/* * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ #include "precompiled.hpp" #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp" #include "gc_implementation/parNew/parNewGeneration.hpp" #include "gc_implementation/parNew/parOopClosures.inline.hpp" #include "gc_implementation/shared/adaptiveSizePolicy.hpp" #include "gc_implementation/shared/ageTable.hpp" #include "gc_implementation/shared/parGCAllocBuffer.hpp" #include "gc_implementation/shared/gcHeapSummary.hpp" #include "gc_implementation/shared/gcTimer.hpp" #include "gc_implementation/shared/gcTrace.hpp" #include "gc_implementation/shared/gcTraceTime.hpp" #include "gc_implementation/shared/copyFailedInfo.hpp" #include "gc_implementation/shared/spaceDecorator.hpp" #include "memory/defNewGeneration.inline.hpp" #include "memory/genCollectedHeap.hpp" #include "memory/genOopClosures.inline.hpp" #include "memory/generation.hpp" #include "memory/generation.inline.hpp" #include "memory/referencePolicy.hpp" #include "memory/resourceArea.hpp" #include "memory/sharedHeap.hpp" #include "memory/space.hpp" #include "oops/objArrayOop.hpp" #include "oops/oop.inline.hpp" #include "oops/oop.pcgc.inline.hpp" #include "runtime/handles.hpp" #include "runtime/handles.inline.hpp" #include "runtime/java.hpp" #include "runtime/thread.inline.hpp" #include "utilities/copy.hpp" #include "utilities/globalDefinitions.hpp" #include "utilities/workgroup.hpp" PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC #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_, Stack* overflow_stacks_, size_t desired_plab_sz_, ParallelTaskTerminator& term_) : _to_space(to_space_), _old_gen(old_gen_), _young_gen(gen_), _thread_num(thread_num_), _work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false), _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL), _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), _strong_roots_time(0.0), _term_time(0.0) { #if TASKQUEUE_STATS _term_attempts = 0; _overflow_refills = 0; _overflow_refill_objs = 0; #endif // TASKQUEUE_STATS _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"); } 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(); do { while (queue->size() > (juint)max_size) { oop obj_to_scan; if (queue->pop_local(obj_to_scan)) { 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); } } } // For the case of compressed oops, we have a private, non-shared // overflow stack, so we eagerly drain it so as to more evenly // distribute load early. Note: this may be good to do in // general rather than delay for the final stealing phase. // If applicable, we'll transfer a set of objects over to our // work queue, allowing them to be stolen and draining our // private overflow stack. } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this)); } bool ParScanThreadState::take_from_overflow_stack() { assert(ParGCUseLocalOverflow, "Else should not call"); assert(young_gen()->overflow_list() == NULL, "Error"); ObjToScanQueue* queue = work_queue(); Stack* const of_stack = overflow_stack(); const size_t num_overflow_elems = of_stack->size(); const size_t space_available = queue->max_elems() - queue->size(); const size_t num_take_elems = MIN3(space_available / 4, ParGCDesiredObjsFromOverflowList, num_overflow_elems); // Transfer the most recent num_take_elems from the overflow // stack to our work queue. for (size_t i = 0; i != num_take_elems; i++) { oop cur = of_stack->pop(); oop obj_to_push = cur->forwardee(); assert(Universe::heap()->is_in_reserved(cur), "Should be in heap"); assert(!old_gen()->is_in_reserved(cur), "Should be in young gen"); assert(Universe::heap()->is_in_reserved(obj_to_push), "Should be in heap"); if (should_be_partially_scanned(obj_to_push, cur)) { assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); obj_to_push = cur; } bool ok = queue->push(obj_to_push); assert(ok, "Should have succeeded"); } assert(young_gen()->overflow_list() == NULL, "Error"); return num_take_elems > 0; // was something transferred? } void ParScanThreadState::push_on_overflow_stack(oop p) { assert(ParGCUseLocalOverflow, "Else should not call"); overflow_stack()->push(p); assert(young_gen()->overflow_list() == NULL, "Error"); } 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 { CollectedHeap::fill_with_object(obj, word_sz); } } void ParScanThreadState::print_promotion_failure_size() { if (_promotion_failed_info.has_failed() && PrintPromotionFailure) { gclog_or_tty->print(" (%d: promotion failure size = " SIZE_FORMAT ") ", _thread_num, _promotion_failed_info.first_size()); } } 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, Stack* overflow_stacks_, size_t desired_plab_sz, ParallelTaskTerminator& term); ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); } inline ParScanThreadState& thread_state(int i); void trace_promotion_failed(YoungGCTracer& gc_tracer); void reset(int active_workers, bool promotion_failed); void flush(); #if TASKQUEUE_STATS static void print_termination_stats_hdr(outputStream* const