parNewGeneration.cpp revision 10977:9c5d445a7962
1/* 2 * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25#include "precompiled.hpp" 26#include "gc/cms/compactibleFreeListSpace.hpp" 27#include "gc/cms/concurrentMarkSweepGeneration.hpp" 28#include "gc/cms/parNewGeneration.inline.hpp" 29#include "gc/cms/parOopClosures.inline.hpp" 30#include "gc/serial/defNewGeneration.inline.hpp" 31#include "gc/shared/adaptiveSizePolicy.hpp" 32#include "gc/shared/ageTable.inline.hpp" 33#include "gc/shared/copyFailedInfo.hpp" 34#include "gc/shared/gcHeapSummary.hpp" 35#include "gc/shared/gcTimer.hpp" 36#include "gc/shared/gcTrace.hpp" 37#include "gc/shared/gcTraceTime.inline.hpp" 38#include "gc/shared/genCollectedHeap.hpp" 39#include "gc/shared/genOopClosures.inline.hpp" 40#include "gc/shared/generation.hpp" 41#include "gc/shared/plab.inline.hpp" 42#include "gc/shared/preservedMarks.inline.hpp" 43#include "gc/shared/referencePolicy.hpp" 44#include "gc/shared/space.hpp" 45#include "gc/shared/spaceDecorator.hpp" 46#include "gc/shared/strongRootsScope.hpp" 47#include "gc/shared/taskqueue.inline.hpp" 48#include "gc/shared/workgroup.hpp" 49#include "logging/log.hpp" 50#include "memory/resourceArea.hpp" 51#include "oops/objArrayOop.hpp" 52#include "oops/oop.inline.hpp" 53#include "runtime/atomic.inline.hpp" 54#include "runtime/handles.hpp" 55#include "runtime/handles.inline.hpp" 56#include "runtime/java.hpp" 57#include "runtime/thread.inline.hpp" 58#include "utilities/copy.hpp" 59#include "utilities/globalDefinitions.hpp" 60#include "utilities/stack.inline.hpp" 61 62ParScanThreadState::ParScanThreadState(Space* to_space_, 63 ParNewGeneration* young_gen_, 64 Generation* old_gen_, 65 int thread_num_, 66 ObjToScanQueueSet* work_queue_set_, 67 Stack<oop, mtGC>* overflow_stacks_, 68 PreservedMarks* preserved_marks_, 69 size_t desired_plab_sz_, 70 ParallelTaskTerminator& term_) : 71 _to_space(to_space_), 72 _old_gen(old_gen_), 73 _young_gen(young_gen_), 74 _thread_num(thread_num_), 75 _work_queue(work_queue_set_->queue(thread_num_)), 76 _to_space_full(false), 77 _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL), 78 _preserved_marks(preserved_marks_), 79 _ageTable(false), // false ==> not the global age table, no perf data. 80 _to_space_alloc_buffer(desired_plab_sz_), 81 _to_space_closure(young_gen_, this), 82 _old_gen_closure(young_gen_, this), 83 _to_space_root_closure(young_gen_, this), 84 _old_gen_root_closure(young_gen_, this), 85 _older_gen_closure(young_gen_, this), 86 _evacuate_followers(this, &_to_space_closure, &_old_gen_closure, 87 &_to_space_root_closure, young_gen_, &_old_gen_root_closure, 88 work_queue_set_, &term_), 89 _is_alive_closure(young_gen_), 90 _scan_weak_ref_closure(young_gen_, this), 91 _keep_alive_closure(&_scan_weak_ref_closure), 92 _strong_roots_time(0.0), 93 _term_time(0.0) 94{ 95 #if TASKQUEUE_STATS 96 _term_attempts = 0; 97 _overflow_refills = 0; 98 _overflow_refill_objs = 0; 99 #endif // TASKQUEUE_STATS 100 101 _survivor_chunk_array = (ChunkArray*) old_gen()->get_data_recorder(thread_num()); 102 _hash_seed = 17; // Might want to take time-based random value. 103 _start = os::elapsedTime(); 104 _old_gen_closure.set_generation(old_gen_); 105 _old_gen_root_closure.set_generation(old_gen_); 106} 107 108void ParScanThreadState::record_survivor_plab(HeapWord* plab_start, 109 size_t plab_word_size) { 110 ChunkArray* sca = survivor_chunk_array(); 111 if (sca != NULL) { 112 // A non-null SCA implies that we want the PLAB data recorded. 113 sca->record_sample(plab_start, plab_word_size); 114 } 115} 116 117bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const { 118 return new_obj->is_objArray() && 119 arrayOop(new_obj)->length() > ParGCArrayScanChunk && 120 new_obj != old_obj; 121} 122 123void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) { 124 assert(old->is_objArray(), "must be obj array"); 125 assert(old->is_forwarded(), "must be forwarded"); 126 assert(GenCollectedHeap::heap()->is_in_reserved(old), "must be in heap."); 127 assert(!old_gen()->is_in(old), "must be in young generation."); 128 129 objArrayOop obj = objArrayOop(old->forwardee()); 130 // Process ParGCArrayScanChunk elements now 131 // and push the remainder back onto queue 132 int start = arrayOop(old)->length(); 133 int end = obj->length(); 134 int remainder = end - start; 135 assert(start <= end, "just checking"); 136 if (remainder > 2 * ParGCArrayScanChunk) { 137 // Test above combines last partial chunk with a full chunk 138 end = start + ParGCArrayScanChunk; 139 arrayOop(old)->set_length(end); 140 // Push remainder. 141 bool ok = work_queue()->push(old); 142 assert(ok, "just popped, push must be okay"); 143 } else { 144 // Restore length so that it can be used if there 145 // is a promotion failure and forwarding pointers 146 // must be removed. 147 arrayOop(old)->set_length(end); 148 } 149 150 // process our set of indices (include header in first chunk) 151 // should make sure end is even (aligned to HeapWord in case of compressed oops) 152 if ((HeapWord *)obj < young_old_boundary()) { 153 // object is in to_space 154 obj->oop_iterate_range(&_to_space_closure, start, end); 155 } else { 156 // object is in old generation 157 obj->oop_iterate_range(&_old_gen_closure, start, end); 158 } 159} 160 161void ParScanThreadState::trim_queues(int max_size) { 162 ObjToScanQueue* queue = work_queue(); 163 do { 164 while (queue->size() > (juint)max_size) { 165 oop obj_to_scan; 166 if (queue->pop_local(obj_to_scan)) { 167 if ((HeapWord *)obj_to_scan < young_old_boundary()) { 168 if (obj_to_scan->is_objArray() && 169 obj_to_scan->is_forwarded() && 170 obj_to_scan->forwardee() != obj_to_scan) { 171 scan_partial_array_and_push_remainder(obj_to_scan); 172 } else { 173 // object is in to_space 174 obj_to_scan->oop_iterate(&_to_space_closure); 175 } 176 } else { 177 // object is in old generation 178 obj_to_scan->oop_iterate(&_old_gen_closure); 179 } 180 } 181 } 182 // For the case of compressed oops, we have a private, non-shared 183 // overflow stack, so we eagerly drain it so as to more evenly 184 // distribute load early. Note: this may be good to do in 185 // general rather than delay for the final stealing phase. 186 // If applicable, we'll transfer a set of objects over to our 187 // work queue, allowing them to be stolen and draining our 188 // private overflow stack. 