diff -r 000000000000 -r f90c822e73f8 src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp Wed Apr 27 01:25:04 2016 +0800 @@ -0,0 +1,9568 @@ +/* + * Copyright (c) 2001, 2014, 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/classLoaderData.hpp" +#include "classfile/symbolTable.hpp" +#include "classfile/systemDictionary.hpp" +#include "code/codeCache.hpp" +#include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp" +#include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp" +#include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp" +#include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp" +#include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp" +#include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp" +#include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp" +#include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp" +#include "gc_implementation/parNew/parNewGeneration.hpp" +#include "gc_implementation/shared/collectorCounters.hpp" +#include "gc_implementation/shared/gcTimer.hpp" +#include "gc_implementation/shared/gcTrace.hpp" +#include "gc_implementation/shared/gcTraceTime.hpp" +#include "gc_implementation/shared/isGCActiveMark.hpp" +#include "gc_interface/collectedHeap.inline.hpp" +#include "memory/allocation.hpp" +#include "memory/cardTableRS.hpp" +#include "memory/collectorPolicy.hpp" +#include "memory/gcLocker.inline.hpp" +#include "memory/genCollectedHeap.hpp" +#include "memory/genMarkSweep.hpp" +#include "memory/genOopClosures.inline.hpp" +#include "memory/iterator.hpp" +#include "memory/padded.hpp" +#include "memory/referencePolicy.hpp" +#include "memory/resourceArea.hpp" +#include "memory/tenuredGeneration.hpp" +#include "oops/oop.inline.hpp" +#include "prims/jvmtiExport.hpp" +#include "runtime/globals_extension.hpp" +#include "runtime/handles.inline.hpp" +#include "runtime/java.hpp" +#include "runtime/vmThread.hpp" +#include "services/memoryService.hpp" +#include "services/runtimeService.hpp" + +PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC + +// 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 supsicion, 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 intereference 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 + MutexLockerEx _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) + { } +}; + + +// Wrapper class to temporarily disable icms during a foreground cms collection. +class ICMSDisabler: public StackObj { + public: + // The ctor disables icms and wakes up the thread so it notices the change; + // the dtor re-enables icms. Note that the CMSCollector methods will check + // CMSIncrementalMode. + ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); } + ~ICMSDisabler() { CMSCollector::enable_icms(); } +}; + +////////////////////////////////////////////////////////////////// +// Concurrent Mark-Sweep Generation ///////////////////////////// +////////////////////////////////////////////////////////////////// + +NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;) + +// This struct contains per-thread things necessary to support parallel +// young-gen collection. +class CMSParGCThreadState: public CHeapObj { + public: + CFLS_LAB lab; + PromotionInfo promo; + + // Constructor. + CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) { + promo.setSpace(cfls); + } +}; + +ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration( + ReservedSpace rs, size_t initial_byte_size, int level, + CardTableRS* ct, bool use_adaptive_freelists, + FreeBlockDictionary::DictionaryChoice dictionaryChoice) : + CardGeneration(rs, initial_byte_size, level, ct), + _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))), + _debug_collection_type(Concurrent_collection_type), + _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), + use_adaptive_freelists, + dictionaryChoice); + NOT_PRODUCT(debug_cms_space = _cmsSpace;) + if (_cmsSpace == NULL) { + vm_exit_during_initialization( + "CompactibleFreeListSpace allocation failure"); + } + _cmsSpace->_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"); + ) + if (CollectedHeap::use_parallel_gc_threads()) { + typedef CMSParGCThreadState* CMSParGCThreadStatePtr; + _par_gc_thread_states = + NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC); + if (_par_gc_thread_states == NULL) { + vm_exit_during_initialization("Could not allocate par gc structs"); + } + for (uint i = 0; i < ParallelGCThreads; i++) { + _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace()); + if (_par_gc_thread_states[i] == NULL) { + vm_exit_during_initialization("Could not allocate par gc structs"); + } + } + } else { + _par_gc_thread_states = NULL; + } + _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 mimimum + // 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"); +} + + +// 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 +// +// _intiating_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, // span + (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing + (int) ParallelGCThreads, // mt processing degree + _cmsGen->refs_discovery_is_mt(), // mt discovery + (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree + _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic + &_is_alive_closure); // closure for liveness info + // Initialize the _ref_processor field of CMSGen + _cmsGen->set_ref_processor(_ref_processor); + + } +} + +CMSAdaptiveSizePolicy* CMSCollector::size_policy() { + GenCollectedHeap* gch = GenCollectedHeap::heap(); + assert(gch->kind() == CollectedHeap::GenCollectedHeap, + "Wrong type of heap"); + CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*) + gch->gen_policy()->size_policy(); + assert(sp->is_gc_cms_adaptive_size_policy(), + "Wrong type of size policy"); + return sp; +} + +CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() { + CMSGCAdaptivePolicyCounters* results = + (CMSGCAdaptivePolicyCounters*) collector_policy()->counters(); + assert( + results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind, + "Wrong gc policy counter kind"); + return results; +} + + +void ConcurrentMarkSweepGeneration::initialize_performance_counters() { + + const char* gen_name = "old"; + + // Generation Counters - generation 1, 1 subspace + _gen_counters = new GenerationCounters(gen_name, 1, 1, &_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; + _icms_duty_cycle = CMSIncrementalDutyCycle; +} + +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(); + GenCollectedHeap* gch = GenCollectedHeap::heap(); + size_t expected_promotion = MIN2(gch->get_gen(0)->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 minor 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; + + if (PrintGCDetails && Verbose) { + gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free " + SIZE_FORMAT " expected_promotion " SIZE_FORMAT, + cms_free, expected_promotion); + gclog_or_tty->print_cr(" 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) { + if (Verbose && PrintGCDetails) { + gclog_or_tty->print( + " 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; +} + +// Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the +// amount of change to prevent wild oscillation. +unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle, + unsigned int new_duty_cycle) { + assert(old_duty_cycle <= 100, "bad input value"); + assert(new_duty_cycle <= 100, "bad input value"); + + // Note: use subtraction with caution since it may underflow (values are + // unsigned). Addition is safe since we're in the range 0-100. + unsigned int damped_duty_cycle = new_duty_cycle; + if (new_duty_cycle < old_duty_cycle) { + const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U); + if (new_duty_cycle + largest_delta < old_duty_cycle) { + damped_duty_cycle = old_duty_cycle - largest_delta; + } + } else if (new_duty_cycle > old_duty_cycle) { + const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U); + if (new_duty_cycle > old_duty_cycle + largest_delta) { + damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U); + } + } + assert(damped_duty_cycle <= 100, "invalid duty cycle computed"); + + if (CMSTraceIncrementalPacing) { + gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ", + old_duty_cycle, new_duty_cycle, damped_duty_cycle); + } + return damped_duty_cycle; +} + +unsigned int CMSStats::icms_update_duty_cycle_impl() { + assert(CMSIncrementalPacing && valid(), + "should be handled in icms_update_duty_cycle()"); + + double cms_time_so_far = cms_timer().seconds(); + double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M; + double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far); + + // Avoid division by 0. + double time_until_full = MAX2(time_until_cms_gen_full(), 0.01); + double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full; + + unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U); + if (new_duty_cycle > _icms_duty_cycle) { + // Avoid very small duty cycles (1 or 2); 0 is allowed. + if (new_duty_cycle > 2) { + _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, + new_duty_cycle); + } + } else if (_allow_duty_cycle_reduction) { + // The duty cycle is reduced only once per cms cycle (see record_cms_end()). + new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle); + // Respect the minimum duty cycle. + unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin; + _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle); + } + + if (PrintGCDetails || CMSTraceIncrementalPacing) { + gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle); + } + + _allow_duty_cycle_reduction = false; + return _icms_duty_cycle; +} + +#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_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT, + cms_duration(), cms_duration_per_mb(), + 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 (CMSIncrementalMode) { + st->print(",dc=%d", icms_duty_cycle()); + } + + 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->print(" "); +} +#endif // #ifndef PRODUCT + +CMSCollector::CollectorState CMSCollector::_collectorState = + CMSCollector::Idling; +bool CMSCollector::_foregroundGCIsActive = false; +bool CMSCollector::_foregroundGCShouldWait = false; + +CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen, + CardTableRS* ct, + ConcurrentMarkSweepPolicy* cp): + _cmsGen(cmsGen), + _ct(ct), + _ref_processor(NULL), // will be set later + _conc_workers(NULL), // may be set later + _abort_preclean(false), + _start_sampling(false), + _between_prologue_and_epilogue(false), + _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"), + _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize), + -1 /* lock-free */, "No_lock" /* dummy */), + _modUnionClosure(&_modUnionTable), + _modUnionClosurePar(&_modUnionTable), + // Adjust my span to cover old (cms) gen + _span(cmsGen->reserved()), + // Construct the is_alive_closure with _span & markBitMap + _is_alive_closure(_span, &_markBitMap), + _restart_addr(NULL), + _overflow_list(NULL), + _stats(cmsGen), + _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)), + _eden_chunk_array(NULL), // may be set in ctor body + _eden_chunk_capacity(0), // -- ditto -- + _eden_chunk_index(0), // -- ditto -- + _survivor_plab_array(NULL), // -- ditto -- + _survivor_chunk_array(NULL), // -- ditto -- + _survivor_chunk_capacity(0), // -- ditto -- + _survivor_chunk_index(0), // -- ditto -- + _ser_pmc_preclean_ovflw(0), + _ser_kac_preclean_ovflw(0), + _ser_pmc_remark_ovflw(0), + _par_pmc_remark_ovflw(0), + _ser_kac_ovflw(0), + _par_kac_ovflw(0), +#ifndef PRODUCT + _num_par_pushes(0), +#endif + _collection_count_start(0), + _verifying(false), + _icms_start_limit(NULL), + _icms_stop_limit(NULL), + _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"), + _completed_initialization(false), + _collector_policy(cp), + _should_unload_classes(CMSClassUnloadingEnabled), + _concurrent_cycles_since_last_unload(0), + _roots_scanning_options(SharedHeap::SO_None), + _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) +{ + if (ExplicitGCInvokesConcurrentAndUnloadsClasses) { + ExplicitGCInvokesConcurrent = true; + } + // 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 + { + MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag); + if (!_markBitMap.allocate(_span)) { + warning("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)) { + warning("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("Parallel CMS Threads", + ConcGCThreads, true); + if (_conc_workers == NULL) { + warning("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"); + + // 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 = (uint) MAX2(ParallelGCThreads, ConcGCThreads); + + if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled + || ParallelRefProcEnabled) + && num_queues > 0) { + _task_queues = new OopTaskQueueSet(num_queues); + if (_task_queues == NULL) { + warning("task_queues allocation failure."); + return; + } + _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC); + if (_hash_seed == NULL) { + warning("_hash_seed array allocation failure"); + return; + } + + typedef Padded PaddedOopTaskQueue; + for (i = 0; i < num_queues; i++) { + PaddedOopTaskQueue *q = new PaddedOopTaskQueue(); + if (q == NULL) { + warning("work_queue allocation failure."); + return; + } + _task_queues->register_queue(i, q); + } + for (i = 0; i < num_queues; i++) { + _task_queues->queue(i)->initialize(); + _hash_seed[i] = 17; // copied from ParNew + } + } + } + + _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio); + + // Clip CMSBootstrapOccupancy between 0 and 100. + _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100; + + _full_gcs_since_conc_gc = 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 + GenCollectedHeap* gch = GenCollectedHeap::heap(); + _young_gen = gch->prev_gen(_cmsGen); + if (gch->supports_inline_contig_alloc()) { + _top_addr = gch->top_addr(); + _end_addr = gch->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); + if (_eden_chunk_array == NULL) { + _eden_chunk_capacity = 0; + warning("GC/CMS: _eden_chunk_array allocation failure"); + } + } + assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error"); + + // Support for parallelizing survivor space rescan + if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) { + const size_t max_plab_samples = + ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize; + + _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC); + _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC); + _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC); + if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL + || _cursor == NULL) { + warning("Failed to allocate survivor plab/chunk array"); + if (_survivor_plab_array != NULL) { + FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC); + _survivor_plab_array = NULL; + } + if (_survivor_chunk_array != NULL) { + FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC); + _survivor_chunk_array = NULL; + } + if (_cursor != NULL) { + FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC); + _cursor = NULL; + } + } else { + _survivor_chunk_capacity = 2*max_plab_samples; + for (uint i = 0; i < ParallelGCThreads; i++) { + HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC); + if (vec == NULL) { + warning("Failed to allocate survivor plab array"); + for (int j = i; j > 0; j--) { + FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC); + } + FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC); + FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC); + _survivor_plab_array = NULL; + _survivor_chunk_array = NULL; + _survivor_chunk_capacity = 0; + break; + } else { + 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"); + } + } + } + } + assert( ( _survivor_plab_array != NULL + && _survivor_chunk_array != NULL) + || ( _survivor_chunk_capacity == 0 + && _survivor_chunk_index == 0), + "Error"); + + NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;) + _gc_counters = new CollectorCounters("CMS", 1); + _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 + +void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) { + GenCollectedHeap* gch = GenCollectedHeap::heap(); + if (PrintGCDetails) { + if (Verbose) { + gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]", + level(), short_name(), s, used(), capacity()); + } else { + gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]", + level(), short_name(), s, used() / K, capacity() / K); + } + } + if (Verbose) { + gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")", + gch->used(), gch->capacity()); + } else { + gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)", + gch->used() / K, gch->capacity() / K); + } +} + +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::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); + if (Verbose && PrintGCDetails) { + gclog_or_tty->print_cr( + "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() { + if (CMSDumpAtPromotionFailure) { + cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty); + } +} + +CompactibleSpace* +ConcurrentMarkSweepGeneration::first_compaction_space() const { + return _cmsSpace; +} + +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. + if (CollectedHeap::use_parallel_gc_threads()) { + for (uint i = 0; i < ParallelGCThreads; i++) { + _par_gc_thread_states[i]->promo.reset(); + } + } +} + +void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) { + blk->do_space(_cmsSpace); +} + +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); + if (PrintGCDetails && Verbose) { + size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); + gclog_or_tty->print_cr("\nFrom compute_new_size: "); + gclog_or_tty->print_cr(" Free fraction %f", free_percentage); + gclog_or_tty->print_cr(" Desired free fraction %f", + desired_free_percentage); + gclog_or_tty->print_cr(" Maximum free fraction %f", + maximum_free_percentage); + gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000); + gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT, + desired_capacity/1000); + int prev_level = level() - 1; + if (prev_level >= 0) { + size_t prev_size = 0; + GenCollectedHeap* gch = GenCollectedHeap::heap(); + Generation* prev_gen = gch->_gens[prev_level]; + prev_size = prev_gen->capacity(); + gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT, + prev_size/1000); + } + gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT, + unsafe_max_alloc_nogc()/1000); + gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT, + contiguous_available()/1000); + gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)", + expand_bytes); + } + // safe if expansion fails + expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio); + if (PrintGCDetails && Verbose) { + gclog_or_tty->print_cr(" 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; + MutexLockerEx 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) { + MutexLockerEx 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, + (HeapWord*)round_to((intptr_t)(start + obj_size), + CardTableModRefBS::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); + } + } + } + } +} + +static inline size_t percent_of_space(Space* space, HeapWord* addr) +{ + size_t delta = pointer_delta(addr, space->bottom()); + return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize)); +} + +void CMSCollector::icms_update_allocation_limits() +{ + Generation* gen0 = GenCollectedHeap::heap()->get_gen(0); + EdenSpace* eden = gen0->as_DefNewGeneration()->eden(); + + const unsigned int duty_cycle = stats().icms_update_duty_cycle(); + if (CMSTraceIncrementalPacing) { + stats().print(); + } + + assert(duty_cycle <= 100, "invalid duty cycle"); + if (duty_cycle != 0) { + // The duty_cycle is a percentage between 0 and 100; convert to words and + // then compute the offset from the endpoints of the space. + size_t free_words = eden->free() / HeapWordSize; + double free_words_dbl = (double)free_words; + size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0); + size_t offset_words = (free_words - duty_cycle_words) / 2; + + _icms_start_limit = eden->top() + offset_words; + _icms_stop_limit = eden->end() - offset_words; + + // The limits may be adjusted (shifted to the right) by + // CMSIncrementalOffset, to allow the application more mutator time after a + // young gen gc (when all mutators were stopped) and before CMS starts and + // takes away one or more cpus. + if (CMSIncrementalOffset != 0) { + double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0; + size_t adjustment = (size_t)adjustment_dbl; + HeapWord* tmp_stop = _icms_stop_limit + adjustment; + if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) { + _icms_start_limit += adjustment; + _icms_stop_limit = tmp_stop; + } + } + } + if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) { + _icms_start_limit = _icms_stop_limit = eden->end(); + } + + // Install the new start limit. + eden->set_soft_end(_icms_start_limit); + + if (CMSTraceIncrementalMode) { + gclog_or_tty->print(" icms alloc limits: " + PTR_FORMAT "," PTR_FORMAT + " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ", + p2i(_icms_start_limit), p2i(_icms_stop_limit), + percent_of_space(eden, _icms_start_limit), + percent_of_space(eden, _icms_stop_limit)); + if (Verbose) { + gclog_or_tty->print("eden: "); + eden->print_on(gclog_or_tty); + } + } +} + +// Any changes here should try to maintain the invariant +// that if this method is called with _icms_start_limit +// and _icms_stop_limit both NULL, then it should return NULL +// and not notify the icms thread. +HeapWord* +CMSCollector::allocation_limit_reached(Space* space, HeapWord* top, + size_t word_size) +{ + // A start_limit equal to end() means the duty cycle is 0, so treat that as a + // nop. + if (CMSIncrementalMode && _icms_start_limit != space->end()) { + if (top <= _icms_start_limit) { + if (CMSTraceIncrementalMode) { + space->print_on(gclog_or_tty); + gclog_or_tty->stamp(); + gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT + ", new limit=" PTR_FORMAT + " (" SIZE_FORMAT "%%)", + p2i(top), p2i(_icms_stop_limit), + percent_of_space(space, _icms_stop_limit)); + } + ConcurrentMarkSweepThread::start_icms(); + assert(top < _icms_stop_limit, "Tautology"); + if (word_size < pointer_delta(_icms_stop_limit, top)) { + return _icms_stop_limit; + } + + // The allocation will cross both the _start and _stop limits, so do the + // stop notification also and return end(). + if (CMSTraceIncrementalMode) { + space->print_on(gclog_or_tty); + gclog_or_tty->stamp(); + gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT + ", new limit=" PTR_FORMAT + " (" SIZE_FORMAT "%%)", + p2i(top), p2i(space->end()), + percent_of_space(space, space->end())); + } + ConcurrentMarkSweepThread::stop_icms(); + return space->end(); + } + + if (top <= _icms_stop_limit) { + if (CMSTraceIncrementalMode) { + space->print_on(gclog_or_tty); + gclog_or_tty->stamp(); + gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT + ", new limit=" PTR_FORMAT + " (" SIZE_FORMAT "%%)", + top, space->end(), + percent_of_space(space, space->end())); + } + ConcurrentMarkSweepThread::stop_icms(); + return space->end(); + } + + if (CMSTraceIncrementalMode) { + space->print_on(gclog_or_tty); + gclog_or_tty->stamp(); + gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT + ", new limit=" PTR_FORMAT, + top, NULL); + } + } + + return NULL; +} + +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 (Universe::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(s*HeapWordSize, MinHeapDeltaBytes, + CMSExpansionCause::_satisfy_promotion); + // Since there's currently no next generation, we don't try to promote + // into a more senior generation. + assert(next_gen() == NULL, "assumption, based upon which no attempt " + "is made to pass on a possibly failing " + "promotion to next generation"); + res = _cmsSpace->promote(obj, obj_size); + } + if (res != NULL) { + // See comment in allocate() about when objects should + // be allocated live. + assert(obj->is_oop(), "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; +} + + +HeapWord* +ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space, + HeapWord* top, + size_t word_sz) +{ + return collector()->allocation_limit_reached(space, top, word_sz); +} + +// 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, markOop m, + size_t word_sz) { +#ifndef PRODUCT + if (Universe::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->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(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(old->is_oop(), "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(obj->is_oop() && 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_ptr(&_numObjectsPromoted); + Atomic::add_ptr(alloc_sz, &_numWordsPromoted); + ) + + return obj; +} + +void +ConcurrentMarkSweepGeneration:: +par_promote_alloc_undo(int thread_num, + HeapWord* obj, size_t word_sz) { + // CMS does not support promotion undo. + ShouldNotReachHere(); +} + +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_nv(dummy_cl); +} + +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() { + if (_full_gc_requested) { + if (Verbose && PrintGCDetails) { + gclog_or_tty->print_cr("CMSCollector: collect because of explicit " + " gc request (or gc_locker)"); + } + return true; + } + + // For debugging purposes, change the type of collection. + // If the rotation is not on the concurrent collection + // type, don't start a concurrent collection. + NOT_PRODUCT( + if (RotateCMSCollectionTypes && + (_cmsGen->debug_collection_type() != + ConcurrentMarkSweepGeneration::Concurrent_collection_type)) { + assert(_cmsGen->debug_collection_type() != + ConcurrentMarkSweepGeneration::Unknown_collection_type, + "Bad cms collection type"); + return false; + } + ) + + FreelistLocker x(this); + // ------------------------------------------------------------------ + // Print out lots of information which affects the initiation of + // a collection. + if (PrintCMSInitiationStatistics && stats().valid()) { + gclog_or_tty->print("CMSCollector shouldConcurrentCollect: "); + gclog_or_tty->stamp(); + gclog_or_tty->cr(); + stats().print_on(gclog_or_tty); + gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f", + stats().time_until_cms_gen_full()); + gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free()); + gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT, + _cmsGen->contiguous_available()); + gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate()); + gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate()); + gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy()); + gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy()); + gclog_or_tty->print_cr("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) { + if (Verbose && PrintGCDetails) { + gclog_or_tty->print_cr( + " 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()) { + if (Verbose && PrintGCDetails) { + gclog_or_tty->print_cr("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. + GenCollectedHeap* gch = GenCollectedHeap::heap(); + assert(gch->collector_policy()->is_two_generation_policy(), + "You may want to check the correctness of the following"); + if (gch->incremental_collection_will_fail(true /* consult_young */)) { + if (Verbose && PrintGCDetails) { + gclog_or_tty->print("CMSCollector: collect because incremental collection will fail "); + } + return true; + } + + if (MetaspaceGC::should_concurrent_collect()) { + if (Verbose && PrintGCDetails) { + gclog_or_tty->print("CMSCollector: collect for metadata allocation "); + } + 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()) { + if (PrintGCDetails && Verbose) { + gclog_or_tty->print(" %s: collect because of occupancy %f / %f ", + short_name(), occupancy(), initiating_occupancy()); + } + return true; + } + if (UseCMSInitiatingOccupancyOnly) { + return false; + } + if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) { + if (PrintGCDetails && Verbose) { + gclog_or_tty->print(" %s: collect because expanded for allocation ", + short_name()); + } + return true; + } + if (_cmsSpace->should_concurrent_collect()) { + if (PrintGCDetails && Verbose) { + gclog_or_tty->print(" %s: collect because cmsSpace says so ", + 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) +{ + if (!UseCMSCollectionPassing && _collectorState > Idling) { + // For debugging purposes skip the collection if the state + // is not currently idle + if (TraceCMSState) { + gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d", + Thread::current(), full, _collectorState); + } + return; + } + + // The following "if" branch is present for defensive reasons. + // In the current uses of this interface, it can be replaced with: + // assert(!GC_locker.is_active(), "Can't be called otherwise"); + // But I am not placing that assert here to allow future + // generality in invoking this interface. + if (GC_locker::is_active()) { + // A consistency test for GC_locker + assert(GC_locker::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); + _full_gcs_since_conc_gc++; +} + +void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) { + GenCollectedHeap* gch = GenCollectedHeap::heap(); + unsigned int gc_count = gch->total_full_collections(); + if (gc_count == full_gc_count) { + MutexLockerEx 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 = GenCollectedHeap::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()) { + if (PrintGCDetails) { + gclog_or_tty->print(" (concurrent mode interrupted)"); + } + } else { + if (PrintGCDetails) { + gclog_or_tty->print(" (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; + + // Disable incremental mode during a foreground collection. + ICMSDisabler icms_disabler; + + // 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(); + { + MutexLockerEx 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, + "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(Mutex::_no_safepoint_check_flag); + // 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(); + if (TraceCMSState) { + gclog_or_tty->print_cr("CMS foreground collector has asked for control " + INTPTR_FORMAT " with first state %d", Thread::current(), first_state); + gclog_or_tty->print_cr(" gets control with state %d", _collectorState); + } + + // Check if we need to do a compaction, or if not, whether + // we need to start the mark-sweep from scratch. + bool should_compact = false; + bool should_start_over = false; + decide_foreground_collection_type(clear_all_soft_refs, + &should_compact, &should_start_over); + +NOT_PRODUCT( + if (RotateCMSCollectionTypes) { + if (_cmsGen->debug_collection_type() == + ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) { + should_compact = true; + } else if (_cmsGen->debug_collection_type() == + ConcurrentMarkSweepGeneration::MS_foreground_collection_type) { + should_compact = false; + } + } +) + + if (first_state > Idling) { + report_concurrent_mode_interruption(); + } + + set_did_compact(should_compact); + if (should_compact) { + // If the collection is being acquired from the background + // collector, there may be references on the discovered + // references lists that have NULL referents (being those + // that were concurrently cleared by a mutator) or + // that are no longer active (having been enqueued concurrently + // by the mutator). + // Scrub the list of those references because Mark-Sweep-Compact + // code assumes referents are not NULL and that all discovered + // Reference objects are active. + ref_processor()->clean_up_discovered_references(); + + if (first_state > Idling) { + save_heap_summary(); + } + + do_compaction_work(clear_all_soft_refs); + + // Has the GC time limit been exceeded? + DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration(); + size_t max_eden_size = young_gen->max_capacity() - + young_gen->to()->capacity() - + young_gen->from()->capacity(); + GenCollectedHeap* gch = GenCollectedHeap::heap(); + GCCause::Cause gc_cause = gch->gc_cause(); + size_policy()->check_gc_overhead_limit(_young_gen->used(), + young_gen->eden()->used(), + _cmsGen->max_capacity(), + max_eden_size, + full, + gc_cause, + gch->collector_policy()); + } else { + do_mark_sweep_work(clear_all_soft_refs, first_state, + should_start_over); + } + // 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(); +} + +// A work method used by foreground collection to determine +// what type of collection (compacting or not, continuing or fresh) +// it should do. +// NOTE: the intent is to make UseCMSCompactAtFullCollection +// and CMSCompactWhenClearAllSoftRefs the default in the future +// and do away with the flags after a suitable period. +void CMSCollector::decide_foreground_collection_type( + bool clear_all_soft_refs, bool* should_compact, + bool* should_start_over) { + // Normally, we'll compact only if the UseCMSCompactAtFullCollection + // flag is set, and we have either requested a System.gc() or + // the number of full gc's since the last concurrent cycle + // has exceeded the threshold set by CMSFullGCsBeforeCompaction, + // or if an incremental collection has failed + GenCollectedHeap* gch = GenCollectedHeap::heap(); + assert(gch->collector_policy()->is_two_generation_policy(), + "You may want to check the correctness of the following"); + // Inform cms gen if this was due to partial collection failing. + // The CMS gen may use this fact to determine its expansion policy. + if (gch->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(); + } + *should_compact = + UseCMSCompactAtFullCollection && + ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) || + GCCause::is_user_requested_gc(gch->gc_cause()) || + gch->incremental_collection_will_fail(true /* consult_young */)); + *should_start_over = false; + if (clear_all_soft_refs && !*should_compact) { + // We are about to do a last ditch collection attempt + // so it would normally make sense to do a compaction + // to reclaim as much space as possible. + if (CMSCompactWhenClearAllSoftRefs) { + // Default: The rationale is that in this case either + // we are past the final marking phase, in which case + // we'd have to start over, or so little has been done + // that there's little point in saving that work. Compaction + // appears to be the sensible choice in either case. + *should_compact = true; + } else { + // We have been asked to clear all soft refs, but not to + // compact. Make sure that we aren't past the final checkpoint + // phase, for that is where we process soft refs. If we are already + // past that phase, we'll need to redo the refs discovery phase and + // if necessary clear soft refs that weren't previously + // cleared. We do so by remembering the phase in which + // we came in, and if we are past the refs processing + // phase, we'll choose to just redo the mark-sweep + // collection from scratch. + if (_collectorState > FinalMarking) { + // We are past the refs processing phase; + // start over and do a fresh synchronous CMS cycle + _collectorState = Resetting; // skip to reset to start new cycle + reset(false /* == !asynch */); + *should_start_over = true; + } // else we can continue a possibly ongoing current cycle + } + } +} + +// A work method used by the foreground collector to do +// a mark-sweep-compact. +void CMSCollector::do_compaction_work(bool clear_all_soft_refs) { + GenCollectedHeap* gch = GenCollectedHeap::heap(); + + STWGCTimer* gc_timer = GenMarkSweep::gc_timer(); + gc_timer->register_gc_start(); + + SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer(); + gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start()); + + GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL); + if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) { + gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d " + "collections passed to foreground collector", _full_gcs_since_conc_gc); + } + + // Sample collection interval time and reset for collection pause. + if (UseAdaptiveSizePolicy) { + size_policy()->msc_collection_begin(); + } + + // Temporarily widen the span of the weak reference processing to + // the entire heap. + MemRegion new_span(GenCollectedHeap::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(false /*verify_disabled*/, false /*check_no_refs*/); + 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->klass_rem_set()->mod_union_is_clear(), + "mod union for klasses should be clear if the baton was passed"); + _ct->klass_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(_cmsGen->level(), + 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(false /* == !asynch */); + _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(); + + // Sample collection pause time and reset for collection interval. + if (UseAdaptiveSizePolicy) { + size_policy()->msc_collection_end(gch->gc_cause()); + } + + 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. +} + +// A work method used by the foreground collector to do +// a mark-sweep, after taking over from a possibly on-going +// concurrent mark-sweep collection. +void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs, + CollectorState first_state, bool should_start_over) { + if (PrintGC && Verbose) { + gclog_or_tty->print_cr("Pass concurrent collection to foreground " + "collector with count %d", + _full_gcs_since_conc_gc); + } + switch (_collectorState) { + case Idling: + if (first_state == Idling || should_start_over) { + // The background GC was not