st = gclog_or_tty); void print_termination_stats(outputStream* const st = gclog_or_tty); static void print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty); void print_taskqueue_stats(outputStream* const st = gclog_or_tty); void reset_stats(); #endif // TASKQUEUE_STATS private: ParallelTaskTerminator& _term; ParNewGeneration& _gen; Generation& _next_gen; public: bool is_valid(int id) const { return id < length(); } ParallelTaskTerminator* terminator() { return &_term; } }; ParScanThreadStateSet::ParScanThreadStateSet( int num_threads, Space& to_space, ParNewGeneration& gen, Generation& old_gen, ObjToScanQueueSet& queue_set, Stack* overflow_stacks, size_t desired_plab_sz, ParallelTaskTerminator& term) : ResourceArray(sizeof(ParScanThreadState), num_threads), _gen(gen), _next_gen(old_gen), _term(term) { assert(num_threads > 0, "sanity check!"); assert(ParGCUseLocalOverflow == (overflow_stacks != NULL), "overflow_stack allocation mismatch"); // Initialize states. for (int i = 0; i < num_threads; ++i) { new ((ParScanThreadState*)_data + i) ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set, overflow_stacks, desired_plab_sz, term); } } inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i) { assert(i >= 0 && i < length(), "sanity check!"); return ((ParScanThreadState*)_data)[i]; } void ParScanThreadStateSet::trace_promotion_failed(YoungGCTracer& gc_tracer) { for (int i = 0; i < length(); ++i) { if (thread_state(i).promotion_failed()) { gc_tracer.report_promotion_failed(thread_state(i).promotion_failed_info()); thread_state(i).promotion_failed_info().reset(); } } } void ParScanThreadStateSet::reset(int active_threads, bool promotion_failed) { _term.reset_for_reuse(active_threads); if (promotion_failed) { for (int i = 0; i < length(); ++i) { thread_state(i).print_promotion_failure_size(); } } } #if TASKQUEUE_STATS void ParScanThreadState::reset_stats() { taskqueue_stats().reset(); _term_attempts = 0; _overflow_refills = 0; _overflow_refill_objs = 0; } void ParScanThreadStateSet::reset_stats() { for (int i = 0; i < length(); ++i) { thread_state(i).reset_stats(); } } void ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st) { st->print_raw_cr("GC Termination Stats"); st->print_raw_cr(" elapsed --strong roots-- " "-------termination-------"); st->print_raw_cr("thr ms ms % " " ms % attempts"); st->print_raw_cr("--- --------- --------- ------ " "--------- ------ --------"); } void ParScanThreadStateSet::print_termination_stats(outputStream* const st) { print_termination_stats_hdr(st); for (int i = 0; i < length(); ++i) { const ParScanThreadState & pss = thread_state(i); const double elapsed_ms = pss.elapsed_time() * 1000.0; const double s_roots_ms = pss.strong_roots_time() * 1000.0; const double term_ms = pss.term_time() * 1000.0; st->print_cr("%3d %9.2f %9.2f %6.2f " "%9.2f %6.2f " SIZE_FORMAT_W(8), i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms, term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts()); } } // Print stats related to work queue activity. void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st) { st->print_raw_cr("GC Task Stats"); st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr(); st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr(); } void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st) { print_taskqueue_stats_hdr(st); TaskQueueStats totals; for (int i = 0; i < length(); ++i) { const ParScanThreadState & pss = thread_state(i); const TaskQueueStats & stats = pss.taskqueue_stats(); st->print("%3d ", i); stats.print(st); st->cr(); totals += stats; if (pss.overflow_refills() > 0) { st->print_cr(" " SIZE_FORMAT_W(10) " overflow refills " SIZE_FORMAT_W(10) " overflow objects", pss.overflow_refills(), pss.overflow_refill_objs()); } } st->print("tot "); totals.print(st); st->cr(); DEBUG_ONLY(totals.verify()); } #endif // TASKQUEUE_STATS void ParScanThreadStateSet::flush() { // Work in this loop should be kept as lightweight as // possible since this might otherwise become a bottleneck // to scaling. Should we add heavy-weight work into this // loop, consider parallelizing the loop into the worker threads. for (int i = 0; i < length(); ++i) { ParScanThreadState& par_scan_state = thread_state(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(), true /* end_of_gc */, 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); } if (UseConcMarkSweepGC && ParallelGCThreads > 0) { // We need to call this even when ResizeOldPLAB is disabled // so as to avoid breaking some asserts. While we may be able // to avoid this by reorganizing the code a bit, I am loathe // to do that unless we find cases where ergo leads to bad // performance. CFLS_LAB::compute_desired_plab_size(); } } ParScanClosure::ParScanClosure(ParNewGeneration* g, ParScanThreadState* par_scan_state) : OopsInKlassOrGenClosure(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. if (task_queues()->steal(par_scan_state()->thread_num(), par_scan_state()->hash_seed(), obj_to_scan)) { bool