parNewGeneration.cpp revision 9473:5132864a5d5f
1/* 2 * Copyright (c) 2001, 2015, 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.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.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/referencePolicy.hpp" 43#include "gc/shared/space.hpp" 44#include "gc/shared/spaceDecorator.hpp" 45#include "gc/shared/strongRootsScope.hpp" 46#include "gc/shared/taskqueue.inline.hpp" 47#include "gc/shared/workgroup.hpp" 48#include "memory/resourceArea.hpp" 49#include "oops/objArrayOop.hpp" 50#include "oops/oop.inline.hpp" 51#include "runtime/atomic.inline.hpp" 52#include "runtime/handles.hpp" 53#include "runtime/handles.inline.hpp" 54#include "runtime/java.hpp" 55#include "runtime/thread.inline.hpp" 56#include "utilities/copy.hpp" 57#include "utilities/globalDefinitions.hpp" 58#include "utilities/stack.inline.hpp" 59 60ParScanThreadState::ParScanThreadState(Space* to_space_, 61 ParNewGeneration* young_gen_, 62 Generation* old_gen_, 63 int thread_num_, 64 ObjToScanQueueSet* work_queue_set_, 65 Stack<oop, mtGC>* overflow_stacks_, 66 size_t desired_plab_sz_, 67 ParallelTaskTerminator& term_) : 68 _to_space(to_space_), 69 _old_gen(old_gen_), 70 _young_gen(young_gen_), 71 _thread_num(thread_num_), 72 _work_queue(work_queue_set_->queue(thread_num_)), 73 _to_space_full(false), 74 _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL), 75 _ageTable(false), // false ==> not the global age table, no perf data. 76 _to_space_alloc_buffer(desired_plab_sz_), 77 _to_space_closure(young_gen_, this), 78 _old_gen_closure(young_gen_, this), 79 _to_space_root_closure(young_gen_, this), 80 _old_gen_root_closure(young_gen_, this), 81 _older_gen_closure(young_gen_, this), 82 _evacuate_followers(this, &_to_space_closure, &_old_gen_closure, 83 &_to_space_root_closure, young_gen_, &_old_gen_root_closure, 84 work_queue_set_, &term_), 85 _is_alive_closure(young_gen_), 86 _scan_weak_ref_closure(young_gen_, this), 87 _keep_alive_closure(&_scan_weak_ref_closure), 88 _strong_roots_time(0.0), 89 _term_time(0.0) 90{ 91 #if TASKQUEUE_STATS 92 _term_attempts = 0; 93 _overflow_refills = 0; 94 _overflow_refill_objs = 0; 95 #endif // TASKQUEUE_STATS 96 97 _survivor_chunk_array = (ChunkArray*) old_gen()->get_data_recorder(thread_num()); 98 _hash_seed = 17; // Might want to take time-based random value. 99 _start = os::elapsedTime(); 100 _old_gen_closure.set_generation(old_gen_); 101 _old_gen_root_closure.set_generation(old_gen_); 102} 103 104void ParScanThreadState::record_survivor_plab(HeapWord* plab_start, 105 size_t plab_word_size) { 106 ChunkArray* sca = survivor_chunk_array(); 107 if (sca != NULL) { 108 // A non-null SCA implies that we want the PLAB data recorded. 109 sca->record_sample(plab_start, plab_word_size); 110 } 111} 112 113bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const { 114 return new_obj->is_objArray() && 115 arrayOop(new_obj)->length() > ParGCArrayScanChunk && 116 new_obj != old_obj; 117} 118 119void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) { 120 assert(old->is_objArray(), "must be obj array"); 121 assert(old->is_forwarded(), "must be forwarded"); 122 assert(GenCollectedHeap::heap()->is_in_reserved(old), "must be in heap."); 123 assert(!old_gen()->is_in(old), "must be in young generation."); 124 125 objArrayOop obj = objArrayOop(old->forwardee()); 126 // Process ParGCArrayScanChunk elements now 127 // and push the remainder back onto queue 128 int start = arrayOop(old)->length(); 129 int end = obj->length(); 130 int remainder = end - start; 131 assert(start <= end, "just checking"); 132 if (remainder > 2 * ParGCArrayScanChunk) { 133 // Test above combines last partial chunk with a full chunk 134 end = start + ParGCArrayScanChunk; 135 arrayOop(old)->set_length(end); 136 // Push remainder. 137 bool ok = work_queue()->push(old); 138 assert(ok, "just popped, push must be okay"); 139 } else { 140 // Restore length so that it can be used if there 141 // is a promotion failure and forwarding pointers 142 // must be removed. 143 arrayOop(old)->set_length(end); 144 } 145 146 // process our set of indices (include header in first chunk) 147 // should make sure end is even (aligned to HeapWord in case of compressed oops) 148 if ((HeapWord *)obj < young_old_boundary()) { 149 // object is in to_space 150 obj->oop_iterate_range(&_to_space_closure, start, end); 151 } else { 152 // object is in old generation 153 obj->oop_iterate_range(&_old_gen_closure, start, end); 154 } 155} 156 157void ParScanThreadState::trim_queues(int max_size) { 158 ObjToScanQueue* queue = work_queue(); 159 do { 160 while (queue->size() > (juint)max_size) { 161 oop obj_to_scan; 162 if (queue->pop_local(obj_to_scan)) { 163 if ((HeapWord *)obj_to_scan < young_old_boundary()) { 164 if (obj_to_scan->is_objArray() && 165 obj_to_scan->is_forwarded() && 166 obj_to_scan->forwardee() != obj_to_scan) { 167 scan_partial_array_and_push_remainder(obj_to_scan); 168 } else { 169 // object is in to_space 170 obj_to_scan->oop_iterate(&_to_space_closure); 171 } 172 } else { 173 // object is in old generation 174 obj_to_scan->oop_iterate(&_old_gen_closure); 175 } 176 } 177 } 178 // For the case of compressed oops, we have a private, non-shared 179 // overflow stack, so we eagerly drain it so as to more evenly 180 // distribute load early. Note: this may be good to do in 181 // general rather than delay for the final stealing phase. 