active, or should + // restarted from scratch; start the cycle. + _collectorState = InitialMarking; + } + // If first_state was not Idling, then a background GC + // was in progress and has now finished. No need to do it + // again. Leave the state as Idling. + break; + case Precleaning: + // In the foreground case don't do the precleaning since + // it is not done concurrently and there is extra work + // required. + _collectorState = FinalMarking; + } + collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause()); + + // For a mark-sweep, compute_new_size() will be called + // in the heap's do_collection() method. +} + + +void CMSCollector::print_eden_and_survivor_chunk_arrays() { + DefNewGeneration* dng = _young_gen->as_DefNewGeneration(); + EdenSpace* eden_space = dng->eden(); + ContiguousSpace* from_space = dng->from(); + ContiguousSpace* to_space = dng->to(); + // Eden + if (_eden_chunk_array != NULL) { + gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")", + eden_space->bottom(), eden_space->top(), + eden_space->end(), eden_space->capacity()); + gclog_or_tty->print_cr("_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++) { + gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, + i, _eden_chunk_array[i]); + } + } + // Survivor + if (_survivor_chunk_array != NULL) { + gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")", + from_space->bottom(), from_space->top(), + from_space->end(), from_space->capacity()); + gclog_or_tty->print_cr("_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++) { + gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, + i, _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"); + MutexLockerEx 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?"); + MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); + _c->_foregroundGCShouldWait = true; + } +}; + +// There are separate collect_in_background and collect_in_foreground because of +// the different locking requirements of the background collector and the +// foreground collector. There was originally an attempt to share +// one "collect" method between the background collector and the foreground +// collector but the if-then-else required made it cleaner to have +// separate methods. +void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) { + assert(Thread::current()->is_ConcurrentGC_thread(), + "A CMS asynchronous collection is only allowed on a CMS thread."); + + GenCollectedHeap* gch = GenCollectedHeap::heap(); + { + bool safepoint_check = Mutex::_no_safepoint_check_flag; + MutexLockerEx hl(Heap_lock, safepoint_check); + FreelistLocker fll(this); + MutexLockerEx x(CGC_lock, safepoint_check); + if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) { + // The foreground collector is active or we're + // not using asynchronous collections. 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 + gch->increment_total_full_collections(); // ... starting a collection cycle + _collection_count_start = gch->total_full_collections(); + } + + // Used for PrintGC + size_t prev_used; + if (PrintGC && Verbose) { + prev_used = _cmsGen->used(); // XXXPERM + } + + // 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) { + if (TraceCMSState) { + gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d", + 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()"); + if (TraceCMSState) { + gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT + " exiting collection CMS state %d", + 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(true)) { // we were successful + assert(_collectorState == Precleaning, "Collector state should " + "have changed"); + } else { + assert(_foregroundGCIsActive, "Internal state inconsistency"); + } + break; + case Precleaning: + if (UseAdaptiveSizePolicy) { + size_policy()->concurrent_precleaning_begin(); + } + // marking from roots in markFromRoots has been completed + preclean(); + if (UseAdaptiveSizePolicy) { + size_policy()->concurrent_precleaning_end(); + } + assert(_collectorState == AbortablePreclean || + _collectorState == FinalMarking, + "Collector state should have changed"); + break; + case AbortablePreclean: + if (UseAdaptiveSizePolicy) { + size_policy()->concurrent_phases_resume(); + } + abortable_preclean(); + if (UseAdaptiveSizePolicy) { + size_policy()->concurrent_precleaning_end(); + } + 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: + if (UseAdaptiveSizePolicy) { + size_policy()->concurrent_sweeping_begin(); + } + // final marking in checkpointRootsFinal has been completed + sweep(true); + assert(_collectorState == Resizing, "Collector state change " + "to Resizing must be done under the free_list_lock"); + _full_gcs_since_conc_gc = 0; + + // Stop the timers for adaptive size policy for the concurrent phases + if (UseAdaptiveSizePolicy) { + size_policy()->concurrent_sweeping_end(); + size_policy()->concurrent_phases_end(gch->gc_cause(), + gch->prev_gen(_cmsGen)->capacity(), + _cmsGen->free()); + } + + 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 + MutexLockerEx 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(true); + 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; + } + if (TraceCMSState) { + gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d", + Thread::current(), _collectorState); + } + assert(_foregroundGCShouldWait, "block post-condition"); + } + + // Should this be in gc_epilogue? + collector_policy()->counters()->update_counters(); + + { + // Clear _foregroundGCShouldWait and, in the event that the + // foreground collector is waiting, notify it, before + // returning. + MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); + _foregroundGCShouldWait = false; + if (_foregroundGCIsActive) { + CGC_lock->notify(); + } + assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), + "Possible deadlock"); + } + if (TraceCMSState) { + gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT + " exiting collection CMS state %d", + Thread::current(), _collectorState); + } + if (PrintGC && Verbose) { + _cmsGen->print_heap_change(prev_used); + } +} + +void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) { + if (!_cms_start_registered) { + register_gc_start(cause); + } +} + +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() { + GenCollectedHeap* gch = GenCollectedHeap::heap(); + _last_heap_summary = gch->create_heap_summary(); + _last_metaspace_summary = gch->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); +} + +void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) { + assert(_foregroundGCIsActive && !_foregroundGCShouldWait, + "Foreground collector should be waiting, not executing"); + assert(Thread::current()->is_VM_thread(), "A foreground collection" + "may only be done by the VM Thread with the world stopped"); + assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), + "VM thread should have CMS token"); + + NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose, + true, NULL);) + if (UseAdaptiveSizePolicy) { + size_policy()->ms_collection_begin(); + } + COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact); + + HandleMark hm; // Discard invalid handles created during verification + + if (VerifyBeforeGC && + GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { + Universe::verify(); + } + + // Snapshot the soft reference policy to be used in this collection cycle. + ref_processor()->setup_policy(clear_all_soft_refs); + + // Decide if class unloading should be done + update_should_unload_classes(); + + bool init_mark_was_synchronous = false; // until proven otherwise + while (_collectorState != Idling) { + if (TraceCMSState) { + gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d", + Thread::current(), _collectorState); + } + switch (_collectorState) { + case InitialMarking: + register_foreground_gc_start(cause); + init_mark_was_synchronous = true; // fact to be exploited in re-mark + checkpointRootsInitial(false); + assert(_collectorState == Marking, "Collector state should have changed" + " within checkpointRootsInitial()"); + break; + case Marking: + // initial marking in checkpointRootsInitialWork has been completed + if (VerifyDuringGC && + GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { + Universe::verify("Verify before initial mark: "); + } + { + bool res = markFromRoots(false); + assert(res && _collectorState == FinalMarking, "Collector state should " + "have changed"); + break; + } + case FinalMarking: + if (VerifyDuringGC && + GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { + Universe::verify("Verify before re-mark: "); + } + checkpointRootsFinal(false, clear_all_soft_refs, + init_mark_was_synchronous); + assert(_collectorState == Sweeping, "Collector state should not " + "have changed within checkpointRootsFinal()"); + break; + case Sweeping: + // final marking in checkpointRootsFinal has been completed + if (VerifyDuringGC && + GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { + Universe::verify("Verify before sweep: "); + } + sweep(false); + assert(_collectorState == Resizing, "Incorrect state"); + break; + case Resizing: { + // Sweeping has been completed; the actual resize in this case + // is done separately; nothing to be done in this state. + _collectorState = Resetting; + break; + } + case Resetting: + // The heap has been resized. + if (VerifyDuringGC && + GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { + Universe::verify("Verify before reset: "); + } + save_heap_summary(); + reset(false); + assert(_collectorState == Idling, "Collector state should " + "have changed"); + break; + case Precleaning: + case AbortablePreclean: + // Elide the preclean phase + _collectorState = FinalMarking; + break; + default: + ShouldNotReachHere(); + } + if (TraceCMSState) { + gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d", + Thread::current(), _collectorState); + } + } + + if (UseAdaptiveSizePolicy) { + GenCollectedHeap* gch = GenCollectedHeap::heap(); + size_policy()->ms_collection_end(gch->gc_cause()); + } + + if (VerifyAfterGC && + GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { + Universe::verify(); + } + if (TraceCMSState) { + gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT + " exiting collection CMS state %d", + Thread::current(), _collectorState); + } +} + +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. + MutexLockerEx 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(); + if (TraceCMSState) { + gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d", + Thread::current(), _collectorState); + } + while (_foregroundGCIsActive) { + CGC_lock->wait(Mutex::_no_safepoint_check_flag); + } + ConcurrentMarkSweepThread::set_CMS_flag( + ConcurrentMarkSweepThread::CMS_cms_has_token); + ConcurrentMarkSweepThread::clear_CMS_flag( + ConcurrentMarkSweepThread::CMS_cms_wants_token); + } + if (TraceCMSState) { + gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d", + 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 varaible _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->klass_rem_set()->set_accumulate_modified_oops(true); + } + + bool registerClosure = duringMarking; + + ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ? + &_modUnionClosurePar + : &_modUnionClosure; + _cmsGen->gc_prologue_work(full, registerClosure, muc); + + if (!full) { + stats().record_gc0_begin(); + } +} + +void ConcurrentMarkSweepGeneration::gc_prologue(bool full) { + + _capacity_at_prologue = capacity(); + _used_at_prologue = used(); + + // 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"); + if (Verbose && PrintGC) { + gclog_or_tty->print("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->klass_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(); + + // 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); + + if (CMSIncrementalMode) { + icms_update_allocation_limits(); + } + + 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); + + // Also reset promotion tracking in par gc thread states. + if (CollectedHeap::use_parallel_gc_threads()) { + for (uint i = 0; i < ParallelGCThreads; i++) { + _par_gc_thread_states[i]->promo.stopTrackingPromotions(i); + } + } +} + +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"); + if (Verbose && PrintGC) { + gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, " + SIZE_FORMAT" bytes", + _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord)); + } + _numObjectsPromoted = 0; + _numWordsPromoted = 0; + ) + + if (PrintGC && Verbose) { + // Call down the chain in contiguous_available needs the freelistLock + // so print this out before releasing the freeListLock. + gclog_or_tty->print(" 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; +} +#endif + +// 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 intersted 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 + gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr, + _markBitMap.isMarked(addr) ? "" : " not"); + + if (verify_after_remark()) { + MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); + bool result = verification_mark_bm()->isMarked(addr); + gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr, + result ? "IS" : "is NOT"); + return result; + } else { + gclog_or_tty->print_cr("Could not compute result"); + return false; + } +} + + +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, bitmap); + bitmap->print_on_error(st, " Bits: "); + + st->cr(); + + CMSBitMap* mut_bitmap = &collector->_modUnionTable; + st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, 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)) { + oop(addr)->print_on(gclog_or_tty); + gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr); + _failed = true; + } + return true; + } + + bool failed() { return _failed; } +}; + +bool CMSCollector::verify_after_remark(bool silent) { + if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... "); + MutexLockerEx 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 intefere in any + // way with the marking information used by GC. + NoRefDiscovery no_discovery(ref_processor()); + + COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) + + // 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(); + + GenCollectedHeap* gch = GenCollectedHeap::heap(); + gch->ensure_parsability(false); // fill TLABs, but no need to retire them + // Update the saved marks which may affect the root scans. + gch->save_marks(); + + if (CMSRemarkVerifyVariant == 1) { + // In this first variant of verification, we complete + // all marking, then check if the new marks-verctor is + // a subset of the CMS marks-vector. + verify_after_remark_work_1(); + } else if (CMSRemarkVerifyVariant == 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(); + } else { + warning("Unrecognized value %d for CMSRemarkVerifyVariant", + CMSRemarkVerifyVariant); + } + if (!silent) gclog_or_tty->print(" done] "); + return true; +} + +void CMSCollector::verify_after_remark_work_1() { + ResourceMark rm; + HandleMark hm; + GenCollectedHeap* gch = GenCollectedHeap::heap(); + + // Get a clear set of claim bits for the strong roots processing to work with. + ClassLoaderDataGraph::clear_claimed_marks(); + + // Mark from roots one level into CMS + MarkRefsIntoClosure notOlder(_span, verification_mark_bm()); + gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. + + gch->gen_process_strong_roots(_cmsGen->level(), + true, // younger gens are roots + true, // activate StrongRootsScope + false, // not scavenging + SharedHeap::ScanningOption(roots_scanning_options()), + ¬Older, + true, // walk code active on stacks + NULL, + NULL); // SSS: Provide correct closure + + // 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()) { + gclog_or_tty->print("Verification failed"); + Universe::heap()->print_on(gclog_or_tty); + fatal("CMS: failed marking verification after remark"); + } +} + +class VerifyKlassOopsKlassClosure : public KlassClosure { + class VerifyKlassOopsClosure : public OopClosure { + CMSBitMap* _bitmap; + public: + VerifyKlassOopsClosure(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: + VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {} + void do_klass(Klass* k) { + k->oops_do(&_oop_closure); + } +}; + +void CMSCollector::verify_after_remark_work_2() { + ResourceMark rm; + HandleMark hm; + GenCollectedHeap* gch = GenCollectedHeap::heap(); + + // Get a clear set of claim bits for the strong roots processing to work with. + ClassLoaderDataGraph::clear_claimed_marks(); + + // Mark from roots one level into CMS + MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(), + markBitMap()); + CMKlassClosure klass_closure(¬Older); + + gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. + gch->gen_process_strong_roots(_cmsGen->level(), + true, // younger gens are roots + true, // activate StrongRootsScope + false, // not scavenging + SharedHeap::ScanningOption(roots_scanning_options()), + ¬Older, + true, // walk code active on stacks + NULL, + &klass_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(); + + VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm()); + ClassLoaderDataGraph::classes_do(&verify_klass_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(); + for (uint i = 0; i < ParallelGCThreads; i++) { + _par_gc_thread_states[i]->promo.startTrackingPromotions(); + } +} + +bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() { + return cmsSpace()->no_allocs_since_save_marks(); +} + +#define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \ + \ +void ConcurrentMarkSweepGeneration:: \ +oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \ + cl->set_generation(this); \ + cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \ + cl->reset_generation(); \ + save_marks(); \ +} + +ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN) + +void +ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) { + cl->set_generation(this); + younger_refs_in_space_iterate(_cmsSpace, cl); + cl->reset_generation(); +} + +void +ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) { + if (freelistLock()->owned_by_self()) { + Generation::oop_iterate(mr, cl); + } else { + MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); + Generation::oop_iterate(mr, cl); + } +} + +void +ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) { + if (freelistLock()->owned_by_self()) { + Generation::oop_iterate(cl); + } else { + MutexLockerEx 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 { + MutexLockerEx 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 { + MutexLockerEx 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 { + MutexLockerEx 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 { + MutexLockerEx 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: +// (1) an explicit gc request has been made and the flag +// ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR +// (2) (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; + // Condition 1 above + if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) { + _should_unload_classes = true; + } else if (CMSClassUnloadingEnabled) { // Condition 2.a above + // Disjuncts 2.b.