res = work_q->push(obj_to_scan); assert(res, "Empty queue should have room for a 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(); } assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0, "Broken overflow list?"); // 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) {} // Reset the terminator for the given number of // active threads. void ParNewGenTask::set_for_termination(int active_workers) { _state_set->reset(active_workers, _gen->promotion_failed()); // Should the heap be passed in? There's only 1 for now so // grab it instead. GenCollectedHeap* gch = GenCollectedHeap::heap(); gch->set_n_termination(active_workers); } void ParNewGenTask::work(uint worker_id) { 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. assert(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_state(worker_id); assert(_state_set->is_valid(worker_id), "Should not have been called"); par_scan_state.set_young_old_boundary(_young_old_boundary); KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(), gch->rem_set()->klass_rem_set()); int so = SharedHeap::SO_AllClasses | SharedHeap::SO_Strings | SharedHeap::SO_ScavengeCodeCache; par_scan_state.start_strong_roots(); gch->gen_process_strong_roots(_gen->level(), true, // Process younger gens, if any, // as strong roots. false, // no scope; this is parallel code SharedHeap::ScanningOption(so), &par_scan_state.to_space_root_closure(), &par_scan_state.older_gen_closure(), &klass_scan_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) { NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;) NOT_PRODUCT(_num_par_pushes = 0;) _task_queues = new ObjToScanQueueSet(ParallelGCThreads); guarantee(_task_queues != NULL, "task_queues allocation failure."); for (uint i1 = 0; i1 < ParallelGCThreads; i1++) { ObjToScanQueue *q = new ObjToScanQueue(); guarantee(q != NULL, "work_queue Allocation failure."); _task_queues->register_queue(i1, q); } for (uint i2 = 0; i2 < ParallelGCThreads; i2++) _task_queues->queue(i2)->initialize(); _overflow_stacks = NULL; if (ParGCUseLocalOverflow) { // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal // with ',' typedef Stack GCOopStack; _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC); for (size_t i = 0; i < ParallelGCThreads; ++i) { new (_overflow_stacks + i) Stack(); } } 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(uint worker_id); virtual void set_for_termination(int active_workers) { _state_set.terminator()->reset_for_reuse(active_workers); } 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(uint worker_id) { ResourceMark rm; HandleMark hm; ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id); par_scan_state.set_young_old_boundary(_young_old_boundary); _task.work(worker_id, 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(uint worker_id) { _task.work(worker_id); } }; void ParNewRefProcTaskExecutor::execute(ProcessTask& task) { GenCollectedHeap* gch = GenCollectedHeap::heap(); assert(gch->kind() == CollectedHeap::GenCollectedHeap, "not a generational heap"); FlexibleWorkGang* workers = gch->workers(); assert(workers != NULL, "Need parallel worker threads."); _state_set.reset(workers->active_workers(), _generation.promotion_failed()); ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(), _generation.reserved().end(), _state_set); workers->run_task(&rp_task); _state_set.reset(0 /* bad value in debug if not reset */, _generation.promotion_failed()); } void ParNewRefProcTaskExecutor::execute(EnqueueTask& task) { GenCollectedHeap* gch = GenCollectedHeap::heap(); FlexibleWorkGang* 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)); } // A Generation that does parallel young-gen collection. bool ParNewGeneration::_avoid_promotion_undo = false; void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set, ParNewTracer& gc_tracer) { assert(_promo_failure_scan_stack.is_empty(), "post condition"); _promo_failure_scan_stack.clear(true); // Clear cached segments. 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_failed(); // Inform the next generation that a promotion failure occurred. _next_gen->promotion_failure_occurred(); // Trace promotion failure in the parallel GC threads thread_state_set.trace_promotion_failed(gc_tracer); // Single threaded code may have reported promotion failure to the global state if (_promotion_failed_info.has_failed()) { gc_tracer.report_promotion_failed(_promotion_failed_info); } // Reset the PromotionFailureALot counters. NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();) } 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(); _gc_timer->register_gc_start(); assert(gch->kind() == CollectedHeap::GenCollectedHeap, "not a CMS generational heap"); AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy(); FlexibleWorkGang* workers = gch->workers(); assert(workers != NULL, "Need workgang for parallel work"); int active_workers = AdaptiveSizePolicy::calc_active_workers(workers->total_workers(), workers->active_workers(), Threads::number_of_non_daemon_threads()); workers->set_active_workers(active_workers); assert(gch->n_gens() == 2, "Par collection currently only works with single older gen."); _next_gen = gch->next_gen(this); // 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 accommodate worst-case promotion // from this generation, pass on collection; let the next generation // do it. if (!collection_attempt_is_safe()) { gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one return; } assert(to()->is_empty(), "Else not collection_attempt_is_safe"); ParNewTracer gc_tracer; gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start()); gch->trace_heap_before_gc(&gc_tracer); init_assuming_no_promotion_failure(); if (UseAdaptiveSizePolicy) { set_survivor_overflow(false); size_policy->minor_collection_begin(); } GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, gc_tracer.gc_id()); // 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."); int n_workers = active_workers; // Set the correct parallelism (number of queues) in the reference processor ref_processor()->set_active_mt_degree(n_workers); // Always set the terminator for the active number of workers // because only those workers go through the termination protocol. ParallelTaskTerminator _term(n_workers, task_queues()); ParScanThreadStateSet thread_state_set(workers->active_workers(), *to(), *this, *_next_gen, *task_queues(), _overflow_stacks, desired_plab_sz(), _term); ParNewGenTask tsk(this, _next_gen, reserved().end(), &thread_state_set); gch->set_par_threads(n_workers); 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) { GenCollectedHeap::StrongRootsScope srs(gch); workers->run_task(&tsk); } else { GenCollectedHeap::StrongRootsScope srs(gch); tsk.work(0); } thread_state_set.reset(0 /* Bad value in debug if not reset */, promotion_failed()); // 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->setup_policy(clear_all_soft_refs); // Can the mt_degree be set later (at run_task() time would be best)? rp->set_active_mt_degree(active_workers); ReferenceProcessorStats stats; if (rp->processing_is_mt()) { ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); stats = rp->process_discovered_references(&is_alive, &keep_alive, &evacuate_followers, &task_executor, _gc_timer, gc_tracer.gc_id()); } else { thread_state_set.flush(); gch->set_par_threads(0); // 0 ==> non-parallel. gch->save_marks(); stats = rp->process_discovered_references(&is_alive, &keep_alive, &evacuate_followers, NULL, _gc_timer, gc_tracer.gc_id()); } gc_tracer.report_gc_reference_stats(stats); 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(); // A successful scavenge should restart the GC time limit count which is // for full GC's. size_policy->reset_gc_overhead_limit_count(); assert(to()->is_empty(), "to space should be empty now"); adjust_desired_tenuring_threshold(); } else { handle_promotion_failed(gch, thread_state_set, gc_tracer); } // 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()); if (ResizePLAB) { plab_stats()->adjust_desired_plab_sz(n_workers); } if (PrintGC && !PrintGCDetails) { gch->print_heap_change(gch_prev_used); } if (PrintGCDetails && ParallelGCVerbose) { TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats()); TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats()); } if (UseAdaptiveSizePolicy) { size_policy->minor_collection_end(gch->gc_cause()); size_policy->avg_survived()->sample(from()->used()); } // We need to use a monotonically non-deccreasing time in ms // or we will see time-warp warnings and os::javaTimeMillis() // does not guarantee monotonicity. jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; update_time_of_last_gc(now); 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(); gch->trace_heap_after_gc(&gc_tracer); gc_tracer.report_tenuring_threshold(tenuring_threshold()); _gc_timer->register_gc_end(); gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions()); } static int sum; void ParNewGeneration::waste_some_time() { for (int i = 0; i < 100; i++) { sum += i; } } static const oop ClaimedForwardPtr = cast_to_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->must_be_preserved_for_promotion_failure(obj)) { // We should really have separate per-worker stacks, rather // than use locking of a common pair of stacks. MutexLocker ml(ParGCRareEvent_lock); preserve_mark(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) { // promotion failed, forward to self _promotion_failed = true; new_obj = old; preserve_mark_if_necessary(old, m); par_scan_state->register_promotion_failure(sz); } 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"); #ifndef PRODUCT // This code must come after the CAS test, or it will print incorrect // information. if (TraceScavenge) { gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}", is_in_reserved(new_obj) ? "copying" : "tenuring", new_obj->klass()->internal_name(), (void *)old, (void *)new_obj, new_obj->size()); } #endif 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. bool simulate_overflow = false; NOT_PRODUCT( if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) { // simulate a stack overflow simulate_overflow = true; } ) if (simulate_overflow || !