189 } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this)); 190} 191 192bool ParScanThreadState::take_from_overflow_stack() { 193 assert(ParGCUseLocalOverflow, "Else should not call"); 194 assert(young_gen()->overflow_list() == NULL, "Error"); 195 ObjToScanQueue* queue = work_queue(); 196 Stack<oop, mtGC>* const of_stack = overflow_stack(); 197 const size_t num_overflow_elems = of_stack->size(); 198 const size_t space_available = queue->max_elems() - queue->size(); 199 const size_t num_take_elems = MIN3(space_available / 4, 200 ParGCDesiredObjsFromOverflowList, 201 num_overflow_elems); 202 // Transfer the most recent num_take_elems from the overflow 203 // stack to our work queue. 204 for (size_t i = 0; i != num_take_elems; i++) { 205 oop cur = of_stack->pop(); 206 oop obj_to_push = cur->forwardee(); 207 assert(GenCollectedHeap::heap()->is_in_reserved(cur), "Should be in heap"); 208 assert(!old_gen()->is_in_reserved(cur), "Should be in young gen"); 209 assert(GenCollectedHeap::heap()->is_in_reserved(obj_to_push), "Should be in heap"); 210 if (should_be_partially_scanned(obj_to_push, cur)) { 211 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 212 obj_to_push = cur; 213 } 214 bool ok = queue->push(obj_to_push); 215 assert(ok, "Should have succeeded"); 216 } 217 assert(young_gen()->overflow_list() == NULL, "Error"); 218 return num_take_elems > 0; // was something transferred? 219} 220 221void ParScanThreadState::push_on_overflow_stack(oop p) { 222 assert(ParGCUseLocalOverflow, "Else should not call"); 223 overflow_stack()->push(p); 224 assert(young_gen()->overflow_list() == NULL, "Error"); 225} 226 227HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) { 228 // If the object is small enough, try to reallocate the buffer. 229 HeapWord* obj = NULL; 230 if (!_to_space_full) { 231 PLAB* const plab = to_space_alloc_buffer(); 232 Space* const sp = to_space(); 233 if (word_sz * 100 < ParallelGCBufferWastePct * plab->word_sz()) { 234 // Is small enough; abandon this buffer and start a new one. 235 plab->retire(); 236 size_t buf_size = plab->word_sz(); 237 HeapWord* buf_space = sp->par_allocate(buf_size); 238 if (buf_space == NULL) { 239 const size_t min_bytes = 240 PLAB::min_size() << LogHeapWordSize; 241 size_t free_bytes = sp->free(); 242 while(buf_space == NULL && free_bytes >= min_bytes) { 243 buf_size = free_bytes >> LogHeapWordSize; 244 assert(buf_size == (size_t)align_object_size(buf_size), "Invariant"); 245 buf_space = sp->par_allocate(buf_size); 246 free_bytes = sp->free(); 247 } 248 } 249 if (buf_space != NULL) { 250 plab->set_buf(buf_space, buf_size); 251 record_survivor_plab(buf_space, buf_size); 252 obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes); 253 // Note that we cannot compare buf_size < word_sz below 254 // because of AlignmentReserve (see PLAB::allocate()). 255 assert(obj != NULL || plab->words_remaining() < word_sz, 256 "Else should have been able to allocate"); 257 // It's conceivable that we may be able to use the 258 // buffer we just grabbed for subsequent small requests 259 // even if not for this one. 260 } else { 261 // We're used up. 262 _to_space_full = true; 263 } 264 } else { 265 // Too large; allocate the object individually. 266 obj = sp->par_allocate(word_sz); 267 } 268 } 269 return obj; 270} 271 272void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, size_t word_sz) { 273 to_space_alloc_buffer()->undo_allocation(obj, word_sz); 274} 275 276void ParScanThreadState::print_promotion_failure_size() { 277 if (_promotion_failed_info.has_failed()) { 278 log_trace(gc, promotion)(" (%d: promotion failure size = " SIZE_FORMAT ") ", 279 _thread_num, _promotion_failed_info.first_size()); 280 } 281} 282 283class ParScanThreadStateSet: StackObj { 284public: 285 // Initializes states for the specified number of threads; 286 ParScanThreadStateSet(int num_threads, 287 Space& to_space, 288 ParNewGeneration& young_gen, 289 Generation& old_gen, 290 ObjToScanQueueSet& queue_set, 291 Stack<oop, mtGC>* overflow_stacks_, 292 PreservedMarksSet& preserved_marks_set, 293 size_t desired_plab_sz, 294 ParallelTaskTerminator& term); 295 296 ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); } 297 298 inline ParScanThreadState& thread_state(int i); 299 300 void trace_promotion_failed(const YoungGCTracer* gc_tracer); 301 void reset(uint active_workers, bool promotion_failed); 302 void flush(); 303 304 #if TASKQUEUE_STATS 305 static void 306 print_termination_stats_hdr(outputStream* const st); 307 void print_termination_stats(); 308 static void 309 print_taskqueue_stats_hdr(outputStream* const st); 310 void print_taskqueue_stats(); 311 void reset_stats(); 312 #endif // TASKQUEUE_STATS 313 314private: 315 ParallelTaskTerminator& _term; 316 ParNewGeneration& _young_gen; 317 Generation& _old_gen; 318 ParScanThreadState* _per_thread_states; 319 const int _num_threads; 320 public: 321 bool is_valid(int id) const { return id < _num_threads; } 322 ParallelTaskTerminator* terminator() { return &_term; } 323}; 324 325ParScanThreadStateSet::ParScanThreadStateSet(int num_threads, 326 Space& to_space, 327 ParNewGeneration& young_gen, 328 Generation& old_gen, 329 ObjToScanQueueSet& queue_set, 330 Stack<oop, mtGC>* overflow_stacks, 331 PreservedMarksSet& preserved_marks_set, 332 size_t desired_plab_sz, 333 ParallelTaskTerminator& term) 334 : _young_gen(young_gen), 335 _old_gen(old_gen), 336 _term(term), 337 _per_thread_states(NEW_RESOURCE_ARRAY(ParScanThreadState, num_threads)), 338 _num_threads(num_threads) 339{ 340 assert(num_threads > 0, "sanity check!"); 341 assert(ParGCUseLocalOverflow == (overflow_stacks != NULL), 342 "overflow_stack allocation mismatch"); 343 // Initialize states. 344 for (int i = 0; i < num_threads; ++i) { 345 new(_per_thread_states + i) 346 ParScanThreadState(&to_space, &young_gen, &old_gen, i, &queue_set, 347 overflow_stacks, preserved_marks_set.get(i), 348 desired_plab_sz, term); 349 } 350} 351 352inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i) { 353 assert(i >= 0 && i < _num_threads, "sanity check!"); 354 return _per_thread_states[i]; 355} 356 357void ParScanThreadStateSet::trace_promotion_failed(const YoungGCTracer* gc_tracer) { 358 for (int i = 0; i < _num_threads; ++i) { 359 if (thread_state(i).promotion_failed()) { 360 gc_tracer->report_promotion_failed(thread_state(i).promotion_failed_info()); 361 thread_state(i).promotion_failed_info().reset(); 362 } 363 } 364} 365 366void ParScanThreadStateSet::reset(uint active_threads, bool promotion_failed) { 367 _term.reset_for_reuse(active_threads); 368 if (promotion_failed) { 369 for (int i = 0; i < _num_threads; ++i) { 370 thread_state(i).print_promotion_failure_size(); 371 } 372 } 373} 374 375#if TASKQUEUE_STATS 376void ParScanThreadState::reset_stats() { 377 taskqueue_stats().reset(); 378 _term_attempts = 0; 379 _overflow_refills = 0; 380 _overflow_refill_objs = 0; 381} 382 383void ParScanThreadStateSet::reset_stats() { 384 for (int i = 0; i < _num_threads; ++i) { 385 thread_state(i).reset_stats(); 386 } 387} 388 389void ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st) { 390 st->print_raw_cr("GC Termination Stats"); 391 st->print_raw_cr(" elapsed --strong roots-- -------termination-------"); 392 st->print_raw_cr("thr ms ms % ms % attempts"); 393 st->print_raw_cr("--- --------- --------- ------ --------- ------ --------"); 394} 395 396void ParScanThreadStateSet::print_termination_stats() { 397 LogHandle(gc, task, stats) log; 398 if (!log.is_debug()) { 399 return; 400 } 401 402 ResourceMark rm; 403 outputStream* st = log.debug_stream(); 404 405 print_termination_stats_hdr(st); 406 407 for (int i = 0; i < _num_threads; ++i) { 408 const ParScanThreadState & pss = thread_state(i); 409 const double elapsed_ms = pss.elapsed_time() * 1000.0; 410 const double s_roots_ms = pss.strong_roots_time() * 1000.0; 411 const double term_ms = pss.term_time() * 1000.0; 412 st->print_cr("%3d %9.2f %9.2f %6.2f %9.2f %6.2f " SIZE_FORMAT_W(8), 413 i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms, 414 term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts()); 415 } 416} 417 418// Print stats related to work queue activity. 419void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st) { 420 st->print_raw_cr("GC Task Stats"); 421 st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr(); 422 st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr(); 423} 424 425void ParScanThreadStateSet::print_taskqueue_stats() { 426 if (!log_develop_is_enabled(Trace, gc, task, stats)) { 427 return; 428 } 429 LogHandle(gc, task, stats) log; 430 ResourceMark rm; 431 outputStream* st = log.trace_stream(); 432 print_taskqueue_stats_hdr(st); 433 434 TaskQueueStats totals; 435 for (int i = 0; i < _num_threads; ++i) { 436 const ParScanThreadState & pss = thread_state(i); 437 const TaskQueueStats & stats = pss.taskqueue_stats(); 438 st->print("%3d ", i); stats.print(st); st->cr(); 439 totals += stats; 440 441 if (pss.overflow_refills() > 0) { 442 st->print_cr(" " SIZE_FORMAT_W(10) " overflow refills " 443 SIZE_FORMAT_W(10) " overflow objects", 444 pss.overflow_refills(), pss.overflow_refill_objs()); 445 } 446 } 447 st->print("tot "); totals.print(st); st->cr(); 448 449 DEBUG_ONLY(totals.verify()); 450} 451#endif // TASKQUEUE_STATS 452 453void ParScanThreadStateSet::flush() { 454 // Work in this loop should be kept as lightweight as 455 // possible since this might otherwise become a bottleneck 456 // to scaling. Should we add heavy-weight work into this 457 // loop, consider parallelizing the loop into the worker threads. 458 for (int i = 0; i < _num_threads; ++i) { 459 ParScanThreadState& par_scan_state = thread_state(i); 460 461 // Flush stats related to To-space PLAB activity and 462 // retire the last buffer. 463 par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_young_gen.plab_stats()); 464 465 // Every thread has its own age table. We need to merge 466 // them all into one. 467 AgeTable *local_table = par_scan_state.age_table(); 468 _young_gen.age_table()->merge(local_table); 469 470 // Inform old gen that we're done. 471 _old_gen.par_promote_alloc_done(i); 472 _old_gen.par_oop_since_save_marks_iterate_done(i); 473 } 474 475 if (UseConcMarkSweepGC) { 476 // We need to call this even when ResizeOldPLAB is disabled 477 // so as to avoid breaking some asserts. While we may be able 478 // to avoid this by reorganizing the code a bit, I am loathe 479 // to do that unless we find cases where ergo leads to bad 480 // performance. 481 CompactibleFreeListSpaceLAB::compute_desired_plab_size(); 482 } 483} 484 485ParScanClosure::ParScanClosure(ParNewGeneration* g, 486 ParScanThreadState* par_scan_state) : 487 OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g) { 488 _boundary = _g->reserved().end(); 489} 490 491void ParScanWithBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, false); } 492void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); } 493 494void ParScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, false); } 495void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); } 496 497void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); } 498void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); } 499 500void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); } 501void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); } 502 503ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g, 504 ParScanThreadState* par_scan_state) 505 : ScanWeakRefClosure(g), _par_scan_state(par_scan_state) 506{} 507 508void ParScanWeakRefClosure::do_oop(oop* p) { ParScanWeakRefClosure::do_oop_work(p); } 509void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); } 510 511#ifdef WIN32 512#pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */ 513#endif 514 515ParEvacuateFollowersClosure::ParEvacuateFollowersClosure( 516 ParScanThreadState* par_scan_state_, 517 ParScanWithoutBarrierClosure* to_space_closure_, 518 ParScanWithBarrierClosure* old_gen_closure_, 519 ParRootScanWithoutBarrierClosure* to_space_root_closure_, 520 ParNewGeneration* par_gen_, 521 ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_, 522 ObjToScanQueueSet* task_queues_, 523 ParallelTaskTerminator* terminator_) : 524 525 _par_scan_state(par_scan_state_), 526 _to_space_closure(to_space_closure_), 527 _old_gen_closure(old_gen_closure_), 528 _to_space_root_closure(to_space_root_closure_), 529 _old_gen_root_closure(old_gen_root_closure_), 530 _par_gen(par_gen_), 531 _task_queues(task_queues_), 532 _terminator(terminator_) 533{} 534 535void ParEvacuateFollowersClosure::do_void() { 536 ObjToScanQueue* work_q = par_scan_state()->work_queue(); 537 538 while (true) { 539 // Scan to-space and old-gen objs until we run out of both. 540 oop obj_to_scan; 541 par_scan_state()->trim_queues(0); 542 543 // We have no local work, attempt to steal from other threads. 544 545 // Attempt to steal work from promoted. 546 if (task_queues()->steal(par_scan_state()->thread_num(), 547 par_scan_state()->hash_seed(), 548 obj_to_scan)) { 549 bool res = work_q->push(obj_to_scan); 550 assert(res, "Empty queue should have room for a push."); 551 552 // If successful, goto Start. 553 continue; 554 555 // Try global overflow list. 556 } else if (par_gen()->take_from_overflow_list(par_scan_state())) { 557 continue; 558 } 559 560 // Otherwise, offer termination. 561 par_scan_state()->start_term_time(); 562 if (terminator()->offer_termination()) break; 563 par_scan_state()->end_term_time(); 564 } 565 assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0, 566 "Broken overflow list?"); 567 // Finish the last termination pause. 