(i,ii,iii) above + _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 = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache; + + // We set the proper root for this CMS cycle here. + if (should_unload_classes()) { // Should unload classes this cycle + remove_root_scanning_option(SharedHeap::SO_AllClasses); + add_root_scanning_option(SharedHeap::SO_SystemClasses); + 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(), "Inconsitency!"); + remove_root_scanning_option(SharedHeap::SO_SystemClasses); + add_root_scanning_option(SharedHeap::SO_AllClasses); + + if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) { + // Include symbols, strings and code cache elements to prevent their resurrection. + add_root_scanning_option(rso); + 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"); + MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); + expand(word_size*HeapWordSize, MinHeapDeltaBytes, + CMSExpansionCause::_satisfy_allocation); + if (GCExpandToAllocateDelayMillis > 0) { + os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); + } + return have_lock_and_allocate(word_size, tlab); +} + +// YSR: All of this generation expansion/shrinking stuff is an exact copy of +// OneContigSpaceCardGeneration, which makes me wonder if we should move this +// to CardGeneration and share it... +bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) { + return CardGeneration::expand(bytes, expand_bytes); +} + +void ConcurrentMarkSweepGeneration::expand(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); + if (PrintGCDetails && Verbose) { + gclog_or_tty->print_cr("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(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 agaion. + if (GCExpandToAllocateDelayMillis > 0) { + os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); + } + } +} + + +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(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::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); + } + } +} + + +void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) { + assert_locked_or_safepoint(ExpandHeap_lock); + // Shrink committed space + _virtual_space.shrink_by(bytes); + // Shrink space; this also shrinks the space's BOT + _cmsSpace->set_end((HeapWord*) _virtual_space.high()); + size_t new_word_size = heap_word_size(_cmsSpace->capacity()); + // Shrink the shared block offset array + _bts->resize(new_word_size); + MemRegion mr(_cmsSpace->bottom(), new_word_size); + // Shrink the card table + Universe::heap()->barrier_set()->resize_covered_region(mr); + + if (Verbose && PrintGC) { + size_t new_mem_size = _virtual_space.committed_size(); + size_t old_mem_size = new_mem_size + bytes; + gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K", + name(), old_mem_size/K, new_mem_size/K); + } +} + +void ConcurrentMarkSweepGeneration::shrink(size_t bytes) { + assert_locked_or_safepoint(Heap_lock); + size_t size = ReservedSpace::page_align_size_down(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 (size > 0 && did_compact()) { + shrink_by(size); + } +} + +bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) { + assert_locked_or_safepoint(Heap_lock); + bool result = _virtual_space.expand_by(bytes); + if (result) { + size_t new_word_size = + heap_word_size(_virtual_space.committed_size()); + MemRegion mr(_cmsSpace->bottom(), new_word_size); + _bts->resize(new_word_size); // resize the block offset shared array + Universe::heap()->barrier_set()->resize_covered_region(mr); + // Hmmmm... why doesn't CFLS::set_end verify locking? + // This is quite ugly; FIX ME XXX + _cmsSpace->assert_locked(freelistLock()); + _cmsSpace->set_end((HeapWord*)_virtual_space.high()); + + // update the space and generation capacity counters + if (UsePerfData) { + _space_counters->update_capacity(); + _gen_counters->update_all(); + } + + if (Verbose && PrintGC) { + size_t new_mem_size = _virtual_space.committed_size(); + size_t old_mem_size = new_mem_size - bytes; + gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K", + name(), old_mem_size/K, bytes/K, new_mem_size/K); + } + } + return result; +} + +bool ConcurrentMarkSweepGeneration::grow_to_reserved() { + assert_locked_or_safepoint(Heap_lock); + bool success = true; + const size_t remaining_bytes = _virtual_space.uncommitted_size(); + if (remaining_bytes > 0) { + success = grow_by(remaining_bytes); + DEBUG_ONLY(if (!success) warning("grow to reserved failed");) + } + return success; +} + +void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) { + assert_locked_or_safepoint(Heap_lock); + assert_lock_strong(freelistLock()); + if (PrintGCDetails && Verbose) { + warning("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 *phase, + bool print_cr = true); + ~CMSPhaseAccounting(); + + private: + CMSCollector *_collector; + const char *_phase; + elapsedTimer _wallclock; + bool _print_cr; + + public: + // Not MT-safe; so do not pass around these StackObj's + // where they may be accessed by other threads. + jlong wallclock_millis() { + assert(_wallclock.is_active(), "Wall clock should not stop"); + _wallclock.stop(); // to record time + jlong ret = _wallclock.milliseconds(); + _wallclock.start(); // restart + return ret; + } +}; + +CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector, + const char *phase, + bool print_cr) : + _collector(collector), _phase(phase), _print_cr(print_cr) { + + if (PrintCMSStatistics != 0) { + _collector->resetYields(); + } + if (PrintGCDetails) { + gclog_or_tty->date_stamp(PrintGCDateStamps); + gclog_or_tty->stamp(PrintGCTimeStamps); + gclog_or_tty->print_cr("[%s-concurrent-%s-start]", + _collector->cmsGen()->short_name(), _phase); + } + _collector->resetTimer(); + _wallclock.start(); + _collector->startTimer(); +} + +CMSPhaseAccounting::~CMSPhaseAccounting() { + assert(_wallclock.is_active(), "Wall clock should not have stopped"); + _collector->stopTimer(); + _wallclock.stop(); + if (PrintGCDetails) { + gclog_or_tty->date_stamp(PrintGCDateStamps); + gclog_or_tty->stamp(PrintGCTimeStamps); + gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]", + _collector->cmsGen()->short_name(), + _phase, _collector->timerValue(), _wallclock.seconds()); + if (_print_cr) { + gclog_or_tty->cr(); + } + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase, + _collector->yields()); + } + } +} + +// CMS work + +// The common parts of CMSParInitialMarkTask and CMSParRemarkTask. +class CMSParMarkTask : public AbstractGangTask { + protected: + CMSCollector* _collector; + int _n_workers; + CMSParMarkTask(const char* name, CMSCollector* collector, int 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(uint worker_id, OopsInGenClosure* cl, + ContiguousSpace* space, + HeapWord** chunk_array, size_t chunk_top); + void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl); +}; + +// Parallel initial mark task +class CMSParInitialMarkTask: public CMSParMarkTask { + public: + CMSParInitialMarkTask(CMSCollector* collector, int n_workers) : + CMSParMarkTask("Scan roots and young gen for initial mark in parallel", + collector, n_workers) {} + 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(bool asynch) { + assert(_collectorState == InitialMarking, "Wrong collector state"); + check_correct_thread_executing(); + TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause()); + + save_heap_summary(); + report_heap_summary(GCWhen::BeforeGC); + + ReferenceProcessor* rp = ref_processor(); + SpecializationStats::clear(); + assert(_restart_addr == NULL, "Control point invariant"); + if (asynch) { + // acquire locks for subsequent manipulations + MutexLockerEx x(bitMapLock(), + Mutex::_no_safepoint_check_flag); + checkpointRootsInitialWork(asynch); + // enable ("weak") refs discovery + rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/); + _collectorState = Marking; + } else { + // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection + // which recognizes if we are a CMS generation, and doesn't try to turn on + // discovery; verify that they aren't meddling. + assert(!rp->discovery_is_atomic(), + "incorrect setting of discovery predicate"); + assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control " + "ref discovery for this generation kind"); + // already have locks + checkpointRootsInitialWork(asynch); + // now enable ("weak") refs discovery + rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/); + _collectorState = Marking; + } + SpecializationStats::print(); +} + +void CMSCollector::checkpointRootsInitialWork(bool asynch) { + assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped"); + assert(_collectorState == InitialMarking, "just checking"); + + // If there has not been a GC[n-1] since last GC[n] cycle completed, + // precede our marking with a collection of all + // younger generations to keep floating garbage to a minimum. + // XXX: we won't do this for now -- it's an optimization to be done later. + + // 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(); + + NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork", + PrintGCDetails && Verbose, true, _gc_timer_cm);) + if (UseAdaptiveSizePolicy) { + size_policy()->checkpoint_roots_initial_begin(); + } + + // Reset all the PLAB chunk arrays if necessary. + if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) { + reset_survivor_plab_arrays(); + } + + ResourceMark rm; + HandleMark hm; + + FalseClosure falseClosure; + // In the case of a synchronous collection, we will elide the + // remark step, so it's important to catch all the nmethod oops + // in this step. + // The final 'true' flag to gen_process_strong_roots will ensure this. + // If 'async' is true, we can relax the nmethod tracing. + MarkRefsIntoClosure notOlder(_span, &_markBitMap); + GenCollectedHeap* gch = GenCollectedHeap::heap(); + + verify_work_stacks_empty(); + verify_overflow_empty(); + + gch->ensure_parsability(false); // fill TLABs, but no need to retire them + // Update the saved marks which may affect the root scans. + gch->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(); + + if (CMSPrintEdenSurvivorChunks) { + print_eden_and_survivor_chunk_arrays(); + } + + { + COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) + if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) { + // The parallel version. + FlexibleWorkGang* workers = gch->workers(); + assert(workers != NULL, "Need parallel worker threads."); + int n_workers = workers->active_workers(); + CMSParInitialMarkTask tsk(this, n_workers); + gch->set_par_threads(n_workers); + initialize_sequential_subtasks_for_young_gen_rescan(n_workers); + if (n_workers > 1) { + GenCollectedHeap::StrongRootsScope srs(gch); + workers->run_task(&tsk); + } else { + GenCollectedHeap::StrongRootsScope srs(gch); + tsk.work(0); + } + gch->set_par_threads(0); + } else { + // The serial version. + CMKlassClosure klass_closure(¬Older); + gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. + gch->gen_process_strong_roots(_cmsGen->level(), + true, // younger gens are roots + true, // activate StrongRootsScope + false, // not scavenging + SharedHeap::ScanningOption(roots_scanning_options()), + ¬Older, + true, // walk all of code cache if (so & SO_CodeCache) + NULL, + &klass_closure); + } + } + + // Clear mod-union table; it will be dirtied in the prologue of + // CMS generation per each younger 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->klass_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(); + if (UseAdaptiveSizePolicy) { + size_policy()->checkpoint_roots_initial_end(gch->gc_cause()); + } + verify_overflow_empty(); +} + +bool CMSCollector::markFromRoots(bool asynch) { + // we might be tempted to assert that: + // assert(asynch == !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 younger 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(); + + bool res; + if (asynch) { + + // Start the timers for adaptive size policy for the concurrent phases + // Do it here so that the foreground MS can use the concurrent + // timer since a foreground MS might has the sweep done concurrently + // or STW. + if (UseAdaptiveSizePolicy) { + size_policy()->concurrent_marking_begin(); + } + + // Weak ref discovery note: We may be discovering weak + // refs in this generation concurrent (but interleaved) with + // weak ref discovery by a younger generation collector. + + CMSTokenSyncWithLocks ts(true, bitMapLock()); + TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); + CMSPhaseAccounting pa(this, "mark", !PrintGCDetails); + res = markFromRootsWork(asynch); + 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"); + if (PrintGCDetails) { + gclog_or_tty->print_cr("bailing out to foreground collection"); + } + } + if (UseAdaptiveSizePolicy) { + size_policy()->concurrent_marking_end(); + } + } else { + assert(SafepointSynchronize::is_at_safepoint(), + "inconsistent with asynch == false"); + if (UseAdaptiveSizePolicy) { + size_policy()->ms_collection_marking_begin(); + } + // already have locks + res = markFromRootsWork(asynch); + _collectorState = FinalMarking; + if (UseAdaptiveSizePolicy) { + GenCollectedHeap* gch = GenCollectedHeap::heap(); + size_policy()->ms_collection_marking_end(gch->gc_cause()); + } + } + verify_overflow_empty(); + return res; +} + +bool CMSCollector::markFromRootsWork(bool asynch) { + // 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 younger generation collectors) 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(asynch); + } else { + result = do_marking_st(asynch); + } + return result; +} + +// Forward decl +class CMSConcMarkingTask; + +class CMSConcMarkingTerminator: 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. + CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) : + ParallelTaskTerminator(n_threads, queue_set), + _collector(collector) { } + + void set_task(CMSConcMarkingTask* task) { + _task = task; + } +}; + +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; + int _n_workers; // requested/desired # workers + bool _asynch; + bool _result; + CompactibleFreeListSpace* _cms_space; + char _pad_front[64]; // padding to ... + HeapWord* _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 + CMSConcMarkingTerminator _term; + CMSConcMarkingTerminatorTerminator _term_term; + + public: + CMSConcMarkingTask(CMSCollector* collector, + CompactibleFreeListSpace* cms_space, + bool asynch, + YieldingFlexibleWorkGang* workers, + OopTaskQueueSet* task_queues): + YieldingFlexibleGangTask("Concurrent marking done multi-threaded"), + _collector(collector), + _cms_space(cms_space), + _asynch(asynch), _n_workers(0), _result(true), + _task_queues(task_queues), + _term(_n_workers, task_queues, _collector), + _bit_map_lock(collector->bitMapLock()) + { + _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** global_finger_addr() { return &_global_finger; } + + CMSConcMarkingTerminator* terminator() { return &_term; } + + virtual void set_for_termination(int active_workers) { + terminator()->reset_for_reuse(active_workers); + } + + void work(uint worker_id); + bool should_yield() { + return ConcurrentMarkSweepThread::should_yield() + && !_collector->foregroundGCIsActive() + && _asynch; + } + + 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.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 CMSConcMarkingTerminator::yield() { + if (_task->should_yield()) { + _task->yield(); + } else { + ParallelTaskTerminator::yield(); + } +} + +//////////////////////////////////////////////////////////////// +// 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(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec", + worker_id, _timer.seconds()); + // XXX: need xxx/xxx type of notation, two timers + } + + // ... do work stealing + _timer.reset(); + _timer.start(); + do_work_steal(worker_id); + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec", + worker_id, _timer.seconds()); + // XXX: need xxx/xxx type of notation, two timers + } + 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 = (HeapWord*) Atomic::cmpxchg_ptr(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"); + MutexLockerEx 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 = + (HeapWord*)align_size_down((uintptr_t)_restart_addr, + CardTableModRefBS::card_size); + } + + size_t chunk_size = sp->marking_task_size(); + while (!pst->is_task_claimed(/* 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. + Par_MarkFromRootsClosure cl(this, _collector, my_span, + &_collector->_markBitMap, + work_queue(i), + &_collector->_markStack, + _asynch); + _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 Par_ConcMarkingClosure: public CMSOopClosure { + private: + CMSCollector* _collector; + CMSConcMarkingTask* _task; + MemRegion _span; + CMSBitMap* _bit_map; + CMSMarkStack* _overflow_stack; + OopTaskQueue* _work_queue; + protected: + DO_OOP_WORK_DEFN + public: + Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue, + CMSBitMap* bit_map, CMSMarkStack* overflow_stack): + CMSOopClosure(collector->ref_processor()), + _collector(collector), + _task(task), + _span(collector->_span), + _work_queue(work_queue), + _bit_map(bit_map), + _overflow_stack(overflow_stack) + { } + 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(); + } + } +}; + +// 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 Par_ConcMarkingClosure::do_oop(oop obj) { + assert(obj->is_oop_or_null(true), "expected an oop or NULL"); + 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 + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr("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 Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); } +void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); } + +void Par_ConcMarkingClosure::trim_queue(size_t max) { + while (_work_queue->size() > max) { + oop new_oop; + if (_work_queue->pop_local(new_oop)) { + assert(new_oop->is_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 Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) { + // We need to do this under a mutex to prevent other + // workers from interfering with the work done below. + MutexLockerEx 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); + int* seed = _collector->hash_seed(i); + Par_ConcMarkingClosure 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, seed, /* reference */ obj_to_scan)) { + assert(obj_to_scan->is_oop(), "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); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + _collector->stopTimer(); + if (PrintCMSStatistics != 0) { + _collector->incrementYields(); + } + _collector->icms_wait(); + + // 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 maintenability and + // readability. See 6445193. + // + // Tony 2006.06.29 + for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount && + ConcurrentMarkSweepThread::should_yield() && + !CMSCollector::foregroundGCIsActive(); ++i) { + os::sleep(Thread::current(), 1, false); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + } + + ConcurrentMarkSweepThread::synchronize(true); + _bit_map_lock->lock_without_safepoint_check(); + _collector->startTimer(); +} + +bool CMSCollector::do_marking_mt(bool asynch) { + assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition"); + int num_workers = AdaptiveSizePolicy::calc_active_conc_workers( + conc_workers()->total_workers(), + conc_workers()->active_workers(), + Threads::number_of_non_daemon_threads()); + conc_workers()->set_active_workers(num_workers); + + CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); + + CMSConcMarkingTask tsk(this, + cms_space, + asynch, + 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 && asynch) { + // 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(bool asynch) { + 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 && asynch); + // 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 && asynch) { + // 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; + } + TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); + CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails); + 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 avove. By choosing + // CMSScheduleRemarkEdenSizeThreshold >= max eden size + // we will never do an actual abortable preclean cycle. + if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) { + TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); + CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails); + // 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::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) { + if (PrintGCDetails) { + gclog_or_tty->print(" CMS: abort preclean due to loops "); + } + break; + } + if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) { + if (PrintGCDetails) { + gclog_or_tty->print(" 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++; + } + } + if (PrintCMSStatistics > 0) { + gclog_or_tty->print(" [%d iterations, %d waits, %d 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(rp->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) + assert(_young_gen->kind() == Generation::DefNew || + _young_gen->kind() == Generation::ParNew || + _young_gen->kind() == Generation::ASParNew, + "incorrect type for cast"); + DefNewGeneration* dng = (DefNewGeneration*)_young_gen; + 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 = + GenCollectedHeap::heap()->total_collections(); + SurvivorSpacePrecleanClosure + sss_cl(this, _span, &_markBitMap, &_markStack, + &pam_cl, before_count, CMSYield); + dng->from()->object_iterate_careful(&sss_cl); + dng->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); + if (Verbose && PrintGCDetails) { + gclog_or_tty->print(" (modUnionTable: %d 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_klasses(&mrias_cl, _cmsGen->freelistLock()); + + curNumCards = preclean_card_table(_cmsGen, &smoac_cl); + cumNumCards += curNumCards; + if (PrintGCDetails && PrintCMSStatistics != 0) { + gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d 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* 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 = gen->reserved().start(); + HeapWord* endAddr = gen->reserved().end(); + + cl->setFreelistLock(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, gen->freelistLock(), + bitMapLock()); + startTimer(); + { + verify_work_stacks_empty(); + verify_overflow_empty(); + sample_eden(); + stop_point = + 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* 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*)(gen->_virtual_space.high()); + HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low()); + + cl->setFreelistLock(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->ct_bs()->dirty_card_range_after_reset( + MemRegion(nextAddr, endAddr), + true, + CardTableModRefBS::precleaned_card_val()); + + assert(dirtyRegion.start() >= nextAddr, + "returned region inconsistent?"); + } + lastAddr = dirtyRegion.end(); + numDirtyCards = + dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words; + + if (!dirtyRegion.is_empty()) { + stopTimer(); + CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock()); + startTimer(); + sample_eden(); + verify_work_stacks_empty(); + verify_overflow_empty(); + HeapWord* stop_point = + gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); + if (stop_point != NULL) { + assert((_collectorState == AbortablePreclean && should_abort_preclean()), + "Should only be AbortablePreclean."); + _ct->ct_bs()->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 PrecleanKlassClosure : public KlassClosure { + CMKlassClosure _cm_klass_closure; + public: + PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {} + void do_klass(Klass* k) { + if (k->has_accumulated_modified_oops()) { + k->clear_accumulated_modified_oops(); + + _cm_klass_closure.do_klass(k); + } + } +}; + +// The freelist lock is needed to prevent asserts, is it really needed? +void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) { + + 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? + PrecleanKlassClosure preclean_klass_closure(cl); + ClassLoaderDataGraph::classes_do(&preclean_klass_closure); + + verify_work_stacks_empty(); + verify_overflow_empty(); +} + +void CMSCollector::checkpointRootsFinal(bool asynch, + bool clear_all_soft_refs, bool init_mark_was_synchronous) { + 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,GenCollectedHeap::heap()->gc_cause()); + + verify_work_stacks_empty(); + verify_overflow_empty(); + + SpecializationStats::clear(); + if (PrintGCDetails) { + gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]", + _young_gen->used() / K, + _young_gen->capacity() / K); + } + if (asynch) { + if (CMSScavengeBeforeRemark) { + GenCollectedHeap* gch = GenCollectedHeap::heap(); + // Temporarily set flag to false, GCH->do_collection will + // expect it to be false and set to true + FlagSetting fl(gch->_is_gc_active, false); + NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark", + PrintGCDetails && Verbose, true, _gc_timer_cm);) + int level = _cmsGen->level() - 1; + if (level >= 0) { + gch->do_collection(true, // full (i.e. force, see below) + false, // !clear_all_soft_refs + 0, // size + false, // is_tlab + level // max_level + ); + } + } + FreelistLocker x(this); + MutexLockerEx y(bitMapLock(), + Mutex::_no_safepoint_check_flag); + assert(!init_mark_was_synchronous, "but that's impossible!"); + checkpointRootsFinalWork(asynch, clear_all_soft_refs, false); + } else { + // already have all the locks + checkpointRootsFinalWork(asynch, clear_all_soft_refs, + init_mark_was_synchronous); + } + verify_work_stacks_empty(); + verify_overflow_empty(); + SpecializationStats::print(); +} + +void CMSCollector::checkpointRootsFinalWork(bool asynch, + bool clear_all_soft_refs, bool init_mark_was_synchronous) { + + NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);) + + assert(haveFreelistLocks(), "must have free list locks"); + assert_lock_strong(bitMapLock()); + + if (UseAdaptiveSizePolicy) { + size_policy()->checkpoint_roots_final_begin(); + } + + ResourceMark rm; + HandleMark hm; + + GenCollectedHeap* gch = GenCollectedHeap::heap(); + + if (should_unload_classes()) { + CodeCache::gc_prologue(); + } + assert(haveFreelistLocks(), "must have free list locks"); + assert_lock_strong(bitMapLock()); + + if (!init_mark_was_synchronous) { + // 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. + gch->ensure_parsability(false); // fill TLAB's, but no need to retire them + // Update the saved marks which may affect the root scans. + gch->save_marks(); + + if (CMSPrintEdenSurvivorChunks) { + print_eden_and_survivor_chunk_arrays(); + } + + { + COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) + + // 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 && CollectedHeap::use_parallel_gc_threads()) { + GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm); + do_remark_parallel(); + } else { + GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false, + _gc_timer_cm); + do_remark_non_parallel(); + } + } + } else { + assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode"); + // The initial mark was stop-world, so there's no rescanning to + // do; go straight on to the next step below. + } + verify_work_stacks_empty(); + verify_overflow_empty(); + + { + NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);) + refProcessingWork(asynch, clear_all_soft_refs); + } + verify_work_stacks_empty(); + verify_overflow_empty(); + + if (should_unload_classes()) { + CodeCache::gc_epilogue(); + } + JvmtiExport::gc_epilogue(); + + // 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) { + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr("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) { + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr("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 (PrintCMSStatistics != 0) { + if (_markStack._hit_limit > 0) { + gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")", + _markStack._hit_limit); + } + if (_markStack._failed_double > 0) { + gclog_or_tty->print_cr(" (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) && + GenCollectedHeap::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->klass_rem_set()->mod_union_is_clear(), + "Should be clear by end of the final marking"); + if (UseAdaptiveSizePolicy) { + size_policy()->checkpoint_roots_final_end(gch->gc_cause()); + } +} + +void CMSParInitialMarkTask::work(uint worker_id) { + elapsedTimer _timer; + ResourceMark rm; + HandleMark hm; + + // ---------- scan from roots -------------- + _timer.start(); + GenCollectedHeap* gch = GenCollectedHeap::heap(); + Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap)); + CMKlassClosure klass_closure(&par_mri_cl); + + // ---------- young gen roots -------------- + { + work_on_young_gen_roots(worker_id, &par_mri_cl); + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr( + "Finished young gen initial mark scan work in %dth thread: %3.3f sec", + worker_id, _timer.seconds()); + } + } + + // ---------- remaining roots -------------- + _timer.reset(); + _timer.start(); + gch->gen_process_strong_roots(_collector->_cmsGen->level(), + false, // yg was scanned above + false, // this is parallel code + false, // not scavenging + SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), + &par_mri_cl, + true, // walk all of code cache if (so & SO_CodeCache) + NULL, + &klass_closure); + assert(_collector->should_unload_classes() + || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache), + "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr( + "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; + ParallelTaskTerminator _term; + + 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, + int n_workers, FlexibleWorkGang* workers, + OopTaskQueueSet* task_queues): + CMSParMarkTask("Rescan roots and grey objects in parallel", + collector, n_workers), + _cms_space(cms_space), + _task_queues(task_queues), + _term(n_workers, task_queues) { } + + OopTaskQueueSet* task_queues() { return _task_queues; } + + OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } + + ParallelTaskTerminator* terminator() { return &_term; } + int 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, + Par_MarkRefsIntoAndScanClosure* cl); + + // ... work stealing for the above + void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed); +}; + +class RemarkKlassClosure : public KlassClosure { + CMKlassClosure _cm_klass_closure; + public: + RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {} + void do_klass(Klass* k) { + // Check if we have modified any oops in the Klass during the concurrent marking. + if (k->has_accumulated_modified_oops()) { + k->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 (k->has_modified_oops()) { + // Don't clear anything, this info is needed by the next young collection. + } else { + // No modified oops in the Klass. + return; + } + + // The klass has modified fields, need to scan the klass. + _cm_klass_closure.do_klass(k); + } +}; + +void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) { + DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration(); + EdenSpace* eden_space = dng->eden(); + ContiguousSpace* from_space = dng->from(); + ContiguousSpace* to_space = dng->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(worker_id, cl, to_space, NULL, 0); + do_young_space_rescan(worker_id, cl, from_space, sca, sct); + do_young_space_rescan(worker_id, cl, eden_space, eca, ect); +} + +// work_queue(i) is passed to the closure +// Par_MarkRefsIntoAndScanClosure. 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(); + GenCollectedHeap* gch = GenCollectedHeap::heap(); + Par_MarkRefsIntoAndScanClosure 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(worker_id, &par_mrias_cl); + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr( + "Finished young gen rescan work in %dth thread: %3.3f sec", + worker_id, _timer.seconds()); + } + } + + // ---------- remaining roots -------------- + _timer.reset(); + _timer.start(); + gch->gen_process_strong_roots(_collector->_cmsGen->level(), + false, // yg was scanned above + false, // this is parallel code + false, // not scavenging + SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), + &par_mrias_cl, + true, // walk all of code cache if (so & SO_CodeCache) + NULL, + NULL); // The dirty klasses will be handled below + assert(_collector->should_unload_classes() + || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache), + "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr( + "Finished remaining root rescan work in %dth thread: %3.3f sec", + worker_id, _timer.seconds()); + } + + // ---------- unhandled CLD scanning ---------- + if (worker_id == 0) { // Single threaded at the moment. + _timer.reset(); + _timer.start(); + + // Scan all new class loader data objects and new dependencies that were + // introduced during concurrent marking. + ResourceMark rm; + GrowableArray* array = ClassLoaderDataGraph::new_clds(); + for (int i = 0; i < array->length(); i++) { + par_mrias_cl.do_class_loader_data(array->at(i)); + } + + // We don't need to keep track of new CLDs anymore. + ClassLoaderDataGraph::remember_new_clds(false); + + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr( + "Finished unhandled CLD scanning work in %dth thread: %3.3f sec", + worker_id, _timer.seconds()); + } + } + + // ---------- dirty klass 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. + RemarkKlassClosure remark_klass_closure(&par_mrias_cl); + ClassLoaderDataGraph::classes_do(&remark_klass_closure); + + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr( + "Finished dirty klass 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 point to newly allocated objects + // that are guaranteed to be kept alive. Either by the direct allocation + // code, or when the young collector processes the strong roots. Hence, + // we don't have to revisit the _handles block during the remark phase. + + // ---------- 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(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr( + "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, _collector->hash_seed(worker_id)); + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr( + "Finished work stealing in %dth thread: %3.3f sec", + worker_id, _timer.seconds()); + } +} + +// Note that parameter "i" is not used. +void +CMSParMarkTask::do_young_space_rescan(uint worker_id, + 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->is_task_claimed(/* 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 EdenSpace 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() || oop(mr.start())->is_oop(), + "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, + Par_MarkRefsIntoAndScanClosure* 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 + // imbedded in it a (subtype of) UpwardsObjectClosure. The + // use of that state in the imbedded 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 + // behaviour 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 = CardTableModRefBS::card_size * BitsPerWord; + MemRegion span = sp->used_region(); + HeapWord* start_addr = span.start(); + HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(), + alignment); + const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units + assert((HeapWord*)round_to((intptr_t)start_addr, alignment) == + start_addr, "Check alignment"); + assert((size_t)round_to((intptr_t)chunk_size, alignment) == + chunk_size, "Check alignment"); + + while (!pst->is_task_claimed(/* reference */ nth_task)) { + // Having claimed the nth_task, compute corresponding mem-region, + // which is a-fortiori aligned correctly (i.e. at a MUT bopundary). + // 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->ct_bs()->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, Par_MarkRefsIntoAndScanClosure* cl, + int* seed) { + 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, seed, /* reference */ obj_to_scan)) { + NOT_PRODUCT(num_steals++;) + assert(obj_to_scan->is_oop(), "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 + } + } + NOT_PRODUCT( + if (PrintCMSStatistics != 0) { + gclog_or_tty->print("\n\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) + if (PrintCMSStatistics > 0) { + gclog_or_tty->print(" (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++) { + if (PrintCMSStatistics > 0) { + gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ", + i, _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"); + DefNewGeneration* dng = (DefNewGeneration*)_young_gen; + + // Eden space + if (!dng->eden()->is_empty()) { + SequentialSubTasksDone* pst = dng->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(dng->from(), n_threads); + } else { + assert(_survivor_chunk_index == 0, "Error"); + } + + // To space + { + SequentialSubTasksDone* pst = dng->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 = dng->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() { + GenCollectedHeap* gch = GenCollectedHeap::heap(); + FlexibleWorkGang* workers = gch->workers(); + assert(workers != NULL, "Need parallel worker threads."); + // Choose to use the number of GC workers most recently set + // into "active_workers". If active_workers is not set, set it + // to ParallelGCThreads. + int n_workers = workers->active_workers(); + if (n_workers == 0) { + assert(n_workers > 0, "Should have been set during scavenge"); + n_workers = ParallelGCThreads; + workers->set_active_workers(n_workers); + } + CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); + + CMSParRemarkTask tsk(this, + cms_space, + n_workers, workers, task_queues()); + + // Set up for parallel process_strong_roots work. + gch->set_par_threads(n_workers); + // 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 + // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel + + // The young gen rescan work will not be done as part of + // process_strong_roots (which currently doesn't knw 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 EdenSpace, 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 younger 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); + GenCollectedHeap::StrongRootsScope srs(gch); + workers->run_task(&tsk); + } else { + ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); + GenCollectedHeap::StrongRootsScope srs(gch); + tsk.work(0); + } + + gch->set_par_threads(0); // 0 ==> non-parallel. + // 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; + GenCollectedHeap* gch = GenCollectedHeap::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 t("grey object rescan", PrintGCDetails, false, _gc_timer_cm); + // Iterate over the dirty cards, setting the corresponding bits in the + // mod union table. + { + ModUnionClosure modUnionClosure(&_modUnionTable); + _ct->ct_bs()->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 = + CardTableModRefBS::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 = (HeapWord*)round_to((intptr_t)ur.end(), alignment); + MemRegion cms_span(lb, ub); + _modUnionTable.dirty_range_iterate_clear(cms_span, + &markFromDirtyCardsClosure); + verify_work_stacks_empty(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ", + markFromDirtyCardsClosure.num_dirty_cards()); + } + } + } + if (VerifyDuringGC && + GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { + HandleMark hm; // Discard invalid handles created during verification + Universe::verify(); + } + { + GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm); + + verify_work_stacks_empty(); + + gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. + GenCollectedHeap::StrongRootsScope srs(gch); + gch->gen_process_strong_roots(_cmsGen->level(), + true, // younger gens as roots + false, // use the local StrongRootsScope + false, // not scavenging + SharedHeap::ScanningOption(roots_scanning_options()), + &mrias_cl, + true, // walk code active on stacks + NULL, + NULL); // The dirty klasses will be handled below + + assert(should_unload_classes() + || (roots_scanning_options() & SharedHeap::SO_CodeCache), + "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); + } + + { + GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm); + + verify_work_stacks_empty(); + + // Scan all class loader data objects that might have been introduced + // during concurrent marking. + ResourceMark rm; + GrowableArray* array = ClassLoaderDataGraph::new_clds(); + for (int i = 0; i < array->length(); i++) { + mrias_cl.do_class_loader_data(array->at(i)); + } + + // We don't need to keep track of new CLDs anymore. + ClassLoaderDataGraph::remember_new_clds(false); + + verify_work_stacks_empty(); + } + + { + GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm); + + verify_work_stacks_empty(); + + RemarkKlassClosure remark_klass_closure(&mrias_cl); + ClassLoaderDataGraph::classes_do(&remark_klass_closure); + + verify_work_stacks_empty(); + } + + // We might have added oops to ClassLoaderData::_handles during the + // concurrent marking phase. These oops point to newly allocated objects + // that are guaranteed to be kept alive. Either by the direct allocation + // code, or when the young collector processes the strong roots. Hence, + // we don't have to revisit the _handles block during the remark phase. + + verify_work_stacks_empty(); + // Restore evacuated mark words, if any, used for overflow list links + if (!CMSOverflowEarlyRestoration) { + restore_preserved_marks_if_any(); + } + verify_overflow_empty(); +} + +//////////////////////////////////////////////////////// +// Parallel Reference Processing Task Proxy Class +//////////////////////////////////////////////////////// +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): + // XXX Should superclass AGTWOQ also know about AWG since it knows + // about the task_queues used by the AWG? Then it could initialize + // the terminator() object. See 6984287. The set_for_termination() + // below is a temporary band-aid for the regression in 6984287. + AbstractGangTaskWOopQueues("Process referents by policy in parallel", + task_queues), + _task(task), + _collector(collector), _span(span), _mark_bit_map(mark_bit_map) + { + assert(_collector->_span.equals(_span) && !_span.is_empty(), + "Inconsistency in _span"); + set_for_termination(workers->active_workers()); + } + + 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, + int* seed); + + virtual void work(uint worker_id); +}; + +void CMSRefProcTaskProxy::work(uint worker_id) { + 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, + _collector->hash_seed(worker_id)); + } + assert(work_queue(worker_id)->size() == 0, "work_queue should be empty"); + assert(_collector->_overflow_list == NULL, "non-empty _overflow_list"); +} + +class CMSRefEnqueueTaskProxy: public AbstractGangTask { + typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; + EnqueueTask& _task; + +public: + CMSRefEnqueueTaskProxy(EnqueueTask& task) + : AbstractGangTask("Enqueue reference objects in parallel"), + _task(task) + { } + + virtual void work(uint worker_id) + { + _task.work(worker_id); + } +}; + +CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector, + MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue): + _span(span), + _bit_map(bit_map), + _work_queue(work_queue), + _mark_and_push(collector, span, bit_map, work_queue), + _low_water_mark(MIN2((uint)(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, + int* seed) { + 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, seed, /* reference */ obj_to_scan)) { + NOT_PRODUCT(num_steals++;) + assert(obj_to_scan->is_oop(), "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 + } + } + NOT_PRODUCT( + if (PrintCMSStatistics != 0) { + gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals); + } + ) +} + +void CMSRefProcTaskExecutor::execute(ProcessTask& task) +{ + GenCollectedHeap* gch = GenCollectedHeap::heap(); + FlexibleWorkGang* workers = gch->workers(); + assert(workers != NULL, "Need parallel worker threads."); + CMSRefProcTaskProxy rp_task(task, &_collector, + _collector.ref_processor()->span(), + _collector.markBitMap(), + workers, _collector.task_queues()); + workers->run_task(&rp_task); +} + +void CMSRefProcTaskExecutor::execute(EnqueueTask& task) +{ + + GenCollectedHeap* gch = GenCollectedHeap::heap(); + FlexibleWorkGang* workers = gch->workers(); + assert(workers != NULL, "Need parallel worker threads."); + CMSRefEnqueueTaskProxy enq_task(task); + workers->run_task(&enq_task); +} + +void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) { + + ResourceMark rm; + HandleMark hm; + + ReferenceProcessor* rp = ref_processor(); + assert(rp->span().equals(_span), "Spans should be equal"); + assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete"); + // Process weak references. + rp->setup_policy(clear_all_soft_refs); + verify_work_stacks_empty(); + + CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap, + &_markStack, false /* !preclean */); + CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this, + _span, &_markBitMap, &_markStack, + &cmsKeepAliveClosure, false /* !preclean */); + { + GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm); + + 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()). + GenCollectedHeap* gch = GenCollectedHeap::heap(); + int active_workers = ParallelGCThreads; + FlexibleWorkGang* workers = gch->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, + _gc_timer_cm); + } else { + stats = rp->process_discovered_references(&_is_alive_closure, + &cmsKeepAliveClosure, + &cmsDrainMarkingStackClosure, + NULL, + _gc_timer_cm); + } + _gc_tracer_cm->report_gc_reference_stats(stats); + + } + + // This is the point where the entire marking should have completed. + verify_work_stacks_empty(); + + if (should_unload_classes()) { + { + GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm); + + // Unload classes and purge the SystemDictionary. + bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure); + + // Unload nmethods. + CodeCache::do_unloading(&_is_alive_closure, purged_class); + + // Prune dead klasses from subklass/sibling/implementor lists. + Klass::clean_weak_klass_links(&_is_alive_closure); + } + + { + GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm); + // Clean up unreferenced symbols in symbol table. + SymbolTable::unlink(); + } + } + + // CMS doesn't use the StringTable as hard roots when class unloading is turned off. + // Need to check if we really scanned the StringTable. + if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) { + GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm); + // Delete entries for dead interned strings. + StringTable::unlink(&_is_alive_closure); + } + + // 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); + if (rp->processing_is_mt()) { + rp->balance_all_queues(); + CMSRefProcTaskExecutor task_executor(*this); + rp->enqueue_discovered_references(&task_executor); + } else { + rp->enqueue_discovered_references(NULL); + } + rp->verify_no_references_recorded(); + assert(!rp->discovery_enabled(), "should have been disabled"); +} + +#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(bool asynch) { + assert(_collectorState == Sweeping, "just checking"); + check_correct_thread_executing(); + verify_work_stacks_empty(); + verify_overflow_empty(); + increment_sweep_count(); + TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause()); + + _inter_sweep_timer.stop(); + _inter_sweep_estimate.sample(_inter_sweep_timer.seconds()); + size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free()); + + assert(!_intra_sweep_timer.is_active(), "Should not be active"); + _intra_sweep_timer.reset(); + _intra_sweep_timer.start(); + if (asynch) { + TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); + CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails); + // First sweep the old gen + { + CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(), + bitMapLock()); + sweepWork(_cmsGen, asynch); + } + + // 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(); + _collectorState = Resizing; + } + } else { + // already have needed locks + sweepWork(_cmsGen, asynch); + // Update heap occupancy information which is used as + // input to soft ref clearing policy at the next gc. + Universe::update_heap_info_at_gc(); + _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-deccreasing 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. + GenCollectedHeap* gch = GenCollectedHeap::heap(); + gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up + gch->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; + if (PrintFLSStatistics != 0) { + gclog_or_tty->print_cr( + "CMS: Large Block: " PTR_FORMAT ";" + " Proximity: " PTR_FORMAT " -> " PTR_FORMAT, + largestAddr, + _cmsSpace->nearLargestChunk(), 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(int current_level, + bool full) { + // The next lower level has been collected. Gather any statistics + // that are of interest at this point. + if (!full && (current_level + 1) == level()) { + // Gather statistics on the young generation collection. + collector()->stats().record_gc0_end(used()); + } +} + +CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() { + GenCollectedHeap* gch = GenCollectedHeap::heap(); + assert(gch->kind() == CollectedHeap::GenCollectedHeap, + "Wrong type of heap"); + CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*) + gch->gen_policy()->size_policy(); + assert(sp->is_gc_cms_adaptive_size_policy(), + "Wrong type of size policy"); + return sp; +} + +void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() { + if (PrintGCDetails && Verbose) { + gclog_or_tty->print("Rotate from %d ", _debug_collection_type); + } + _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1); + _debug_collection_type = + (CollectionTypes) (_debug_collection_type % Unknown_collection_type); + if (PrintGCDetails && Verbose) { + gclog_or_tty->print_cr("to %d ", _debug_collection_type); + } +} + +void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen, + bool asynch) { + // 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( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token()) + || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()), + "Should possess CMS token to sweep"); + assert_lock_strong(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"); + gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), + _inter_sweep_estimate.padded_average(), + _intra_sweep_estimate.padded_average()); + gen->setNearLargestChunk(); + + { + SweepClosure sweepClosure(this, gen, &_markBitMap, + CMSYield && asynch); + 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. + } + gen->cmsSpace()->sweep_completed(); + 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(bool asynch) { + GenCollectedHeap* gch = GenCollectedHeap::heap(); + CMSAdaptiveSizePolicy* sp = size_policy(); + AdaptiveSizePolicyOutput(sp, gch->total_collections()); + if (asynch) { + 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. + TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); + CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails); + + 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); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + stopTimer(); + if (PrintCMSStatistics != 0) { + incrementYields(); + } + icms_wait(); + + // See the comment in coordinator_yield() + for (unsigned i = 0; i < CMSYieldSleepCount && + ConcurrentMarkSweepThread::should_yield() && + !CMSCollector::foregroundGCIsActive(); ++i) { + os::sleep(Thread::current(), 1, false); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + } + + 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. + sp->reset_gc_overhead_limit_count(); + _collectorState = Idling; + } else { + // already have the lock + assert(_collectorState == Resetting, "just checking"); + assert_lock_strong(bitMapLock()); + _markBitMap.clear_all(); + _collectorState = Idling; + } + + // Stop incremental mode after a cycle completes, so that any future cycles + // are triggered by allocation. + stop_icms(); + + NOT_PRODUCT( + if (RotateCMSCollectionTypes) { + _cmsGen->rotate_debug_collection_type(); + } + ) + + register_gc_end(); +} + +void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) { + gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps); + TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); + GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL); + TraceCollectorStats tcs(counters()); + + switch (op) { + case CMS_op_checkpointRootsInitial: { + SvcGCMarker sgcm(SvcGCMarker::OTHER); + checkpointRootsInitial(true); // asynch + if (PrintGC) { + _cmsGen->printOccupancy("initial-mark"); + } + break; + } + case CMS_op_checkpointRootsFinal: { + SvcGCMarker sgcm(SvcGCMarker::OTHER); + checkpointRootsFinal(true, // asynch + false, // !clear_all_soft_refs + false); // !init_mark_was_synchronous + if (PrintGC) { + _cmsGen->printOccupancy("remark"); + } + 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() != 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 = (HeapWord*)round_to((uintptr_t)next_block, + CardTableModRefBS::card_size); + assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) < + round_down((uintptr_t)next_card, CardTableModRefBS::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): + _bm(), + _shifter(shifter), + _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : 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()) { + warning("CMS bit map allocation failure"); + return false; + } + // For now we'll just commit all of the bit map up fromt. + // Later on we'll try to be more parsimonious with swap. + if (!_virtual_space.initialize(brs, brs.size())) { + warning("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?"); + _bm.set_map((BitMap::bm_word_t*)_virtual_space.low()); + assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >= + _bmWordSize, "inconsistency in bit map sizing"); + _bm.set_size(_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() == (HeapWord*)round_to((intptr_t)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()) { + warning("CMSMarkStack allocation failure"); + return false; + } + if (!_virtual_space.initialize(rs, rs.size())) { + warning("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 recallibrate the two +// lock-ranks involved in order to be able to rpint 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 && PrintGCDetails) { + // We print a warning message only once per CMS cycle. + gclog_or_tty->print_cr(" (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 && PrintGCDetails) { + // Failed to double capacity, continue; + // we print a detail message only once per CMS cycle. + gclog_or_tty->print(" (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_processor == 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(obj->is_oop(), "expected an oop"); + HeapWord* addr = (HeapWord*)obj; + if (_span.contains(addr)) { + // this should be made more efficient + _bitMap->mark(addr); + } +} + +void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); } +void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); } + +Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure( + MemRegion span, CMSBitMap* bitMap): + _span(span), + _bitMap(bitMap) +{ + assert(_ref_processor == NULL, "deliberately left NULL"); + assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); +} + +void Par_MarkRefsIntoClosure::do_oop(oop obj) { + // if p points into _span, then mark corresponding bit in _markBitMap + assert(obj->is_oop(), "expected an oop"); + HeapWord* addr = (HeapWord*)obj; + if (_span.contains(addr)) { + // this should be made more efficient + _bitMap->par_mark(addr); + } +} + +void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); } +void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); } + +// 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_processor == 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(obj->is_oop(), "expected an oop"); + HeapWord* addr = (HeapWord*)obj; + if (_span.contains(addr)) { + _verification_bm->mark(addr); + if (!