Mercurial > hg > graal-jvmci-8
diff src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp @ 0:a61af66fc99e jdk7-b24
Initial load
author | duke |
---|---|
date | Sat, 01 Dec 2007 00:00:00 +0000 |
parents | |
children | 2faf283ce688 |
line wrap: on
line diff
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp Sat Dec 01 00:00:00 2007 +0000 @@ -0,0 +1,8787 @@ +/* + * Copyright 2001-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, + * CA 95054 USA or visit www.sun.com if you need additional information or + * have any questions. + * + */ + +# include "incls/_precompiled.incl" +# include "incls/_concurrentMarkSweepGeneration.cpp.incl" + +// statics +CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL; +bool CMSCollector::_full_gc_requested = false; + +////////////////////////////////////////////////////////////////// +// 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)(oopDesc::header_size()))), + _debug_collection_type(Concurrent_collection_type) +{ + 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(junk->prev_addr() == (void*)(oop(junk)->klass_addr()), + "Offset of FreeChunk::_prev within FreeChunk must match" + " that of OopDesc::_klass within OopDesc"); + ) + if (ParallelGCThreads > 0) { + typedef CMSParGCThreadState* CMSParGCThreadStatePtr; + _par_gc_thread_states = + NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads); + 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 >= oopDesc::header_size(), "just checking"); + assert(_dilatation_factor >= 1.0, "from previous assert"); +} + +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 = ReferenceProcessor::create_ref_processor( + _span, // span + _cmsGen->refs_discovery_is_atomic(), // atomic_discovery + _cmsGen->refs_discovery_is_mt(), // mt_discovery + &_is_alive_closure, + ParallelGCThreads, + ParallelRefProcEnabled); + // Initialize the _ref_processor field of CMSGen + _cmsGen->set_ref_processor(_ref_processor); + + // Allocate a dummy ref processor for perm gen. + ReferenceProcessor* rp2 = new ReferenceProcessor(); + if (rp2 == NULL) { + vm_exit_during_initialization("Could not allocate ReferenceProcessor object"); + } + _permGen->set_ref_processor(rp2); + } +} + +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; +} + +// 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 = gch->get_gen(0)->capacity(); + if (HandlePromotionFailure) { + expected_promotion = MIN2( + (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average(), + expected_promotion); + } + 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; + cms_free_dbl = cms_free_dbl * (100.0 - CMSIncrementalSafetyFactor) / 100.0; + + 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 (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, + ConcurrentMarkSweepGeneration* permGen, + CardTableRS* ct, + ConcurrentMarkSweepPolicy* cp): + _cmsGen(cmsGen), + _permGen(permGen), + _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"), + _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"), + _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize), + -1 /* lock-free */, "No_lock" /* dummy */), + _modUnionClosure(&_modUnionTable), + _modUnionClosurePar(&_modUnionTable), + _is_alive_closure(&_markBitMap), + _restart_addr(NULL), + _overflow_list(NULL), + _preserved_oop_stack(NULL), + _preserved_mark_stack(NULL), + _stats(cmsGen), + _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_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), + _unload_classes(false), + _unloaded_classes_last_cycle(false), + _sweep_estimate(CMS_SweepWeight, CMS_SweepPadding) +{ + 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. + + // First check that _permGen is adjacent to _cmsGen and above it. + assert( _cmsGen->reserved().word_size() > 0 + && _permGen->reserved().word_size() > 0, + "generations should not be of zero size"); + assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(), + "_cmsGen and _permGen should not overlap"); + assert(_cmsGen->reserved().end() == _permGen->reserved().start(), + "_cmsGen->end() different from _permGen->start()"); + + // For use by dirty card to oop closures. + _cmsGen->cmsSpace()->set_collector(this); + _permGen->cmsSpace()->set_collector(this); + + // Adjust my span to cover old (cms) gen and perm gen + _span = _cmsGen->reserved()._union(_permGen->reserved()); + // Initialize the span of is_alive_closure + _is_alive_closure.set_span(_span); + + // 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(CMSMarkStackSize)) { + warning("Failed to allocate CMS Marking Stack"); + return; + } + if (!_revisitStack.allocate(CMSRevisitStackSize)) { + warning("Failed to allocate CMS Revisit Stack"); + return; + } + + // Support for multi-threaded concurrent phases + if (ParallelGCThreads > 0 && CMSConcurrentMTEnabled) { + if (FLAG_IS_DEFAULT(ParallelCMSThreads)) { + // just for now + FLAG_SET_DEFAULT(ParallelCMSThreads, (ParallelGCThreads + 3)/4); + } + if (ParallelCMSThreads > 1) { + _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads", + ParallelCMSThreads, true); + if (_conc_workers == NULL) { + warning("GC/CMS: _conc_workers allocation failure: " + "forcing -CMSConcurrentMTEnabled"); + CMSConcurrentMTEnabled = false; + } + } else { + CMSConcurrentMTEnabled = false; + } + } + if (!CMSConcurrentMTEnabled) { + ParallelCMSThreads = 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) == (ParallelCMSThreads > 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, ParallelCMSThreads); + + 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); + if (_hash_seed == NULL) { + warning("_hash_seed array allocation failure"); + return; + } + + // XXX use a global constant instead of 64! + typedef struct OopTaskQueuePadded { + OopTaskQueue work_queue; + char pad[64 - sizeof(OopTaskQueue)]; // prevent false sharing + } OopTaskQueuePadded; + + for (i = 0; i < num_queues; i++) { + OopTaskQueuePadded *q_padded = new OopTaskQueuePadded(); + if (q_padded == NULL) { + warning("work_queue allocation failure."); + return; + } + _task_queues->register_queue(i, &q_padded->work_queue); + } + for (i = 0; i < num_queues; i++) { + _task_queues->queue(i)->initialize(); + _hash_seed[i] = 17; // copied from ParNew + } + } + } + + // "initiatingOccupancy" is the occupancy ratio at which we trigger + // a new collection cycle. Unless explicitly specified via + // CMSTriggerRatio, it is calculated by: + // Let "f" be MinHeapFreeRatio in + // + // intiatingOccupancy = 100-f + + // f * (CMSTriggerRatio/100) + // 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. + if (CMSInitiatingOccupancyFraction > 0) { + _initiatingOccupancy = (double)CMSInitiatingOccupancyFraction / 100.0; + } else { + _initiatingOccupancy = ((100 - MinHeapFreeRatio) + + (double)(CMSTriggerRatio * + MinHeapFreeRatio) / 100.0) + / 100.0; + } + // Clip CMSBootstrapOccupancy between 0 and 100. + _bootstrap_occupancy = ((double)MIN2((intx)100, MAX2((intx)0, 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); + 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) { + size_t max_plab_samples = MaxNewSize/((SurvivorRatio+2)*MinTLABSize); + _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads); + _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples); + _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads); + 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); + _survivor_plab_array = NULL; + } + if (_survivor_chunk_array != NULL) { + FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array); + _survivor_chunk_array = NULL; + } + if (_cursor != NULL) { + FREE_C_HEAP_ARRAY(size_t, _cursor); + _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); + 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()); + } + FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array); + FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array); + _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"); + + // Choose what strong roots should be scanned depending on verification options + // and perm gen collection mode. + if (!CMSClassUnloadingEnabled) { + // If class unloading is disabled we want to include all classes into the root set. + add_root_scanning_option(SharedHeap::SO_AllClasses); + } else { + add_root_scanning_option(SharedHeap::SO_SystemClasses); + } + + NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;) + _gc_counters = new CollectorCounters("CMS", 1); + _completed_initialization = true; + _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, + bool younger_handles_promotion_failure) const { + + // This is the most conservative test. Full promotion is + // guaranteed if this is used. The multiplicative factor is to + // account for the worst case "dilatation". + double adjusted_max_promo_bytes = _dilatation_factor * max_promotion_in_bytes; + if (adjusted_max_promo_bytes > (double)max_uintx) { // larger than size_t + adjusted_max_promo_bytes = (double)max_uintx; + } + bool result = (max_contiguous_available() >= (size_t)adjusted_max_promo_bytes); + + if (younger_handles_promotion_failure && !result) { + // Full promotion is not guaranteed because fragmentation + // of the cms generation can prevent the full promotion. + result = (max_available() >= (size_t)adjusted_max_promo_bytes); + + if (!result) { + // With promotion failure handling the test for the ability + // to support the promotion does not have to be guaranteed. + // Use an average of the amount promoted. + result = max_available() >= (size_t) + gc_stats()->avg_promoted()->padded_average(); + if (PrintGC && Verbose && result) { + gclog_or_tty->print_cr( + "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe" + " max_available: " SIZE_FORMAT + " avg_promoted: " SIZE_FORMAT, + max_available(), (size_t) + gc_stats()->avg_promoted()->padded_average()); + } + } else { + if (PrintGC && Verbose) { + gclog_or_tty->print_cr( + "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe" + " max_available: " SIZE_FORMAT + " adj_max_promo_bytes: " SIZE_FORMAT, + max_available(), (size_t)adjusted_max_promo_bytes); + } + } + } else { + if (PrintGC && Verbose) { + gclog_or_tty->print_cr( + "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe" + " contiguous_available: " SIZE_FORMAT + " adj_max_promo_bytes: " SIZE_FORMAT, + max_contiguous_available(), (size_t)adjusted_max_promo_bytes); + } + } + return result; +} + +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 (ParallelGCThreads > 0) { + 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; + } + + size_t expand_bytes = 0; + 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"); + expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes); + } + if (expand_bytes > 0) { + 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()); + } + } +} + +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) { + 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) { + 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] + // 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 sweeper can skip over it + // if it's uninitialized when the sweeper reaches it. + _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() == 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 sweeper gets to look at it. + 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 "%%) ", + _icms_start_limit, _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 "%%)", + top, _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 "%%)", + top, 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, oop* ref) { + 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, ref); + 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, ref); + } + 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); +} + +// 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"); + HeapWord* obj_ptr = ps->lab.alloc(word_sz); + if (obj_ptr == NULL) { + obj_ptr = expand_and_par_lab_allocate(ps, word_sz); + if (obj_ptr == NULL) { + return NULL; + } + } + oop obj = oop(obj_ptr); + assert(obj->klass() == NULL, "Object should be uninitialized here."); + // Otherwise, copy the object. Here we must be careful to insert the + // klass pointer last, since this marks the block as an allocated object. + HeapWord* old_ptr = (HeapWord*)old; + 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()); + } + // Restore the mark word copied above. + obj->set_mark(m); + // 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()); + } + // Finally, install the klass pointer. + obj->set_klass(old->klass()); + + assert(old->is_oop(), "Will dereference klass ptr below"); + collector()->promoted(true, // parallel + obj_ptr, old->is_objArray(), word_sz); + + NOT_PRODUCT( + Atomic::inc(&_numObjectsPromoted); + Atomic::add((jint)CompactibleFreeListSpace::adjustObjectSize(obj->size()), + &_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(); +#if CFLS_LAB_REFILL_STATS + if (thread_num == 0) { + _cmsSpace->print_par_alloc_stats(); + } +#endif +} + +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); +} + +// XXXPERM +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) { + assert(ExplicitGCInvokesConcurrent, "Unexpected state"); + if (Verbose && PrintGCDetails) { + gclog_or_tty->print_cr("CMSCollector: collect because of explicit " + " gc request"); + } + 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->print_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", initiatingOccupancy()); + } + // ------------------------------------------------------------------ + + // 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 either the perm gen or + // 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. + if (_cmsGen->shouldConcurrentCollect(initiatingOccupancy())) { + if (Verbose && PrintGCDetails) { + gclog_or_tty->print_cr("CMS old gen initiated"); + } + return true; + } + + if (cms_should_unload_classes() && + _permGen->shouldConcurrentCollect(initiatingOccupancy())) { + if (Verbose && PrintGCDetails) { + gclog_or_tty->print_cr("CMS perm gen initiated"); + } + return true; + } + + return false; +} + +// Clear _expansion_cause fields of constituent generations +void CMSCollector::clear_expansion_cause() { + _cmsGen->clear_expansion_cause(); + _permGen->clear_expansion_cause(); +} + +bool ConcurrentMarkSweepGeneration::shouldConcurrentCollect( + double initiatingOccupancy) { + // 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 initiating occupancy, or + // . we recently needed to expand and have not since that expansion, + // collected, or + // . we are not using adaptive free lists and linear allocation is + // going to fail, or + // . (for old gen) incremental collection has already failed or + // may soon fail in the near future as we may not be able to absorb + // promotions. + assert_lock_strong(freelistLock()); + + if (occupancy() > initiatingOccupancy) { + if (PrintGCDetails && Verbose) { + gclog_or_tty->print(" %s: collect because of occupancy %f / %f ", + short_name(), occupancy(), initiatingOccupancy); + } + 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; + } + 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()) { + if (PrintGCDetails && Verbose) { + gclog_or_tty->print(" %s: collect because incremental collection will fail ", + short_name()); + } + return true; + } + if (!_cmsSpace->adaptive_freelists() && + _cmsSpace->linearAllocationWouldFail()) { + if (PrintGCDetails && Verbose) { + gclog_or_tty->print(" %s: collect because of linAB ", + 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) { + 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; + CGC_lock->notify(); // nudge CMS thread + } +} + + +// 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 (PrintGCDetails && first_state > Idling) { + GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause(); + if (GCCause::is_user_requested_gc(cause) || + GCCause::is_serviceability_requested_gc(cause)) { + gclog_or_tty->print(" (concurrent mode interrupted)"); + } else { + gclog_or_tty->print(" (concurrent mode failure)"); + } + } + + 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(); + + do_compaction_work(clear_all_soft_refs); + + // Has the GC time limit been exceeded? + check_gc_time_limit(); + + } 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; +} + +void CMSCollector::check_gc_time_limit() { + + // Ignore explicit GC's. Exiting here does not set the flag and + // does not reset the count. Updating of the averages for system + // GC's is still controlled by UseAdaptiveSizePolicyWithSystemGC. + GCCause::Cause gc_cause = GenCollectedHeap::heap()->gc_cause(); + if (GCCause::is_user_requested_gc(gc_cause) || + GCCause::is_serviceability_requested_gc(gc_cause)) { + return; + } + + // Calculate the fraction of the CMS generation was freed during + // the last collection. + // Only consider the STW compacting cost for now. + // + // Note that the gc time limit test only works for the collections + // of the young gen + tenured gen and not for collections of the + // permanent gen. That is because the calculation of the space + // freed by the collection is the free space in the young gen + + // tenured gen. + + double fraction_free = + ((double)_cmsGen->free())/((double)_cmsGen->max_capacity()); + if ((100.0 * size_policy()->compacting_gc_cost()) > + ((double) GCTimeLimit) && + ((fraction_free * 100) < GCHeapFreeLimit)) { + size_policy()->inc_gc_time_limit_count(); + if (UseGCOverheadLimit && + (size_policy()->gc_time_limit_count() > + AdaptiveSizePolicyGCTimeLimitThreshold)) { + size_policy()->set_gc_time_limit_exceeded(true); + // Avoid consecutive OOM due to the gc time limit by resetting + // the counter. + size_policy()->reset_gc_time_limit_count(); + if (PrintGCDetails) { + gclog_or_tty->print_cr(" GC is exceeding overhead limit " + "of %d%%", GCTimeLimit); + } + } else { + if (PrintGCDetails) { + gclog_or_tty->print_cr(" GC would exceed overhead limit " + "of %d%%", GCTimeLimit); + } + } + } else { + size_policy()->reset_gc_time_limit_count(); + } +} + +// Resize the perm generation and 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); + _permGen->compute_new_size(); + _cmsGen->compute_new_size(); +} + +// 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()) { + 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()); + *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(); + TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty); + 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 x(ref_processor(), new_span); + + // Temporarily, clear the "is_alive_non_header" field of the + // reference processor. + ReferenceProcessorIsAliveMutator y(ref_processor(), NULL); + + // Temporarily make reference _processing_ single threaded (non-MT). + ReferenceProcessorMTProcMutator z(ref_processor(), false); + + // Temporarily make refs discovery atomic + ReferenceProcessorAtomicMutator w(ref_processor(), true); + + ref_processor()->set_enqueuing_is_done(false); + ref_processor()->enable_discovery(); + // 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(); + + // 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(_sweep_timer.is_active(), "We should never see the timer inactive"); + _sweep_timer.stop(); + // Note that we do not use this sample to update the _sweep_estimate. + _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()), + _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()->totalChunkSize( + 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(); + + if (verifying() && !cms_should_unload_classes()) { + perm_gen_verify_bit_map()->clear_all(); + } + + // 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(sweepCount() /* fake */); + // Restart the "sweep timer" for next epoch. + _sweep_timer.reset(); + _sweep_timer.start(); + + // Sample collection pause time and reset for collection interval. + if (UseAdaptiveSizePolicy) { + size_policy()->msc_collection_end(gch->gc_cause()); + } + + // 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; + } + if (PrintGCDetails && + (_collectorState > Idling || + !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) { + gclog_or_tty->print(" (concurrent mode failure)"); + } + collect_in_foreground(clear_all_soft_refs); + + // For a mark-sweep, compute_new_size() will be called + // in the heap's do_collection() method. +} + + +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(); + _permGen->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(); + _permGen->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()); + assert_lock_strong(_permGen->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) { + 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); + 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; + // Reset the expansion cause, now that we are about to begin + // a new cycle. + clear_expansion_cause(); + } + _unloaded_classes_last_cycle = cms_should_unload_classes(); // ... from last cycle + // This controls class unloading in response to an explicit gc request. + // If ExplicitGCInvokesConcurrentAndUnloadsClasses is set, then + // we will unload classes even if CMSClassUnloadingEnabled is not set. + // See CR 6541037 and related CRs. + _unload_classes = _full_gc_requested // ... for this cycle + && ExplicitGCInvokesConcurrentAndUnloadsClasses; + _full_gc_requested = false; // acks all outstanding full gc requests + // 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(); + _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"); + 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::collect_in_foreground(bool clear_all_soft_refs) { + 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(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose, + true, gclog_or_tty);) + 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(true); + } + + 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: + 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) { + gclog_or_tty->print("Verify before initial mark: "); + Universe::verify(true); + } + { + bool res = markFromRoots(false); + assert(res && _collectorState == FinalMarking, "Collector state should " + "have changed"); + break; + } + case FinalMarking: + if (VerifyDuringGC && + GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { + gclog_or_tty->print("Verify before re-mark: "); + Universe::verify(true); + } + 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) { + gclog_or_tty->print("Verify before sweep: "); + Universe::verify(true); + } + 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) { + gclog_or_tty->print("Verify before reset: "); + Universe::verify(true); + } + 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(true); + } + 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 each CMSGen and PermGen that + // 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" (including PermGen if any) 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 and PermGen that we are responsible for. + + 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 registerClosure = _collectorState >= Marking + && _collectorState < Sweeping; + ModUnionClosure* muc = ParallelGCThreads > 0 ? &_modUnionClosurePar + : &_modUnionClosure; + _cmsGen->gc_prologue_work(full, registerClosure, muc); + _permGen->gc_prologue_work(full, registerClosure, muc); + + if (!full) { + stats().record_gc0_begin(); + } +} + +void ConcurrentMarkSweepGeneration::gc_prologue(bool full) { + // 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()); + + _cmsGen->gc_epilogue_work(full); + _permGen->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(); + size_t perm_used = _permGen->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); + _permGen->update_counters(perm_used); + + if (CMSIncrementalMode) { + icms_update_allocation_limits(); + } + + bitMapLock()->unlock(); + releaseFreelistLocks(); + + _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 (ParallelGCThreads > 0) { + for (uint i = 0; i < ParallelGCThreads; i++) { + _par_gc_thread_states[i]->promo.stopTrackingPromotions(); + } + } +} + +void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) { + assert(!incremental_collection_failed(), "Should have been cleared"); + cmsSpace()->setPreconsumptionDirtyCardClosure(NULL); + cmsSpace()->gc_epilogue(); + // Print stat counters + NOT_PRODUCT( + assert(_numObjectsAllocated == 0, "check"); + assert(_numWordsAllocated == 0, "check"); + 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; + } +} + +//////////////////////////////////////////////////////// +// 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) {} + + void do_bit(size_t offset) { + HeapWord* addr = _marks->offsetToHeapWord(offset); + if (!