/* * Copyright 2001-2008 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/_parNewGeneration.cpp.incl" #ifdef _MSC_VER #pragma warning( push ) #pragma warning( disable:4355 ) // 'this' : used in base member initializer list #endif ParScanThreadState::ParScanThreadState(Space* to_space_, ParNewGeneration* gen_, Generation* old_gen_, int thread_num_, ObjToScanQueueSet* work_queue_set_, size_t desired_plab_sz_, ParallelTaskTerminator& term_) : _to_space(to_space_), _old_gen(old_gen_), _thread_num(thread_num_), _work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false), _ageTable(false), // false ==> not the global age table, no perf data. _to_space_alloc_buffer(desired_plab_sz_), _to_space_closure(gen_, this), _old_gen_closure(gen_, this), _to_space_root_closure(gen_, this), _old_gen_root_closure(gen_, this), _older_gen_closure(gen_, this), _evacuate_followers(this, &_to_space_closure, &_old_gen_closure, &_to_space_root_closure, gen_, &_old_gen_root_closure, work_queue_set_, &term_), _is_alive_closure(gen_), _scan_weak_ref_closure(gen_, this), _keep_alive_closure(&_scan_weak_ref_closure), _pushes(0), _pops(0), _steals(0), _steal_attempts(0), _term_attempts(0), _strong_roots_time(0.0), _term_time(0.0) { _survivor_chunk_array = (ChunkArray*) old_gen()->get_data_recorder(thread_num()); _hash_seed = 17; // Might want to take time-based random value. _start = os::elapsedTime(); _old_gen_closure.set_generation(old_gen_); _old_gen_root_closure.set_generation(old_gen_); } #ifdef _MSC_VER #pragma warning( pop ) #endif void ParScanThreadState::record_survivor_plab(HeapWord* plab_start, size_t plab_word_size) { ChunkArray* sca = survivor_chunk_array(); if (sca != NULL) { // A non-null SCA implies that we want the PLAB data recorded. sca->record_sample(plab_start, plab_word_size); } } bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const { return new_obj->is_objArray() && arrayOop(new_obj)->length() > ParGCArrayScanChunk && new_obj != old_obj; } void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) { assert(old->is_objArray(), "must be obj array"); assert(old->is_forwarded(), "must be forwarded"); assert(Universe::heap()->is_in_reserved(old), "must be in heap."); assert(!_old_gen->is_in(old), "must be in young generation."); objArrayOop obj = objArrayOop(old->forwardee()); // Process ParGCArrayScanChunk elements now // and push the remainder back onto queue int start = arrayOop(old)->length(); int end = obj->length(); int remainder = end - start; assert(start <= end, "just checking"); if (remainder > 2 * ParGCArrayScanChunk) { // Test above combines last partial chunk with a full chunk end = start + ParGCArrayScanChunk; arrayOop(old)->set_length(end); // Push remainder. bool ok = work_queue()->push(old); assert(ok, "just popped, push must be okay"); note_push(); } else { // Restore length so that it can be used if there // is a promotion failure and forwarding pointers // must be removed. arrayOop(old)->set_length(end); } // process our set of indices (include header in first chunk) // should make sure end is even (aligned to HeapWord in case of compressed oops) if ((HeapWord *)obj < young_old_boundary()) { // object is in to_space obj->oop_iterate_range(&_to_space_closure, start, end); } else { // object is in old generation obj->oop_iterate_range(&_old_gen_closure, start, end); } } void ParScanThreadState::trim_queues(int max_size) { ObjToScanQueue* queue = work_queue(); while (queue->size() > (juint)max_size) { oop obj_to_scan; if (queue->pop_local(obj_to_scan)) { note_pop(); if ((HeapWord *)obj_to_scan < young_old_boundary()) { if (obj_to_scan->is_objArray() && obj_to_scan->is_forwarded() && obj_to_scan->forwardee() != obj_to_scan) { scan_partial_array_and_push_remainder(obj_to_scan); } else { // object is in to_space obj_to_scan->oop_iterate(&_to_space_closure); } } else { // object is in old generation obj_to_scan->oop_iterate(&_old_gen_closure); } } } } HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) { // Otherwise, if the object is small enough, try to reallocate the // buffer. HeapWord* obj = NULL; if (!