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); TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0)); } 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) { // 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); par_scan_state->register_promotion_failure(sz); } } 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"); #ifndef PRODUCT // This code must come after the CAS test, or it will print incorrect // information. if (TraceScavenge) { gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}", is_in_reserved(new_obj) ? "copying" : "tenuring", new_obj->klass()->internal_name(), (void *)old, (void *)new_obj, new_obj->size()); } #endif // 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. bool simulate_overflow = false; NOT_PRODUCT( if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) { // simulate a stack overflow simulate_overflow = true; } ) if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) { // Add stats for overflow pushes. push_on_overflow_list(old, par_scan_state); TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0)); } 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; } #ifndef PRODUCT // 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 ParNewGeneration::should_simulate_overflow() { if (_overflow_counter-- <= 0) { // just being defensive _overflow_counter = ParGCWorkQueueOverflowInterval; return true; } else { return false; } } #endif // In case we are using compressed oops, we need to be careful. // If the object being pushed is an object array, then its length // field keeps track of the "grey boundary" at which the next // incremental scan will be done (see ParGCArrayScanChunk). // When using compressed oops, this length field is kept in the // lower 32 bits of the erstwhile klass word and cannot be used // for the overflow chaining pointer (OCP below). As such the OCP // would itself need to be compressed into the top 32-bits in this // case. Unfortunately, see below, in the event that we have a // promotion failure, the node to be pushed on the list can be // outside of the Java heap, so the heap-based pointer compression // would not work (we would have potential aliasing between C-heap // and Java-heap pointers). For this reason, when using compressed // oops, we simply use a worker-thread-local, non-shared overflow // list in the form of a growable array, with a slightly different // overflow stack draining strategy. If/when we start using fat // stacks here, we can go back to using (fat) pointer chains // (although some performance comparisons would be useful since // single global lists have their own performance disadvantages // as we were made painfully aware not long ago, see 6786503). #define BUSY (cast_to_oop(0x1aff1aff)) void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) { assert(is_in_reserved(from_space_obj), "Should be from this generation"); if (ParGCUseLocalOverflow) { // In the case of compressed oops, we use a private, not-shared // overflow stack. par_scan_state->push_on_overflow_stack(from_space_obj); } else { assert(!UseCompressedOops, "Error"); // 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. // XXX This is horribly inefficient when a promotion failure occurs // and should be fixed. XXX FIX ME !!! #ifndef PRODUCT Atomic::inc_ptr(&_num_par_pushes); assert(_num_par_pushes > 0, "Tautology"); #endif if (from_space_obj->forwardee() == from_space_obj) { oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC); listhead->forward_to(from_space_obj); from_space_obj = listhead; } oop observed_overflow_list = _overflow_list; oop cur_overflow_list; do { cur_overflow_list = observed_overflow_list; if (cur_overflow_list != BUSY) { from_space_obj->set_klass_to_list_ptr(cur_overflow_list); } else { from_space_obj->set_klass_to_list_ptr(NULL); } observed_overflow_list = (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list); } while (cur_overflow_list != observed_overflow_list); } } bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) { bool res; if (ParGCUseLocalOverflow) { res = par_scan_state->take_from_overflow_stack(); } else { assert(!UseCompressedOops, "Error"); res = take_from_overflow_list_work(par_scan_state); } return res; } // *NOTE*: The overflow list manipulation code here and // in CMSCollector:: are very similar in shape, // except that in the CMS case we thread the objects // directly into the list via their mark word, and do // not need to deal with special cases below related // to chunking of object arrays and promotion failure // handling. // CR 6797058 has been filed to attempt consolidation of // the common code. // Because of the common code, if you make any changes in // the code below, please check the CMS version to see if // similar changes might