_cms_bm->isMarked(addr)) { + oop(addr)->print(); + gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr); + fatal("... aborting"); + } + } +} + +void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); } +void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); } + +////////////////////////////////////////////////// +// MarkRefsIntoAndScanClosure +////////////////////////////////////////////////// + +MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span, + ReferenceProcessor* rp, + CMSBitMap* bit_map, + CMSBitMap* mod_union_table, + CMSMarkStack* mark_stack, + CMSCollector* collector, + bool should_yield, + bool concurrent_precleaning): + _collector(collector), + _span(span), + _bit_map(bit_map), + _mark_stack(mark_stack), + _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table, + mark_stack, concurrent_precleaning), + _yield(should_yield), + _concurrent_precleaning(concurrent_precleaning), + _freelistLock(NULL) +{ + _ref_processor = rp; + assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); +} + +// 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(obj->is_oop(), "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 && new_oop->is_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"); + // We could restore evacuated mark words, if any, used for + // overflow list links here because the overflow list is + // provably empty here. That would reduce the maximum + // size requirements for preserved_{oop,mark}_stack. + // But we'll just postpone it until we are all done + // so we can just stream through. + if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) { + _collector->restore_preserved_marks_if_any(); + assert(_collector->no_preserved_marks(), "No preserved marks"); + } + assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(), + "All preserved marks should have been restored above"); + } +} + +void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); } +void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); } + +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); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + _collector->stopTimer(); + GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); + if (PrintCMSStatistics != 0) { + _collector->incrementYields(); + } + _collector->icms_wait(); + + // See the comment in coordinator_yield() + for (unsigned i = 0; + i < CMSYieldSleepCount && + ConcurrentMarkSweepThread::should_yield() && + !CMSCollector::foregroundGCIsActive(); + ++i) { + os::sleep(Thread::current(), 1, false); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + } + + ConcurrentMarkSweepThread::synchronize(true); + _freelistLock->lock_without_safepoint_check(); + _bit_map->lock()->lock_without_safepoint_check(); + _collector->startTimer(); +} + +/////////////////////////////////////////////////////////// +// Par_MarkRefsIntoAndScanClosure: a parallel version of +// MarkRefsIntoAndScanClosure +/////////////////////////////////////////////////////////// +Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure( + CMSCollector* collector, MemRegion span, ReferenceProcessor* rp, + CMSBitMap* bit_map, OopTaskQueue* work_queue): + _span(span), + _bit_map(bit_map), + _work_queue(work_queue), + _low_water_mark(MIN2((uint)(work_queue->max_elems()/4), + (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))), + _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue) +{ + _ref_processor = rp; + assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); +} + +// 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 Par_MarkRefsIntoAndScanClosure::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(obj->is_oop(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 + } + } +} + +void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); } +void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); } + +// 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() != NULL) { + // an initialized object; ignore mark word in verification below + // since we are running concurrent with mutators + assert(p->is_oop(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(_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(_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"); + if (!_bitMap->isMarked(addr+1)) { + _bitMap->verifyNoOneBitsInRange(addr+2, addr+size); + } else { + _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1); + assert(_bitMap->isMarked(addr+size-1), + "inconsistent Printezis mark"); + } + #endif // ASSERT + } else { + // an unitialized 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 (signalling the completion of initialization). + } + } else { + // Either a not yet marked object or an uninitialized object + if (p->klass_or_null() == 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(p->is_oop(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); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + _collector->stopTimer(); + GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); + if (PrintCMSStatistics != 0) { + _collector->incrementYields(); + } + _collector->icms_wait(); + + // See the comment in coordinator_yield() + for (unsigned i = 0; i < CMSYieldSleepCount && + ConcurrentMarkSweepThread::should_yield() && + !CMSCollector::foregroundGCIsActive(); ++i) { + os::sleep(Thread::current(), 1, false); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + } + + 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 initializd"); + // an initialized object; ignore mark word in verification below + // since we are running concurrent with mutators + assert(p->is_oop(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(_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 && new_oop->is_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 = + GenCollectedHeap::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); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + _collector->stopTimer(); + GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); + if (PrintCMSStatistics != 0) { + _collector->incrementYields(); + } + _collector->icms_wait(); + + // See the comment in coordinator_yield() + for (unsigned i = 0; i < CMSYieldSleepCount && + ConcurrentMarkSweepThread::should_yield() && + !CMSCollector::foregroundGCIsActive(); ++i) { + os::sleep(Thread::current(), 1, false); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + } + + 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(p->is_oop_or_null(true), "expected an oop or null"); + 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 = (HeapWord*)round_to( + (intptr_t)_finger, CardTableModRefBS::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() == 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 = (HeapWord*)round_to( + (intptr_t)(addr+sz), CardTableModRefBS::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() != 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); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + _collector->stopTimer(); + GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); + if (PrintCMSStatistics != 0) { + _collector->incrementYields(); + } + _collector->icms_wait(); + + // See the comment in coordinator_yield() + for (unsigned i = 0; i < CMSYieldSleepCount && + ConcurrentMarkSweepThread::should_yield() && + !CMSCollector::foregroundGCIsActive(); ++i) { + os::sleep(Thread::current(), 1, false); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + } + + 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(obj->is_oop(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 (especially if running iCMS). 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(old_threshold == (HeapWord*)round_to( + (intptr_t)old_threshold, CardTableModRefBS::card_size), + "_threshold should always be card-aligned"); + _threshold = (HeapWord*)round_to( + (intptr_t)_finger, CardTableModRefBS::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(new_oop->is_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"); +} + +Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task, + CMSCollector* collector, MemRegion span, + CMSBitMap* bit_map, + OopTaskQueue* work_queue, + CMSMarkStack* overflow_stack, + bool should_yield): + _collector(collector), + _whole_span(collector->_span), + _span(span), + _bit_map(bit_map), + _mut(&collector->_modUnionTable), + _work_queue(work_queue), + _overflow_stack(overflow_stack), + _yield(should_yield), + _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 Par_MarkFromRootsClosure::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() == 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 Par_MarkFromRootsClosure::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(obj->is_oop(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 (especially if running iCMS). 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(old_threshold == (HeapWord*)round_to( + (intptr_t)old_threshold, CardTableModRefBS::card_size), + "_threshold should always be card-aligned"); + _threshold = (HeapWord*)round_to( + (intptr_t)_finger, CardTableModRefBS::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** gfa = _task->global_finger_addr(); + Par_PushOrMarkClosure 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(new_oop->is_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 Par_MarkFromRootsClosure::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(obj->is_oop(), "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(new_oop->is_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): + CMSOopClosure(collector->ref_processor()), + _collector(collector), + _span(span), + _verification_bm(verification_bm), + _cms_bm(cms_bm), + _mark_stack(mark_stack) +{ } + +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(obj->is_oop_or_null(), "expected an oop or NULL"); + 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)) { + oop(addr)->print(); + gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", + addr); + fatal("... aborting"); + } + + if (!_mark_stack->push(obj)) { // stack overflow + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr("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) : + CMSOopClosure(collector->ref_processor()), + _collector(collector), + _span(span), + _bitMap(bitMap), + _markStack(markStack), + _finger(finger), + _parent(parent) +{ } + +Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector, + MemRegion span, + CMSBitMap* bit_map, + OopTaskQueue* work_queue, + CMSMarkStack* overflow_stack, + HeapWord* finger, + HeapWord** global_finger_addr, + Par_MarkFromRootsClosure* parent) : + CMSOopClosure(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 Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { + // We need to do this under a mutex to prevent other + // workers from interfering with the work done below. + MutexLockerEx 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 CMKlassClosure::do_klass(Klass* k) { + assert(_oop_closure != NULL, "Not initialized?"); + k->oops_do(_oop_closure); +} + +void PushOrMarkClosure::do_oop(oop obj) { + // Ignore mark word because we are running concurrent with mutators. + assert(obj->is_oop_or_null(true), "expected an oop or NULL"); + 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 + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr("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 PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); } +void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); } + +void Par_PushOrMarkClosure::do_oop(oop obj) { + // Ignore mark word because we are running concurrent with mutators. + assert(obj->is_oop_or_null(true), "expected an oop or NULL"); + 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 + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr("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(); + } +} + +void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); } +void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); } + +PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector, + MemRegion span, + ReferenceProcessor* rp, + CMSBitMap* bit_map, + CMSBitMap* mod_union_table, + CMSMarkStack* mark_stack, + bool concurrent_precleaning): + CMSOopClosure(rp), + _collector(collector), + _span(span), + _bit_map(bit_map), + _mod_union_table(mod_union_table), + _mark_stack(mark_stack), + _concurrent_precleaning(concurrent_precleaning) +{ + assert(_ref_processor != NULL, "_ref_processor 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(obj->is_oop_or_null(true /* ignore mark word */), + "expected an oop or NULL"); + 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 intefering 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 = (HeapWord*)round_to( + (intptr_t)(addr+sz), CardTableModRefBS::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++; + } + } + } +} + +Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector, + MemRegion span, + ReferenceProcessor* rp, + CMSBitMap* bit_map, + OopTaskQueue* work_queue): + CMSOopClosure(rp), + _collector(collector), + _span(span), + _bit_map(bit_map), + _work_queue(work_queue) +{ + assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); +} + +void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); } +void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); } + +// Grey object rescan during second checkpoint phase -- +// the parallel version. +void Par_PushAndMarkClosure::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(obj->is_oop_or_null(true), + "expected an oop or NULL"); + 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 Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); } +void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); } + +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); + + ConcurrentMarkSweepThread::acknowledge_yield_request(); + + _collector->stopTimer(); + GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); + if (PrintCMSStatistics != 0) { + _collector->incrementYields(); + } + _collector->icms_wait(); + + // See the comment in coordinator_yield() + for (unsigned i = 0; i < CMSYieldSleepCount && + ConcurrentMarkSweepThread::should_yield() && + !CMSCollector::foregroundGCIsActive(); ++i) { + os::sleep(Thread::current(), 1, false); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + } + + ConcurrentMarkSweepThread::synchronize(true); + bml->lock(); + + _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())%CardTableModRefBS::card_size_in_words == 0, + "mr should be aligned to start at a card boundary"); + // We'd like to assert: + // assert(mr.word_size()%CardTableModRefBS::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. + if (PrintCMSStatistics != 0) { + _num_dirty_cards += + mr.word_size()/CardTableModRefBS::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), + _yield(should_yield), + _inFreeRange(false), // No free range at beginning of sweep + _freeRangeInFreeLists(false), // No free range at beginning of sweep + _lastFreeRangeCoalesced(false), + _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"); + if (CMSTraceSweeper) { + gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT, + _limit); + } +} + +void SweepClosure::print_on(outputStream* st) const { + tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")", + _sp->bottom(), _sp->end()); + tty->print_cr("_limit = " PTR_FORMAT, _limit); + tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger); + NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);) + tty->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()) { + warning("inFreeRange() should have been reset; dumping state of SweepClosure"); + print(); + ShouldNotReachHere(); + } + if (Verbose && PrintGC) { + gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes", + _numObjectsFreed, _numWordsFreed*sizeof(HeapWord)); + gclog_or_tty->print_cr("\nLive "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); + gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes); + + if (PrintCMSStatistics && 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; + gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes); + gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes", + indexListReturnedBytes); + gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes", + dict_returned_bytes); + } + } + if (CMSTraceSweeper) { + gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================", + _limit); + } +} +#endif // PRODUCT + +void SweepClosure::initialize_free_range(HeapWord* freeFinger, + bool freeRangeInFreeLists) { + if (CMSTraceSweeper) { + gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n", + 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, + err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger())); + flush_cur_free_chunk(freeFinger(), + pointer_delta(addr, freeFinger())); + if (CMSTraceSweeper) { + gclog_or_tty->print("Sweep: last chunk: "); + gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") " + "[coalesced:"SIZE_FORMAT"]\n", + freeFinger(), pointer_delta(addr, freeFinger()), + lastFreeRangeCoalesced()); + } + } + + // 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. + if (_sp->adaptive_freelists()) { + // All the work is done in + do_post_free_or_garbage_chunk(fc, size); + } else { // Not adaptive free lists + // this is a free chunk that can potentially be coalesced by the sweeper; + if (!inFreeRange()) { + // if the next chunk is a free block that can't be coalesced + // it doesn't make sense to remove this chunk from the free lists + FreeChunk* nextChunk = (FreeChunk*)(addr + size); + assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?"); + if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ... + nextChunk->is_free() && // ... which is free... + nextChunk->cantCoalesce()) { // ... but can't be coalesced + // nothing to do + } else { + // Potentially the start of a new free range: + // Don't eagerly remove it from the free lists. + // No need to remove it if it will just be put + // back again. (Also from a pragmatic point of view + // if it is a free block in a region that is beyond + // any allocated blocks, an assertion will fail) + // Remember the start of a free run. + initialize_free_range(addr, true); + // end - can coalesce with next chunk + } + } else { + // the midst of a free range, we are coalescing + print_free_block_coalesced(fc); + if (CMSTraceSweeper) { + gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size); + } + // remove