_to_space_full) { ParGCAllocBuffer* const plab = to_space_alloc_buffer(); Space* const sp = to_space(); if (word_sz * 100 < ParallelGCBufferWastePct * plab->word_sz()) { // Is small enough; abandon this buffer and start a new one. plab->retire(false, false); size_t buf_size = plab->word_sz(); HeapWord* buf_space = sp->par_allocate(buf_size); if (buf_space == NULL) { const size_t min_bytes = ParGCAllocBuffer::min_size() << LogHeapWordSize; size_t free_bytes = sp->free(); while(buf_space == NULL && free_bytes >= min_bytes) { buf_size = free_bytes >> LogHeapWordSize; assert(buf_size == (size_t)align_object_size(buf_size), "Invariant"); buf_space = sp->par_allocate(buf_size); free_bytes = sp->free(); } } if (buf_space != NULL) { plab->set_word_size(buf_size); plab->set_buf(buf_space); record_survivor_plab(buf_space, buf_size); obj = plab->allocate(word_sz); // Note that we cannot compare buf_size < word_sz below // because of AlignmentReserve (see ParGCAllocBuffer::allocate()). assert(obj != NULL || plab->words_remaining() < word_sz, "Else should have been able to allocate"); // It's conceivable that we may be able to use the // buffer we just grabbed for subsequent small requests // even if not for this one. } else { // We're used up. _to_space_full = true; } } else { // Too large; allocate the object individually. obj = sp->par_allocate(word_sz); } } return obj; } void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, size_t word_sz) { // Is the alloc in the current alloc buffer? if (to_space_alloc_buffer()->contains(obj)) { assert(to_space_alloc_buffer()->contains(obj + word_sz - 1), "Should contain whole object."); to_space_alloc_buffer()->undo_allocation(obj, word_sz); } else { SharedHeap::fill_region_with_object(MemRegion(obj, word_sz)); } } class ParScanThreadStateSet: private ResourceArray { public: // Initializes states for the specified number of threads; ParScanThreadStateSet(int num_threads, Space& to_space, ParNewGeneration& gen, Generation& old_gen, ObjToScanQueueSet& queue_set, size_t desired_plab_sz, ParallelTaskTerminator& term); inline ParScanThreadState& thread_sate(int i); int pushes() { return _pushes; } int pops() { return _pops; } int steals() { return _steals; } void reset(); void flush(); private: ParallelTaskTerminator& _term; ParNewGeneration& _gen; Generation& _next_gen; // staticstics int _pushes; int _pops; int _steals; }; ParScanThreadStateSet::ParScanThreadStateSet( int num_threads, Space& to_space, ParNewGeneration& gen, Generation& old_gen, ObjToScanQueueSet& queue_set, size_t desired_plab_sz, ParallelTaskTerminator& term) : ResourceArray(sizeof(ParScanThreadState), num_threads), _gen(gen), _next_gen(old_gen), _term(term), _pushes(0), _pops(0), _steals(0) { assert(num_threads > 0, "sanity check!"); // Initialize states. for (int i = 0; i < num_threads; ++i) { new ((ParScanThreadState*)_data + i) ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set, desired_plab_sz, term); } } inline ParScanThreadState& ParScanThreadStateSet::thread_sate(int i) { assert(i >= 0 && i < length(), "sanity check!"); return ((ParScanThreadState*)_data)[i]; } void ParScanThreadStateSet::reset() { _term.reset_for_reuse(); } void ParScanThreadStateSet::flush() { for (int i = 0; i < length(); ++i) { ParScanThreadState& par_scan_state = thread_sate(i); // Flush stats related to To-space PLAB activity and // retire the last buffer. par_scan_state.to_space_alloc_buffer()-> flush_stats_and_retire(_gen.plab_stats(), false /* !retain */); // Every thread has its own age table. We need to merge // them all into one. ageTable *local_table = par_scan_state.age_table(); _gen.age_table()->merge(local_table); // Inform old gen that we're done. _next_gen.par_promote_alloc_done(i); _next_gen.par_oop_since_save_marks_iterate_done(i); // Flush stats related to work queue activity (push/pop/steal) // This could conceivably become a bottleneck; if so, we'll put the // stat's gathering under the flag. if (PAR_STATS_ENABLED) { _pushes += par_scan_state.pushes(); _pops += par_scan_state.pops(); _steals += par_scan_state.steals(); if (ParallelGCVerbose) { gclog_or_tty->print("Thread %d complete:\n" " Pushes: %7d Pops: %7d Steals %7d (in %d attempts)\n", i, par_scan_state.pushes(), par_scan_state.pops(), par_scan_state.steals(), par_scan_state.steal_attempts()); if (par_scan_state.overflow_pushes() > 0 || par_scan_state.overflow_refills() > 0) { gclog_or_tty->print(" Overflow pushes: %7d " "Overflow refills: %7d for %d objs.\n", par_scan_state.overflow_pushes(), par_scan_state.overflow_refills(), par_scan_state.overflow_refill_objs()); } double elapsed = par_scan_state.elapsed(); double strong_roots = par_scan_state.strong_roots_time(); double term = par_scan_state.term_time(); gclog_or_tty->print( " Elapsed: %7.2f ms.