's oops. - bool simulate_overflow = false; - NOT_PRODUCT( - if (CMSMarkStackOverflowALot && - _collector->simulate_overflow()) { - // simulate a stack overflow - simulate_overflow = true; - } - ) - if (simulate_overflow || - !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) { - // stack overflow - log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity()); - // We cannot assert that the overflow stack is full because - // it may have been emptied since. - assert(simulate_overflow || - _work_queue->size() == _work_queue->max_elems(), - "Else push should have succeeded"); - handle_stack_overflow(addr); - } - do_yield_check(); - } -} - -PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector, - MemRegion span, - ReferenceDiscoverer* rd, - CMSBitMap* bit_map, - CMSBitMap* mod_union_table, - CMSMarkStack* mark_stack, - bool concurrent_precleaning): - MetadataVisitingOopIterateClosure(rd), - _collector(collector), - _span(span), - _bit_map(bit_map), - _mod_union_table(mod_union_table), - _mark_stack(mark_stack), - _concurrent_precleaning(concurrent_precleaning) -{ - assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL"); -} - -// Grey object rescan during pre-cleaning and second checkpoint phases -- -// the non-parallel version (the parallel version appears further below.) -void PushAndMarkClosure::do_oop(oop obj) { - // Ignore mark word verification. If during concurrent precleaning, - // the object monitor may be locked. If during the checkpoint - // phases, the object may already have been reached by a different - // path and may be at the end of the global overflow list (so - // the mark word may be NULL). - assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */), - "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); - HeapWord* addr = (HeapWord*)obj; - // Check if oop points into the CMS generation - // and is not marked - if (_span.contains(addr) && !_bit_map->isMarked(addr)) { - // a white object ... - _bit_map->mark(addr); // ... now grey - // push on the marking stack (grey set) - bool simulate_overflow = false; - NOT_PRODUCT( - if (CMSMarkStackOverflowALot && - _collector->simulate_overflow()) { - // simulate a stack overflow - simulate_overflow = true; - } - ) - if (simulate_overflow || !_mark_stack->push(obj)) { - if (_concurrent_precleaning) { - // During precleaning we can just dirty the appropriate card(s) - // in the mod union table, thus ensuring that the object remains - // in the grey set and continue. In the case of object arrays - // we need to dirty all of the cards that the object spans, - // since the rescan of object arrays will be limited to the - // dirty cards. - // Note that no one can be interfering with us in this action - // of dirtying the mod union table, so no locking or atomics - // are required. - if (obj->is_objArray()) { - size_t sz = obj->size(); - HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size); - MemRegion redirty_range = MemRegion(addr, end_card_addr); - assert(!redirty_range.is_empty(), "Arithmetical tautology"); - _mod_union_table->mark_range(redirty_range); - } else { - _mod_union_table->mark(addr); - } - _collector->_ser_pmc_preclean_ovflw++; - } else { - // During the remark phase, we need to remember this oop - // in the overflow list. - _collector->push_on_overflow_list(obj); - _collector->_ser_pmc_remark_ovflw++; - } - } - } -} - -ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector, - MemRegion span, - ReferenceDiscoverer* rd, - CMSBitMap* bit_map, - OopTaskQueue* work_queue): - MetadataVisitingOopIterateClosure(rd), - _collector(collector), - _span(span), - _bit_map(bit_map), - _work_queue(work_queue) -{ - assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL"); -} - -// Grey object rescan during second checkpoint phase -- -// the parallel version. -void ParPushAndMarkClosure::do_oop(oop obj) { - // In the assert below, we ignore the mark word because - // this oop may point to an already visited object that is - // on the overflow stack (in which case the mark word has - // been hijacked for chaining into the overflow stack -- - // if this is the last object in the overflow stack then - // its mark word will be NULL). Because this object may - // have been subsequently popped off the global overflow - // stack, and the mark word possibly restored to the prototypical - // value, by the time we get to examined this failing assert in - // the debugger, is_oop_or_null(false) may subsequently start - // to hold. - assert(oopDesc::is_oop_or_null(obj, true), - "Expected an oop or NULL at " PTR_FORMAT, p2i(obj)); - HeapWord* addr = (HeapWord*)obj; - // Check if oop points into the CMS generation - // and is not marked - if (_span.contains(addr) && !_bit_map->isMarked(addr)) { - // a white object ... - // If we manage to "claim" the object, by being the - // first thread to mark it, then we push it on our - // marking stack - if (_bit_map->par_mark(addr)) { // ... now grey - // push on work queue (grey set) - bool simulate_overflow = false; - NOT_PRODUCT( - if (CMSMarkStackOverflowALot && - _collector->par_simulate_overflow()) { - // simulate a stack overflow - simulate_overflow = true; - } - ) - if (simulate_overflow || !_work_queue->push(obj)) { - _collector->par_push_on_overflow_list(obj); - _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS - } - } // Else, some other thread got there first - } -} - -void CMSPrecleanRefsYieldClosure::do_yield_work() { - Mutex* bml = _collector->bitMapLock(); - assert_lock_strong(bml); - assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "CMS thread should hold CMS token"); - - bml->unlock(); - ConcurrentMarkSweepThread::desynchronize(true); - - _collector->stopTimer(); - _collector->incrementYields(); - - // See the comment in coordinator_yield() - for (unsigned i = 0; i < CMSYieldSleepCount && - ConcurrentMarkSweepThread::should_yield() && - !CMSCollector::foregroundGCIsActive(); ++i) { - os::naked_short_sleep(1); - } - - ConcurrentMarkSweepThread::synchronize(true); - bml->lock_without_safepoint_check(); - - _collector->startTimer(); -} - -bool CMSPrecleanRefsYieldClosure::should_return() { - if (ConcurrentMarkSweepThread::should_yield()) { - do_yield_work(); - } - return _collector->foregroundGCIsActive(); -} - -void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) { - assert(((size_t)mr.start())%CardTable::card_size_in_words == 0, - "mr should be aligned to start at a card boundary"); - // We'd like to assert: - // assert(mr.word_size()%CardTable::card_size_in_words == 0, - // "mr should be a range of cards"); - // However, that would be too strong in one case -- the last - // partition ends at _unallocated_block which, in general, can be - // an arbitrary boundary, not necessarily card aligned. - _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words; - _space->object_iterate_mem(mr, &_scan_cl); -} - -SweepClosure::SweepClosure(CMSCollector* collector, - ConcurrentMarkSweepGeneration* g, - CMSBitMap* bitMap, bool should_yield) : - _collector(collector), - _g(g), - _sp(g->cmsSpace()), - _limit(_sp->sweep_limit()), - _freelistLock(_sp->freelistLock()), - _bitMap(bitMap), - _inFreeRange(false), // No free range at beginning of sweep - _freeRangeInFreeLists(false), // No free range at beginning of sweep - _lastFreeRangeCoalesced(false), - _yield(should_yield), - _freeFinger(g->used_region().start()) -{ - NOT_PRODUCT( - _numObjectsFreed = 0; - _numWordsFreed = 0; - _numObjectsLive = 0; - _numWordsLive = 0; - _numObjectsAlreadyFree = 0; - _numWordsAlreadyFree = 0; - _last_fc = NULL; - - _sp->initializeIndexedFreeListArrayReturnedBytes(); - _sp->dictionary()->initialize_dict_returned_bytes(); - ) - assert(_limit >= _sp->bottom() && _limit <= _sp->end(), - "sweep _limit out of bounds"); - log_develop_trace(gc, sweep)("===================="); - log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit)); -} - -void SweepClosure::print_on(outputStream* st) const { - st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")", - p2i(_sp->bottom()), p2i(_sp->end())); - st->print_cr("_limit = " PTR_FORMAT, p2i(_limit)); - st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger)); - NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));) - st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d", - _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced); -} - -#ifndef PRODUCT -// Assertion checking only: no useful work in product mode -- -// however, if any of the flags below become product flags, -// you may need to review this code to see if it needs to be -// enabled in product mode. -SweepClosure::~SweepClosure() { - assert_lock_strong(_freelistLock); - assert(_limit >= _sp->bottom() && _limit <= _sp->end(), - "sweep _limit out of bounds"); - if (inFreeRange()) { - Log(gc, sweep) log; - log.error("inFreeRange() should have been reset; dumping state of SweepClosure"); - ResourceMark rm; - LogStream ls(log.error()); - print_on(&ls); - ShouldNotReachHere(); - } - - if (log_is_enabled(Debug, gc, sweep)) { - log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes", - _numObjectsFreed, _numWordsFreed*sizeof(HeapWord)); - log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes", - _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord)); - size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord); - log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes); - } - - if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) { - size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes(); - size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes(); - size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes; - log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes", - returned_bytes, indexListReturnedBytes, dict_returned_bytes); - } - log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit)); - log_develop_trace(gc, sweep)("================"); -} -#endif // PRODUCT - -void SweepClosure::initialize_free_range(HeapWord* freeFinger, - bool freeRangeInFreeLists) { - log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)", - p2i(freeFinger), freeRangeInFreeLists); - assert(!inFreeRange(), "Trampling existing free range"); - set_inFreeRange(true); - set_lastFreeRangeCoalesced(false); - - set_freeFinger(freeFinger); - set_freeRangeInFreeLists(freeRangeInFreeLists); - if (CMSTestInFreeList) { - if (freeRangeInFreeLists) { - FreeChunk* fc = (FreeChunk*) freeFinger; - assert(fc->is_free(), "A chunk on the free list should be free."); - assert(fc->size() > 0, "Free range should have a size"); - assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists"); - } - } -} - -// Note that the sweeper runs concurrently with mutators. Thus, -// it is possible for direct allocation in this generation to happen -// in the middle of the sweep. Note that the sweeper also coalesces -// contiguous free blocks. Thus, unless the sweeper and the allocator -// synchronize appropriately freshly allocated blocks may get swept up. -// This is accomplished by the sweeper locking the free lists while -// it is sweeping. Thus blocks that are determined to be free are -// indeed free. There is however one additional complication: -// blocks that have been allocated since the final checkpoint and -// mark, will not have been marked and so would be treated as -// unreachable and swept up. To prevent this, the allocator marks -// the bit map when allocating during the sweep phase. This leads, -// however, to a further complication -- objects may have been allocated -// but not yet initialized -- in the sense that the header isn't yet -// installed. The sweeper can not then determine the size of the block -// in order to skip over it. To deal with this case, we use a technique -// (due to Printezis) to encode such uninitialized block sizes in the -// bit map. Since the bit map uses a bit per every HeapWord, but the -// CMS generation has a minimum object size of 3 HeapWords, it follows -// that "normal marks" won't be adjacent in the bit map (there will -// always be at least two 0 bits between successive 1 bits). We make use -// of these "unused" bits to represent uninitialized blocks -- the bit -// corresponding to the start of the uninitialized object and the next -// bit are both set. Finally, a 1 bit marks the end of the object that -// started with the two consecutive 1 bits to indicate its potentially -// uninitialized state. - -size_t SweepClosure::do_blk_careful(HeapWord* addr) { - FreeChunk* fc = (FreeChunk*)addr; - size_t res; - - // Check if we are done sweeping. Below we check "addr >= _limit" rather - // than "addr == _limit" because although _limit was a block boundary when - // we started the sweep, it may no longer be one because heap expansion - // may have caused us to coalesce the block ending at the address _limit - // with a newly expanded chunk (this happens when _limit was set to the - // previous _end of the space), so we may have stepped past _limit: - // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740. - if (addr >= _limit) { // we have swept up to or past the limit: finish up - assert(_limit >= _sp->bottom() && _limit <= _sp->end(), - "sweep _limit out of bounds"); - assert(addr < _sp->end(), "addr out of bounds"); - // Flush any free range we might be holding as a single - // coalesced chunk to the appropriate free list. - if (inFreeRange()) { - assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit, - "freeFinger() " PTR_FORMAT " is out of bounds", p2i(freeFinger())); - flush_cur_free_chunk(freeFinger(), - pointer_delta(addr, freeFinger())); - log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]", - p2i(freeFinger()), pointer_delta(addr, freeFinger()), - lastFreeRangeCoalesced() ? 1 : 0); - } - - // help the iterator loop finish - return pointer_delta(_sp->end(), addr); - } - - assert(addr < _limit, "sweep invariant"); - // check if we should yield - do_yield_check(addr); - if (fc->is_free()) { - // Chunk that is already free - res = fc->size(); - do_already_free_chunk(fc); - debug_only(_sp->verifyFreeLists()); - // If we flush the chunk at hand in lookahead_and_flush() - // and it's coalesced with a preceding chunk, then the - // process of "mangling" the payload of the coalesced block - // will cause erasure of the size information from the - // (erstwhile) header of all the coalesced blocks but the - // first, so the first disjunct in the assert will not hold - // in that specific case (in which case the second disjunct - // will hold). - assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit, - "Otherwise the size info doesn't change at this step"); - NOT_PRODUCT( - _numObjectsAlreadyFree++; - _numWordsAlreadyFree += res; - ) - NOT_PRODUCT(_last_fc = fc;) - } else if (!_bitMap->isMarked(addr)) { - // Chunk is fresh garbage - res = do_garbage_chunk(fc); - debug_only(_sp->verifyFreeLists()); - NOT_PRODUCT( - _numObjectsFreed++; - _numWordsFreed += res; - ) - } else { - // Chunk that is alive. - res = do_live_chunk(fc); - debug_only(_sp->verifyFreeLists()); - NOT_PRODUCT( - _numObjectsLive++; - _numWordsLive += res; - ) - } - return res; -} - -// For the smart allocation, record following -// split deaths - a free chunk is removed from its free list because -// it is being split into two or more chunks. -// split birth - a free chunk is being added to its free list because -// a larger free chunk has been split and resulted in this free chunk. -// coal death - a free chunk is being removed from its free list because -// it is being coalesced into a large free chunk. -// coal birth - a free chunk is being added to its free list because -// it was created when two or more free chunks where coalesced into -// this free chunk. -// -// These statistics are used to determine the desired number of free -// chunks of a given size. The desired number is chosen to be relative -// to the end of a CMS sweep. The desired number at the end of a sweep -// is the -// count-at-end-of-previous-sweep (an amount that was enough) -// - count-at-beginning-of-current-sweep (the excess) -// + split-births (gains in this size during interval) -// - split-deaths (demands on this size during interval) -// where the interval is from the end of one sweep to the end of the -// next. -// -// When sweeping the sweeper maintains an accumulated chunk which is -// the chunk that is made up of chunks that have been coalesced. That -// will be termed the left-hand chunk. A new chunk of garbage that -// is being considered for coalescing will be referred to as the -// right-hand chunk. -// -// When making a decision on whether to coalesce a right-hand chunk with -// the current left-hand chunk, the current count vs. the desired count -// of the left-hand chunk is considered. Also if the right-hand chunk -// is near the large chunk at the end of the heap (see -// ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the -// left-hand chunk is coalesced. -// -// When making a decision about whether to split a chunk, the desired count -// vs. the current count of the candidate to be split is also considered. -// If the candidate is underpopulated (currently fewer chunks than desired) -// a chunk of an overpopulated (currently more chunks than desired) size may -// be chosen. The "hint" associated with a free list, if non-null, points -// to a free list which may be overpopulated. -// - -void SweepClosure::do_already_free_chunk(FreeChunk* fc) { - const size_t size = fc->size(); - // Chunks that cannot be coalesced are not in the - // free lists. - if (CMSTestInFreeList && !fc->cantCoalesce()) { - assert(_sp->verify_chunk_in_free_list(fc), - "free chunk should be in free lists"); - } - // a chunk that is already free, should not have been - // marked in the bit map - HeapWord* const addr = (HeapWord*) fc; - assert(!_bitMap->isMarked(addr), "free chunk should be unmarked"); - // Verify that the bit map has no bits marked between - // addr and purported end of this block. - _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); - - // Some chunks cannot be coalesced under any circumstances. - // See the definition of cantCoalesce(). - if (!fc->cantCoalesce()) { - // This chunk can potentially be coalesced. - // All the work is done in - do_post_free_or_garbage_chunk(fc, size); - // Note that if the chunk is not coalescable (the else arm - // below), we unconditionally flush, without needing to do - // a "lookahead," as we do below. - if (inFreeRange()) lookahead_and_flush(fc, size); - } else { - // Code path common to both original and adaptive free lists. - - // cant coalesce with previous block; this should be treated - // as the end of a free run if any - if (inFreeRange()) { - // we kicked some butt; time to pick up the garbage - assert(freeFinger() < addr, "freeFinger points too high"); - flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); - } - // else, nothing