--- a/src/hotspot/share/gc/cms/concurrentMarkSweepGeneration.cpp Fri Nov 08 14:54:17 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<mtGC> {
- 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<OopTaskQueue> 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<ClassLoaderData*>* 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<ClassLoaderData*>* 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 <class T> 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<intptr_t>(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();
- }
-}