diff -r 4ebc2e2fb97c -r 71c04702a3d5 src/hotspot/share/gc/shared/referenceProcessor.cpp --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/hotspot/share/gc/shared/referenceProcessor.cpp Tue Sep 12 19:03:39 2017 +0200 @@ -0,0 +1,1260 @@ +/* + * Copyright (c) 2001, 2017, 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/javaClasses.inline.hpp" +#include "classfile/systemDictionary.hpp" +#include "gc/shared/collectedHeap.hpp" +#include "gc/shared/collectedHeap.inline.hpp" +#include "gc/shared/gcTimer.hpp" +#include "gc/shared/gcTraceTime.inline.hpp" +#include "gc/shared/referencePolicy.hpp" +#include "gc/shared/referenceProcessor.inline.hpp" +#include "logging/log.hpp" +#include "memory/allocation.hpp" +#include "memory/resourceArea.hpp" +#include "oops/oop.inline.hpp" +#include "runtime/java.hpp" +#include "runtime/jniHandles.hpp" + +ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL; +ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL; +jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0; + +void referenceProcessor_init() { + ReferenceProcessor::init_statics(); +} + +void ReferenceProcessor::init_statics() { + // We need a monotonically non-decreasing time in ms but + // os::javaTimeMillis() does not guarantee monotonicity. + jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; + + // Initialize the soft ref timestamp clock. + _soft_ref_timestamp_clock = now; + // Also update the soft ref clock in j.l.r.SoftReference + java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock); + + _always_clear_soft_ref_policy = new AlwaysClearPolicy(); + if (is_server_compilation_mode_vm()) { + _default_soft_ref_policy = new LRUMaxHeapPolicy(); + } else { + _default_soft_ref_policy = new LRUCurrentHeapPolicy(); + } + if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) { + vm_exit_during_initialization("Could not allocate reference policy object"); + } + guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || + RefDiscoveryPolicy == ReferentBasedDiscovery, + "Unrecognized RefDiscoveryPolicy"); +} + +void ReferenceProcessor::enable_discovery(bool check_no_refs) { +#ifdef ASSERT + // Verify that we're not currently discovering refs + assert(!_discovering_refs, "nested call?"); + + if (check_no_refs) { + // Verify that the discovered lists are empty + verify_no_references_recorded(); + } +#endif // ASSERT + + // Someone could have modified the value of the static + // field in the j.l.r.SoftReference class that holds the + // soft reference timestamp clock using reflection or + // Unsafe between GCs. Unconditionally update the static + // field in ReferenceProcessor here so that we use the new + // value during reference discovery. + + _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); + _discovering_refs = true; +} + +ReferenceProcessor::ReferenceProcessor(MemRegion span, + bool mt_processing, + uint mt_processing_degree, + bool mt_discovery, + uint mt_discovery_degree, + bool atomic_discovery, + BoolObjectClosure* is_alive_non_header) : + _discovering_refs(false), + _enqueuing_is_done(false), + _is_alive_non_header(is_alive_non_header), + _processing_is_mt(mt_processing), + _next_id(0) +{ + _span = span; + _discovery_is_atomic = atomic_discovery; + _discovery_is_mt = mt_discovery; + _num_q = MAX2(1U, mt_processing_degree); + _max_num_q = MAX2(_num_q, mt_discovery_degree); + _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList, + _max_num_q * number_of_subclasses_of_ref(), mtGC); + + if (_discovered_refs == NULL) { + vm_exit_during_initialization("Could not allocated RefProc Array"); + } + _discoveredSoftRefs = &_discovered_refs[0]; + _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q]; + _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q]; + _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q]; + + // Initialize all entries to NULL + for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { + _discovered_refs[i].set_head(NULL); + _discovered_refs[i].set_length(0); + } + + setup_policy(false /* default soft ref policy */); +} + +#ifndef PRODUCT +void ReferenceProcessor::verify_no_references_recorded() { + guarantee(!_discovering_refs, "Discovering refs?"); + for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { + guarantee(_discovered_refs[i].is_empty(), + "Found non-empty discovered list at %u", i); + } +} +#endif + +void ReferenceProcessor::weak_oops_do(OopClosure* f) { + for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { + if (UseCompressedOops) { + f->do_oop((narrowOop*)_discovered_refs[i].adr_head()); + } else { + f->do_oop((oop*)_discovered_refs[i].adr_head()); + } + } +} + +void ReferenceProcessor::update_soft_ref_master_clock() { + // Update (advance) the soft ref master clock field. This must be done + // after processing the soft ref list. + + // We need a monotonically non-decreasing time in ms but + // os::javaTimeMillis() does not guarantee monotonicity. + jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; + jlong soft_ref_clock = java_lang_ref_SoftReference::clock(); + assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync"); + + NOT_PRODUCT( + if (now < _soft_ref_timestamp_clock) { + log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, + _soft_ref_timestamp_clock, now); + } + ) + // The