to do, just continue - } -} - -size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) { - // This is a chunk of garbage. It is not in any free list. - // Add it to a free list or let it possibly be coalesced into - // a larger chunk. - HeapWord* const addr = (HeapWord*) fc; - const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); - - // Verify that the bit map has no bits marked between - // addr and purported end of just dead object. - _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); - do_post_free_or_garbage_chunk(fc, size); - - assert(_limit >= addr + size, - "A freshly garbage chunk can't possibly straddle over _limit"); - if (inFreeRange()) lookahead_and_flush(fc, size); - return size; -} - -size_t SweepClosure::do_live_chunk(FreeChunk* fc) { - HeapWord* addr = (HeapWord*) fc; - // The sweeper has just found a live object. Return any accumulated - // left hand chunk to the free lists. - if (inFreeRange()) { - assert(freeFinger() < addr, "freeFinger points too high"); - flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); - } - - // This object is live: we'd normally expect this to be - // an oop, and like to assert the following: - // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop"); - // However, as we commented above, this may be an object whose - // header hasn't yet been initialized. - size_t size; - assert(_bitMap->isMarked(addr), "Tautology for this control point"); - if (_bitMap->isMarked(addr + 1)) { - // Determine the size from the bit map, rather than trying to - // compute it from the object header. - HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); - size = pointer_delta(nextOneAddr + 1, addr); - assert(size == CompactibleFreeListSpace::adjustObjectSize(size), - "alignment problem"); - -#ifdef ASSERT - if (oop(addr)->klass_or_null_acquire() != NULL) { - // Ignore mark word because we are running concurrent with mutators - assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop"); - assert(size == - CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()), - "P-mark and computed size do not agree"); - } -#endif - - } else { - // This should be an initialized object that's alive. - assert(oop(addr)->klass_or_null_acquire() != NULL, - "Should be an initialized object"); - // Ignore mark word because we are running concurrent with mutators - assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop"); - // Verify that the bit map has no bits marked between - // addr and purported end of this block. - size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); - assert(size >= 3, "Necessary for Printezis marks to work"); - assert(!_bitMap->isMarked(addr+1), "Tautology for this control point"); - DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);) - } - return size; -} - -void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc, - size_t chunkSize) { - // do_post_free_or_garbage_chunk() should only be called in the case - // of the adaptive free list allocator. - const bool fcInFreeLists = fc->is_free(); - assert((HeapWord*)fc <= _limit, "sweep invariant"); - if (CMSTestInFreeList && fcInFreeLists) { - assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists"); - } - - log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize); - - HeapWord* const fc_addr = (HeapWord*) fc; - - bool coalesce = false; - const size_t left = pointer_delta(fc_addr, freeFinger()); - const size_t right = chunkSize; - switch (FLSCoalescePolicy) { - // numeric value forms a coalition aggressiveness metric - case 0: { // never coalesce - coalesce = false; - break; - } - case 1: { // coalesce if left & right chunks on overpopulated lists - coalesce = _sp->coalOverPopulated(left) && - _sp->coalOverPopulated(right); - break; - } - case 2: { // coalesce if left chunk on overpopulated list (default) - coalesce = _sp->coalOverPopulated(left); - break; - } - case 3: { // coalesce if left OR right chunk on overpopulated list - coalesce = _sp->coalOverPopulated(left) || - _sp->coalOverPopulated(right); - break; - } - case 4: { // always coalesce - coalesce = true; - break; - } - default: - ShouldNotReachHere(); - } - - // Should the current free range be coalesced? - // If the chunk is in a free range and either we decided to coalesce above - // or the chunk is near the large block at the end of the heap - // (isNearLargestChunk() returns true), then coalesce this chunk. - const bool doCoalesce = inFreeRange() - && (coalesce || _g->isNearLargestChunk(fc_addr)); - if (doCoalesce) { - // Coalesce the current free range on the left with the new - // chunk on the right. If either is on a free list, - // it must be removed from the list and stashed in the closure. - if (freeRangeInFreeLists()) { - FreeChunk* const ffc = (FreeChunk*)freeFinger(); - assert(ffc->size() == pointer_delta(fc_addr, freeFinger()), - "Size of free range is inconsistent with chunk size."); - if (CMSTestInFreeList) { - assert(_sp->verify_chunk_in_free_list(ffc), - "Chunk is not in free lists"); - } - _sp->coalDeath(ffc->size()); - _sp->removeFreeChunkFromFreeLists(ffc); - set_freeRangeInFreeLists(false); - } - if (fcInFreeLists) { - _sp->coalDeath(chunkSize); - assert(fc->size() == chunkSize, - "The chunk has the wrong size or is not in the free lists"); - _sp->removeFreeChunkFromFreeLists(fc); - } - set_lastFreeRangeCoalesced(true); - print_free_block_coalesced(fc); - } else { // not in a free range and/or should not coalesce - // Return the current free range and start a new one. - if (inFreeRange()) { - // In a free range but cannot coalesce with the right hand chunk. - // Put the current free range into the free lists. - flush_cur_free_chunk(freeFinger(), - pointer_delta(fc_addr, freeFinger())); - } - // Set up for new free range. Pass along whether the right hand - // chunk is in the free lists. - initialize_free_range((HeapWord*)fc, fcInFreeLists); - } -} - -// Lookahead flush: -// If we are tracking a free range, and this is the last chunk that -// we'll look at because its end crosses past _limit, we'll preemptively -// flush it along with any free range we may be holding on to. Note that -// this can be the case only for an already free or freshly garbage -// chunk. If this block is an object, it can never straddle -// over _limit. The "straddling" occurs when _limit is set at -// the previous end of the space when this cycle started, and -// a subsequent heap expansion caused the previously co-terminal -// free block to be coalesced with the newly expanded portion, -// thus rendering _limit a non-block-boundary making it dangerous -// for the sweeper to step over and examine. -void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) { - assert(inFreeRange(), "Should only be called if currently in a free range."); - HeapWord* const eob = ((HeapWord*)fc) + chunk_size; - assert(_sp->used_region().contains(eob - 1), - "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT - " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")" - " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")", - p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size); - if (eob >= _limit) { - assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit"); - log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block " - "[" PTR_FORMAT "," PTR_FORMAT ") in space " - "[" PTR_FORMAT "," PTR_FORMAT ")", - p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end())); - // Return the storage we are tracking back into the free lists. - log_develop_trace(gc, sweep)("Flushing ... "); - assert(freeFinger() < eob, "Error"); - flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger())); - } -} - -void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) { - assert(inFreeRange(), "Should only be called if currently in a free range."); - assert(size > 0, - "A zero sized chunk cannot be added to the free lists."); - if (!freeRangeInFreeLists()) { - if (CMSTestInFreeList) { - FreeChunk* fc = (FreeChunk*) chunk; - fc->set_size(size); - assert(!_sp->verify_chunk_in_free_list(fc), - "chunk should not be in free lists yet"); - } - log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size); - // A new free range is going to be starting. The current - // free range has not been added to the free lists yet or - // was removed so add it back. - // If the current free range was coalesced, then the death - // of the free range was recorded. Record a birth now. - if (lastFreeRangeCoalesced()) { - _sp->coalBirth(size); - } - _sp->addChunkAndRepairOffsetTable(chunk, size, - lastFreeRangeCoalesced()); - } else { - log_develop_trace(gc, sweep)("Already in free list: nothing to flush"); - } - set_inFreeRange(false); - set_freeRangeInFreeLists(false); -} - -// We take a break if we've been at this for a while, -// so as to avoid monopolizing the locks involved. -void SweepClosure::do_yield_work(HeapWord* addr) { - // Return current free chunk being used for coalescing (if any) - // to the appropriate freelist. After yielding, the next - // free block encountered will start a coalescing range of - // free blocks. If the next free block is adjacent to the - // chunk just flushed, they will need to wait for the next - // sweep to be coalesced. - if (inFreeRange()) { - flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); - } - - // First give up the locks, then yield, then re-lock. - // We should probably use a constructor/destructor idiom to - // do this unlock/lock or modify the MutexUnlocker class to - // serve our purpose. XXX - assert_lock_strong(_bitMap->lock()); - assert_lock_strong(_freelistLock); - assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), - "CMS thread should hold CMS token"); - _bitMap->lock()->unlock(); - _freelistLock->unlock(); - ConcurrentMarkSweepThread::desynchronize(true); - _collector->stopTimer(); - _collector->incrementYields(); - - // See the comment in coordinator_yield() - for (unsigned i = 0; i < CMSYieldSleepCount && - ConcurrentMarkSweepThread::should_yield() && - !CMSCollector::foregroundGCIsActive(); ++i) { - os::naked_short_sleep(1); - } - - ConcurrentMarkSweepThread::synchronize(true); - _freelistLock->lock_without_safepoint_check(); - _bitMap->lock()->lock_without_safepoint_check(); - _collector->startTimer(); -} - -#ifndef PRODUCT -// This is actually very useful in a product build if it can -// be called from the debugger. Compile it into the product -// as needed. -bool debug_verify_chunk_in_free_list(FreeChunk* fc) { - return debug_cms_space->verify_chunk_in_free_list(fc); -} -#endif - -void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const { - log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")", - p2i(fc), fc->size()); -} - -// CMSIsAliveClosure -bool CMSIsAliveClosure::do_object_b(oop obj) { - HeapWord* addr = (HeapWord*)obj; - return addr != NULL && - (!_span.contains(addr) || _bit_map->isMarked(addr)); -} - -CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector, - MemRegion span, - CMSBitMap* bit_map, CMSMarkStack* mark_stack, - bool cpc): - _collector(collector), - _span(span), - _mark_stack(mark_stack), - _bit_map(bit_map), - _concurrent_precleaning(cpc) { - assert(!_span.is_empty(), "Empty span could spell trouble"); -} - - -// CMSKeepAliveClosure: the serial version -void CMSKeepAliveClosure::do_oop(oop obj) { - HeapWord* addr = (HeapWord*)obj; - if (_span.contains(addr) && - !_bit_map->isMarked(addr)) { - _bit_map->mark(addr); - bool simulate_overflow = false; - NOT_PRODUCT( - if (CMSMarkStackOverflowALot && - _collector->simulate_overflow()) { - // simulate a stack overflow - simulate_overflow = true; - } - ) - if (simulate_overflow || !_mark_stack->push(obj)) { - if (_concurrent_precleaning) { - // We dirty the overflown object and let the remark - // phase deal with it. - assert(_collector->overflow_list_is_empty(), "Error"); - // In the case of object arrays, we need to dirty all of - // the cards that the object spans. No locking or atomics - // are needed since no one else can be mutating the mod union - // table. - if (obj->is_objArray()) { - size_t sz = obj->size(); - HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size); - MemRegion redirty_range = MemRegion(addr, end_card_addr); - assert(!redirty_range.is_empty(), "Arithmetical tautology"); - _collector->_modUnionTable.mark_range(redirty_range); - } else { - _collector->_modUnionTable.mark(addr); - } - _collector->_ser_kac_preclean_ovflw++; - } else { - _collector->push_on_overflow_list(obj); - _collector->_ser_kac_ovflw++; - } - } - } -} - -// CMSParKeepAliveClosure: a parallel version of the above. -// The work queues are private to each closure (thread), -// but (may be) available for stealing by other threads. -void CMSParKeepAliveClosure::do_oop(oop obj) { - HeapWord* addr = (HeapWord*)obj; - if (_span.contains(addr) && - !