be needed. // See CMSCollector::par_take_from_overflow_list() for // more extensive documentation comments. bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) { ObjToScanQueue* work_q = par_scan_state->work_queue(); // How many to take? size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, (size_t)ParGCDesiredObjsFromOverflowList); assert(!UseCompressedOops, "Error"); assert(par_scan_state->overflow_stack() == NULL, "Error"); if (_overflow_list == NULL) return false; // Otherwise, there was something there; try claiming the list. oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); // Trim off a prefix of at most objsFromOverflow items Thread* tid = Thread::current(); size_t spin_count = (size_t)ParallelGCThreads; size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100); for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) { // someone grabbed it before we did ... // ... we spin for a short while... os::sleep(tid, sleep_time_millis, false); if (_overflow_list == NULL) { // nothing left to take return false; } else if (_overflow_list != BUSY) { // try and grab the prefix prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); } } if (prefix == NULL || prefix == BUSY) { // Nothing to take or waited long enough if (prefix == NULL) { // Write back the NULL in case we overwrote it with BUSY above // and it is still the same value. (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); } return false; } assert(prefix != NULL && prefix != BUSY, "Error"); size_t i = 1; oop cur = prefix; while (i < objsFromOverflow && cur->klass_or_null() != NULL) { i++; cur = cur->list_ptr_from_klass(); } // Reattach remaining (suffix) to overflow list if (cur->klass_or_null() == NULL) { // Write back the NULL in lieu of the BUSY we wrote // above and it is still the same value. if (_overflow_list == BUSY) { (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); } } else { assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error"); oop suffix = cur->list_ptr_from_klass(); // suffix will be put back on global list cur->set_klass_to_list_ptr(NULL); // break off suffix // It's possible that the list is still in the empty(busy) state // we left it in a short while ago; in that case we may be // able to place back the suffix. oop observed_overflow_list = _overflow_list; oop cur_overflow_list = observed_overflow_list; bool attached = false; while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { observed_overflow_list = (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); if (cur_overflow_list == observed_overflow_list) { attached = true; break; } else cur_overflow_list = observed_overflow_list; } if (!attached) { // Too bad, someone else got in in between; we'll need to do a splice. // Find the last item of suffix list oop last = suffix; while (last->klass_or_null() != NULL) { last = last->list_ptr_from_klass(); } // Atomically prepend suffix to current overflow list observed_overflow_list = _overflow_list; do { cur_overflow_list = observed_overflow_list; if (cur_overflow_list != BUSY) { // Do the splice ... last->set_klass_to_list_ptr(cur_overflow_list); } else { // cur_overflow_list == BUSY last->set_klass_to_list_ptr(NULL); } observed_overflow_list = (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); } while (cur_overflow_list != observed_overflow_list); } } // Push objects on prefix list onto this thread's work queue assert(prefix != NULL && prefix != BUSY, "program logic"); cur = prefix; ssize_t n = 0; while (cur != NULL) { oop obj_to_push = cur->forwardee(); oop next = cur->list_ptr_from_klass(); cur->set_klass(obj_to_push->klass()); // This may be an array object that is self-forwarded. In that case, the list pointer // space, cur, is not in the Java heap, but rather in the C-heap and should be freed. if (!is_in_reserved(cur)) { // This can become a scaling bottleneck when there is work queue overflow coincident // with promotion failure. oopDesc* f = cur; FREE_C_HEAP_ARRAY(oopDesc, f, mtGC); } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) { assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); obj_to_push = cur; } bool ok = work_q->push(obj_to_push); assert(ok, "Should have succeeded"); cur = next; n++; } TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n)); #ifndef PRODUCT assert(_num_par_pushes >= n, "Too many pops?"); Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes); #endif return true; } #undef BUSY void ParNewGeneration::ref_processor_init() { if (_ref_processor == NULL) { // Allocate and initialize a reference processor _ref_processor = new ReferenceProcessor(_reserved, // span ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing (int) ParallelGCThreads, // mt processing degree refs_discovery_is_mt(), // mt discovery (int) ParallelGCThreads, // mt discovery degree refs_discovery_is_atomic(), // atomic_discovery NULL); // is_alive_non_header } } const char* ParNewGeneration::name() const { return "par new generation"; }