values of now and _soft_ref_timestamp_clock are set using + // javaTimeNanos(), which is guaranteed to be monotonically + // non-decreasing provided the underlying platform provides such + // a time source (and it is bug free). + // In product mode, however, protect ourselves from non-monotonicity. + if (now > _soft_ref_timestamp_clock) { + _soft_ref_timestamp_clock = now; + java_lang_ref_SoftReference::set_clock(now); + } + // Else leave clock stalled at its old value until time progresses + // past clock value. +} + +size_t ReferenceProcessor::total_count(DiscoveredList lists[]) const { + size_t total = 0; + for (uint i = 0; i < _max_num_q; ++i) { + total += lists[i].length(); + } + return total; +} + +ReferenceProcessorStats ReferenceProcessor::process_discovered_references( + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc, + AbstractRefProcTaskExecutor* task_executor, + ReferenceProcessorPhaseTimes* phase_times) { + + double start_time = os::elapsedTime(); + + assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); + // Stop treating discovered references specially. + disable_discovery(); + + // If discovery was concurrent, someone could have modified + // the value of the static field in the j.l.r.SoftReference + // class that holds the soft reference timestamp clock using + // reflection or Unsafe between when discovery was enabled and + // now. Unconditionally update the static field in ReferenceProcessor + // here so that we use the new value during processing of the + // discovered soft refs. + + _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); + + ReferenceProcessorStats stats(total_count(_discoveredSoftRefs), + total_count(_discoveredWeakRefs), + total_count(_discoveredFinalRefs), + total_count(_discoveredPhantomRefs)); + + // Soft references + { + RefProcPhaseTimesTracker tt(REF_SOFT, phase_times, this); + process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true, + is_alive, keep_alive, complete_gc, task_executor, phase_times); + } + + update_soft_ref_master_clock(); + + // Weak references + { + RefProcPhaseTimesTracker tt(REF_WEAK, phase_times, this); + process_discovered_reflist(_discoveredWeakRefs, NULL, true, + is_alive, keep_alive, complete_gc, task_executor, phase_times); + } + + // Final references + { + RefProcPhaseTimesTracker tt(REF_FINAL, phase_times, this); + process_discovered_reflist(_discoveredFinalRefs, NULL, false, + is_alive, keep_alive, complete_gc, task_executor, phase_times); + } + + // Phantom references + { + RefProcPhaseTimesTracker tt(REF_PHANTOM, phase_times, this); + process_discovered_reflist(_discoveredPhantomRefs, NULL, true, + is_alive, keep_alive, complete_gc, task_executor, phase_times); + } + + // Weak global JNI references. It would make more sense (semantically) to + // traverse these simultaneously with the regular weak references above, but + // that is not how the JDK1.2 specification is. See #4126360. Native code can + // thus use JNI weak references to circumvent the phantom references and + // resurrect a "post-mortem" object. + { + GCTraceTime(Debug, gc, ref) tt("JNI Weak Reference", phase_times->gc_timer()); + if (task_executor != NULL) { + task_executor->set_single_threaded_mode(); + } + process_phaseJNI(is_alive, keep_alive, complete_gc); + } + + phase_times->set_total_time_ms((os::elapsedTime() - start_time) * 1000); + + log_develop_trace(gc, ref)("JNI Weak Reference count: " SIZE_FORMAT, count_jni_refs()); + + return stats; +} + +#ifndef PRODUCT +// Calculate the number of jni handles. +size_t ReferenceProcessor::count_jni_refs() { + class CountHandleClosure: public OopClosure { + private: + size_t _count; + public: + CountHandleClosure(): _count(0) {} + void do_oop(oop* unused) { _count++; } + void do_oop(narrowOop* unused) { ShouldNotReachHere(); } + size_t count() { return _count; } + }; + CountHandleClosure global_handle_count; + JNIHandles::weak_oops_do(&global_handle_count); + return global_handle_count.count(); +} +#endif + +void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc) { + JNIHandles::weak_oops_do(is_alive, keep_alive); + complete_gc->do_void(); +} + +void ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor, + ReferenceProcessorPhaseTimes* phase_times) { + // Enqueue references that are not made active again, and + // clear the decks for the next collection (cycle). + enqueue_discovered_reflists(task_executor, phase_times); + + // Stop treating discovered references specially. + disable_discovery(); +} + +void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list) { + // Given a list of refs linked through the "discovered" field + // (java.lang.ref.Reference.discovered), self-loop their "next" field + // thus distinguishing them from active References, then + // prepend them to the pending list. + // + // The Java threads will see the Reference objects linked together through + // the discovered field. Instead of trying to do the write barrier updates + // in all places in the reference processor where we manipulate the discovered + // field we make sure to do the barrier here where we anyway iterate through + // all linked Reference objects. Note that it is important to not dirty any + // cards during reference processing since this will cause card