_marks->isMarked(addr)) { + oop(addr)->print(); + gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr); + _failed = true; + } + } + + bool failed() { return _failed; } +}; + +bool CMSCollector::verify_after_remark() { + 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"); + assert(overflow_list_is_empty(), "overflow list should be 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); + } + gclog_or_tty->print(" done] "); + return true; +} + +void CMSCollector::verify_after_remark_work_1() { + ResourceMark rm; + HandleMark hm; + GenCollectedHeap* gch = GenCollectedHeap::heap(); + + // Mark from roots one level into CMS + MarkRefsIntoClosure notOlder(_span, verification_mark_bm(), true /* nmethods */); + gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. + + gch->gen_process_strong_roots(_cmsGen->level(), + true, // younger gens are roots + true, // collecting perm gen + SharedHeap::ScanningOption(roots_scanning_options()), + NULL, ¬Older); + + // Now mark from the roots + assert(_revisitStack.isEmpty(), "Should be empty"); + MarkFromRootsClosure markFromRootsClosure(this, _span, + verification_mark_bm(), verification_mark_stack(), &_revisitStack, + 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(); + // Should reset the revisit stack above, since no class tree + // surgery is forthcoming. + _revisitStack.reset(); // throwing away all contents + + // 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(); + fatal(" ... aborting"); + } +} + +void CMSCollector::verify_after_remark_work_2() { + ResourceMark rm; + HandleMark hm; + GenCollectedHeap* gch = GenCollectedHeap::heap(); + + // Mark from roots one level into CMS + MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(), + markBitMap(), true /* nmethods */); + gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. + gch->gen_process_strong_roots(_cmsGen->level(), + true, // younger gens are roots + true, // collecting perm gen + SharedHeap::ScanningOption(roots_scanning_options()), + NULL, ¬Older); + + // Now mark from the roots + assert(_revisitStack.isEmpty(), "Should be empty"); + 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(); + // Should reset the revisit stack above, since no class tree + // surgery is forthcoming. + _revisitStack.reset(); // throwing away all contents + + // 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::object_iterate_since_last_GC(ObjectClosure* blk) +{ + // Not currently implemented; need to do the following. -- ysr. + // dld -- I think that is used for some sort of allocation profiler. So it + // really means the objects allocated by the mutator since the last + // GC. We could potentially implement this cheaply by recording only + // the direct allocations in a side data structure. + // + // I think we probably ought not to be required to support these + // iterations at any arbitrary point; I think there ought to be some + // call to enable/disable allocation profiling in a generation/space, + // and the iterator ought to return the objects allocated in the + // gen/space since the enable call, or the last iterator call (which + // will probably be at a GC.) That way, for gens like CM&S that would + // require some extra data structure to support this, we only pay the + // cost when it's in use... + cmsSpace()->object_iterate_since_last_GC(blk); +} + +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, OopClosure* 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(OopClosure* 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::pre_adjust_pointers() { +} + +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(bool allow_dirty /* ignored */) { + // 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(false /* ignored */); + } else { + MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag); + cmsSpace()->verify(false /* ignored */); + } +} + +void CMSCollector::verify(bool allow_dirty /* ignored */) { + _cmsGen->verify(allow_dirty); + _permGen->verify(allow_dirty); +} + +#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 + +void CMSCollector::setup_cms_unloading_and_verification_state() { + const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC + || VerifyBeforeExit; + const int rso = SharedHeap::SO_Symbols | SharedHeap::SO_Strings + | SharedHeap::SO_CodeCache; + + if (cms_should_unload_classes()) { // Should unload classes this cycle + remove_root_scanning_option(rso); // Shrink the root set appropriately + set_verifying(should_verify); // Set verification state for this cycle + return; // Nothing else needs to be done at this time + } + + // Not unloading classes this cycle + assert(!cms_should_unload_classes(), "Inconsitency!"); + if ((!verifying() || cms_unloaded_classes_last_cycle()) && should_verify) { + // We were not verifying, or we _were_ unloading classes in the last cycle, + // AND some verification options are enabled this cycle; in this case, + // we must make sure that the deadness map is allocated if not already so, + // and cleared (if already allocated previously -- + // CMSBitMap::sizeInBits() is used to determine if it's allocated). + if (perm_gen_verify_bit_map()->sizeInBits() == 0) { + if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) { + warning("Failed to allocate permanent generation verification CMS Bit Map;\n" + "permanent generation verification disabled"); + return; // Note that we leave verification disabled, so we'll retry this + // allocation next cycle. We _could_ remember this failure + // and skip further attempts and permanently disable verification + // attempts if that is considered more desirable. + } + assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()), + "_perm_gen_ver_bit_map inconsistency?"); + } else { + perm_gen_verify_bit_map()->clear_all(); + } + // 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); + } else { + assert(_permGen->cmsSpace()->is_in_reserved(addr), + "Inconsistent _span?"); + return _permGen->cmsSpace()->block_start(p); + } + } + return NULL; +} +#endif + +HeapWord* +ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size, + bool tlab, + bool parallel) { + 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); + } + size_t adj_word_sz = CompactibleFreeListSpace::adjustObjectSize(word_size); + if (parallel) { + return cmsSpace()->par_allocate(adj_word_sz); + } else { + return cmsSpace()->allocate(adj_word_sz); + } +} + +// 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... +void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes, + CMSExpansionCause::Cause cause) +{ + assert_locked_or_safepoint(Heap_lock); + + size_t aligned_bytes = ReservedSpace::page_align_size_up(bytes); + size_t aligned_expand_bytes = ReservedSpace::page_align_size_up(expand_bytes); + bool success = false; + if (aligned_expand_bytes > aligned_bytes) { + success = grow_by(aligned_expand_bytes); + } + if (!success) { + success = grow_by(aligned_bytes); + } + if (!success) { + size_t remaining_bytes = _virtual_space.uncommitted_size(); + if (remaining_bytes > 0) { + success = grow_by(remaining_bytes); + } + } + if (GC_locker::is_active()) { + if (PrintGC && Verbose) { + gclog_or_tty->print_cr("Garbage collection disabled, expanded heap instead"); + } + } + // 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(size_t bytes) { + assert_locked_or_safepoint(Heap_lock); + size_t size = ReservedSpace::page_align_size_down(bytes); + if (size > 0) { + 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) { + HeapWord* old_end = _cmsSpace->end(); + 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(); + _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 %ldK by %ldK to %ldK", + 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_by(size_t bytes) { + assert_locked_or_safepoint(Heap_lock); + assert_lock_strong(freelistLock()); + // XXX Fix when compaction is implemented. + 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 && PrintGCTimeStamps) { + gclog_or_tty->date_stamp(PrintGCDateStamps); + gclog_or_tty->stamp(); + 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); + if (PrintGCTimeStamps) { + gclog_or_tty->stamp(); + gclog_or_tty->print(": "); + } + 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->print_cr(""); + } + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase, + _collector->yields()); + } + } +} + +// CMS work + +// 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(); + 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); + rp->verify_no_references_recorded(); + rp->enable_discovery(); // enable ("weak") refs discovery + _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); + rp->enable_discovery(); // now enable ("weak") refs discovery + _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(TraceTime t("\ncheckpointRootsInitialWork", + PrintGCDetails && Verbose, true, gclog_or_tty);) + 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; hence the last argument to the constrcutor below. + MarkRefsIntoClosure notOlder(_span, &_markBitMap, !asynch /* nmethods */); + 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); + + { + COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) + gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. + gch->gen_process_strong_roots(_cmsGen->level(), + true, // younger gens are roots + true, // collecting perm gen + SharedHeap::ScanningOption(roots_scanning_options()), + NULL, ¬Older); + } + + // 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."); + + // Temporarily disabled, since pre/post-consumption closures don't + // care about precleaned cards + #if 0 + { + MemRegion mr = MemRegion((HeapWord*)_virtual_space.low(), + (HeapWord*)_virtual_space.high()); + _ct->ct_bs()->preclean_dirty_cards(mr); + } + #endif + + // 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()); + + // Clear the revisit stack, just in case there are any + // obsolete contents from a short-circuited previous CMS cycle. + _revisitStack.reset(); + verify_work_stacks_empty(); + verify_overflow_empty(); + assert(_revisitStack.isEmpty(), "tabula rasa"); + + bool result = false; + if (CMSConcurrentMTEnabled && ParallelCMSThreads > 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; + bool _yield; + protected: + virtual void yield(); + public: + // "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, bool yield) : + ParallelTaskTerminator(n_threads, queue_set), + _collector(collector), + _yield(yield) { } + + void set_task(CMSConcMarkingTask* task) { + _task = task; + } +}; + +// MT Concurrent Marking Task +class CMSConcMarkingTask: public YieldingFlexibleGangTask { + CMSCollector* _collector; + YieldingFlexibleWorkGang* _workers; // the whole gang + int _n_workers; // requested/desired # workers + bool _asynch; + bool _result; + CompactibleFreeListSpace* _cms_space; + CompactibleFreeListSpace* _perm_space; + HeapWord* _global_finger; + + // Exposed here for yielding support + Mutex* const _bit_map_lock; + + // The per thread work queues, available here for stealing + OopTaskQueueSet* _task_queues; + CMSConcMarkingTerminator _term; + + public: + CMSConcMarkingTask(CMSCollector* collector, + CompactibleFreeListSpace* cms_space, + CompactibleFreeListSpace* perm_space, + bool asynch, int n_workers, + YieldingFlexibleWorkGang* workers, + OopTaskQueueSet* task_queues): + YieldingFlexibleGangTask("Concurrent marking done multi-threaded"), + _collector(collector), + _cms_space(cms_space), + _perm_space(perm_space), + _asynch(asynch), _n_workers(n_workers), _result(true), + _workers(workers), _task_queues(task_queues), + _term(n_workers, task_queues, _collector, asynch), + _bit_map_lock(collector->bitMapLock()) + { + assert(n_workers <= workers->total_workers(), + "Else termination won't work correctly today"); // XXX FIX ME! + _requested_size = n_workers; + _term.set_task(this); + assert(_cms_space->bottom() < _perm_space->bottom(), + "Finger incorrectly initialized below"); + _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; } + + void work(int i); + + virtual void coordinator_yield(); // stuff done by coordinator + bool result() { return _result; } + + void reset(HeapWord* 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); +}; + +void CMSConcMarkingTerminator::yield() { + if (ConcurrentMarkSweepThread::should_yield() && + !