\n" " Strong roots: %7.2f ms (%6.2f%%)\n" " Termination: %7.2f ms (%6.2f%%) (in %d entries)\n", elapsed * 1000.0, strong_roots * 1000.0, (strong_roots*100.0/elapsed), term * 1000.0, (term*100.0/elapsed), par_scan_state.term_attempts()); } } } } ParScanClosure::ParScanClosure(ParNewGeneration* g, ParScanThreadState* par_scan_state) : OopsInGenClosure(g), _par_scan_state(par_scan_state), _g(g) { assert(_g->level() == 0, "Optimized for youngest generation"); _boundary = _g->reserved().end(); } void ParScanWithBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, false); } void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); } void ParScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, false); } void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); } void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); } void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); } void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); } void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); } ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g, ParScanThreadState* par_scan_state) : ScanWeakRefClosure(g), _par_scan_state(par_scan_state) {} void ParScanWeakRefClosure::do_oop(oop* p) { ParScanWeakRefClosure::do_oop_work(p); } void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); } #ifdef WIN32 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */ #endif ParEvacuateFollowersClosure::ParEvacuateFollowersClosure( ParScanThreadState* par_scan_state_, ParScanWithoutBarrierClosure* to_space_closure_, ParScanWithBarrierClosure* old_gen_closure_, ParRootScanWithoutBarrierClosure* to_space_root_closure_, ParNewGeneration* par_gen_, ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_, ObjToScanQueueSet* task_queues_, ParallelTaskTerminator* terminator_) : _par_scan_state(par_scan_state_), _to_space_closure(to_space_closure_), _old_gen_closure(old_gen_closure_), _to_space_root_closure(to_space_root_closure_), _old_gen_root_closure(old_gen_root_closure_), _par_gen(par_gen_), _task_queues(task_queues_), _terminator(terminator_) {} void ParEvacuateFollowersClosure::do_void() { ObjToScanQueue* work_q = par_scan_state()->work_queue(); while (true) { // Scan to-space and old-gen objs until we run out of both. oop obj_to_scan; par_scan_state()->trim_queues(0); // We have no local work, attempt to steal from other threads. // attempt to steal work from promoted. par_scan_state()->note_steal_attempt(); if (task_queues()->steal(par_scan_state()->thread_num(), par_scan_state()->hash_seed(), obj_to_scan)) { par_scan_state()->note_steal(); bool res = work_q->push(obj_to_scan); assert(res, "Empty queue should have room for a push."); par_scan_state()->note_push(); // if successful, goto Start. continue; // try global overflow list. } else if (par_gen()->take_from_overflow_list(par_scan_state())) { continue; } // Otherwise, offer termination. par_scan_state()->start_term_time(); if (terminator()->offer_termination()) break; par_scan_state()->end_term_time(); } // Finish the last termination pause. par_scan_state()->end_term_time(); } ParNewGenTask::ParNewGenTask(ParNewGeneration* gen, Generation* next_gen, HeapWord* young_old_boundary, ParScanThreadStateSet* state_set) : AbstractGangTask("ParNewGeneration collection"), _gen(gen), _next_gen(next_gen), _young_old_boundary(young_old_boundary), _state_set(state_set) {} void ParNewGenTask::work(int i) { GenCollectedHeap* gch = GenCollectedHeap::heap(); // Since this is being done in a separate thread, need new resource // and handle marks. ResourceMark rm; HandleMark hm; // We would need multiple old-gen queues otherwise. guarantee(gch->n_gens() == 2, "Par young collection currently only works with one older gen."); Generation* old_gen = gch->next_gen(_gen); ParScanThreadState& par_scan_state = _state_set->thread_sate(i); par_scan_state.set_young_old_boundary(_young_old_boundary); par_scan_state.start_strong_roots(); gch->gen_process_strong_roots(_gen->level(), true, // Process younger gens, if any, // as strong roots. false,// not collecting perm generation. SharedHeap::SO_AllClasses, &par_scan_state.older_gen_closure(), &par_scan_state.to_space_root_closure()); par_scan_state.end_strong_roots(); // "evacuate followers". par_scan_state.evacuate_followers_closure().do_void(); } #ifdef _MSC_VER #pragma warning( push ) #pragma warning( disable:4355 ) // 'this' : used in base member initializer list #endif ParNewGeneration:: ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level) : DefNewGeneration(rs, initial_byte_size, level, "PCopy"), _overflow_list(NULL), _is_alive_closure(this), _plab_stats(YoungPLABSize, PLABWeight) { _task_queues = new ObjToScanQueueSet(ParallelGCThreads); guarantee(_task_queues != NULL, "task_queues allocation failure."); for (uint i1 = 0; i1 < ParallelGCThreads; i1++) { ObjToScanQueuePadded *q_padded = new ObjToScanQueuePadded(); guarantee(q_padded != NULL, "work_queue Allocation failure."); _task_queues->register_queue(i1, &q_padded->work_queue); } for (uint i2 = 0; i2 < ParallelGCThreads; i2++) _task_queues->queue(i2)->initialize(); if (UsePerfData) { EXCEPTION_MARK; ResourceMark rm; const char* cname = PerfDataManager::counter_name(_gen_counters->name_space(), "threads"); PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None, ParallelGCThreads, CHECK); } } #ifdef _MSC_VER #pragma warning( pop ) #endif // ParNewGeneration:: ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) : DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {} template void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) { #ifdef ASSERT { assert(!oopDesc::is_null(*p), "expected non-null ref"); oop obj = oopDesc::load_decode_heap_oop_not_null(p); // We never expect to see a null reference being processed // as a weak reference. assert(obj->is_oop(), "expected an oop while scanning weak refs"); } #endif // ASSERT _par_cl->do_oop_nv(p); if (Universe::heap()->is_in_reserved(p)) { oop obj = oopDesc::load_decode_heap_oop_not_null(p); _rs->write_ref_field_gc_par(p, obj); } } void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); } void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); } // ParNewGeneration:: KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) : DefNewGeneration::KeepAliveClosure(cl) {} template void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) { #ifdef ASSERT { assert(!oopDesc::is_null(*p), "expected non-null ref"); oop obj = oopDesc::load_decode_heap_oop_not_null(p); // We never expect to see a null reference being processed // as a weak reference. assert(obj->is_oop(), "expected an oop while scanning weak refs"); } #endif // ASSERT _cl->do_oop_nv(p); if (Universe::heap()->is_in_reserved(p)) { oop obj = oopDesc::load_decode_heap_oop_not_null(p); _rs->write_ref_field_gc_par(p, obj); } } void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); } void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); } template void ScanClosureWithParBarrier::do_oop_work(T* p) { T heap_oop = oopDesc::load_heap_oop(p); if (!oopDesc::is_null(heap_oop)) { oop obj = oopDesc::decode_heap_oop_not_null(heap_oop); if ((HeapWord*)obj < _boundary) { assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?"); oop new_obj = obj->is_forwarded() ? obj->forwardee() : _g->DefNewGeneration::copy_to_survivor_space(obj); oopDesc::encode_store_heap_oop_not_null(p, new_obj); } if (_gc_barrier) { // If p points to a younger generation, mark the card. if ((HeapWord*)obj < _gen_boundary) { _rs->write_ref_field_gc_par(p, obj); } } } } void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); } void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); } class ParNewRefProcTaskProxy: public AbstractGangTask { typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; public: ParNewRefProcTaskProxy(ProcessTask& task, ParNewGeneration& gen, Generation& next_gen, HeapWord* young_old_boundary, ParScanThreadStateSet& state_set); private: virtual void work(int i); private: ParNewGeneration& _gen; ProcessTask& _task; Generation& _next_gen; HeapWord* _young_old_boundary; ParScanThreadStateSet& _state_set; }; ParNewRefProcTaskProxy::ParNewRefProcTaskProxy( ProcessTask& task, ParNewGeneration& gen, Generation& next_gen, HeapWord* young_old_boundary, ParScanThreadStateSet& state_set) : AbstractGangTask("ParNewGeneration parallel reference processing"), _gen(gen), _task(task), _next_gen(next_gen), _young_old_boundary(young_old_boundary), _state_set(state_set) { } void ParNewRefProcTaskProxy::work(int i) { ResourceMark rm; HandleMark hm; ParScanThreadState& par_scan_state = _state_set.thread_sate(i); par_scan_state.set_young_old_boundary(_young_old_boundary); _task.work(i, par_scan_state.is_alive_closure(), par_scan_state.keep_alive_closure(), par_scan_state.evacuate_followers_closure()); } class ParNewRefEnqueueTaskProxy: public AbstractGangTask { typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; EnqueueTask& _task; public: ParNewRefEnqueueTaskProxy(EnqueueTask& task) : AbstractGangTask("ParNewGeneration parallel reference enqueue"), _task(task) { } virtual void work(int i) { _task.work(i); } }; void ParNewRefProcTaskExecutor::execute(ProcessTask& task) { GenCollectedHeap* gch = GenCollectedHeap::heap(); assert(gch->kind() == CollectedHeap::GenCollectedHeap, "not a generational heap"); WorkGang* workers = gch->workers(); assert(workers != NULL, "Need parallel worker threads."); ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(), _generation.reserved().end(), _state_set); workers->run_task(&rp_task); _state_set.reset(); } void ParNewRefProcTaskExecutor::execute(EnqueueTask& task) { GenCollectedHeap* gch = GenCollectedHeap::heap(); WorkGang* workers = gch->workers(); assert(workers != NULL, "Need parallel worker threads."); ParNewRefEnqueueTaskProxy enq_task(task); workers->run_task(&enq_task); } void ParNewRefProcTaskExecutor::set_single_threaded_mode() { _state_set.flush(); GenCollectedHeap* gch = GenCollectedHeap::heap(); gch->set_par_threads(0); // 0 ==> non-parallel. gch->save_marks(); } ScanClosureWithParBarrier:: ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) : ScanClosure(g, gc_barrier) {} EvacuateFollowersClosureGeneral:: EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, int level, OopsInGenClosure* cur, OopsInGenClosure* older) : _gch(gch), _level(level), _scan_cur_or_nonheap(cur), _scan_older(older) {} void EvacuateFollowersClosureGeneral::do_void() { do { // Beware: this call will lead to closure applications via virtual // calls. _gch->oop_since_save_marks_iterate(_level, _scan_cur_or_nonheap, _scan_older); } while (!_gch->no_allocs_since_save_marks(_level)); } bool ParNewGeneration::_avoid_promotion_undo = false; void ParNewGeneration::adjust_desired_tenuring_threshold() { // Set the desired survivor size to half the real survivor space _tenuring_threshold = age_table()->compute_tenuring_threshold(to()->capacity()/HeapWordSize); } // A Generation that does parallel young-gen collection. void ParNewGeneration::collect(bool full, bool clear_all_soft_refs, size_t size, bool is_tlab) { assert(full || size > 0, "otherwise we don't want to collect"); GenCollectedHeap* gch = GenCollectedHeap::heap(); assert(gch->kind() == CollectedHeap::GenCollectedHeap, "not a CMS generational heap"); AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy(); WorkGang* workers = gch->workers(); _next_gen = gch->next_gen(this); assert(_next_gen != NULL, "This must be the youngest gen, and not the only gen"); assert(gch->n_gens() == 2, "Par collection currently only works with single older gen."); // Do we have to avoid promotion_undo? if (gch->collector_policy()->is_concurrent_mark_sweep_policy()) { set_avoid_promotion_undo(true); } // If the next generation is too full to accomodate worst-case promotion // from this generation, pass on collection; let the next generation // do it. if (!collection_attempt_is_safe()) { gch->set_incremental_collection_will_fail(); return; } assert(to()->is_empty(), "Else not collection_attempt_is_safe"); init_assuming_no_promotion_failure(); if (UseAdaptiveSizePolicy) { set_survivor_overflow(false); size_policy->minor_collection_begin(); } TraceTime t1("GC", PrintGC && !PrintGCDetails, true, gclog_or_tty); // Capture heap used before collection (for printing). size_t gch_prev_used = gch->used(); SpecializationStats::clear(); age_table()->clear(); to()->clear(SpaceDecorator::Mangle); gch->save_marks(); assert(workers != NULL, "Need parallel worker threads."); ParallelTaskTerminator _term(workers->total_workers(), task_queues()); ParScanThreadStateSet thread_state_set(workers->total_workers(), *to(), *this, *_next_gen, *task_queues(), desired_plab_sz(), _term); ParNewGenTask tsk(this, _next_gen, reserved().end(), &thread_state_set); int n_workers = workers->total_workers(); gch->set_par_threads(n_workers); gch->change_strong_roots_parity(); gch->rem_set()->prepare_for_younger_refs_iterate(true); // 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) { workers->run_task(&tsk); } else { tsk.work(0); } thread_state_set.reset(); if (PAR_STATS_ENABLED && ParallelGCVerbose) { gclog_or_tty->print("Thread totals:\n" " Pushes: %7d Pops: %7d Steals %7d (sum = %7d).\n", thread_state_set.pushes(), thread_state_set.pops(), thread_state_set.steals(), thread_state_set.pops()+thread_state_set.steals()); } assert(thread_state_set.pushes() == thread_state_set.pops() + thread_state_set.steals(), "Or else the queues are leaky."); // Process (weak) reference objects found during scavenge. ReferenceProcessor* rp = ref_processor(); IsAliveClosure is_alive(this); ScanWeakRefClosure scan_weak_ref(this); KeepAliveClosure keep_alive(&scan_weak_ref); ScanClosure scan_without_gc_barrier(this, false); ScanClosureWithParBarrier scan_with_gc_barrier(this, true); set_promo_failure_scan_stack_closure(&scan_without_gc_barrier); EvacuateFollowersClosureGeneral evacuate_followers(gch, _level, &scan_without_gc_barrier, &scan_with_gc_barrier); rp->snap_policy(clear_all_soft_refs); if (rp->processing_is_mt()) { ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); rp->process_discovered_references(&is_alive, &keep_alive, &evacuate_followers, &task_executor); } else { thread_state_set.flush(); gch->set_par_threads(0); // 0 ==> non-parallel. gch->save_marks(); rp->process_discovered_references(&is_alive, &keep_alive, &evacuate_followers, NULL); } if (!promotion_failed()) { // Swap the survivor spaces. eden()->clear(SpaceDecorator::Mangle); from()->clear(SpaceDecorator::Mangle); if (ZapUnusedHeapArea) { // This is now done here because of the piece-meal mangling which // can check for valid mangling at intermediate points in the // collection(s). When a minor collection fails to collect // sufficient space resizing of the young generation can occur // an redistribute the spaces in the young generation. Mangle // here so that unzapped regions don't get distributed to // other spaces. to()->mangle_unused_area(); } swap_spaces(); assert(to()->is_empty(), "to space should be empty now"); } else { assert(HandlePromotionFailure, "Should only be here if promotion failure handling is on"); if (_promo_failure_scan_stack != NULL) { // Can be non-null because of reference processing. // Free stack with its elements. delete _promo_failure_scan_stack; _promo_failure_scan_stack = NULL; } remove_forwarding_pointers(); if (PrintGCDetails) { gclog_or_tty->print(" (promotion failed)"); } // All the spaces are in play for mark-sweep. swap_spaces(); // Make life simpler for CMS || rescan; see 6483690. from()->set_next_compaction_space(to()); gch->set_incremental_collection_will_fail(); // Reset the PromotionFailureALot counters. NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();) } // set new iteration safe limit for the survivor spaces from()->set_concurrent_iteration_safe_limit(from()->top()); to()->set_concurrent_iteration_safe_limit(to()->top()); adjust_desired_tenuring_threshold(); if (ResizePLAB) { plab_stats()->adjust_desired_plab_sz(); } if (PrintGC && !PrintGCDetails) { gch->print_heap_change(gch_prev_used); } if (UseAdaptiveSizePolicy) { size_policy->minor_collection_end(gch->gc_cause()); size_policy->avg_survived()->sample(from()->used()); } update_time_of_last_gc(os::javaTimeMillis()); SpecializationStats::print(); rp->set_enqueuing_is_done(true); if (rp->processing_is_mt()) { ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); rp->enqueue_discovered_references(&task_executor); } else { rp->enqueue_discovered_references(NULL); } rp->verify_no_references_recorded(); } static int sum; void ParNewGeneration::waste_some_time() { for (int i = 0; i < 100; i++) { sum += i; } } static const oop ClaimedForwardPtr = oop(0x4); // Because of concurrency, there are times where an object for which // "is_forwarded()" is true contains an "interim" forwarding pointer // value. Such a value will soon be overwritten with a real value. // This method requires "obj" to have a forwarding pointer, and waits, if // necessary for a real one to be inserted, and returns it. oop ParNewGeneration::real_forwardee(oop obj) { oop forward_ptr = obj->forwardee(); if (forward_ptr != ClaimedForwardPtr) { return forward_ptr; } else { return real_forwardee_slow(obj); } } oop ParNewGeneration::real_forwardee_slow(oop obj) { // Spin-read if it is claimed but not yet written by another thread. oop forward_ptr = obj->forwardee(); while (forward_ptr == ClaimedForwardPtr) { waste_some_time(); assert(obj->is_forwarded(), "precondition"); forward_ptr = obj->forwardee(); } return forward_ptr; } #ifdef ASSERT bool ParNewGeneration::is_legal_forward_ptr(oop p) { return (_avoid_promotion_undo && p == ClaimedForwardPtr) || Universe::heap()->is_in_reserved(p); } #endif void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) { if ((m != markOopDesc::prototype()) && (!UseBiasedLocking || (m != markOopDesc::biased_locking_prototype()))) { MutexLocker ml(ParGCRareEvent_lock); DefNewGeneration::preserve_mark_if_necessary(obj, m); } } // Multiple GC threads may try to promote an object. If the object // is successfully promoted, a forwarding pointer will be installed in // the object in the young generation. This method claims the right // to install the forwarding pointer before it copies the object, // thus avoiding the need to undo the copy as in // copy_to_survivor_space_avoiding_with_undo. oop ParNewGeneration::copy_to_survivor_space_avoiding_promotion_undo( ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) { // In the sequential version, this assert also says that the object is // not forwarded. That might not be the case here. It is the case that // the caller observed it to be not forwarded at some time in the past. assert(is_in_reserved(old), "shouldn't be scavenging this oop"); // The sequential code read "old->age()" below. That doesn't work here, // since the age is in the mark word, and that might be overwritten with // a forwarding pointer by a parallel thread. So we must save the mark // word in a local and then