table + // verification to fail for G1. + log_develop_trace(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(&refs_list)); + + oop obj = NULL; + oop next_d = refs_list.head(); + // Walk down the list, self-looping the next field + // so that the References are not considered active. + while (obj != next_d) { + obj = next_d; + assert(obj->is_instance(), "should be an instance object"); + assert(InstanceKlass::cast(obj->klass())->is_reference_instance_klass(), "should be reference object"); + next_d = java_lang_ref_Reference::discovered(obj); + log_develop_trace(gc, ref)(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, p2i(obj), p2i(next_d)); + assert(java_lang_ref_Reference::next(obj) == NULL, + "Reference not active; should not be discovered"); + // Self-loop next, so as to make Ref not active. + java_lang_ref_Reference::set_next_raw(obj, obj); + if (next_d != obj) { + oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d); + } else { + // This is the last object. + // Swap refs_list into pending list and set obj's + // discovered to what we read from the pending list. + oop old = Universe::swap_reference_pending_list(refs_list.head()); + java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL + oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old); + } + } +} + +// Parallel enqueue task +class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { +public: + RefProcEnqueueTask(ReferenceProcessor& ref_processor, + DiscoveredList discovered_refs[], + int n_queues, + ReferenceProcessorPhaseTimes* phase_times) + : EnqueueTask(ref_processor, discovered_refs, n_queues, phase_times) + { } + + virtual void work(unsigned int work_id) { + RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefEnqueue, _phase_times, work_id); + + assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds"); + // Simplest first cut: static partitioning. + int index = work_id; + // The increment on "index" must correspond to the maximum number of queues + // (n_queues) with which that ReferenceProcessor was created. That + // is because of the "clever" way the discovered references lists were + // allocated and are indexed into. + assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected"); + for (int j = 0; + j < ReferenceProcessor::number_of_subclasses_of_ref(); + j++, index += _n_queues) { + _ref_processor.enqueue_discovered_reflist(_refs_lists[index]); + _refs_lists[index].set_head(NULL); + _refs_lists[index].set_length(0); + } + } +}; + +// Enqueue references that are not made active again +void ReferenceProcessor::enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor, + ReferenceProcessorPhaseTimes* phase_times) { + + ReferenceProcessorStats stats(total_count(_discoveredSoftRefs), + total_count(_discoveredWeakRefs), + total_count(_discoveredFinalRefs), + total_count(_discoveredPhantomRefs)); + + RefProcEnqueueTimeTracker tt(phase_times, stats); + + if (_processing_is_mt && task_executor != NULL) { + // Parallel code + RefProcEnqueueTask tsk(*this, _discovered_refs, _max_num_q, phase_times); + task_executor->execute(tsk); + } else { + // Serial code: call the parent class's implementation + for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { + enqueue_discovered_reflist(_discovered_refs[i]); + _discovered_refs[i].set_head(NULL); + _discovered_refs[i].set_length(0); + } + } +} + +void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { + _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref); + oop discovered = java_lang_ref_Reference::discovered(_ref); + assert(_discovered_addr && oopDesc::is_oop_or_null(discovered), + "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)); + _next = discovered; + _referent_addr = java_lang_ref_Reference::referent_addr(_ref); + _referent = java_lang_ref_Reference::referent(_ref); + assert(Universe::heap()->is_in_reserved_or_null(_referent), + "Wrong oop found in java.lang.Reference object"); + assert(allow_null_referent ? + oopDesc::is_oop_or_null(_referent) + : oopDesc::is_oop(_referent), + "Expected an oop%s for referent field at " PTR_FORMAT, + (allow_null_referent ? " or NULL" : ""), + p2i(_referent)); +} + +void DiscoveredListIterator::remove() { + assert(oopDesc::is_oop(_ref), "Dropping a bad reference"); + oop_store_raw(_discovered_addr, NULL); + + // First _prev_next ref actually points into DiscoveredList (gross). + oop new_next; + if (_next == _ref) { + // At the end of the list, we should make _prev point to itself. + // If _ref is the first ref, then _prev_next will be in the DiscoveredList, + // and _prev will be NULL. + new_next = _prev; + } else { + new_next = _next; + } + // Remove Reference object from discovered list. Note that G1 does not need a + // pre-barrier here because we know the Reference has already been found/marked, + // that's how it ended up in the discovered list in the first place. + oop_store_raw(_prev_next, new_next); + NOT_PRODUCT(_removed++); + _refs_list.dec_length(1); +} + +void DiscoveredListIterator::clear_referent() { + oop_store_raw(_referent_addr, NULL); +} + +// NOTE: process_phase*() are largely similar, and at a high level +// merely iterate over the extant list applying a predicate to +// each of its elements and possibly removing that element from the +// list and