_collector->foregroundGCIsActive() && + _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(int i) { + 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(i)->size() == 0, "Expected to be empty"); + // Scan the bitmap covering _cms_space, tracing through grey objects. + _timer.start(); + do_scan_and_mark(i, _cms_space); + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec", + i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers + } + + // ... do the same for the _perm_space + _timer.reset(); + _timer.start(); + do_scan_and_mark(i, _perm_space); + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec", + i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers + } + + // ... do work stealing + _timer.reset(); + _timer.start(); + do_work_steal(i); + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec", + i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers + } + assert(_collector->_markStack.isEmpty(), "Should have been emptied"); + assert(work_queue(i)->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. + assert(_global_finger > _cms_space->end() && + _global_finger >= _perm_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()/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, "Uninitializd use?"); + int nth_task = 0; + + HeapWord* start = sp->bottom(); + 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(start + nth_task*chunk_size, + 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 + // 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. + HeapWord* 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, + &_collector->_revisitStack, + _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 OopClosure { + CMSCollector* _collector; + MemRegion _span; + CMSBitMap* _bit_map; + CMSMarkStack* _overflow_stack; + CMSMarkStack* _revisit_stack; // XXXXXX Check proper use + OopTaskQueue* _work_queue; + + public: + Par_ConcMarkingClosure(CMSCollector* collector, OopTaskQueue* work_queue, + CMSBitMap* bit_map, CMSMarkStack* overflow_stack): + _collector(collector), + _span(_collector->_span), + _work_queue(work_queue), + _bit_map(bit_map), + _overflow_stack(overflow_stack) { } // need to initialize revisit stack etc. + + void do_oop(oop* p); + void trim_queue(size_t max); + void handle_stack_overflow(HeapWord* lost); +}; + +// Grey object rescan during work stealing phase -- +// the salient assumption here is that stolen oops must +// always be initialized, so we do not need to check for +// uninitialized objects before scanning here. +void Par_ConcMarkingClosure::do_oop(oop* p) { + oop this_oop = *p; + assert(this_oop->is_oop_or_null(), + "expected an oop or NULL"); + HeapWord* addr = (HeapWord*)this_oop; + // 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(this_oop) || _overflow_stack->par_push(this_oop))) { + // 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 + } +} + +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"); + assert(new_oop->is_parsable(), "Should be parsable"); + new_oop->oop_iterate(this); // do_oop() above + } + } +} + +// 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 expansion 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, 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()) { + assert(work_q->size() == 0, "Impossible!"); + break; + } + } +} + +// 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(ParallelCMSThreads > 0 && conc_workers() != NULL, "precondition"); + // In the future this would be determined ergonomically, based + // on #cpu's, # active mutator threads (and load), and mutation rate. + int num_workers = ParallelCMSThreads; + + CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); + CompactibleFreeListSpace* perm_space = _permGen->cmsSpace(); + + CMSConcMarkingTask tsk(this, cms_space, perm_space, + asynch, num_workers /* number requested XXX */, + 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); + perm_space->initialize_sequential_subtasks_for_marking(num_workers); + + // Refs discovery is already non-atomic. + assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic"); + // Mutate the Refs discovery so it is MT during the + // multi-threaded marking phase. + ReferenceProcessorMTMutator mt(ref_processor(), num_workers > 1); + + 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 + // occured; 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); + perm_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; + + MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap, + &_markStack, &_revisitStack, 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 + // occured; 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) { + _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; + } + if (_eden_chunk_array) { + 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; + // Do one pass of scrubbing the discovered reference lists + // to remove any reference objects with strongly-reachable + // referents. + if (clean_refs) { + ReferenceProcessor* rp = ref_processor(); + CMSPrecleanRefsYieldClosure yield_cl(this); + assert(rp->span().equals(_span), "Spans should be equal"); + CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap, + &_markStack); + CMSDrainMarkingStackClosure complete_trace(this, + _span, &_markBitMap, &_markStack, + &keep_alive); + + // 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. + rp->preclean_discovered_references( + rp->is_alive_non_header(), &keep_alive, &complete_trace, + &yield_cl); + } + + 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, &_revisitStack, + 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, &_revisitStack, 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, &_revisitStack, &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 (CMSPermGenPrecleaningEnabled) { + curNumCards += preclean_mod_union_table(_permGen, &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; + } + } + curNumCards = preclean_card_table(_cmsGen, &smoac_cl); + if (CMSPermGenPrecleaningEnabled) { + curNumCards += preclean_card_table(_permGen, &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(); + 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(); + 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((CMSPermGenPrecleaningEnabled && (gen == _permGen)) || + (_collectorState == AbortablePreclean && should_abort_preclean()), + "Unparsable objects should only be in perm gen."); + + stopTimer(); + CMSTokenSyncWithLocks ts(true, bitMapLock()); + startTimer(); + _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_preclean( + MemRegion(nextAddr, endAddr)); + 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) { + // The careful iteration stopped early because it found an + // uninitialized object. Redirty the bits corresponding to the + // partially-scanned or unscanned cards, and start again at the + // next block boundary. + assert(CMSPermGenPrecleaningEnabled || + (_collectorState == AbortablePreclean && should_abort_preclean()), + "Unparsable objects should only be in perm gen."); + _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; +} + +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"); + 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(TraceTime t("Scavenge-Before-Remark", + PrintGCDetails && Verbose, true, gclog_or_tty);) + 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(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);) + + 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 (cms_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(); + + { + 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 && ParallelGCThreads > 0) { + TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty); + do_remark_parallel(); + } else { + TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false, + gclog_or_tty); + 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(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);) + refProcessingWork(asynch, clear_all_soft_refs); + } + verify_work_stacks_empty(); + verify_overflow_empty(); + + if (cms_should_unload_classes()) { + CodeCache::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; + 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")", + _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, + _ser_kac_ovflw); + } + _markStack.expand(); + _ser_pmc_remark_ovflw = 0; + _ser_pmc_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(); + } + + // Change under the freelistLocks. + _collectorState = Sweeping; + // Call isAllClear() under bitMapLock + assert(_modUnionTable.isAllClear(), "Should be clear by end of the" + " final marking"); + if (UseAdaptiveSizePolicy) { + size_policy()->checkpoint_roots_final_end(gch->gc_cause()); + } +} + +// Parallel remark task +class CMSParRemarkTask: public AbstractGangTask { + CMSCollector* _collector; + WorkGang* _workers; + int _n_workers; + CompactibleFreeListSpace* _cms_space; + CompactibleFreeListSpace* _perm_space; + + // The per-thread work queues, available here for stealing. + OopTaskQueueSet* _task_queues; + ParallelTaskTerminator _term; + + public: + CMSParRemarkTask(CMSCollector* collector, + CompactibleFreeListSpace* cms_space, + CompactibleFreeListSpace* perm_space, + int n_workers, WorkGang* workers, + OopTaskQueueSet* task_queues): + AbstractGangTask("Rescan roots and grey objects in parallel"), + _collector(collector), + _cms_space(cms_space), _perm_space(perm_space), + _n_workers(n_workers), + _workers(workers), + _task_queues(task_queues), + _term(workers->total_workers(), task_queues) { } + + OopTaskQueueSet* task_queues() { return _task_queues; } + + OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } + + ParallelTaskTerminator* terminator() { return &_term; } + + void work(int i); + + private: + // Work method in support of parallel rescan ... of young gen spaces + void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl, + ContiguousSpace* space, + HeapWord** chunk_array, size_t chunk_top); + + // ... 