_bit_map->isMarked(addr)) { - // In general, during recursive tracing, several threads - // may be concurrently getting here; the first one to - // "tag" it, claims it. - if (_bit_map->par_mark(addr)) { - bool res = _work_queue->push(obj); - assert(res, "Low water mark should be much less than capacity"); - // Do a recursive trim in the hope that this will keep - // stack usage lower, but leave some oops for potential stealers - trim_queue(_low_water_mark); - } // Else, another thread got there first - } -} - -void CMSParKeepAliveClosure::trim_queue(uint max) { - while (_work_queue->size() > max) { - oop new_oop; - if (_work_queue->pop_local(new_oop)) { - assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop"); - assert(_bit_map->isMarked((HeapWord*)new_oop), - "no white objects on this stack!"); - assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); - // iterate over the oops in this oop, marking and pushing - // the ones in CMS heap (i.e. in _span). - new_oop->oop_iterate(&_mark_and_push); - } - } -} - -CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure( - CMSCollector* collector, - MemRegion span, CMSBitMap* bit_map, - OopTaskQueue* work_queue): - _collector(collector), - _span(span), - _work_queue(work_queue), - _bit_map(bit_map) { } - -void CMSInnerParMarkAndPushClosure::do_oop(oop obj) { - HeapWord* addr = (HeapWord*)obj; - if (_span.contains(addr) && - !_bit_map->isMarked(addr)) { - if (_bit_map->par_mark(addr)) { - bool simulate_overflow = false; - NOT_PRODUCT( - if (CMSMarkStackOverflowALot && - _collector->par_simulate_overflow()) { - // simulate a stack overflow - simulate_overflow = true; - } - ) - if (simulate_overflow || !_work_queue->push(obj)) { - _collector->par_push_on_overflow_list(obj); - _collector->_par_kac_ovflw++; - } - } // Else another thread got there already - } -} - -////////////////////////////////////////////////////////////////// -// CMSExpansionCause ///////////////////////////// -////////////////////////////////////////////////////////////////// -const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) { - switch (cause) { - case _no_expansion: - return "No expansion"; - case _satisfy_free_ratio: - return "Free ratio"; - case _satisfy_promotion: - return "Satisfy promotion"; - case _satisfy_allocation: - return "allocation"; - case _allocate_par_lab: - return "Par LAB"; - case _allocate_par_spooling_space: - return "Par Spooling Space"; - case _adaptive_size_policy: - return "Ergonomics"; - default: - return "unknown"; - } -} - -void CMSDrainMarkingStackClosure::do_void() { - // the max number to take from overflow list at a time - const size_t num = _mark_stack->capacity()/4; - assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(), - "Overflow list should be NULL during concurrent phases"); - while (!_mark_stack->isEmpty() || - // if stack is empty, check the overflow list - _collector->take_from_overflow_list(num, _mark_stack)) { - oop obj = _mark_stack->pop(); - HeapWord* addr = (HeapWord*)obj; - assert(_span.contains(addr), "Should be within span"); - assert(_bit_map->isMarked(addr), "Should be marked"); - assert(oopDesc::is_oop(obj), "Should be an oop"); - obj->oop_iterate(_keep_alive); - } -} - -void CMSParDrainMarkingStackClosure::do_void() { - // drain queue - trim_queue(0); -} - -// Trim our work_queue so its length is below max at return -void CMSParDrainMarkingStackClosure::trim_queue(uint max) { - while (_work_queue->size() > max) { - oop new_oop; - if (_work_queue->pop_local(new_oop)) { - assert(oopDesc::is_oop(new_oop), "Expected an oop"); - assert(_bit_map->isMarked((HeapWord*)new_oop), - "no white objects on this stack!"); - assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); - // iterate over the oops in this oop, marking and pushing - // the ones in CMS heap (i.e. in _span). - new_oop->oop_iterate(&_mark_and_push); - } - } -} - -//////////////////////////////////////////////////////////////////// -// Support for Marking Stack Overflow list handling and related code -//////////////////////////////////////////////////////////////////// -// Much of the following code is similar in shape and spirit to the -// code used in ParNewGC. We should try and share that code -// as much as possible in the future. - -#ifndef PRODUCT -// Debugging support for CMSStackOverflowALot - -// It's OK to call this multi-threaded; the worst thing -// that can happen is that we'll get a bunch of closely -// spaced simulated overflows, but that's OK, in fact -// probably good as it would exercise the overflow code -// under contention. -bool CMSCollector::simulate_overflow() { - if (_overflow_counter-- <= 0) { // just being defensive - _overflow_counter = CMSMarkStackOverflowInterval; - return true; - } else { - return false; - } -} - -bool CMSCollector::par_simulate_overflow() { - return simulate_overflow(); -} -#endif - -// Single-threaded -bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) { - assert(stack->isEmpty(), "Expected precondition"); - assert(stack->capacity() > num, "Shouldn't bite more than can chew"); - size_t i = num; - oop cur = _overflow_list; - const markWord proto = markWord::prototype(); - NOT_PRODUCT(ssize_t n = 0;) - for (oop next; i > 0 && cur != NULL; cur = next, i--) { - next = oop(cur->mark_raw().to_pointer()); - cur->set_mark_raw(proto); // until proven otherwise - assert(oopDesc::is_oop(cur), "Should be an oop"); - bool res = stack->push(cur); - assert(res, "Bit off more than can chew?"); - NOT_PRODUCT(n++;) - } - _overflow_list = cur; -#ifndef PRODUCT - assert(_num_par_pushes >= n, "Too many pops?"); - _num_par_pushes -=n; -#endif - return !stack->isEmpty(); -} - -#define BUSY (cast_to_oop(0x1aff1aff)) -// (MT-safe) Get a prefix of at most "num" from the list. -// The overflow list is chained through the mark word of -// each object in the list. We fetch the entire list, -// break off a prefix of the right size and return the -// remainder. If other threads try to take objects from -// the overflow list at that time, they will