applying some further closures to that element. +// We should consider the possibility of replacing these +// process_phase*() methods by abstracting them into +// a single general iterator invocation that receives appropriate +// closures that accomplish this work. + +// (SoftReferences only) Traverse the list and remove any SoftReferences whose +// referents are not alive, but that should be kept alive for policy reasons. +// Keep alive the transitive closure of all such referents. +void +ReferenceProcessor::process_phase1(DiscoveredList& refs_list, + ReferencePolicy* policy, + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc) { + assert(policy != NULL, "Must have a non-NULL policy"); + DiscoveredListIterator iter(refs_list, keep_alive, is_alive); + // Decide which softly reachable refs should be kept alive. + while (iter.has_next()) { + iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); + bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); + if (referent_is_dead && + !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) { + log_develop_trace(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", + p2i(iter.obj()), iter.obj()->klass()->internal_name()); + // Remove Reference object from list + iter.remove(); + // keep the referent around + iter.make_referent_alive(); + iter.move_to_next(); + } else { + iter.next(); + } + } + // Close the reachable set + complete_gc->do_void(); + log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT, + iter.removed(), iter.processed(), p2i(&refs_list)); +} + +// Traverse the list and remove any Refs that are not active, or +// whose referents are either alive or NULL. +void +ReferenceProcessor::pp2_work(DiscoveredList& refs_list, + BoolObjectClosure* is_alive, + OopClosure* keep_alive) { + assert(discovery_is_atomic(), "Error"); + DiscoveredListIterator iter(refs_list, keep_alive, is_alive); + while (iter.has_next()) { + iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); + DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());) + assert(next == NULL, "Should not discover inactive Reference"); + if (iter.is_referent_alive()) { + log_develop_trace(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", + p2i(iter.obj()), iter.obj()->klass()->internal_name()); + // The referent is reachable after all. + // Remove Reference object from list. + iter.remove(); + // Update the referent pointer as necessary: Note that this + // should not entail any recursive marking because the + // referent must already have been traversed. + iter.make_referent_alive(); + iter.move_to_next(); + } else { + iter.next(); + } + } + NOT_PRODUCT( + if (iter.processed() > 0) { + log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT + " Refs in discovered list " INTPTR_FORMAT, + iter.removed(), iter.processed(), p2i(&refs_list)); + } + ) +} + +void +ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list, + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc) { + assert(!discovery_is_atomic(), "Error"); + DiscoveredListIterator iter(refs_list, keep_alive, is_alive); + while (iter.has_next()) { + iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); + HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); + oop next = java_lang_ref_Reference::next(iter.obj()); + if ((iter.referent() == NULL || iter.is_referent_alive() || + next != NULL)) { + assert(oopDesc::is_oop_or_null(next), "Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next)); + // Remove Reference object from list + iter.remove(); + // Trace the cohorts + iter.make_referent_alive(); + if (UseCompressedOops) { + keep_alive->do_oop((narrowOop*)next_addr); + } else { + keep_alive->do_oop((oop*)next_addr); + } + iter.move_to_next(); + } else { + iter.next(); + } + } + // Now close the newly reachable set + complete_gc->do_void(); + NOT_PRODUCT( + if (iter.processed() > 0) { + log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT + " Refs in discovered list " INTPTR_FORMAT, + iter.removed(), iter.processed(), p2i(&refs_list)); + } + ) +} + +// Traverse the list and process the referents, by either +// clearing them or keeping them (and their reachable +// closure) alive. +void +ReferenceProcessor::process_phase3(DiscoveredList& refs_list, + bool clear_referent, + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc) { + ResourceMark rm; + DiscoveredListIterator iter(refs_list, keep_alive, is_alive); + while (iter.has_next()) { + iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); + if (clear_referent) { + // NULL out referent pointer + iter.clear_referent(); + } else { + // keep the referent around + iter.make_referent_alive(); + } + log_develop_trace(gc, ref)("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", + clear_referent ? "cleared " : "", p2i(iter.obj()), iter.obj()->klass()->internal_name()); + assert(oopDesc::is_oop(iter.obj(), UseConcMarkSweepGC), "Adding a bad reference"); + iter.next(); + } + // Close the reachable set + complete_gc->do_void(); +} + +void +ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) { + oop obj = NULL; + oop next = refs_list.head(); + while (next != obj) { + obj = next; + next = java_lang_ref_Reference::discovered(obj); + java_lang_ref_Reference::set_discovered_raw(obj, NULL); + } + refs_list.set_head(NULL); + refs_list.set_length(0); +} + +void