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); +}; + +void CMSParRemarkTask::work(int i) { + 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(i), &(_collector->_revisitStack)); + + // 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 -------------- + { + 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(i, &par_mrias_cl, to_space, NULL, 0); + do_young_space_rescan(i, &par_mrias_cl, from_space, sca, sct); + do_young_space_rescan(i, &par_mrias_cl, eden_space, eca, ect); + + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr( + "Finished young gen rescan work in %dth thread: %3.3f sec", + i, _timer.seconds()); + } + } + + // ---------- remaining roots -------------- + _timer.reset(); + _timer.start(); + gch->gen_process_strong_roots(_collector->_cmsGen->level(), + false, // yg was scanned above + true, // collecting perm gen + SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), + NULL, &par_mrias_cl); + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr( + "Finished remaining root rescan work in %dth thread: %3.3f sec", + i, _timer.seconds()); + } + + // ---------- rescan dirty cards ------------ + _timer.reset(); + _timer.start(); + + // Do the rescan tasks for each of the two spaces + // (cms_space and perm_space) in turn. + do_dirty_card_rescan_tasks(_cms_space, i, &par_mrias_cl); + do_dirty_card_rescan_tasks(_perm_space, i, &par_mrias_cl); + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr( + "Finished dirty card rescan work in %dth thread: %3.3f sec", + i, _timer.seconds()); + } + + // ---------- steal work from other threads ... + // ---------- ... and drain overflow list. + _timer.reset(); + _timer.start(); + do_work_steal(i, &par_mrias_cl, _collector->hash_seed(i)); + _timer.stop(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print_cr( + "Finished work stealing in %dth thread: %3.3f sec", + i, _timer.seconds()); + } +} + +void +CMSParRemarkTask::do_young_space_rescan(int i, + Par_MarkRefsIntoAndScanClosure* 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(); + assert(pst->valid(), "Uninitialized use?"); + + int nth_task = 0; + int n_tasks = pst->n_tasks(); + + 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 < (jint)chunk_top) { + assert(nth_task >= 1, "Control point invariant"); + start = chunk_array[nth_task - 1]; + end = chunk_array[nth_task]; + } else { + assert(nth_task == (jint)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 + CMSMarkStack* rs = &(_collector->_revisitStack); // shared + MarkFromDirtyCardsClosure + greyRescanClosure(_collector, full_span, // entire span of interest + sp, bm, work_q, rs, cl); + + SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); + assert(pst->valid(), "Uninitialized use?"); + int 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); + size_t num_from_overflow_list = + MIN2((size_t)work_q->max_elems()/4, + (size_t)ParGCDesiredObjsFromOverflowList); + + while (true) { + // Completely finish any left over work from (an) earlier round(s) + cl->trim_queue(0); + // Now check if there's any work in the overflow list + if (_collector->par_take_from_overflow_list(num_from_overflow_list, + work_q)) { + // 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"); +} + +// 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 rescan. +void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv) { + assert(_survivor_plab_array != NULL, "Error"); + assert(_survivor_chunk_array != NULL, "Error"); + assert(_collectorState == FinalMarking, "Error"); + for (uint j = 0; j < ParallelGCThreads; 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 (uint j = 0; j < ParallelGCThreads; 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 (uint j = 0; j < ParallelGCThreads; 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 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 + { + 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"); + pst->set_par_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()); + } else { + assert(_survivor_chunk_index == 0, "Error"); + } + + // To space + { + SequentialSubTasksDone* pst = dng->to()->par_seq_tasks(); + assert(!pst->valid(), "Clobbering existing data?"); + pst->set_par_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"); + pst->set_par_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(); + WorkGang* workers = gch->workers(); + assert(workers != NULL, "Need parallel worker threads."); + int n_workers = workers->total_workers(); + CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); + CompactibleFreeListSpace* perm_space = _permGen->cmsSpace(); + + CMSParRemarkTask tsk(this, + cms_space, perm_space, + n_workers, workers, task_queues()); + + // Set up for parallel process_strong_roots work. + gch->set_par_threads(n_workers); + gch->change_strong_roots_parity(); + // 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); + perm_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 + ReferenceProcessorMTMutator mt(ref_processor(), true); + workers->run_task(&tsk); + } else { + 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(); + MarkRefsIntoAndScanClosure + mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable, + &_markStack, &_revisitStack, this, + false /* should_yield */, false /* not precleaning */); + MarkFromDirtyCardsClosure + markFromDirtyCardsClosure(this, _span, + NULL, // space is set further below + &_markBitMap, &_markStack, &_revisitStack, + &mrias_cl); + { + TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty); + // Iterate over the dirty cards, marking them precleaned, and + // setting the corresponding bits in the mod union table. + { + ModUnionClosure modUnionClosure(&_modUnionTable); + _ct->ct_bs()->dirty_card_iterate( + _cmsGen->used_region(), + &modUnionClosure); + _ct->ct_bs()->dirty_card_iterate( + _permGen->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()); + } + } + { + // .. and then repeat for dirty cards in perm gen + markFromDirtyCardsClosure.set_space(_permGen->cmsSpace()); + MemRegion ur = _permGen->used_region(); + HeapWord* lb = ur.start(); + HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment); + MemRegion perm_span(lb, ub); + _modUnionTable.dirty_range_iterate_clear(perm_span, + &markFromDirtyCardsClosure); + verify_work_stacks_empty(); + if (PrintCMSStatistics != 0) { + gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ", + markFromDirtyCardsClosure.num_dirty_cards()); + } + } + } + if (VerifyDuringGC && + GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { + HandleMark hm; // Discard invalid handles created during verification + Universe::verify(true); + } + { + TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty); + + verify_work_stacks_empty(); + + gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. + gch->gen_process_strong_roots(_cmsGen->level(), + true, // younger gens as roots + true, // collecting perm gen + SharedHeap::ScanningOption(roots_scanning_options()), + NULL, &mrias_cl); + } + 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 AbstractGangTask { + typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; + CMSCollector* _collector; + CMSBitMap* _mark_bit_map; + MemRegion _span; + OopTaskQueueSet* _task_queues; + ParallelTaskTerminator _term; + ProcessTask& _task; + +public: + CMSRefProcTaskProxy(ProcessTask& task, + CMSCollector* collector, + const MemRegion& span, + CMSBitMap* mark_bit_map, + int total_workers, + OopTaskQueueSet* task_queues): + AbstractGangTask("Process referents by policy in parallel"), + _task(task), + _collector(collector), _span(span), _mark_bit_map(mark_bit_map), + _task_queues(task_queues), + _term(total_workers, task_queues) + { } + + OopTaskQueueSet* task_queues() { return _task_queues; } + + OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } + + ParallelTaskTerminator* terminator() { return &_term; } + + void do_work_steal(int i, + CMSParDrainMarkingStackClosure* drain, + CMSParKeepAliveClosure* keep_alive, + int* seed); + + virtual void work(int i); +}; + +void CMSRefProcTaskProxy::work(int i) { + CMSParKeepAliveClosure par_keep_alive(_collector, _span, + _mark_bit_map, work_queue(i)); + CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span, + _mark_bit_map, work_queue(i)); + CMSIsAliveClosure is_alive_closure(_mark_bit_map); + _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack); + if (_task.marks_oops_alive()) { + do_work_steal(i, &par_drain_stack, &par_keep_alive, + _collector->hash_seed(i)); + } + assert(work_queue(i)->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(int i) + { + _task.work(i); + } +}; + +CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector, + MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue): + _collector(collector), + _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; + size_t num_from_overflow_list = + MIN2((size_t)work_q->max_elems()/4, + (size_t)ParGCDesiredObjsFromOverflowList); + + while (true) { + // Completely finish any left over work from (an) earlier round(s) + drain->trim_queue(0); + // Now check if there's any work in the overflow list + if (_collector->par_take_from_overflow_list(num_from_overflow_list, + work_q)) { + // 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(); + WorkGang* workers = gch->workers(); + assert(workers != NULL, "Need parallel worker threads."); + int n_workers = workers->total_workers(); + CMSRefProcTaskProxy rp_task(task, &_collector, + _collector.ref_processor()->span(), + _collector.markBitMap(), + n_workers, _collector.task_queues()); + workers->run_task(&rp_task); +} + +void CMSRefProcTaskExecutor::execute(EnqueueTask& task) +{ + + GenCollectedHeap* gch = GenCollectedHeap::heap(); + WorkGang* 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; + ReferencePolicy* soft_ref_policy; + + assert(!ref_processor()->enqueuing_is_done(), "Enqueuing should not be complete"); + // Process weak references. + if (clear_all_soft_refs) { + soft_ref_policy = new AlwaysClearPolicy(); + } else { +#ifdef COMPILER2 + soft_ref_policy = new LRUMaxHeapPolicy(); +#else + soft_ref_policy = new LRUCurrentHeapPolicy(); +#endif // COMPILER2 + } + verify_work_stacks_empty(); + + ReferenceProcessor* rp = ref_processor(); + assert(rp->span().equals(_span), "Spans should be equal"); + CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap, + &_markStack); + CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this, + _span, &_markBitMap, &_markStack, + &cmsKeepAliveClosure); + { + TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty); + if (rp->processing_is_mt()) { + CMSRefProcTaskExecutor task_executor(*this); + rp->process_discovered_references(soft_ref_policy, + &_is_alive_closure, + &cmsKeepAliveClosure, + &cmsDrainMarkingStackClosure, + &task_executor); + } else { + rp->process_discovered_references(soft_ref_policy, + &_is_alive_closure, + &cmsKeepAliveClosure, + &cmsDrainMarkingStackClosure, + NULL); + } + verify_work_stacks_empty(); + } + + if (cms_should_unload_classes()) { + { + TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty); + + // Follow SystemDictionary roots and unload classes + bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure); + + // Follow CodeCache roots and unload any methods marked for unloading + CodeCache::do_unloading(&_is_alive_closure, + &cmsKeepAliveClosure, + purged_class); + + cmsDrainMarkingStackClosure.do_void(); + verify_work_stacks_empty(); + + // Update subklass/sibling/implementor links in KlassKlass descendants + assert(!