568 par_scan_state()->end_term_time(); 569} 570 571ParNewGenTask::ParNewGenTask(ParNewGeneration* young_gen, 572 Generation* old_gen, 573 HeapWord* young_old_boundary, 574 ParScanThreadStateSet* state_set, 575 StrongRootsScope* strong_roots_scope) : 576 AbstractGangTask("ParNewGeneration collection"), 577 _young_gen(young_gen), _old_gen(old_gen), 578 _young_old_boundary(young_old_boundary), 579 _state_set(state_set), 580 _strong_roots_scope(strong_roots_scope) 581{} 582 583void ParNewGenTask::work(uint worker_id) { 584 GenCollectedHeap* gch = GenCollectedHeap::heap(); 585 // Since this is being done in a separate thread, need new resource 586 // and handle marks. 587 ResourceMark rm; 588 HandleMark hm; 589 590 ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id); 591 assert(_state_set->is_valid(worker_id), "Should not have been called"); 592 593 par_scan_state.set_young_old_boundary(_young_old_boundary); 594 595 KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(), 596 gch->rem_set()->klass_rem_set()); 597 CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure, 598 &par_scan_state.to_space_root_closure(), 599 false); 600 601 par_scan_state.start_strong_roots(); 602 gch->gen_process_roots(_strong_roots_scope, 603 GenCollectedHeap::YoungGen, 604 true, // Process younger gens, if any, as strong roots. 605 GenCollectedHeap::SO_ScavengeCodeCache, 606 GenCollectedHeap::StrongAndWeakRoots, 607 &par_scan_state.to_space_root_closure(), 608 &par_scan_state.older_gen_closure(), 609 &cld_scan_closure); 610 611 par_scan_state.end_strong_roots(); 612 613 // "evacuate followers". 614 par_scan_state.evacuate_followers_closure().do_void(); 615} 616 617ParNewGeneration::ParNewGeneration(ReservedSpace rs, size_t initial_byte_size) 618 : DefNewGeneration(rs, initial_byte_size, "PCopy"), 619 _overflow_list(NULL), 620 _is_alive_closure(this), 621 _plab_stats("Young", YoungPLABSize, PLABWeight) 622{ 623 NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;) 624 NOT_PRODUCT(_num_par_pushes = 0;) 625 _task_queues = new ObjToScanQueueSet(ParallelGCThreads); 626 guarantee(_task_queues != NULL, "task_queues allocation failure."); 627 628 for (uint i = 0; i < ParallelGCThreads; i++) { 629 ObjToScanQueue *q = new ObjToScanQueue(); 630 guarantee(q != NULL, "work_queue Allocation failure."); 631 _task_queues->register_queue(i, q); 632 } 633 634 for (uint i = 0; i < ParallelGCThreads; i++) { 635 _task_queues->queue(i)->initialize(); 636 } 637 638 _overflow_stacks = NULL; 639 if (ParGCUseLocalOverflow) { 640 // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal with ',' 641 typedef Stack<oop, mtGC> GCOopStack; 642 643 _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC); 644 for (size_t i = 0; i < ParallelGCThreads; ++i) { 645 new (_overflow_stacks + i) Stack<oop, mtGC>(); 646 } 647 } 648 649 if (UsePerfData) { 650 EXCEPTION_MARK; 651 ResourceMark rm; 652 653 const char* cname = 654 PerfDataManager::counter_name(_gen_counters->name_space(), "threads"); 655 PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None, 656 ParallelGCThreads, CHECK); 657 } 658} 659 660// ParNewGeneration:: 661ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) : 662 DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {} 663 664template <class T> 665void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) { 666#ifdef ASSERT 667 { 668 assert(!oopDesc::is_null(*p), "expected non-null ref"); 669 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 670 // We never expect to see a null reference being processed 671 // as a weak reference. 672 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 673 } 674#endif // ASSERT 675 676 _par_cl->do_oop_nv(p); 677 678 if (GenCollectedHeap::heap()->is_in_reserved(p)) { 679 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 680 _rs->write_ref_field_gc_par(p, obj); 681 } 682} 683 684void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); } 685void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); } 686 687// ParNewGeneration:: 688KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) : 689 DefNewGeneration::KeepAliveClosure(cl) {} 690 691template <class T> 692void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) { 693#ifdef ASSERT 694 { 695 assert(!oopDesc::is_null(*p), "expected non-null ref"); 696 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 697 // We never expect to see a null reference being processed 698 // as a weak reference. 699 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 700 } 701#endif // ASSERT 702 703 _cl->do_oop_nv(p); 704 705 if (GenCollectedHeap::heap()->is_in_reserved(p)) { 706 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 707 _rs->write_ref_field_gc_par(p, obj); 708 } 709} 710 711void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); } 712void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); } 713 714template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) { 715 T heap_oop = oopDesc::load_heap_oop(p); 716 if (!oopDesc::is_null(heap_oop)) { 717 oop obj = oopDesc::decode_heap_oop_not_null(heap_oop); 718 if ((HeapWord*)obj < _boundary) { 719 assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?"); 720 oop new_obj = obj->is_forwarded() 721 ? obj->forwardee() 722 : _g->DefNewGeneration::copy_to_survivor_space(obj); 723 oopDesc::encode_store_heap_oop_not_null(p, new_obj); 724 } 725 if (_gc_barrier) { 726 // If p points to a younger generation, mark the card. 727 if ((HeapWord*)obj < _gen_boundary) { 728 _rs->write_ref_field_gc_par(p, obj); 729 } 730 } 731 } 732} 733 734void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 735void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 736 737class ParNewRefProcTaskProxy: public AbstractGangTask { 738 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; 739public: 740 ParNewRefProcTaskProxy(ProcessTask& task, 741 ParNewGeneration& young_gen, 742 Generation& old_gen, 743 HeapWord* young_old_boundary, 744 ParScanThreadStateSet& state_set); 745 746private: 747 virtual void work(uint worker_id); 748private: 749 ParNewGeneration& _young_gen; 750 ProcessTask& _task; 751 Generation& _old_gen; 752 HeapWord* _young_old_boundary; 753 ParScanThreadStateSet& _state_set; 754}; 755 756ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task, 757 ParNewGeneration& young_gen, 758 Generation& old_gen, 759 HeapWord* young_old_boundary, 760 ParScanThreadStateSet& state_set) 761 : AbstractGangTask("ParNewGeneration parallel reference processing"), 762 _young_gen(young_gen), 763 _task(task), 764 _old_gen(old_gen), 765 _young_old_boundary(young_old_boundary), 766 _state_set(state_set) 767{ } 768 769void ParNewRefProcTaskProxy::work(uint worker_id) { 770 ResourceMark rm; 771 HandleMark hm; 772 ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id); 773 par_scan_state.set_young_old_boundary(_young_old_boundary); 774 _task.work(worker_id, par_scan_state.is_alive_closure(), 775 par_scan_state.keep_alive_closure(), 776 par_scan_state.evacuate_followers_closure()); 777} 778 779class ParNewRefEnqueueTaskProxy: public AbstractGangTask { 780 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; 781 EnqueueTask& _task; 782 783public: 784 ParNewRefEnqueueTaskProxy(EnqueueTask& task) 785 : AbstractGangTask("ParNewGeneration parallel reference enqueue"), 786 _task(task) 787 { } 788 789 virtual void work(uint worker_id) { 790 _task.work(worker_id); 791 } 792}; 793 794void ParNewRefProcTaskExecutor::execute(ProcessTask& task) { 795 GenCollectedHeap* gch = GenCollectedHeap::heap(); 796 WorkGang* workers = gch->workers(); 797 assert(workers != NULL, "Need parallel worker threads."); 798 _state_set.reset(workers->active_workers(), _young_gen.promotion_failed()); 799 ParNewRefProcTaskProxy rp_task(task, _young_gen, _old_gen, 800 _young_gen.reserved().end(), _state_set); 801 workers->run_task(&rp_task); 802 _state_set.reset(0 /* bad value in debug if not reset */, 803 _young_gen.promotion_failed()); 804} 805 806void ParNewRefProcTaskExecutor::execute(EnqueueTask& task) { 807 GenCollectedHeap* gch = GenCollectedHeap::heap(); 808 WorkGang* workers = gch->workers(); 809 assert(workers != NULL, "Need parallel worker threads."); 810 ParNewRefEnqueueTaskProxy enq_task(task); 811 workers->run_task(&enq_task); 812} 813 814void ParNewRefProcTaskExecutor::set_single_threaded_mode() { 815 _state_set.flush(); 816 GenCollectedHeap* gch = GenCollectedHeap::heap(); 817 gch->save_marks(); 818} 819 820ScanClosureWithParBarrier:: 821ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) : 822 ScanClosure(g, gc_barrier) 823{ } 824 825EvacuateFollowersClosureGeneral:: 826EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, 827 OopsInGenClosure* cur, 828 OopsInGenClosure* older) : 829 _gch(gch), 830 _scan_cur_or_nonheap(cur), _scan_older(older) 831{ } 832 833void EvacuateFollowersClosureGeneral::do_void() { 834 do { 835 // Beware: this call will lead to closure applications via virtual 836 // calls. 837 _gch->oop_since_save_marks_iterate(GenCollectedHeap::YoungGen, 838 _scan_cur_or_nonheap, 839 _scan_older); 840 } while (!_gch->no_allocs_since_save_marks()); 841} 842 843// A Generation that does parallel young-gen collection. 844 845void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set) { 846 assert(_promo_failure_scan_stack.is_empty(), "post condition"); 847 _promo_failure_scan_stack.clear(true); // Clear cached segments. 848 849 remove_forwarding_pointers(); 850 log_info(gc, promotion)("Promotion failed"); 851 // All the spaces are in play for mark-sweep. 852 swap_spaces(); // Make life simpler for CMS || rescan; see 6483690. 853 from()->set_next_compaction_space(to()); 854 gch->set_incremental_collection_failed(); 855 // Inform the next generation that a promotion failure occurred. 856 _old_gen->promotion_failure_occurred(); 857 858 // Trace promotion failure in the parallel GC threads 859 thread_state_set.trace_promotion_failed(gc_tracer()); 860 // Single threaded code may have reported promotion failure to the global state 861 if (_promotion_failed_info.has_failed()) { 862 _gc_tracer.report_promotion_failed(_promotion_failed_info); 863 } 864 // Reset the PromotionFailureALot counters. 865 NOT_PRODUCT(gch->reset_promotion_should_fail();) 866} 867 868void ParNewGeneration::collect(bool full, 869 bool clear_all_soft_refs, 870 size_t size, 871 bool is_tlab) { 872 assert(full || size > 0, "otherwise we don't want to collect"); 873 874 GenCollectedHeap* gch = GenCollectedHeap::heap(); 875 876 _gc_timer->register_gc_start(); 877 878 AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy(); 879 WorkGang* workers = gch->workers(); 880 assert(workers != NULL, "Need workgang for parallel work"); 881 uint active_workers = 882 AdaptiveSizePolicy::calc_active_workers(workers->total_workers(), 883 workers->active_workers(), 884 Threads::number_of_non_daemon_threads()); 885 workers->set_active_workers(active_workers); 886 _old_gen = gch->old_gen(); 887 888 // If the next generation is too full to accommodate worst-case promotion 889 // from this generation, pass on collection; let the next generation 890 // do it. 891 if (!collection_attempt_is_safe()) { 892 gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one 893 return; 894 } 895 assert(to()->is_empty(), "Else not collection_attempt_is_safe"); 896 897 _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start()); 898 gch->trace_heap_before_gc(gc_tracer()); 899 900 init_assuming_no_promotion_failure(); 901 902 if (UseAdaptiveSizePolicy) { 903 set_survivor_overflow(false); 904 size_policy->minor_collection_begin(); 905 } 906 907 GCTraceTime(Trace, gc) t1("ParNew", NULL, gch->gc_cause()); 908 909 age_table()->clear(); 910 to()->clear(SpaceDecorator::Mangle); 911 912 gch->save_marks(); 913 914 // Set the correct parallelism (number of queues) in the reference processor 915 ref_processor()->set_active_mt_degree(active_workers); 916 917 // Need to initialize the preserved marks before the ThreadStateSet c'tor. 918 _preserved_marks_set.init(active_workers); 919 920 // Always set the terminator for the active number of workers 921 // because only those workers go through the termination protocol. 922 ParallelTaskTerminator _term(active_workers, task_queues()); 923 ParScanThreadStateSet thread_state_set(active_workers, 924 *to(), *this, *_old_gen, *task_queues(), 925 _overflow_stacks, _preserved_marks_set, 926 desired_plab_sz(), _term); 927 928 thread_state_set.reset(active_workers, promotion_failed()); 929 930 { 931 StrongRootsScope srs(active_workers); 932 933 ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set, &srs); 934 gch->rem_set()->prepare_for_younger_refs_iterate(true); 935 // It turns out that even when we're using 1 thread, doing the work in a 936 // separate thread causes wide variance in run times. We can't help this 937 // in the multi-threaded case, but we special-case n=1 here to get 938 // repeatable measurements of the 1-thread overhead of the parallel code. 939 if (active_workers > 1) { 940 workers->run_task(&tsk); 941 } else { 942 tsk.work(0); 943 } 944 } 945 946 thread_state_set.reset(0 /* Bad value in debug if not reset */, 947 promotion_failed()); 948 949 // Trace and reset failed promotion info. 950 if (promotion_failed()) { 951 thread_state_set.trace_promotion_failed(gc_tracer()); 952 } 953 954 // Process (weak) reference objects found during scavenge. 