ReferenceProcessor::abandon_partial_discovery() { + // loop over the lists + for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { + if ((i % _max_num_q) == 0) { + log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i)); + } + clear_discovered_references(_discovered_refs[i]); + } +} + +size_t ReferenceProcessor::total_reference_count(ReferenceType type) const { + DiscoveredList* list = NULL; + + switch (type) { + case REF_SOFT: + list = _discoveredSoftRefs; + break; + case REF_WEAK: + list = _discoveredWeakRefs; + break; + case REF_FINAL: + list = _discoveredFinalRefs; + break; + case REF_PHANTOM: + list = _discoveredPhantomRefs; + break; + case REF_OTHER: + case REF_NONE: + default: + ShouldNotReachHere(); + } + return total_count(list); +} + +class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { +public: + RefProcPhase1Task(ReferenceProcessor& ref_processor, + DiscoveredList refs_lists[], + ReferencePolicy* policy, + bool marks_oops_alive, + ReferenceProcessorPhaseTimes* phase_times) + : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times), + _policy(policy) + { } + virtual void work(unsigned int i, BoolObjectClosure& is_alive, + OopClosure& keep_alive, + VoidClosure& complete_gc) + { + RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase1, _phase_times, i); + + _ref_processor.process_phase1(_refs_lists[i], _policy, + &is_alive, &keep_alive, &complete_gc); + } +private: + ReferencePolicy* _policy; +}; + +class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { +public: + RefProcPhase2Task(ReferenceProcessor& ref_processor, + DiscoveredList refs_lists[], + bool marks_oops_alive, + ReferenceProcessorPhaseTimes* phase_times) + : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times) + { } + virtual void work(unsigned int i, BoolObjectClosure& is_alive, + OopClosure& keep_alive, + VoidClosure& complete_gc) + { + RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase2, _phase_times, i); + + _ref_processor.process_phase2(_refs_lists[i], + &is_alive, &keep_alive, &complete_gc); + } +}; + +class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { +public: + RefProcPhase3Task(ReferenceProcessor& ref_processor, + DiscoveredList refs_lists[], + bool clear_referent, + bool marks_oops_alive, + ReferenceProcessorPhaseTimes* phase_times) + : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times), + _clear_referent(clear_referent) + { } + virtual void work(unsigned int i, BoolObjectClosure& is_alive, + OopClosure& keep_alive, + VoidClosure& complete_gc) + { + RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase3, _phase_times, i); + + _ref_processor.process_phase3(_refs_lists[i], _clear_referent, + &is_alive, &keep_alive, &complete_gc); + } +private: + bool _clear_referent; +}; + +#ifndef PRODUCT +void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_refs) { + if (!log_is_enabled(Trace, gc, ref)) { + return; + } + + stringStream st; + for (uint i = 0; i < active_length; ++i) { + st.print(SIZE_FORMAT " ", ref_lists[i].length()); + } + log_develop_trace(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs); +#ifdef ASSERT + for (uint i = active_length; i < _max_num_q; i++) { + assert(ref_lists[i].length() == 0, SIZE_FORMAT " unexpected References in %u", + ref_lists[i].length(), i); + } +#endif +} +#endif + +void ReferenceProcessor::set_active_mt_degree(uint v) { + _num_q = v; + _next_id = 0; +} + +// Balances reference queues. +// Move entries from all queues[0, 1, ..., _max_num_q-1] to +// queues[0, 1, ..., _num_q-1] because only the first _num_q +// corresponding to the active workers will be processed. +void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) +{ + // calculate total length + size_t total_refs = 0; + log_develop_trace(gc, ref)("Balance ref_lists "); + + for (uint i = 0; i < _max_num_q; ++i) { + total_refs += ref_lists[i].length(); + } + log_reflist_counts(ref_lists, _max_num_q, total_refs); + size_t avg_refs = total_refs / _num_q + 1; + uint to_idx = 0; + for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) { + bool move_all = false; + if (from_idx >= _num_q) { + move_all = ref_lists[from_idx].length() > 0; + } + while ((ref_lists[from_idx].length() > avg_refs) || + move_all) { + assert(to_idx < _num_q, "Sanity Check!"); + if (ref_lists[to_idx].length() < avg_refs) { + // move superfluous refs + size_t refs_to_move; + // Move all the Ref's if the from queue will not be processed. + if (move_all) { + refs_to_move = MIN2(ref_lists[from_idx].length(), + avg_refs - ref_lists[to_idx].length()); + } else { + refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, + avg_refs - ref_lists[to_idx].length()); + } + + assert(refs_to_move > 0, "otherwise the code below will fail"); + + oop move_head = ref_lists[from_idx].head(); + oop move_tail = move_head; + oop new_head = move_head; + // find an element to split the list on + for (size_t j = 0; j < refs_to_move; ++j) { + move_tail = new_head; + new_head = java_lang_ref_Reference::discovered(new_head); + } + + // Add the chain to the to list. + if (ref_lists[to_idx].head() == NULL) { + // to list is empty. Make a loop at the end. + java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail); + } else { + java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head()); + } + ref_lists[to_idx].set_head(move_head); + ref_lists[to_idx].inc_length(refs_to_move); + + // Remove the chain from the from list. + if (move_tail == new_head) { + // We found the end of the from list. + ref_lists[from_idx].set_head(NULL); + } else { + ref_lists[from_idx].set_head(new_head); + } + ref_lists[from_idx].dec_length(refs_to_move); + if (ref_lists[from_idx].length() == 0) { + break; + } + } else { + to_idx = (to_idx + 1) % _num_q; + } + } + } +#ifdef ASSERT + size_t balanced_total_refs = 0; + for (uint i = 0; i < _num_q; ++i) { + balanced_total_refs += ref_lists[i].length(); + } + log_reflist_counts(ref_lists, _num_q, balanced_total_refs); + assert(total_refs == balanced_total_refs, "Balancing was incomplete"); +#endif +} + +void ReferenceProcessor::balance_all_queues() { + balance_queues(_discoveredSoftRefs); + balance_queues(_discoveredWeakRefs); + balance_queues(_discoveredFinalRefs); + balance_queues(_discoveredPhantomRefs); +} + +void ReferenceProcessor::process_discovered_reflist( + DiscoveredList refs_lists[], + ReferencePolicy* policy, + bool clear_referent, + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc, + AbstractRefProcTaskExecutor* task_executor, + ReferenceProcessorPhaseTimes* phase_times) +{ + bool mt_processing = task_executor != NULL && _processing_is_mt; + + phase_times->set_processing_is_mt(mt_processing); + + // If discovery used MT and a dynamic number of GC threads, then + // the queues must be balanced for correctness if fewer than the + // maximum number of queues were used. The number of queue used + // during discovery may be different than the number to be used + // for processing so don't depend of _num_q < _max_num_q as part + // of the test. + bool must_balance = _discovery_is_mt; + + if ((mt_processing && ParallelRefProcBalancingEnabled) || + must_balance) { + RefProcBalanceQueuesTimeTracker tt(phase_times); + balance_queues(refs_lists); + } + + // Phase 1 (soft refs only): + // . Traverse the list and remove any SoftReferences whose + // referents are not alive, but that should be kept alive for + // policy reasons. Keep alive the transitive closure of all + // such referents. + if (policy != NULL) { + RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase1, phase_times); + + if (mt_processing) { + RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/, phase_times); + task_executor->execute(phase1); + } else { + for (uint i = 0; i < _max_num_q; i++) { + process_phase1(refs_lists[i], policy, + is_alive, keep_alive, complete_gc); + } + } + } else { // policy == NULL + assert(refs_lists != _discoveredSoftRefs, + "Policy must be specified for soft references."); + } + + // Phase 2: + // . Traverse the list and remove any refs whose referents are alive. + { + RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase2, phase_times); + + if (mt_processing) { + RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/, phase_times); + task_executor->execute(phase2); + } else { + for (uint i = 0; i < _max_num_q; i++) { + process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); + } + } + } + + // Phase 3: + // . Traverse the list and process referents as appropriate. + { + RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase3, phase_times); + + if (mt_processing) { + RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/, phase_times); + task_executor->execute(phase3); + } else { + for (uint i = 0; i < _max_num_q; i++) { + process_phase3(refs_lists[i], clear_referent, + is_alive, keep_alive, complete_gc); + } + } + } +} + +inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { + uint id = 0; + // Determine the queue index to use for this object. + if (_discovery_is_mt) { + // During a multi-threaded discovery phase, + // each thread saves to its "own" list. + Thread* thr = Thread::current(); + id = thr->as_Worker_thread()->id(); + } else { + // single-threaded discovery, we save in round-robin + // fashion to each of the lists. + if (_processing_is_mt) { + id = next_id(); + } + } + assert(id < _max_num_q, "Id is out-of-bounds id %u and max id %u)", id, _max_num_q); + + // Get the discovered queue to which we will add + DiscoveredList* list = NULL; + switch (rt) { + case REF_OTHER: + // Unknown reference type, no special treatment + break; + case REF_SOFT: + list = &_discoveredSoftRefs[id]; + break; + case REF_WEAK: + list = &_discoveredWeakRefs[id]; + break; + case REF_FINAL: + list = &_discoveredFinalRefs[id]; + break; + case REF_PHANTOM: + list = &_discoveredPhantomRefs[id]; + break; + case REF_NONE: + // we should not reach here if we are an InstanceRefKlass + default: + ShouldNotReachHere(); + } + log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list)); + return list; +} + +inline void +ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, + oop obj, + HeapWord* discovered_addr) { + assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); + // First we must make sure this object is only enqueued once. CAS in a non null + // discovered_addr. + oop current_head = refs_list.head(); + // The last ref must have its discovered field pointing to itself. + oop next_discovered = (current_head != NULL) ? current_head : obj; + + oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr, + NULL); + if (retest == NULL) { + // This thread just won the right to enqueue the object. + // We have separate lists for enqueueing, so no synchronization + // is necessary. + refs_list.set_head(obj); + refs_list.inc_length(1); + + log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)", + p2i(obj), obj->klass()->internal_name()); + } else { + // If retest was non NULL, another thread beat us to it: + // The reference has already been discovered... + log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)", + p2i(obj), obj->klass()->internal_name()); + } + } + +#ifndef PRODUCT +// Non-atomic (i.e. concurrent) discovery might allow us +// to observe j.l.References with NULL referents, being those +// cleared concurrently by mutators during (or after) discovery. +void ReferenceProcessor::verify_referent(oop obj) { + bool da = discovery_is_atomic(); + oop referent = java_lang_ref_Reference::referent(obj); + assert(da ? oopDesc::is_oop(referent) : oopDesc::is_oop_or_null(referent), + "Bad referent " INTPTR_FORMAT " found in Reference " + INTPTR_FORMAT " during %satomic discovery ", + p2i(referent), p2i(obj), da ? "" : "non-"); +} +#endif + +// We mention two of several possible choices here: +// #0: if the reference object is not in the "originating generation" +// (or part of the heap being collected, indicated by our "span" +// we don't treat it specially (i.e. we scan it as we would +// a normal oop, treating its references as strong references). +// This means that references can't be discovered unless their +// referent is also in the same span. This is the simplest, +// most "local" and most conservative approach, albeit one +// that may cause weak references to be enqueued least promptly. +// We call this choice the "ReferenceBasedDiscovery" policy. +// #1: the reference object may be in any generation (span), but if +// the referent is in the generation (span) being currently collected +// then we can discover the reference object, provided +// the object has not already been discovered by +// a different concurrently running collector (as may be the +// case, for instance, if the reference object is in CMS and +// the referent in DefNewGeneration), and provided the processing +// of this reference object by the current collector will +// appear atomic to every other collector in the system. +// (Thus, for instance, a concurrent collector may not +// discover references in other generations even if the +// referent is in its own generation). This policy may, +// in certain cases, enqueue references somewhat sooner than +// might Policy #0 above, but at marginally increased cost +// and complexity in processing these references. +// We call this choice the "RefeferentBasedDiscovery" policy. +bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { + // Make sure we are discovering refs (rather than processing discovered refs). + if (!_discovering_refs || !RegisterReferences) { + return false; + } + // We only discover active references. + oop next = java_lang_ref_Reference::next(obj); + if (next != NULL) { // Ref is no longer active + return false; + } + + HeapWord* obj_addr = (HeapWord*)obj; + if (RefDiscoveryPolicy == ReferenceBasedDiscovery && + !_span.contains(obj_addr)) { + // Reference is not in the originating generation; + // don't treat it specially (i.e. we want to scan it as a normal + // object with strong references). + return false; + } + + // We only discover references whose referents are not (yet) + // known to be strongly reachable. + if (is_alive_non_header() != NULL) { + verify_referent(obj); + if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) { + return false; // referent is reachable + } + } + if (rt == REF_SOFT) { + // For soft refs we can decide now if these are not + // current candidates for clearing, in which case we + // can mark through them now, rather than delaying that + // to the reference-processing phase. Since all current + // time-stamp policies advance the soft-ref clock only + // at a full collection cycle, this is always currently + // accurate. + if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) { + return false; + } + } + + ResourceMark rm; // Needed for tracing. + + HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj); + const oop discovered = java_lang_ref_Reference::discovered(obj); + assert(oopDesc::is_oop_or_null(discovered), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)); + if (discovered != NULL) { + // The reference has already been discovered... + log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)", + p2i(obj), obj->klass()->internal_name()); + if (RefDiscoveryPolicy == ReferentBasedDiscovery) { + // assumes that an object is not processed twice; + // if it's been already discovered it must be on another + // generation's discovered list; so we won't discover it. + return false; + } else { + assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, + "Unrecognized policy"); + // Check assumption that an object is not potentially + // discovered twice except by concurrent collectors that potentially + // trace the same Reference object twice. + assert(UseConcMarkSweepGC || UseG1GC, + "Only possible with a concurrent marking collector"); + return