it from the free lists + _sp->removeFreeChunkFromFreeLists(fc); + set_lastFreeRangeCoalesced(true); + // If the chunk is being coalesced and the current free range is + // in the free lists, remove the current free range so that it + // will be returned to the free lists in its entirety - all + // the coalesced pieces included. + if (freeRangeInFreeLists()) { + FreeChunk* ffc = (FreeChunk*) freeFinger(); + assert(ffc->size() == pointer_delta(addr, freeFinger()), + "Size of free range is inconsistent with chunk size."); + if (CMSTestInFreeList) { + assert(_sp->verify_chunk_in_free_list(ffc), + "free range is not in free lists"); + } + _sp->removeFreeChunkFromFreeLists(ffc); + set_freeRangeInFreeLists(false); + } + } + } + // 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()); + + if (_sp->adaptive_freelists()) { + // 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); + } else { + if (!inFreeRange()) { + // start of a new free range + assert(size > 0, "A free range should have a size"); + initialize_free_range(addr, false); + } else { + // this will be swept up when we hit the end of the + // free range + if (CMSTraceSweeper) { + gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size); + } + // If the chunk is being coalesced and the current free range is + // in the free lists, remove the current free range so that it + // will be returned to the free lists in its entirety - all + // the coalesced pieces included. + if (freeRangeInFreeLists()) { + FreeChunk* ffc = (FreeChunk*)freeFinger(); + assert(ffc->size() == pointer_delta(addr, freeFinger()), + "Size of free range is inconsistent with chunk size."); + if (CMSTestInFreeList) { + assert(_sp->verify_chunk_in_free_list(ffc), + "free range is not in free lists"); + } + _sp->removeFreeChunkFromFreeLists(ffc); + set_freeRangeInFreeLists(false); + } + set_lastFreeRangeCoalesced(true); + } + // this will be swept up when we hit the end of the free range + + // Verify that the bit map has no bits marked between + // addr and purported end of just dead object. + _bitMap->verifyNoOneBitsInRange(addr + 1, addr + 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(oop(addr)->is_oop(), "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() != NULL) { + // Ignore mark word because we are running concurrent with mutators + assert(oop(addr)->is_oop(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() != NULL, + "Should be an initialized object"); + // Ignore mark word because we are running concurrent with mutators + assert(oop(addr)->is_oop(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(_sp->adaptive_freelists(), "Should only be used in this case."); + assert((HeapWord*)fc <= _limit, "sweep invariant"); + if (CMSTestInFreeList && fcInFreeLists) { + assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists"); + } + + if (CMSTraceSweeper) { + gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize); + } + + HeapWord* const fc_addr = (HeapWord*) fc; + + bool coalesce; + 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), + err_msg("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 ")", + eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size)); + if (eob >= _limit) { + assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit"); + if (CMSTraceSweeper) { + gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block " + "[" PTR_FORMAT "," PTR_FORMAT ") in space " + "[" PTR_FORMAT "," PTR_FORMAT ")", + _limit, fc, eob, _sp->bottom(), _sp->end()); + } + // Return the storage we are tracking back into the free lists. + if (CMSTraceSweeper) { + gclog_or_tty->print_cr("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"); + } + if (CMSTraceSweeper) { + gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists", + 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 if (CMSTraceSweeper) { + gclog_or_tty->print_cr("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); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + _collector->stopTimer(); + GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); + if (PrintCMSStatistics != 0) { + _collector->incrementYields(); + } + _collector->icms_wait(); + + // See the comment in coordinator_yield() + for (unsigned i = 0; i < CMSYieldSleepCount && + ConcurrentMarkSweepThread::should_yield() && + !CMSCollector::foregroundGCIsActive(); ++i) { + os::sleep(Thread::current(), 1, false); + ConcurrentMarkSweepThread::acknowledge_yield_request(); + } + + ConcurrentMarkSweepThread::synchronize(true); + _freelistLock->lock(); + _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 { + if (CMSTraceSweeper) { + gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")", + 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), + _bit_map(bit_map), + _mark_stack(mark_stack), + _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 = + (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::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++; + } + } + } +} + +void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); } +void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); } + +// 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::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); } +void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); } + +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 && new_oop->is_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), + _bit_map(bit_map), + _work_queue(work_queue) { } + +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 + } +} + +void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); } +void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); } + +////////////////////////////////////////////////////////////////// +// 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(obj->is_oop(), "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(new_oop->is_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 oveflows, 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 markOop proto = markOopDesc::prototype(); + NOT_PRODUCT(ssize_t n = 0;) + for (oop next; i > 0 && cur != NULL; cur = next, i--) { + next = oop(cur->mark()); + cur->set_mark(proto); // until proven otherwise + assert(cur->is_oop(), "Should be an oop"); + bool res = stack->push(cur); + assert(res, "Bit off more than can chew?"); + NOT_PRODUCT(n++;) + } + _overflow_list = cur; +#ifndef PRODUCT + assert(_num_par_pushes >= n, "Too many pops?"); + _num_par_pushes -=n; +#endif + return !stack->isEmpty(); +} + +#define BUSY (cast_to_oop(0x1aff1aff)) +// (MT-safe) Get a prefix of at most "num" from the list. +// The overflow list is chained through the mark word of +// each object in the list. We fetch the entire list, +// break off a prefix of the right size and return the +// remainder. If other threads try to take objects from +// the overflow list at that time, they will wait for +// some time to see if data becomes available. If (and +// only if) another thread places one or more object(s) +// on the global list before we have returned the suffix +// to the global list, we will walk down our local list +// to find its end and append the global list to +// our suffix before returning it. This suffix walk can +// prove to be expensive (quadratic in the amount of traffic) +// when there are many objects in the overflow list and +// there is much producer-consumer contention on the list. +// *NOTE*: The overflow list manipulation code here and +// in ParNewGeneration:: are very similar in shape, +// except that in the ParNew case we use the old (from/eden) +// copy of the object to thread the list via its klass word. +// Because of the common code, if you make any changes in +// the code below, please check the ParNew version to see if +// similar changes might be needed. +// CR 6797058 has been filed to consolidate the common code. +bool CMSCollector::par_take_from_overflow_list(size_t num, + OopTaskQueue* work_q, + int no_of_gc_threads) { + assert(work_q->size() == 0, "First empty local work queue"); + assert(num < work_q->max_elems(), "Can't bite more than we can chew"); + if (_overflow_list == NULL) { + return false; + } + // Grab the entire list; we'll put back a suffix + oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); + Thread* tid = Thread::current(); + // 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::sleep(tid, sleep_time_millis, false); + 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_ptr(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. + (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, 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() != NULL; cur = oop(cur->mark()), i--); + if (cur->mark() == 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) { + (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); + } + } else { + // Chop off the suffix and rerturn it to the global list. + assert(cur->mark() != BUSY, "Error"); + oop suffix_head = cur->mark(); // suffix will be put back on global list + cur->set_mark(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 = + (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, 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() != NULL; cur = (oop)(cur->mark())); + oop suffix_tail = cur; + assert(suffix_tail != NULL && suffix_tail->mark() == 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(markOop(cur_overflow_list)); + } else { // cur_overflow_list == BUSY + suffix_tail->set_mark(NULL); + } + // ... and try to place spliced list back on overflow_list ... + observed_overflow_list = + (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, 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 markOop proto = markOopDesc::prototype(); + oop next; + NOT_PRODUCT(ssize_t n = 0;) + for (cur = prefix; cur != NULL; cur = next) { + next = oop(cur->mark()); + cur->set_mark(proto); // until proven otherwise + assert(cur->is_oop(), "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::add_ptr(-(intptr_t)n, &_num_par_pushes); +#endif + return true; +} + +// Single-threaded +void CMSCollector::push_on_overflow_list(oop p) { + NOT_PRODUCT(_num_par_pushes++;) + assert(p->is_oop(), "Not an oop"); + preserve_mark_if_necessary(p); + p->set_mark((markOop)_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_ptr(&_num_par_pushes);) + assert(p->is_oop(), "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(markOop(cur_overflow_list)); + } else { + p->set_mark(NULL); + } + observed_overflow_list = + (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, 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, markOop m) { + _preserved_oop_stack.push(p); + _preserved_mark_stack.push(m); + assert(m == p->mark(), "Mark word changed"); + assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), + "bijection"); +} + +// Single threaded +void CMSCollector::preserve_mark_if_necessary(oop p) { + markOop m = p->mark(); + if (m->must_be_preserved(p)) { + preserve_mark_work(p, m); + } +} + +void CMSCollector::par_preserve_mark_if_necessary(oop p) { + markOop m = p->mark(); + if (m->must_be_preserved(p)) { + MutexLockerEx 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(). + 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(p->is_oop(), "Should be an oop"); + assert(_span.contains(p), "oop should be in _span"); + assert(p->mark() == markOopDesc::prototype(), + "Set when taken from overflow list"); + markOop m = _preserved_mark_stack.pop(); + p->set_mark(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 + +CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const +{ + GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap(); + CMSAdaptiveSizePolicy* size_policy = + (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy(); + assert(size_policy->is_gc_cms_adaptive_size_policy(), + "Wrong type for size policy"); + return size_policy; +} + +void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size, + size_t desired_promo_size) { + if (cur_promo_size < desired_promo_size) { + size_t expand_bytes = desired_promo_size - cur_promo_size; + if (PrintAdaptiveSizePolicy && Verbose) { + gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize " + "Expanding tenured generation by " SIZE_FORMAT " (bytes)", + expand_bytes); + } + expand(expand_bytes, + MinHeapDeltaBytes, + CMSExpansionCause::_adaptive_size_policy); + } else if (desired_promo_size < cur_promo_size) { + size_t shrink_bytes = cur_promo_size - desired_promo_size; + if (PrintAdaptiveSizePolicy && Verbose) { + gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize " + "Shrinking tenured generation by " SIZE_FORMAT " (bytes)", + shrink_bytes); + } + shrink(shrink_bytes); + } +} + +CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() { + GenCollectedHeap* gch = GenCollectedHeap::heap(); + CMSGCAdaptivePolicyCounters* counters = + (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters(); + assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind, + "Wrong kind of counters"); + return counters; +} + + +void ASConcurrentMarkSweepGeneration::update_counters() { + if (UsePerfData) { + _space_counters->update_all(); + _gen_counters->update_all(); + CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters(); + GenCollectedHeap* gch = GenCollectedHeap::heap(); + CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats(); + assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind, + "Wrong gc statistics type"); + counters->update_counters(gc_stats_l); + } +} + +void ASConcurrentMarkSweepGeneration::update_counters(size_t used) { + if (UsePerfData) { + _space_counters->update_used(used); + _space_counters->update_capacity(); + _gen_counters->update_all(); + + CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters(); + GenCollectedHeap* gch = GenCollectedHeap::heap(); + CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats(); + assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind, + "Wrong gc statistics type"); + counters->update_counters(gc_stats_l); + } +} + +void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) { + assert_locked_or_safepoint(Heap_lock); + assert_lock_strong(freelistLock()); + HeapWord* old_end = _cmsSpace->end(); + HeapWord* unallocated_start = _cmsSpace->unallocated_block(); + assert(old_end >= unallocated_start, "Miscalculation of unallocated_start"); + FreeChunk* chunk_at_end = find_chunk_at_end(); + if (chunk_at_end == NULL) { + // No room to shrink + if (PrintGCDetails && Verbose) { + gclog_or_tty->print_cr("No room to shrink: old_end " + PTR_FORMAT " unallocated_start " PTR_FORMAT + " chunk_at_end " PTR_FORMAT, + old_end, unallocated_start, chunk_at_end); + } + return; + } else { + + // Find the chunk at the end of the space and determine + // how much it can be shrunk. + size_t shrinkable_size_in_bytes = chunk_at_end->size(); + size_t aligned_shrinkable_size_in_bytes = + align_size_down(shrinkable_size_in_bytes, os::vm_page_size()); + assert(unallocated_start <= (HeapWord*) chunk_at_end->end(), + "Inconsistent chunk at end of space"); + size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes); + size_t word_size_before = heap_word_size(_virtual_space.committed_size()); + + // Shrink the underlying space + _virtual_space.shrink_by(bytes); + if (PrintGCDetails && Verbose) { + gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:" + " desired_bytes " SIZE_FORMAT + " shrinkable_size_in_bytes " SIZE_FORMAT + " aligned_shrinkable_size_in_bytes " SIZE_FORMAT + " bytes " SIZE_FORMAT, + desired_bytes, shrinkable_size_in_bytes, + aligned_shrinkable_size_in_bytes, bytes); + gclog_or_tty->print_cr(" old_end " SIZE_FORMAT + " unallocated_start " SIZE_FORMAT, + old_end, unallocated_start); + } + + // If the space did shrink (shrinking is not guaranteed), + // shrink the chunk at the end by the appropriate amount. + if (((HeapWord*)_virtual_space.high()) < old_end) { + size_t new_word_size = + heap_word_size(_virtual_space.committed_size()); + + // Have to remove the chunk from the dictionary because it is changing + // size and might be someplace elsewhere in the dictionary. + + // Get the chunk at end, shrink it, and put it + // back. + _cmsSpace->removeChunkFromDictionary(chunk_at_end); + size_t word_size_change = word_size_before - new_word_size; + size_t chunk_at_end_old_size = chunk_at_end->size(); + assert(chunk_at_end_old_size >= word_size_change, + "Shrink is too large"); + chunk_at_end->set_size(chunk_at_end_old_size - + word_size_change); + _cmsSpace->freed((HeapWord*) chunk_at_end->end(), + word_size_change); + + _cmsSpace->returnChunkToDictionary(chunk_at_end); + + MemRegion mr(_cmsSpace->bottom(), new_word_size); + _bts->resize(new_word_size); // resize the block offset shared array + Universe::heap()->barrier_set()->resize_covered_region(mr); + _cmsSpace->assert_locked(); + _cmsSpace->set_end((HeapWord*)_virtual_space.high()); + + NOT_PRODUCT(_cmsSpace->dictionary()->verify()); + + // update the space and generation capacity counters + if (UsePerfData) { + _space_counters->update_capacity(); + _gen_counters->update_all(); + } + + if (Verbose && PrintGCDetails) { + size_t new_mem_size = _virtual_space.committed_size(); + size_t old_mem_size = new_mem_size + bytes; + gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K", + name(), old_mem_size/K, bytes/K, new_mem_size/K); + } + } + + assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(), + "Inconsistency at end of space"); + assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(), + "Shrinking is inconsistent"); + return; + } +} +// 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() { + + switch (phase) { + case CMSCollector::InitialMarking: + initialize(true /* fullGC */ , + cause /* cause of the GC */, + true /* recordGCBeginTime */, + true /* recordPreGCUsage */, + false /* recordPeakUsage */, + false /* recordPostGCusage */, + true /* recordAccumulatedGCTime */, + false /* recordGCEndTime */, + false /* countCollection */ ); + break; + + case CMSCollector::FinalMarking: + initialize(true /* fullGC */ , + cause /* cause of the GC */, + false /* recordGCBeginTime */, + false /* recordPreGCUsage */, + false /* recordPeakUsage */, + false /* recordPostGCusage */, + true /* recordAccumulatedGCTime */, + false /* recordGCEndTime */, + false /* countCollection */ ); + break; + + case CMSCollector::Sweeping: + initialize(true /* fullGC */ , + cause /* cause of the GC */, + false /* recordGCBeginTime */, + false /* recordPreGCUsage */, + true /* recordPeakUsage */, + true /* recordPostGCusage */, + false /* recordAccumulatedGCTime */, + true /* recordGCEndTime */, + true /* countCollection */ ); + break; + + default: + ShouldNotReachHere(); + } +}