955 ReferenceProcessor* rp = ref_processor(); 956 IsAliveClosure is_alive(this); 957 ScanWeakRefClosure scan_weak_ref(this); 958 KeepAliveClosure keep_alive(&scan_weak_ref); 959 ScanClosure scan_without_gc_barrier(this, false); 960 ScanClosureWithParBarrier scan_with_gc_barrier(this, true); 961 set_promo_failure_scan_stack_closure(&scan_without_gc_barrier); 962 EvacuateFollowersClosureGeneral evacuate_followers(gch, 963 &scan_without_gc_barrier, &scan_with_gc_barrier); 964 rp->setup_policy(clear_all_soft_refs); 965 // Can the mt_degree be set later (at run_task() time would be best)? 966 rp->set_active_mt_degree(active_workers); 967 ReferenceProcessorStats stats; 968 if (rp->processing_is_mt()) { 969 ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set); 970 stats = rp->process_discovered_references(&is_alive, &keep_alive, 971 &evacuate_followers, &task_executor, 972 _gc_timer); 973 } else { 974 thread_state_set.flush(); 975 gch->save_marks(); 976 stats = rp->process_discovered_references(&is_alive, &keep_alive, 977 &evacuate_followers, NULL, 978 _gc_timer); 979 } 980 _gc_tracer.report_gc_reference_stats(stats); 981 _gc_tracer.report_tenuring_threshold(tenuring_threshold()); 982 983 if (!promotion_failed()) { 984 // Swap the survivor spaces. 985 eden()->clear(SpaceDecorator::Mangle); 986 from()->clear(SpaceDecorator::Mangle); 987 if (ZapUnusedHeapArea) { 988 // This is now done here because of the piece-meal mangling which 989 // can check for valid mangling at intermediate points in the 990 // collection(s). When a young collection fails to collect 991 // sufficient space resizing of the young generation can occur 992 // and redistribute the spaces in the young generation. Mangle 993 // here so that unzapped regions don't get distributed to 994 // other spaces. 995 to()->mangle_unused_area(); 996 } 997 swap_spaces(); 998 999 // A successful scavenge should restart the GC time limit count which is 1000 // for full GC's. 1001 size_policy->reset_gc_overhead_limit_count(); 1002 1003 assert(to()->is_empty(), "to space should be empty now"); 1004 1005 adjust_desired_tenuring_threshold(); 1006 } else { 1007 handle_promotion_failed(gch, thread_state_set); 1008 } 1009 _preserved_marks_set.reclaim(); 1010 // set new iteration safe limit for the survivor spaces 1011 from()->set_concurrent_iteration_safe_limit(from()->top()); 1012 to()->set_concurrent_iteration_safe_limit(to()->top()); 1013 1014 plab_stats()->adjust_desired_plab_sz(); 1015 1016 TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats()); 1017 TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats()); 1018 1019 if (UseAdaptiveSizePolicy) { 1020 size_policy->minor_collection_end(gch->gc_cause()); 1021 size_policy->avg_survived()->sample(from()->used()); 1022 } 1023 1024 // We need to use a monotonically non-decreasing time in ms 1025 // or we will see time-warp warnings and os::javaTimeMillis() 1026 // does not guarantee monotonicity. 1027 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 1028 update_time_of_last_gc(now); 1029 1030 rp->set_enqueuing_is_done(true); 1031 if (rp->processing_is_mt()) { 1032 ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set); 1033 rp->enqueue_discovered_references(&task_executor); 1034 } else { 1035 rp->enqueue_discovered_references(NULL); 1036 } 1037 rp->verify_no_references_recorded(); 1038 1039 gch->trace_heap_after_gc(gc_tracer()); 1040 1041 _gc_timer->register_gc_end(); 1042 1043 _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions()); 1044} 1045 1046size_t ParNewGeneration::desired_plab_sz() { 1047 return _plab_stats.desired_plab_sz(GenCollectedHeap::heap()->workers()->active_workers()); 1048} 1049 1050static int sum; 1051void ParNewGeneration::waste_some_time() { 1052 for (int i = 0; i < 100; i++) { 1053 sum += i; 1054 } 1055} 1056 1057static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4); 1058 1059// Because of concurrency, there are times where an object for which 1060// "is_forwarded()" is true contains an "interim" forwarding pointer 1061// value. Such a value will soon be overwritten with a real value. 1062// This method requires "obj" to have a forwarding pointer, and waits, if 1063// necessary for a real one to be inserted, and returns it. 1064 1065oop ParNewGeneration::real_forwardee(oop obj) { 1066 oop forward_ptr = obj->forwardee(); 1067 if (forward_ptr != ClaimedForwardPtr) { 1068 return forward_ptr; 1069 } else { 1070 return real_forwardee_slow(obj); 1071 } 1072} 1073 1074oop ParNewGeneration::real_forwardee_slow(oop obj) { 1075 // Spin-read if it is claimed but not yet written by another thread. 1076 oop forward_ptr = obj->forwardee(); 1077 while (forward_ptr == ClaimedForwardPtr) { 1078 waste_some_time(); 1079 assert(obj->is_forwarded(), "precondition"); 1080 forward_ptr = obj->forwardee(); 1081 } 1082 return forward_ptr; 1083} 1084 1085// Multiple GC threads may try to promote an object. If the object 1086// is successfully promoted, a forwarding pointer will be installed in 1087// the object in the young generation. This method claims the right 1088// to install the forwarding pointer before it copies the object, 1089// thus avoiding the need to undo the copy as in 1090// copy_to_survivor_space_avoiding_with_undo. 1091 1092oop ParNewGeneration::copy_to_survivor_space(ParScanThreadState* par_scan_state, 1093 oop old, 1094 size_t sz, 1095 markOop m) { 1096 // In the sequential version, this assert also says that the object is 1097 // not forwarded. That might not be the case here. It is the case that 1098 // the caller observed it to be not forwarded at some time in the past. 1099 assert(is_in_reserved(old), "shouldn't be scavenging this oop"); 1100 1101 // The sequential code read "old->age()" below. That doesn't work here, 1102 // since the age is in the mark word, and that might be overwritten with 1103 // a forwarding pointer by a parallel thread. So we must save the mark 1104 // word in a local and then analyze it. 1105 oopDesc dummyOld; 1106 dummyOld.set_mark(m); 1107 assert(!dummyOld.is_forwarded(), 1108 "should not be called with forwarding pointer mark word."); 1109 1110 oop new_obj = NULL; 1111 oop forward_ptr; 1112 1113 // Try allocating obj in to-space (unless too old) 1114 if (dummyOld.age() < tenuring_threshold()) { 1115 new_obj = (oop)par_scan_state->alloc_in_to_space(sz); 1116 if (new_obj == NULL) { 1117 set_survivor_overflow(true); 1118 } 1119 } 1120 1121 if (new_obj == NULL) { 1122 // Either to-space is full or we decided to promote try allocating obj tenured 1123 1124 // Attempt to install a null forwarding pointer (atomically), 1125 // to claim the right to install the real forwarding pointer. 