_revisitStack.isEmpty(), "revisit stack should not be empty"); + oop k; + while ((k = _revisitStack.pop()) != NULL) { + ((Klass*)(oopDesc*)k)->follow_weak_klass_links( + &_is_alive_closure, + &cmsKeepAliveClosure); + } + assert(!ClassUnloading || + (_markStack.isEmpty() && overflow_list_is_empty()), + "Should not have found new reachable objects"); + assert(_revisitStack.isEmpty(), "revisit stack should have been drained"); + cmsDrainMarkingStackClosure.do_void(); + verify_work_stacks_empty(); + } + + { + TraceTime t("scrub symbol & string tables", PrintGCDetails, false, gclog_or_tty); + // Now clean up stale oops in SymbolTable and StringTable + SymbolTable::unlink(&_is_alive_closure); + StringTable::unlink(&_is_alive_closure); + } + } + + verify_work_stacks_empty(); + // 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()) { + 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"); + + // JVMTI object tagging is based on JNI weak refs. If any of these + // refs were cleared then JVMTI needs to update its maps and + // maybe post ObjectFrees to agents. + JvmtiExport::cms_ref_processing_epilogue(); +} + +#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(); + incrementSweepCount(); + _sweep_timer.stop(); + _sweep_estimate.sample(_sweep_timer.seconds()); + size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free()); + + // PermGen verification support: If perm gen sweeping is disabled in + // this cycle, we preserve the perm gen object "deadness" information + // in the perm_gen_verify_bit_map. In order to do that we traverse + // all blocks in perm gen and mark all dead objects. + if (verifying() && !cms_should_unload_classes()) { + CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(), + bitMapLock()); + assert(perm_gen_verify_bit_map()->sizeInBits() != 0, + "Should have already been allocated"); + MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(), + markBitMap(), perm_gen_verify_bit_map()); + _permGen->cmsSpace()->blk_iterate(&mdo); + } + + if (asynch) { + TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); + CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails); + // First sweep the old gen then the perm gen + { + CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(), + bitMapLock()); + sweepWork(_cmsGen, asynch); + } + + // Now repeat for perm gen + if (cms_should_unload_classes()) { + CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(), + bitMapLock()); + sweepWork(_permGen, 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(), + _permGen->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); + + if (cms_should_unload_classes()) { + sweepWork(_permGen, 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(); + + _sweep_timer.reset(); + _sweep_timer.start(); + + update_time_of_last_gc(os::javaTimeMillis()); + + // 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, if the GCH's + // incremental_collection_will_fail flag is set, clear it, + // 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. + // I think the incremental_collection_will_fail flag's use + // is specific to a 2 generation collection policy, so i'll + // assert that that's the configuration we are operating within. + // The use of the flag can and should be generalized appropriately + // in the future to deal with a general n-generation system. + + GenCollectedHeap* gch = GenCollectedHeap::heap(); + assert(gch->collector_policy()->is_two_generation_policy(), + "Resetting of incremental_collection_will_fail flag" + " may be incorrect otherwise"); + gch->clear_incremental_collection_will_fail(); + 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 = 0.999; + HeapWord* minAddr = _cmsSpace->bottom(); + HeapWord* largestAddr = + (HeapWord*) _cmsSpace->dictionary()->findLargestDict(); + if (largestAddr == 0) { + // 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; + _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(!_sweep_timer.is_active(), "Was switched off in an outer context"); + gen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()), + _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(sweepCount()); +} + +// 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(); + } + _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(); + } + ) +} + +void CMSCollector::do_CMS_operation(CMS_op_type op) { + gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps); + TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); + TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty); + TraceCollectorStats tcs(counters()); + + switch (op) { + case CMS_op_checkpointRootsInitial: { + checkpointRootsInitial(true); // asynch + if (PrintGC) { + _cmsGen->printOccupancy("initial-mark"); + } + break; + } + case CMS_op_checkpointRootsFinal: { + 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)) { + assert(_markBitMap.isMarked(addr + 1), "Missing Printezis bit?"); + 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; + } else { + assert(!_markBitMap.isMarked(addr + 1), "Bit map inconsistency?"); + return 0; + } +} + +HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const { + size_t sz = 0; + oop p = (oop)addr; + if (p->klass() != NULL && p->is_parsable()) { + 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(NULL,0), + _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((uintptr_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; + } + } +} + +#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 <= CMSMarkStackSizeMax, "stack bigger than permitted"); + if (_capacity == CMSMarkStackSizeMax) { + 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, CMSMarkStackSizeMax); + // 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 (modulo perm gen) +// generation then this will lose younger_gen cards! + +MarkRefsIntoClosure::MarkRefsIntoClosure( + MemRegion span, CMSBitMap* bitMap, bool should_do_nmethods): + _span(span), + _bitMap(bitMap), + _should_do_nmethods(should_do_nmethods) +{ + assert(_ref_processor == NULL, "deliberately left NULL"); + assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); +} + +void MarkRefsIntoClosure::do_oop(oop* p) { + // if p points into _span, then mark corresponding bit in _markBitMap + oop thisOop = *p; + if (thisOop != NULL) { + assert(thisOop->is_oop(), "expected an oop"); + HeapWord* addr = (HeapWord*)thisOop; + if (_span.contains(addr)) { + // this should be made more efficient + _bitMap->mark(addr); + } + } +} + +// A variant of the above, used for CMS marking verification. +MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure( + MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm, + bool should_do_nmethods): + _span(span), + _verification_bm(verification_bm), + _cms_bm(cms_bm), + _should_do_nmethods(should_do_nmethods) { + assert(_ref_processor == NULL, "deliberately left NULL"); + assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch"); +} + +void MarkRefsIntoVerifyClosure::do_oop(oop* p) { + // if p points into _span, then mark corresponding bit in _markBitMap + oop this_oop = *p; + if (this_oop != NULL) { + assert(this_oop->is_oop(), "expected an oop"); + HeapWord* addr = (HeapWord*)this_oop; + 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"); + } + } + } +} + +////////////////////////////////////////////////// +// MarkRefsIntoAndScanClosure +////////////////////////////////////////////////// + +MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span, + ReferenceProcessor* rp, + CMSBitMap* bit_map, + CMSBitMap* mod_union_table, + CMSMarkStack* mark_stack, + CMSMarkStack* revisit_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, revisit_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* p) { + oop this_oop = *p; + if (this_oop != NULL) { + assert(this_oop->is_oop(), "expected an oop"); + HeapWord* addr = (HeapWord*)this_oop; + assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); + assert(_collector->overflow_list_is_empty(), "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(this_oop); + 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(new_oop->is_parsable(), "Found unparsable 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_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, CMSMarkStack* revisit_stack): + _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, + revisit_stack) +{ + _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* p) { + oop this_oop = *p; + if (this_oop != NULL) { + // Ignore mark word because this could be an already marked oop + // that may be chained at the end of the overflow list. + assert(this_oop->is_oop(true /* ignore mark word */), "expected an oop"); + HeapWord* addr = (HeapWord*)this_oop; + 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(this_oop); + assert(res, "Low water mark should be less than capacity?"); + trim_queue(_low_water_mark); + } // Else, another thread claimed the object + } + } +} + +// This closure is used to rescan the marked objects on the dirty cards +// in the mod union table and the card table proper. +size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m( + oop p, MemRegion mr) { + + size_t size = 0; + HeapWord* addr = (HeapWord*)p; + DEBUG_ONLY(_collector->verify_work_stacks_empty();) + assert(_span.contains(addr), "we are scanning the CMS generation"); + // check if it's time to yield + if (do_yield_check()) { + // We yielded for some foreground stop-world work, + // and we have been asked to abort this ongoing preclean cycle. + return 0; + } + if (_bitMap->isMarked(addr)) { + // it's marked; is it potentially uninitialized? + if (p->klass() != NULL) { + if (CMSPermGenPrecleaningEnabled && !p->is_parsable()) { + // Signal precleaning to redirty the card since + // the klass pointer is already installed. + assert(size == 0, "Initial value"); + } else { + assert(p->is_parsable(), "must be parsable."); + // 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 = p->oop_iterate(_scanningClosure, mr); + assert(size == CompactibleFreeListSpace::adjustObjectSize(size), + "adjustObjectSize should be the identity for array sizes, " + "which are necessarily larger than minimum object size of " + "two heap words"); + } 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 DEBUG + 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 // DEBUG + } + } 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() == NULL || !p->is_parsable()) { + // 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() != NULL, "object should be initializd"); + assert(p->is_parsable(), "must be parsable."); + // 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(new_oop->is_parsable(), "Found unparsable 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 DEBUG + if (!_parallel) { + assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); + assert(_collector->overflow_list_is_empty(), + "overflow list should be empty"); + + } + #endif // DEBUG + 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 DEBUG + if (!_parallel) { + assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); + assert(_collector->overflow_list_is_empty(), + "overflow list should be empty"); + + } + #endif // DEBUG + return is_obj_array; +} + +MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector, + MemRegion span, + CMSBitMap* bitMap, CMSMarkStack* markStack, + CMSMarkStack* revisitStack, + bool should_yield, bool verifying): + _collector(collector), + _span(span), + _bitMap(bitMap), + _mut(&collector->_modUnionTable), + _markStack(markStack), + _revisitStack(revisitStack), + _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. +void MarkFromRootsClosure::do_bit(size_t offset) { + if (_skipBits > 0) { + _skipBits--; + return; + } + // 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() == NULL || !p->is_parsable()) { + 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* start_card_addr = (HeapWord*)round_down( + (intptr_t)addr, CardTableModRefBS::card_size); + HeapWord* end_card_addr = (HeapWord*)round_to( + (intptr_t)(addr+sz), CardTableModRefBS::card_size); + MemRegion redirty_range = MemRegion(start_card_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() != NULL) { + // Redirty the range of cards... + _mut->mark_range(redirty_range); + } // ...else the setting of klass will dirty the card anyway. + } + DEBUG_ONLY(}) + return; + } + } + scanOopsInOop(addr); +} + +// 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 this_oop = oop(ptr); + // Ignore mark word in verification below, since we + // may be running concurrent with mutators. + assert(this_oop->is_oop(true), "should be an oop"); + assert(_finger <= ptr, "_finger runneth ahead"); + // advance the finger to right end of this object + _finger = ptr + this_oop->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"); + // XXX When _finger crosses from old gen into perm gen + // we may be doing unnecessary cleaning; do better in the + // future by detecting that condition and clearing fewer + // MUT/CT