wait for -// some time to see if data becomes available. If (and -// only if) another thread places one or more object(s) -// on the global list before we have returned the suffix -// to the global list, we will walk down our local list -// to find its end and append the global list to -// our suffix before returning it. This suffix walk can -// prove to be expensive (quadratic in the amount of traffic) -// when there are many objects in the overflow list and -// there is much producer-consumer contention on the list. -// *NOTE*: The overflow list manipulation code here and -// in ParNewGeneration:: are very similar in shape, -// except that in the ParNew case we use the old (from/eden) -// copy of the object to thread the list via its klass word. -// Because of the common code, if you make any changes in -// the code below, please check the ParNew version to see if -// similar changes might be needed. -// CR 6797058 has been filed to consolidate the common code. -bool CMSCollector::par_take_from_overflow_list(size_t num, - OopTaskQueue* work_q, - int no_of_gc_threads) { - assert(work_q->size() == 0, "First empty local work queue"); - assert(num < work_q->max_elems(), "Can't bite more than we can chew"); - if (_overflow_list == NULL) { - return false; - } - // Grab the entire list; we'll put back a suffix - oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list)); - // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was - // set to ParallelGCThreads. - size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads; - size_t sleep_time_millis = MAX2((size_t)1, num/100); - // If the list is busy, we spin for a short while, - // sleeping between attempts to get the list. - for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) { - os::naked_sleep(sleep_time_millis); - if (_overflow_list == NULL) { - // Nothing left to take - return false; - } else if (_overflow_list != BUSY) { - // Try and grab the prefix - prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list)); - } - } - // If the list was found to be empty, or we spun long - // enough, we give up and return empty-handed. If we leave - // the list in the BUSY state below, it must be the case that - // some other thread holds the overflow list and will set it - // to a non-BUSY state in the future. - if (prefix == NULL || prefix == BUSY) { - // Nothing to take or waited long enough - if (prefix == NULL) { - // Write back the NULL in case we overwrote it with BUSY above - // and it is still the same value. - Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY); - } - return false; - } - assert(prefix != NULL && prefix != BUSY, "Error"); - size_t i = num; - oop cur = prefix; - // Walk down the first "num" objects, unless we reach the end. - for (; i > 1 && cur->mark_raw().to_pointer() != NULL; cur = oop(cur->mark_raw().to_pointer()), i--); - if (cur->mark_raw().to_pointer() == NULL) { - // We have "num" or fewer elements in the list, so there - // is nothing to return to the global list. - // Write back the NULL in lieu of the BUSY we wrote - // above, if it is still the same value. - if (_overflow_list == BUSY) { - Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY); - } - } else { - // Chop off the suffix and return it to the global list. - assert(cur->mark_raw().to_pointer() != (void*)BUSY, "Error"); - oop suffix_head = oop(cur->mark_raw().to_pointer()); // suffix will be put back on global list - cur->set_mark_raw(markWord::from_pointer(NULL)); // break off suffix - // It's possible that the list is still in the empty(busy) state - // we left it in a short while ago; in that case we may be - // able to place back the suffix without incurring the cost - // of a walk down the list. - oop observed_overflow_list = _overflow_list; - oop cur_overflow_list = observed_overflow_list; - bool attached = false; - while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { - observed_overflow_list = - Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list); - if (cur_overflow_list == observed_overflow_list) { - attached = true; - break; - } else cur_overflow_list = observed_overflow_list; - } - if (!attached) { - // Too bad, someone else sneaked in (at least) an element; we'll need - // to do a splice. Find tail of suffix so we can prepend suffix to global - // list. - for (cur = suffix_head; cur->mark_raw().to_pointer() != NULL; cur = (oop)(cur->mark_raw().to_pointer())); - oop suffix_tail = cur; - assert(suffix_tail != NULL && suffix_tail->mark_raw().to_pointer() == NULL, - "Tautology"); - observed_overflow_list = _overflow_list; - do { - cur_overflow_list = observed_overflow_list; - if (cur_overflow_list != BUSY) { - // Do the splice ... - suffix_tail->set_mark_raw(markWord::from_pointer((void*)cur_overflow_list)); - } else { // cur_overflow_list == BUSY - suffix_tail->set_mark_raw(markWord::from_pointer(NULL)); - } - // ... and try to place spliced list back on overflow_list ... - observed_overflow_list = - Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list); - } while (cur_overflow_list != observed_overflow_list); - // ... until we have succeeded in doing so. - } - } - - // Push the prefix elements on work_q - assert(prefix != NULL, "control point invariant"); - const markWord proto = markWord::prototype(); - oop next; - NOT_PRODUCT(ssize_t n = 0;) - for (cur = prefix; cur != NULL; cur = next) { - next = oop(cur->mark_raw().to_pointer()); - cur->set_mark_raw(proto); // until proven otherwise - assert(oopDesc::is_oop(cur), "Should be an oop"); - bool res = work_q->push(cur); - assert(res, "Bit off more than we can chew?"); - NOT_PRODUCT(n++;) - } -#ifndef PRODUCT - assert(_num_par_pushes >= n, "Too many pops?"); - Atomic::sub(n, &_num_par_pushes); -#endif - return true; -} - -// Single-threaded -void CMSCollector::push_on_overflow_list(oop p) { - NOT_PRODUCT(_num_par_pushes++;) - assert(oopDesc::is_oop(p), "Not an oop"); - preserve_mark_if_necessary(p); - p->set_mark_raw(markWord::from_pointer(_overflow_list)); - _overflow_list = p; -} - -// Multi-threaded; use CAS to prepend to overflow list -void CMSCollector::par_push_on_overflow_list(oop p) { - NOT_PRODUCT(Atomic::inc(&_num_par_pushes);) - assert(oopDesc::is_oop(p), "Not an oop"); - par_preserve_mark_if_necessary(p); - oop observed_overflow_list = _overflow_list; - oop cur_overflow_list; - do { - cur_overflow_list = observed_overflow_list; - if (cur_overflow_list != BUSY) { - p->set_mark_raw(markWord::from_pointer((void*)cur_overflow_list)); - } else { - p->set_mark_raw(markWord::from_pointer(NULL)); - } - observed_overflow_list = - Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list); - } while (cur_overflow_list != observed_overflow_list); -} -#undef BUSY - -// Single threaded -// General Note on GrowableArray: pushes may silently fail -// because we are (temporarily) out of C-heap for expanding -// the stack. The problem is quite ubiquitous and affects -// a lot of code in the JVM. The prudent thing for GrowableArray -// to do (for now) is to exit with an error. However, that may -// be too draconian in some cases because the caller may be -// able to recover without much harm. For such cases, we -// should probably introduce a "soft_push" method which returns -// an indication of success or failure with the assumption that -// the caller may be able to recover from a failure; code in -// the VM can then be changed, incrementally, to deal with such -// failures where possible, thus, incrementally hardening the VM -// in such low resource situations. -void CMSCollector::preserve_mark_work(oop p, markWord m) { - _preserved_oop_stack.push(p); - _preserved_mark_stack.push(m); - assert(m == p->mark_raw(), "Mark word changed"); - assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), - "bijection"); -} - -// Single threaded -void CMSCollector::preserve_mark_if_necessary(oop p) { - markWord m = p->mark_raw(); - if (p->mark_must_be_preserved(m)) { - preserve_mark_work(p, m); - } -} - -void CMSCollector::par_preserve_mark_if_necessary(oop p) { - markWord m = p->mark_raw(); - if (p->mark_must_be_preserved(m)) { - MutexLocker x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag); - // Even though we read the mark word without holding - // the lock, we are assured that it will not change - // because we "own" this oop, so no other thread can - // be trying to push it on the overflow list; see - // the assertion in preserve_mark_work() that checks - // that m == p->mark_raw(). - preserve_mark_work(p, m); - } -} - -// We should be able to do this multi-threaded, -// a chunk of stack being a task (this is -// correct because each oop only ever appears -// once in the overflow list. However, it's -// not very easy to completely overlap this with -// other operations, so will generally not be done -// until all work's been completed. Because we -// expect the preserved oop stack (set) to be small, -// it's probably fine to do this single-threaded. -// We can explore cleverer concurrent/overlapped/parallel -// processing of preserved marks if we feel the -// need for this in the future. Stack overflow should -// be so rare in practice and, when it happens, its -// effect on performance so great that this will -// likely just be in the noise anyway. -void CMSCollector::restore_preserved_marks_if_any() { - assert(SafepointSynchronize::is_at_safepoint(), - "world should be stopped"); - assert(Thread::current()->is_ConcurrentGC_thread() || - Thread::current()->is_VM_thread(), - "should be single-threaded"); - assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), - "bijection"); - - while (!_preserved_oop_stack.is_empty()) { - oop p = _preserved_oop_stack.pop(); - assert(oopDesc::is_oop(p), "Should be an oop"); - assert(_span.contains(p), "oop should be in _span"); - assert(p->mark_raw() == markWord::prototype(), - "Set when taken from overflow list"); - markWord m = _preserved_mark_stack.pop(); - p->set_mark_raw(m); - } - assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(), - "stacks were cleared above"); -} - -#ifndef PRODUCT -bool CMSCollector::no_preserved_marks() const { - return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(); -} -#endif - -// Transfer some number of overflown objects to usual marking -// stack. Return true if some objects were transferred. -bool MarkRefsIntoAndScanClosure::take_from_overflow_list() { - size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4, - (size_t)ParGCDesiredObjsFromOverflowList); - - bool res = _collector->take_from_overflow_list(num, _mark_stack); - assert(_collector->overflow_list_is_empty() || res, - "If list is not empty, we should have taken something"); - assert(!res || !_mark_stack->isEmpty(), - "If we took something, it should now be on our stack"); - return res; -} - -size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) { - size_t res = _sp->block_size_no_stall(addr, _collector); - if (_sp->block_is_obj(addr)) { - if (_live_bit_map->isMarked(addr)) { - // It can't have been dead in a previous cycle - guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!"); - } else { - _dead_bit_map->mark(addr); // mark the dead object - } - } - // Could be 0, if the block size could not be computed without stalling. - return res; -} - -TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() { - GCMemoryManager* manager = CMSHeap::heap()->old_manager(); - switch (phase) { - case CMSCollector::InitialMarking: - initialize(manager /* GC manager */ , - cause /* cause of the GC */, - true /* allMemoryPoolsAffected */, - true /* recordGCBeginTime */, - true /* recordPreGCUsage */, - false /* recordPeakUsage */, - false /* recordPostGCusage */, - true /* recordAccumulatedGCTime */, - false /* recordGCEndTime */, - false /* countCollection */ ); - break; - - case CMSCollector::FinalMarking: - initialize(manager /* GC manager */ , - cause /* cause of the GC */, - true /* allMemoryPoolsAffected */, - false /* recordGCBeginTime */, - false /* recordPreGCUsage */, - false /* recordPeakUsage */, - false /* recordPostGCusage */, - true /* recordAccumulatedGCTime */, - false /* recordGCEndTime */, - false /* countCollection */ ); - break; - - case CMSCollector::Sweeping: - initialize(manager /* GC manager */ , - cause /* cause of the GC */, - true /* allMemoryPoolsAffected */, - false /* recordGCBeginTime */, - false /* recordPreGCUsage */, - true /* recordPeakUsage */, - true /* recordPostGCusage */, - false /* recordAccumulatedGCTime */, - true /* recordGCEndTime */, - true /* countCollection */ ); - break; - - default: - ShouldNotReachHere(); - } -}