1126 forward_ptr = old->forward_to_atomic(ClaimedForwardPtr); 1127 if (forward_ptr != NULL) { 1128 // someone else beat us to it. 1129 return real_forwardee(old); 1130 } 1131 1132 if (!_promotion_failed) { 1133 new_obj = _old_gen->par_promote(par_scan_state->thread_num(), 1134 old, m, sz); 1135 } 1136 1137 if (new_obj == NULL) { 1138 // promotion failed, forward to self 1139 _promotion_failed = true; 1140 new_obj = old; 1141 1142 par_scan_state->preserved_marks()->push_if_necessary(old, m); 1143 par_scan_state->register_promotion_failure(sz); 1144 } 1145 1146 old->forward_to(new_obj); 1147 forward_ptr = NULL; 1148 } else { 1149 // Is in to-space; do copying ourselves. 1150 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz); 1151 assert(GenCollectedHeap::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value."); 1152 forward_ptr = old->forward_to_atomic(new_obj); 1153 // Restore the mark word copied above. 1154 new_obj->set_mark(m); 1155 // Increment age if obj still in new generation 1156 new_obj->incr_age(); 1157 par_scan_state->age_table()->add(new_obj, sz); 1158 } 1159 assert(new_obj != NULL, "just checking"); 1160 1161 // This code must come after the CAS test, or it will print incorrect 1162 // information. 1163 log_develop_trace(gc, scavenge)("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}", 1164 is_in_reserved(new_obj) ? "copying" : "tenuring", 1165 new_obj->klass()->internal_name(), p2i(old), p2i(new_obj), new_obj->size()); 1166 1167 if (forward_ptr == NULL) { 1168 oop obj_to_push = new_obj; 1169 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) { 1170 // Length field used as index of next element to be scanned. 1171 // Real length can be obtained from real_forwardee() 1172 arrayOop(old)->set_length(0); 1173 obj_to_push = old; 1174 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push, 1175 "push forwarded object"); 1176 } 1177 // Push it on one of the queues of to-be-scanned objects. 1178 bool simulate_overflow = false; 1179 NOT_PRODUCT( 1180 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) { 1181 // simulate a stack overflow 1182 simulate_overflow = true; 1183 } 1184 ) 1185 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) { 1186 // Add stats for overflow pushes. 1187 log_develop_trace(gc)("Queue Overflow"); 1188 push_on_overflow_list(old, par_scan_state); 1189 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0)); 1190 } 1191 1192 return new_obj; 1193 } 1194 1195 // Oops. Someone beat us to it. Undo the allocation. Where did we 1196 // allocate it? 1197 if (is_in_reserved(new_obj)) { 1198 // Must be in to_space. 1199 assert(to()->is_in_reserved(new_obj), "Checking"); 1200 if (forward_ptr == ClaimedForwardPtr) { 1201 // Wait to get the real forwarding pointer value. 1202 forward_ptr = real_forwardee(old); 1203 } 1204 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz); 1205 } 1206 1207 return forward_ptr; 1208} 1209 1210#ifndef PRODUCT 1211// It's OK to call this multi-threaded; the worst thing 1212// that can happen is that we'll get a bunch of closely 1213// spaced simulated overflows, but that's OK, in fact 1214// probably good as it would exercise the overflow code 1215// under contention. 1216bool ParNewGeneration::should_simulate_overflow() { 1217 if (_overflow_counter-- <= 0) { // just being defensive 1218 _overflow_counter = ParGCWorkQueueOverflowInterval; 1219 return true; 1220 } else { 1221 return false; 1222 } 1223} 1224#endif 1225 1226// In case we are using compressed oops, we need to be careful. 1227// If the object being pushed is an object array, then its length 1228// field keeps track of the "grey boundary" at which the next 1229// incremental scan will be done (see ParGCArrayScanChunk). 1230// When using compressed oops, this length field is kept in the 1231// lower 32 bits of the erstwhile klass word and cannot be used 1232// for the overflow chaining pointer (OCP below). As such the OCP 1233// would itself need to be compressed into the top 32-bits in this 1234// case. Unfortunately, see below, in the event that we have a 1235// promotion failure, the node to be pushed on the list can be 1236// outside of the Java heap, so the heap-based pointer compression 1237// would not work (we would have potential aliasing between C-heap 1238// and Java-heap pointers). For this reason, when using compressed 1239// oops, we simply use a worker-thread-local, non-shared overflow 1240// list in the form of a growable array, with a slightly different 1241// overflow stack draining strategy. If/when we start using fat 1242// stacks here, we can go back to using (fat) pointer chains 1243// (although some performance comparisons would be useful since 1244// single global lists have their own performance disadvantages 1245// as we were made painfully aware not long ago, see 6786503). 1246#define BUSY (cast_to_oop<intptr_t>(0x1aff1aff)) 1247void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) { 1248 assert(is_in_reserved(from_space_obj), "Should be from this generation"); 1249 if (ParGCUseLocalOverflow) { 1250 // In the case of compressed oops, we use a private, not-shared 1251 // overflow stack. 1252 par_scan_state->push_on_overflow_stack(from_space_obj); 1253 } else { 1254 assert(!UseCompressedOops, "Error"); 1255 // if the object has been forwarded to itself, then we cannot 1256 // use the klass pointer for the linked list. Instead we have 1257 // to allocate an oopDesc in the C-Heap and use that for the linked list. 1258 // XXX This is horribly inefficient when a promotion failure occurs 1259 // and should be fixed. XXX FIX ME !!! 