entries. + _mut->clear_range(mr); + } + DEBUG_ONLY(}) + + // Note: the finger doesn't advance while we drain + // the stack below. + PushOrMarkClosure pushOrMarkClosure(_collector, + _span, _bitMap, _markStack, + _revisitStack, + _finger, this); + bool res = _markStack->push(this_oop); + 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, + CMSMarkStack* revisit_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), + _revisit_stack(revisit_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. +void Par_MarkFromRootsClosure::do_bit(size_t offset) { + if (_skip_bits > 0) { + _skip_bits--; + return; + } + // 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() == NULL || !p->is_parsable()) { + // in the case of Clean-on-Enter optimization, redirty card + // and avoid clearing card by increasing the threshold. + return; + } + } + scan_oops_in_oop(addr); +} + +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 this_oop = oop(ptr); + // Ignore mark word in verification below, since we + // may be running concurrent with mutators. + assert(this_oop->is_oop(true), "should be an oop"); + assert(_finger <= ptr, "_finger runneth ahead"); + // advance the finger to right end of this object + _finger = ptr + this_oop->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 ?? + // XXX When _finger crosses from old gen into perm gen + // we may be doing unnecessary cleaning; do better in the + // future by detecting that condition and clearing fewer + // MUT/CT entries. + _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, + _revisit_stack, + _finger, + gfa, this); + bool res = _work_queue->push(this_oop); // 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. +void 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 this_oop = oop(addr); + assert(this_oop->is_oop(), "should be an oop"); + assert(_finger <= addr, "_finger runneth ahead"); + // advance the finger to right end of this object + _finger = addr + this_oop->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(this_oop); + 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"); +} + +PushAndMarkVerifyClosure::PushAndMarkVerifyClosure( + CMSCollector* collector, MemRegion span, + CMSBitMap* verification_bm, CMSBitMap* cms_bm, + CMSMarkStack* mark_stack): + OopClosure(collector->ref_processor()), + _collector(collector), + _span(span), + _verification_bm(verification_bm), + _cms_bm(cms_bm), + _mark_stack(mark_stack) +{ } + + +// 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* p) { + oop this_oop = *p; + assert(this_oop->is_oop_or_null(), "expected an oop or NULL"); + HeapWord* addr = (HeapWord*)this_oop; + 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(this_oop)) { // 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, + CMSMarkStack* revisitStack, + HeapWord* finger, MarkFromRootsClosure* parent) : + OopClosure(collector->ref_processor()), + _collector(collector), + _span(span), + _bitMap(bitMap), + _markStack(markStack), + _revisitStack(revisitStack), + _finger(finger), + _parent(parent), + _should_remember_klasses(collector->cms_should_unload_classes()) +{ } + +Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector, + MemRegion span, + CMSBitMap* bit_map, + OopTaskQueue* work_queue, + CMSMarkStack* overflow_stack, + CMSMarkStack* revisit_stack, + HeapWord* finger, + HeapWord** global_finger_addr, + Par_MarkFromRootsClosure* parent) : + OopClosure(collector->ref_processor()), + _collector(collector), + _whole_span(collector->_span), + _span(span), + _bit_map(bit_map), + _work_queue(work_queue), + _overflow_stack(overflow_stack), + _revisit_stack(revisit_stack), + _finger(finger), + _global_finger_addr(global_finger_addr), + _parent(parent), + _should_remember_klasses(collector->cms_should_unload_classes()) +{ } + + +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 expansion 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 PushOrMarkClosure::do_oop(oop* p) { + oop thisOop = *p; + // Ignore mark word because we are running concurrent with mutators. + assert(thisOop->is_oop_or_null(true), "expected an oop or NULL"); + HeapWord* addr = (HeapWord*)thisOop; + 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(thisOop)) { // 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 Par_PushOrMarkClosure::do_oop(oop* p) { + oop this_oop = *p; + // Ignore mark word because we are running concurrent with mutators. + assert(this_oop->is_oop_or_null(true), "expected an oop or NULL"); + HeapWord* addr = (HeapWord*)this_oop; + 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(this_oop) || _overflow_stack->par_push(this_oop))) { + // 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(); + } +} + + +PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector, + MemRegion span, + ReferenceProcessor* rp, + CMSBitMap* bit_map, + CMSBitMap* mod_union_table, + CMSMarkStack* mark_stack, + CMSMarkStack* revisit_stack, + bool concurrent_precleaning): + OopClosure(rp), + _collector(collector), + _span(span), + _bit_map(bit_map), + _mod_union_table(mod_union_table), + _mark_stack(mark_stack), + _revisit_stack(revisit_stack), + _concurrent_precleaning(concurrent_precleaning), + _should_remember_klasses(collector->cms_should_unload_classes()) +{ + 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* p) { + oop this_oop = *p; + // 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(this_oop->is_oop_or_null(true/* ignore mark word */), + "expected an oop or NULL"); + HeapWord* addr = (HeapWord*)this_oop; + // 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(this_oop)) { + if (_concurrent_precleaning) { + // During precleaning we can just dirty the appropriate card + // in the mod union table, thus ensuring that the object remains + // in the grey set and continue. Note that no one can be intefering + // with us in this action of dirtying the mod union table, so + // no locking is required. + _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(this_oop); + _collector->_ser_pmc_remark_ovflw++; + } + } + } +} + +Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector, + MemRegion span, + ReferenceProcessor* rp, + CMSBitMap* bit_map, + OopTaskQueue* work_queue, + CMSMarkStack* revisit_stack): + OopClosure(rp), + _collector(collector), + _span(span), + _bit_map(bit_map), + _work_queue(work_queue), + _revisit_stack(revisit_stack), + _should_remember_klasses(collector->cms_should_unload_classes()) +{ + assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); +} + +// Grey object rescan during second checkpoint phase -- +// the parallel version. +void Par_PushAndMarkClosure::do_oop(oop* p) { + oop this_oop = *p; + // 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(this_oop->is_oop_or_null(true), + "expected an oop or NULL"); + HeapWord* addr = (HeapWord*)this_oop; + // 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(this_oop)) { + _collector->par_push_on_overflow_list(this_oop); + _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS + } + } // Else, some other thread got there first + } +} + +void PushAndMarkClosure::remember_klass(Klass* k) { + if (!_revisit_stack->push(oop(k))) { + fatal("Revisit stack overflowed in PushAndMarkClosure"); + } +} + +void Par_PushAndMarkClosure::remember_klass(Klass* k) { + if (!_revisit_stack->par_push(oop(k))) { + fatal("Revist stack overflowed in Par_PushAndMarkClosure"); + } +} + +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()->initializeDictReturnedBytes(); + ) + assert(_limit >= _sp->bottom() && _limit <= _sp->end(), + "sweep _limit out of bounds"); + if (CMSTraceSweeper) { + gclog_or_tty->print("\n====================\nStarting new sweep\n"); + } +} + +// We need this destructor to reclaim any space at the end +// of the space, which do_blk below may not have added back to +// the free lists. [basically dealing with the "fringe effect"] +SweepClosure::~SweepClosure() { + assert_lock_strong(_freelistLock); + // this should be treated as the end of a free run if any + // The current free range should be returned to the free lists + // as one coalesced chunk. + if (inFreeRange()) { + flushCurFreeChunk(freeFinger(), + pointer_delta(_limit, freeFinger())); + assert(freeFinger() < _limit, "the finger pointeth off base"); + if (CMSTraceSweeper) { + gclog_or_tty->print("destructor:"); + gclog_or_tty->print("Sweep:put_free_blk 0x%x ("SIZE_FORMAT") " + "[coalesced:"SIZE_FORMAT"]\n", + freeFinger(), pointer_delta(_limit, freeFinger()), + lastFreeRangeCoalesced()); + } + } + NOT_PRODUCT( + 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 dictReturnedBytes = _sp->dictionary()->sumDictReturnedBytes(); + size_t returnedBytes = indexListReturnedBytes + dictReturnedBytes; + gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returnedBytes); + gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes", + indexListReturnedBytes); + gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes", + dictReturnedBytes); + } + } + ) + // Now, in debug mode, just null out the sweep_limit + NOT_PRODUCT(_sp->clear_sweep_limit();) + if (CMSTraceSweeper) { + gclog_or_tty->print("end of sweep\n================\n"); + } +} + +void SweepClosure::initialize_free_range(HeapWord* freeFinger, + bool freeRangeInFreeLists) { + if (CMSTraceSweeper) { + gclog_or_tty->print("---- Start free range 0x%x with free block [%d] (%d)\n", + freeFinger, _sp->block_size(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->isFree(), "A chunk on the free list should be free."); + assert(fc->size() > 0, "Free range should have a size"); + assert(_sp->verifyChunkInFreeLists(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 sweepinrg + if (addr == _limit) { // we have swept up to the limit, do nothing more + assert(_limit >= _sp->bottom() && _limit <= _sp->end(), + "sweep _limit out of bounds"); + // help the closure application finish + return pointer_delta(_sp->end(), _limit); + } + assert(addr <= _limit, "sweep invariant"); + + // check if we should yield + do_yield_check(addr); + if (fc->isFree()) { + // Chunk that is already free + res = fc->size(); + doAlreadyFreeChunk(fc); + debug_only(_sp->verifyFreeLists()); + assert(res == fc->size(), "Don't expect the size to change"); + NOT_PRODUCT( + _numObjectsAlreadyFree++; + _numWordsAlreadyFree += res; + ) + NOT_PRODUCT(_last_fc = fc;) + } else if (!_bitMap->isMarked(addr)) { + // Chunk is fresh garbage + res = doGarbageChunk(fc); + debug_only(_sp->verifyFreeLists()); + NOT_PRODUCT( + _numObjectsFreed++; + _numWordsFreed += res; + ) + } else { + // Chunk that is alive. + res = doLiveChunk(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::doAlreadyFreeChunk(FreeChunk* fc) { + size_t size = fc->size(); + // Chunks that cannot be coalesced are not in the + // free lists. + if (CMSTestInFreeList && !fc->cantCoalesce()) { + assert(_sp->verifyChunkInFreeLists(fc), + "free chunk should be in free lists"); + } + // a chunk that is already free, should not have been + // marked in the bit map + HeapWord* 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 in 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 + doPostIsFreeOrGarbageChunk(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 <= _limit, "sweep invariant"); + if ((HeapWord*)nextChunk < _limit && // there's a next chunk... + nextChunk->isFree() && // which is free... + nextChunk->cantCoalesce()) { // ... but cant 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 + debug_only(record_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->verifyChunkInFreeLists(ffc), + "free range is not in free lists"); + } + _sp->removeFreeChunkFromFreeLists(ffc); + set_freeRangeInFreeLists(false); + } + } + } + } 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, "the finger pointeth off base"); + flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger())); + } + // else, nothing to do, just continue + } +} + +size_t SweepClosure::doGarbageChunk(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* addr = (HeapWord*) fc; + 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); + + doPostIsFreeOrGarbageChunk(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->verifyChunkInFreeLists(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); + } + return size; +} + +size_t SweepClosure::doLiveChunk(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()) { + if (_sp->adaptive_freelists()) { + flushCurFreeChunk(freeFinger(), + pointer_delta(addr, freeFinger())); + } else { // not adaptive freelists + set_inFreeRange(false); + // Add the free range back to the free list if it is not already + // there. + if (!freeRangeInFreeLists()) { + assert(freeFinger() < addr, "the finger pointeth off base"); + if (CMSTraceSweeper) { + gclog_or_tty->print("Sweep:put_free_blk 0x%x (%d) " + "[coalesced:%d]\n", + freeFinger(), pointer_delta(addr, freeFinger()), + lastFreeRangeCoalesced()); + } + _sp->addChunkAndRepairOffsetTable(freeFinger(), + pointer_delta(addr, freeFinger()), lastFreeRangeCoalesced()); + } + } + } + + // Common code path for original and adaptive free lists. + + // 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 DEBUG + if (oop(addr)->klass() != NULL && + ( !