analyze it. oopDesc dummyOld; dummyOld.set_mark(m); assert(!dummyOld.is_forwarded(), "should not be called with forwarding pointer mark word."); oop new_obj = NULL; oop forward_ptr; // Try allocating obj in to-space (unless too old) if (dummyOld.age() < tenuring_threshold()) { new_obj = (oop)par_scan_state->alloc_in_to_space(sz); if (new_obj == NULL) { set_survivor_overflow(true); } } if (new_obj == NULL) { // Either to-space is full or we decided to promote // try allocating obj tenured // Attempt to install a null forwarding pointer (atomically), // to claim the right to install the real forwarding pointer. forward_ptr = old->forward_to_atomic(ClaimedForwardPtr); if (forward_ptr != NULL) { // someone else beat us to it. return real_forwardee(old); } new_obj = _next_gen->par_promote(par_scan_state->thread_num(), old, m, sz); if (new_obj == NULL) { if (!HandlePromotionFailure) { // A failed promotion likely means the MaxLiveObjectEvacuationRatio flag // is incorrectly set. In any case, its seriously wrong to be here! vm_exit_out_of_memory(sz*wordSize, "promotion"); } // promotion failed, forward to self _promotion_failed = true; new_obj = old; preserve_mark_if_necessary(old, m); } old->forward_to(new_obj); forward_ptr = NULL; } else { // Is in to-space; do copying ourselves. Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz); forward_ptr = old->forward_to_atomic(new_obj); // Restore the mark word copied above. new_obj->set_mark(m); // Increment age if obj still in new generation new_obj->incr_age(); par_scan_state->age_table()->add(new_obj, sz); } assert(new_obj != NULL, "just checking"); if (forward_ptr == NULL) { oop obj_to_push = new_obj; if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) { // Length field used as index of next element to be scanned. // Real length can be obtained from real_forwardee() arrayOop(old)->set_length(0); obj_to_push = old; assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push, "push forwarded object"); } // Push it on one of the queues of to-be-scanned objects. if (!par_scan_state->work_queue()->push(obj_to_push)) { // Add stats for overflow pushes. if (Verbose && PrintGCDetails) { gclog_or_tty->print("queue overflow!\n"); } push_on_overflow_list(old); par_scan_state->note_overflow_push(); } par_scan_state->note_push(); return new_obj; } // Oops. Someone beat us to it. Undo the allocation. Where did we // allocate it? if (is_in_reserved(new_obj)) { // Must be in to_space. assert(to()->is_in_reserved(new_obj), "Checking"); if (forward_ptr == ClaimedForwardPtr) { // Wait to get the real forwarding pointer value. forward_ptr = real_forwardee(old); } par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz); } return forward_ptr; } // Multiple GC threads may try to promote the same object. If two // or more GC threads copy the object, only one wins the race to install // the forwarding pointer. The other threads have to undo their copy. oop ParNewGeneration::copy_to_survivor_space_with_undo( ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) { // In the sequential version, this assert also says that the object is // not forwarded. That might not be the case here. It is the case that // the caller observed it to be not forwarded at some time in the past. assert(is_in_reserved(old), "shouldn't be scavenging this oop"); // The sequential code read "old->age()" below. That doesn't work here, // since the age is in the mark word, and that might be overwritten with // a forwarding pointer by a parallel thread. So we must save the mark // word here, install it in a local oopDesc, and then analyze it. oopDesc dummyOld; dummyOld.set_mark(m); assert(!dummyOld.is_forwarded(), "should not be called with forwarding pointer mark word."); bool failed_to_promote = false; oop new_obj = NULL; oop forward_ptr; // Try allocating obj in to-space (unless too old) if (dummyOld.age() < tenuring_threshold()) { new_obj = (oop)par_scan_state->alloc_in_to_space(sz); if (new_obj == NULL) { set_survivor_overflow(true); } } if (new_obj == NULL) { // Either to-space is full or we decided to promote // try allocating obj tenured new_obj = _next_gen->par_promote(par_scan_state->thread_num(), old, m, sz); if (new_obj == NULL) { if (!HandlePromotionFailure) { // A failed promotion likely means the MaxLiveObjectEvacuationRatio // flag is incorrectly set. In any case, its seriously wrong to be // here! vm_exit_out_of_memory(sz*wordSize, "promotion"); } // promotion failed, forward to self forward_ptr = old->forward_to_atomic(old); new_obj = old; if (forward_ptr != NULL) { return forward_ptr; // someone else succeeded } _promotion_failed = true; failed_to_promote = true; preserve_mark_if_necessary(old, m); } } else { // Is in to-space; do copying ourselves. Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz); // Restore the mark word copied above. new_obj->set_mark(m); // Increment age if new_obj still in new generation new_obj->incr_age(); par_scan_state->age_table()->add(new_obj, sz); } assert(new_obj != NULL, "just checking"); // Now attempt to install the forwarding pointer (atomically). // We have to copy the mark word before overwriting with forwarding // ptr, so we can restore it below in the copy. if (!failed_to_promote) { forward_ptr = old->forward_to_atomic(new_obj); } if (forward_ptr == NULL) { oop obj_to_push = new_obj; if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) { // Length field used as index of next element to be scanned. // Real length can be obtained from real_forwardee() arrayOop(old)->set_length(0); obj_to_push = old; assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push, "push forwarded object"); } // Push it on one of the queues of to-be-scanned objects. if (!par_scan_state->work_queue()->push(obj_to_push)) { // Add stats for overflow pushes. push_on_overflow_list(old); par_scan_state->note_overflow_push(); } par_scan_state->note_push(); return new_obj; } // Oops. Someone beat us to it. Undo the allocation. Where did we // allocate it? if (is_in_reserved(new_obj)) { // Must be in to_space. assert(to()->is_in_reserved(new_obj), "Checking"); par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz); } else { assert(!_avoid_promotion_undo, "Should not be here if avoiding."); _next_gen->par_promote_alloc_undo(par_scan_state->thread_num(), (HeapWord*)new_obj, sz); } return forward_ptr; } void ParNewGeneration::push_on_overflow_list(oop from_space_obj) { oop cur_overflow_list = _overflow_list; // if the object has been forwarded to itself, then we cannot // use the klass pointer for the linked list. Instead we have // to allocate an oopDesc in the C-Heap and use that for the linked list. if (from_space_obj->forwardee() == from_space_obj) { oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1); listhead->forward_to(from_space_obj); from_space_obj = listhead; } while (true) { from_space_obj->set_klass_to_list_ptr(cur_overflow_list); oop observed_overflow_list = (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list); if (observed_overflow_list == cur_overflow_list) break; // Otherwise... cur_overflow_list = observed_overflow_list; } } bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) { ObjToScanQueue* work_q = par_scan_state->work_queue(); // How many to take? int objsFromOverflow = MIN2(work_q->max_elems()/4, (juint)ParGCDesiredObjsFromOverflowList); if (_overflow_list == NULL) return false; // Otherwise, there was something there; try claiming the list. oop prefix = (oop)Atomic::xchg_ptr(NULL, &_overflow_list); if (prefix == NULL) { return false; } // Trim off a prefix of at most objsFromOverflow items int i = 1; oop cur = prefix; while (i < objsFromOverflow && cur->klass_or_null() != NULL) { i++; cur = oop(cur->klass()); } // Reattach remaining (suffix) to overflow list if (cur->klass_or_null() != NULL) { oop suffix = oop(cur->klass()); cur->set_klass_to_list_ptr(NULL); // Find last item of suffix list oop last = suffix; while (last->klass_or_null() != NULL) { last = oop(last->klass()); } // Atomically prepend suffix to current overflow list oop cur_overflow_list = _overflow_list; while (true) { last->set_klass_to_list_ptr(cur_overflow_list); oop observed_overflow_list = (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); if (observed_overflow_list == cur_overflow_list) break; // Otherwise... cur_overflow_list = observed_overflow_list; } } // Push objects on prefix list onto this thread's work queue assert(cur != NULL, "program logic"); cur = prefix; int n = 0; while (cur != NULL) { oop obj_to_push = cur->forwardee(); oop next = oop(cur->klass()); cur->set_klass(obj_to_push->klass()); if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) { obj_to_push = cur; assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); } work_q->push(obj_to_push); cur = next; n++; } par_scan_state->note_overflow_refill(n); return true; } void ParNewGeneration::ref_processor_init() { if (_ref_processor == NULL) { // Allocate and initialize a reference processor _ref_processor = ReferenceProcessor::create_ref_processor( _reserved, // span refs_discovery_is_atomic(), // atomic_discovery refs_discovery_is_mt(), // mt_discovery NULL, // is_alive_non_header ParallelGCThreads, ParallelRefProcEnabled); } } const char* ParNewGeneration::name() const { return "par new generation"; }