1260#ifndef PRODUCT 1261 Atomic::inc_ptr(&_num_par_pushes); 1262 assert(_num_par_pushes > 0, "Tautology"); 1263#endif 1264 if (from_space_obj->forwardee() == from_space_obj) { 1265 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC); 1266 listhead->forward_to(from_space_obj); 1267 from_space_obj = listhead; 1268 } 1269 oop observed_overflow_list = _overflow_list; 1270 oop cur_overflow_list; 1271 do { 1272 cur_overflow_list = observed_overflow_list; 1273 if (cur_overflow_list != BUSY) { 1274 from_space_obj->set_klass_to_list_ptr(cur_overflow_list); 1275 } else { 1276 from_space_obj->set_klass_to_list_ptr(NULL); 1277 } 1278 observed_overflow_list = 1279 (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list); 1280 } while (cur_overflow_list != observed_overflow_list); 1281 } 1282} 1283 1284bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) { 1285 bool res; 1286 1287 if (ParGCUseLocalOverflow) { 1288 res = par_scan_state->take_from_overflow_stack(); 1289 } else { 1290 assert(!UseCompressedOops, "Error"); 1291 res = take_from_overflow_list_work(par_scan_state); 1292 } 1293 return res; 1294} 1295 1296 1297// *NOTE*: The overflow list manipulation code here and 1298// in CMSCollector:: are very similar in shape, 1299// except that in the CMS case we thread the objects 1300// directly into the list via their mark word, and do 1301// not need to deal with special cases below related 1302// to chunking of object arrays and promotion failure 1303// handling. 1304// CR 6797058 has been filed to attempt consolidation of 1305// the common code. 1306// Because of the common code, if you make any changes in 1307// the code below, please check the CMS version to see if 1308// similar changes might be needed. 1309// See CMSCollector::par_take_from_overflow_list() for 1310// more extensive documentation comments. 1311bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) { 1312 ObjToScanQueue* work_q = par_scan_state->work_queue(); 1313 // How many to take? 1314 size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 1315 (size_t)ParGCDesiredObjsFromOverflowList); 1316 1317 assert(!UseCompressedOops, "Error"); 1318 assert(par_scan_state->overflow_stack() == NULL, "Error"); 1319 if (_overflow_list == NULL) return false; 1320 1321 // Otherwise, there was something there; try claiming the list. 1322 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1323 // Trim off a prefix of at most objsFromOverflow items 1324 Thread* tid = Thread::current(); 1325 size_t spin_count = ParallelGCThreads; 1326 size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100); 1327 for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) { 1328 // someone grabbed it before we did ... 1329 // ... we spin for a short while... 1330 os::sleep(tid, sleep_time_millis, false); 1331 if (_overflow_list == NULL) { 1332 // nothing left to take 1333 return false; 1334 } else if (_overflow_list != BUSY) { 1335 // try and grab the prefix 1336 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1337 } 1338 } 1339 if (prefix == NULL || prefix == BUSY) { 1340 // Nothing to take or waited long enough 1341 if (prefix == NULL) { 1342 // Write back the NULL in case we overwrote it with BUSY above 1343 // and it is still the same value. 1344 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1345 } 1346 return false; 1347 } 1348 assert(prefix != NULL && prefix != BUSY, "Error"); 1349 size_t i = 1; 1350 oop cur = prefix; 1351 while (i < objsFromOverflow && cur->klass_or_null() != NULL) { 1352 i++; cur = cur->list_ptr_from_klass(); 1353 } 1354 1355 // Reattach remaining (suffix) to overflow list 1356 if (cur->klass_or_null() == NULL) { 1357 // Write back the NULL in lieu of the BUSY we wrote 1358 // above and it is still the same value. 1359 if (_overflow_list == BUSY) { 1360 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1361 } 1362 } else { 1363 assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error"); 1364 oop suffix = cur->list_ptr_from_klass(); // suffix will be put back on global list 1365 cur->set_klass_to_list_ptr(NULL); // break off suffix 1366 // It's possible that the list is still in the empty(busy) state 1367 // we left it in a short while ago; in that case we may be 1368 // able to place back the suffix. 1369 oop observed_overflow_list = _overflow_list; 1370 oop cur_overflow_list = observed_overflow_list; 1371 bool attached = false; 1372 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { 1373 observed_overflow_list = 1374 (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1375 if (cur_overflow_list == observed_overflow_list) { 1376 attached = true; 1377 break; 1378 } else cur_overflow_list = observed_overflow_list; 1379 } 1380 if (!attached) { 1381 // Too bad, someone else got in in between; we'll need to do a splice. 1382 // Find the last item of suffix list 1383 oop last = suffix; 1384 while (last->klass_or_null() != NULL) { 1385 last = last->list_ptr_from_klass(); 1386 } 1387 // Atomically prepend suffix to current overflow list 1388 observed_overflow_list = _overflow_list; 1389 do { 1390 cur_overflow_list = observed_overflow_list; 1391 if (cur_overflow_list != BUSY) { 1392 // Do the splice ... 1393 last->set_klass_to_list_ptr(cur_overflow_list); 1394 } else { // cur_overflow_list == BUSY 1395 last->set_klass_to_list_ptr(NULL); 1396 } 1397 observed_overflow_list = 1398 (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1399 } while (cur_overflow_list != observed_overflow_list); 1400 } 1401 } 1402 1403 // Push objects on prefix list onto this thread's work queue 1404 assert(prefix != NULL && prefix != BUSY, "program logic"); 1405 cur = prefix; 1406 ssize_t n = 0; 1407 while (cur != NULL) { 1408 oop obj_to_push = cur->forwardee(); 1409 oop next = cur->list_ptr_from_klass(); 1410 cur->set_klass(obj_to_push->klass()); 1411 // This may be an array object that is self-forwarded. In that case, the list pointer 1412 // space, cur, is not in the Java heap, but rather in the C-heap and should be freed. 1413 if (!is_in_reserved(cur)) { 1414 // This can become a scaling bottleneck when there is work queue overflow coincident 1415 // with promotion failure. 1416 oopDesc* f = cur; 1417 FREE_C_HEAP_ARRAY(oopDesc, f); 1418 } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) { 1419 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 1420 obj_to_push = cur; 1421 } 1422 bool ok = work_q->push(obj_to_push); 1423 assert(ok, "Should have succeeded"); 1424 cur = next; 1425 n++; 1426 } 1427 TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n)); 1428#ifndef PRODUCT 1429 assert(_num_par_pushes >= n, "Too many pops?"); 1430 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes); 1431#endif 1432 return true; 1433} 1434#undef BUSY 1435 1436void ParNewGeneration::ref_processor_init() { 1437 if (_ref_processor == NULL) { 1438 // Allocate and initialize a reference processor 1439 _ref_processor = 1440 new ReferenceProcessor(_reserved, // span 1441 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing 1442 ParallelGCThreads, // mt processing degree 1443 refs_discovery_is_mt(), // mt discovery 1444 ParallelGCThreads, // mt discovery degree 1445 refs_discovery_is_atomic(), // atomic_discovery 1446 NULL); // is_alive_non_header 1447 } 1448} 1449 1450const char* ParNewGeneration::name() const { 1451 return "par new generation"; 1452} 1453