true; + } + } + + if (RefDiscoveryPolicy == ReferentBasedDiscovery) { + verify_referent(obj); + // Discover if and only if EITHER: + // .. reference is in our span, OR + // .. we are an atomic collector and referent is in our span + if (_span.contains(obj_addr) || + (discovery_is_atomic() && + _span.contains(java_lang_ref_Reference::referent(obj)))) { + // should_enqueue = true; + } else { + return false; + } + } else { + assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && + _span.contains(obj_addr), "code inconsistency"); + } + + // Get the right type of discovered queue head. + DiscoveredList* list = get_discovered_list(rt); + if (list == NULL) { + return false; // nothing special needs to be done + } + + if (_discovery_is_mt) { + add_to_discovered_list_mt(*list, obj, discovered_addr); + } else { + // We do a raw store here: the field will be visited later when processing + // the discovered references. + oop current_head = list->head(); + // The last ref must have its discovered field pointing to itself. + oop next_discovered = (current_head != NULL) ? current_head : obj; + + assert(discovered == NULL, "control point invariant"); + oop_store_raw(discovered_addr, next_discovered); + list->set_head(obj); + list->inc_length(1); + + log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name()); + } + assert(oopDesc::is_oop(obj), "Discovered a bad reference"); + verify_referent(obj); + return true; +} + +bool ReferenceProcessor::has_discovered_references() { + for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { + if (!_discovered_refs[i].is_empty()) { + return true; + } + } + return false; +} + +// Preclean the discovered references by removing those +// whose referents are alive, and by marking from those that +// are not active. These lists can be handled here +// in any order and, indeed, concurrently. +void ReferenceProcessor::preclean_discovered_references( + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc, + YieldClosure* yield, + GCTimer* gc_timer) { + + // Soft references + { + GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer); + for (uint i = 0; i < _max_num_q; i++) { + if (yield->should_return()) { + return; + } + preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, + keep_alive, complete_gc, yield); + } + } + + // Weak references + { + GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer); + for (uint i = 0; i < _max_num_q; i++) { + if (yield->should_return()) { + return; + } + preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, + keep_alive, complete_gc, yield); + } + } + + // Final references + { + GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer); + for (uint i = 0; i < _max_num_q; i++) { + if (yield->should_return()) { + return; + } + preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, + keep_alive, complete_gc, yield); + } + } + + // Phantom references + { + GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer); + for (uint i = 0; i < _max_num_q; i++) { + if (yield->should_return()) { + return; + } + preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, + keep_alive, complete_gc, yield); + } + } +} + +// Walk the given discovered ref list, and remove all reference objects +// whose referents are still alive, whose referents are NULL or which +// are not active (have a non-NULL next field). NOTE: When we are +// thus precleaning the ref lists (which happens single-threaded today), +// we do not disable refs discovery to honor the correct semantics of +// java.lang.Reference. As a result, we need to be careful below +// that ref removal steps interleave safely with ref discovery steps +// (in this thread). +void +ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc, + YieldClosure* yield) { + DiscoveredListIterator iter(refs_list, keep_alive, is_alive); + while (iter.has_next()) { + iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); + oop obj = iter.obj(); + oop next = java_lang_ref_Reference::next(obj); + if (iter.referent() == NULL || iter.is_referent_alive() || + next != NULL) { + // The referent has been cleared, or is alive, or the Reference is not + // active; we need to trace and mark its cohort. + log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)", + p2i(iter.obj()), iter.obj()->klass()->internal_name()); + // Remove Reference object from list + iter.remove(); + // Keep alive its cohort. + iter.make_referent_alive(); + if (UseCompressedOops) { + narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj); + keep_alive->do_oop(next_addr); + } else { + oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj); + keep_alive->do_oop(next_addr); + } + iter.move_to_next(); + } else { + iter.next(); + } + } + // Close the reachable set + complete_gc->do_void(); + + NOT_PRODUCT( + if (iter.processed() > 0) { + log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT, + iter.removed(), iter.processed(), p2i(&refs_list)); + } + ) +} + +const char* ReferenceProcessor::list_name(uint i) { + assert(i <= _max_num_q * number_of_subclasses_of_ref(), + "Out of bounds index"); + + int j = i / _max_num_q; + switch (j) { + case 0: return "SoftRef"; + case 1: return "WeakRef"; + case 2: return "FinalRef"; + case 3: return "PhantomRef"; + } + ShouldNotReachHere(); + return NULL; +}