_collector->cms_should_unload_classes() + || oop(addr)->is_parsable())) { + // 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() != NULL && + (!_collector->cms_should_unload_classes() + || oop(addr)->is_parsable()), + "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::doPostIsFreeOrGarbageChunk(FreeChunk* fc, + size_t chunkSize) { + // doPostIsFreeOrGarbageChunk() should only be called in the smart allocation + // scheme. + bool fcInFreeLists = fc->isFree(); + assert(_sp->adaptive_freelists(), "Should only be used in this case."); + assert((HeapWord*)fc <= _limit, "sweep invariant"); + if (CMSTestInFreeList && fcInFreeLists) { + assert(_sp->verifyChunkInFreeLists(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* addr = (HeapWord*) fc; + + bool coalesce; + size_t left = pointer_delta(addr, freeFinger()); + 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. + bool doCoalesce = inFreeRange() && + (coalesce || _g->isNearLargestChunk((HeapWord*)fc)); + 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* ffc = (FreeChunk*)freeFinger(); + assert(ffc->size() == pointer_delta(addr, freeFinger()), + "Size of free range is inconsistent with chunk size."); + if (CMSTestInFreeList) { + assert(_sp->verifyChunkInFreeLists(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); + } 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. + flushCurFreeChunk(freeFinger(), + pointer_delta(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); + } +} +void SweepClosure::flushCurFreeChunk(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->setSize(size); + assert(!_sp->verifyChunkInFreeLists(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()); + } + 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()) { + flushCurFreeChunk(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_verifyChunkInFreeLists(FreeChunk* fc) { + return debug_cms_space->verifyChunkInFreeLists(fc); +} + +void SweepClosure::record_free_block_coalesced(FreeChunk* fc) const { + if (CMSTraceSweeper) { + gclog_or_tty->print("Sweep:coal_free_blk 0x%x (%d)\n", fc, fc->size()); + } +} +#endif + +// CMSIsAliveClosure +bool CMSIsAliveClosure::do_object_b(oop obj) { + HeapWord* addr = (HeapWord*)obj; + return addr != NULL && + (!_span.contains(addr) || _bit_map->isMarked(addr)); +} + +// CMSKeepAliveClosure: the serial version +void CMSKeepAliveClosure::do_oop(oop* p) { + oop this_oop = *p; + HeapWord* addr = (HeapWord*)this_oop; + 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(this_oop)) { + _collector->push_on_overflow_list(this_oop); + _collector->_ser_kac_ovflw++; + } + } +} + +// CMSParKeepAliveClosure: a parallel version of the above. +// The work queues are private to each closure (thread), +// but (may be) available for stealing by other threads. +void CMSParKeepAliveClosure::do_oop(oop* p) { + oop this_oop = *p; + HeapWord* addr = (HeapWord*)this_oop; + 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(this_oop); + assert(res, "Low water mark should be much less than capacity"); + // Do a recursive trim in the hope that this will keep + // stack usage lower, but leave some oops for potential stealers + trim_queue(_low_water_mark); + } // Else, another thread got there first + } +} + +void CMSParKeepAliveClosure::trim_queue(uint max) { + while (_work_queue->size() > max) { + oop new_oop; + if (_work_queue->pop_local(new_oop)) { + assert(new_oop != NULL && 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); + } + } +} + +void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { + oop this_oop = *p; + HeapWord* addr = (HeapWord*)this_oop; + 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(this_oop)) { + _collector->par_push_on_overflow_list(this_oop); + _collector->_par_kac_ovflw++; + } + } // Else another thread got there already + } +} + +////////////////////////////////////////////////////////////////// +// CMSExpansionCause ///////////////////////////// +////////////////////////////////////////////////////////////////// +const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) { + switch (cause) { + case _no_expansion: + return "No expansion"; + case _satisfy_free_ratio: + return "Free ratio"; + case _satisfy_promotion: + return "Satisfy promotion"; + case _satisfy_allocation: + return "allocation"; + case _allocate_par_lab: + return "Par LAB"; + case _allocate_par_spooling_space: + return "Par Spooling Space"; + case _adaptive_size_policy: + return "Ergonomics"; + default: + return "unknown"; + } +} + +void CMSDrainMarkingStackClosure::do_void() { + // the max number to take from overflow list at a time + const size_t num = _mark_stack->capacity()/4; + while (!_mark_stack->isEmpty() || + // if stack is empty, check the overflow list + _collector->take_from_overflow_list(num, _mark_stack)) { + oop this_oop = _mark_stack->pop(); + HeapWord* addr = (HeapWord*)this_oop; + assert(_span.contains(addr), "Should be within span"); + assert(_bit_map->isMarked(addr), "Should be marked"); + assert(this_oop->is_oop(), "Should be an oop"); + this_oop->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(size_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(); +} + +// Multi-threaded; use CAS to break off a prefix +bool CMSCollector::par_take_from_overflow_list(size_t num, + OopTaskQueue* work_q) { + assert(work_q->size() == 0, "That's the current policy"); + 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 = (oop)Atomic::xchg_ptr(NULL, &_overflow_list); + if (prefix == NULL) { // someone grabbed it before we did ... + // ... we could spin for a short while, but for now we don't + return false; + } + size_t i = num; + oop cur = prefix; + for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--); + if (cur->mark() != NULL) { + oop suffix_head = cur->mark(); // suffix will be put back on global list + cur->set_mark(NULL); // break off suffix + // 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"); + oop observed_overflow_list = _overflow_list; + do { + cur = observed_overflow_list; + suffix_tail->set_mark(markOop(cur)); + observed_overflow_list = + (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur); + } while (cur != observed_overflow_list); + } + + // Push the prefix elements on work_q + assert(prefix != NULL, "control point invariant"); + const markOop proto = markOopDesc::prototype(); + oop next; + NOT_PRODUCT(size_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; + p->set_mark(markOop(cur_overflow_list)); + observed_overflow_list = + (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list); + } while (cur_overflow_list != observed_overflow_list); +} + +// 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 suych 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) { + int PreserveMarkStackSize = 128; + + if (_preserved_oop_stack == NULL) { + assert(_preserved_mark_stack == NULL, + "bijection with preserved_oop_stack"); + // Allocate the stacks + _preserved_oop_stack = new (ResourceObj::C_HEAP) + GrowableArray<oop>(PreserveMarkStackSize, true); + _preserved_mark_stack = new (ResourceObj::C_HEAP) + GrowableArray<markOop>(PreserveMarkStackSize, true); + if (_preserved_oop_stack == NULL || _preserved_mark_stack == NULL) { + vm_exit_out_of_memory(2* PreserveMarkStackSize * sizeof(oop) /* punt */, + "Preserved Mark/Oop Stack for CMS (C-heap)"); + } + } + _preserved_oop_stack->push(p); + _preserved_mark_stack->push(m); + assert(m == p->mark(), "Mark word changed"); + assert(_preserved_oop_stack->length() == _preserved_mark_stack->length(), + "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() { + if (_preserved_oop_stack == NULL) { + assert(_preserved_mark_stack == NULL, + "bijection with preserved_oop_stack"); + return; + } + + assert(SafepointSynchronize::is_at_safepoint(), + "world should be stopped"); + assert(Thread::current()->is_ConcurrentGC_thread() || + Thread::current()->is_VM_thread(), + "should be single-threaded"); + + int length = _preserved_oop_stack->length(); + assert(_preserved_mark_stack->length() == length, "bijection"); + for (int i = 0; i < length; i++) { + oop p = _preserved_oop_stack->at(i); + 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->at(i); + p->set_mark(m); + } + _preserved_mark_stack->clear(); + _preserved_oop_stack->clear(); + 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 == NULL + && _preserved_oop_stack == NULL) + || ( _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); + } +} + +// The desired expansion delta is computed so that: +// . desired free percentage or greater is used +void ASConcurrentMarkSweepGeneration::compute_new_size() { + assert_locked_or_safepoint(Heap_lock); + + GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap(); + + // If incremental collection failed, we just want to expand + // to the limit. + if (incremental_collection_failed()) { + clear_incremental_collection_failed(); + grow_to_reserved(); + return; + } + + assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing"); + + assert(gch->kind() == CollectedHeap::GenCollectedHeap, + "Wrong type of heap"); + int prev_level = level() - 1; + assert(prev_level >= 0, "The cms generation is the lowest generation"); + Generation* prev_gen = gch->get_gen(prev_level); + assert(prev_gen->kind() == Generation::ASParNew, + "Wrong type of young generation"); + ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen; + size_t cur_eden = younger_gen->eden()->capacity(); + CMSAdaptiveSizePolicy* size_policy = cms_size_policy(); + size_t cur_promo = free(); + size_policy->compute_tenured_generation_free_space(cur_promo, + max_available(), + cur_eden); + resize(cur_promo, size_policy->promo_size()); + + // Record the new size of the space in the cms generation + // that is available for promotions. This is temporary. + // It should be the desired promo size. + size_policy->avg_cms_promo()->sample(free()); + size_policy->avg_old_live()->sample(used()); + + if (UsePerfData) { + CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters(); + counters->update_cms_capacity_counter(capacity()); + } +} + +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 <= 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->setSize(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 %ldK by %ldK to %ldK", + 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() == _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()/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); + assert(res != 0, "Should always be able to compute a size"); + 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 + } + } + return res; +}