182 // If applicable, we'll transfer a set of objects over to our 183 // work queue, allowing them to be stolen and draining our 184 // private overflow stack. 185 } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this)); 186} 187 188bool ParScanThreadState::take_from_overflow_stack() { 189 assert(ParGCUseLocalOverflow, "Else should not call"); 190 assert(young_gen()->overflow_list() == NULL, "Error"); 191 ObjToScanQueue* queue = work_queue(); 192 Stack<oop, mtGC>* const of_stack = overflow_stack(); 193 const size_t num_overflow_elems = of_stack->size(); 194 const size_t space_available = queue->max_elems() - queue->size(); 195 const size_t num_take_elems = MIN3(space_available / 4, 196 ParGCDesiredObjsFromOverflowList, 197 num_overflow_elems); 198 // Transfer the most recent num_take_elems from the overflow 199 // stack to our work queue. 200 for (size_t i = 0; i != num_take_elems; i++) { 201 oop cur = of_stack->pop(); 202 oop obj_to_push = cur->forwardee(); 203 assert(GenCollectedHeap::heap()->is_in_reserved(cur), "Should be in heap"); 204 assert(!old_gen()->is_in_reserved(cur), "Should be in young gen"); 205 assert(GenCollectedHeap::heap()->is_in_reserved(obj_to_push), "Should be in heap"); 206 if (should_be_partially_scanned(obj_to_push, cur)) { 207 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 208 obj_to_push = cur; 209 } 210 bool ok = queue->push(obj_to_push); 211 assert(ok, "Should have succeeded"); 212 } 213 assert(young_gen()->overflow_list() == NULL, "Error"); 214 return num_take_elems > 0; // was something transferred? 215} 216 217void ParScanThreadState::push_on_overflow_stack(oop p) { 218 assert(ParGCUseLocalOverflow, "Else should not call"); 219 overflow_stack()->push(p); 220 assert(young_gen()->overflow_list() == NULL, "Error"); 221} 222 223HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) { 224 // If the object is small enough, try to reallocate the buffer. 225 HeapWord* obj = NULL; 226 if (!_to_space_full) { 227 PLAB* const plab = to_space_alloc_buffer(); 228 Space* const sp = to_space(); 229 if (word_sz * 100 < ParallelGCBufferWastePct * plab->word_sz()) { 230 // Is small enough; abandon this buffer and start a new one. 231 plab->retire(); 232 size_t buf_size = plab->word_sz(); 233 HeapWord* buf_space = sp->par_allocate(buf_size); 234 if (buf_space == NULL) { 235 const size_t min_bytes = 236 PLAB::min_size() << LogHeapWordSize; 237 size_t free_bytes = sp->free(); 238 while(buf_space == NULL && free_bytes >= min_bytes) { 239 buf_size = free_bytes >> LogHeapWordSize; 240 assert(buf_size == (size_t)align_object_size(buf_size), "Invariant"); 241 buf_space = sp->par_allocate(buf_size); 242 free_bytes = sp->free(); 243 } 244 } 245 if (buf_space != NULL) { 246 plab->set_buf(buf_space, buf_size); 247 record_survivor_plab(buf_space, buf_size); 248 obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes); 249 // Note that we cannot compare buf_size < word_sz below 250 // because of AlignmentReserve (see PLAB::allocate()). 251 assert(obj != NULL || plab->words_remaining() < word_sz, 252 "Else should have been able to allocate"); 253 // It's conceivable that we may be able to use the 254 // buffer we just grabbed for subsequent small requests 255 // even if not for this one. 256 } else { 257 // We're used up. 258 _to_space_full = true; 259 } 260 } else { 261 // Too large; allocate the object individually. 262 obj = sp->par_allocate(word_sz); 263 } 264 } 265 return obj; 266} 267 268void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, size_t word_sz) { 269 to_space_alloc_buffer()->undo_allocation(obj, word_sz); 270} 271 272void ParScanThreadState::print_promotion_failure_size() { 273 if (_promotion_failed_info.has_failed() && PrintPromotionFailure) { 274 gclog_or_tty->print(" (%d: promotion failure size = " SIZE_FORMAT ") ", 275 _thread_num, _promotion_failed_info.first_size()); 276 } 277} 278 279class ParScanThreadStateSet: private ResourceArray { 280public: 281 // Initializes states for the specified number of threads; 282 ParScanThreadStateSet(int num_threads, 283 Space& to_space, 284 ParNewGeneration& young_gen, 285 Generation& old_gen, 286 ObjToScanQueueSet& queue_set, 287 Stack<oop, mtGC>* overflow_stacks_, 288 size_t desired_plab_sz, 289 ParallelTaskTerminator& term); 290 291 ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); } 292 293 inline ParScanThreadState& thread_state(int i); 294 295 void trace_promotion_failed(const YoungGCTracer* gc_tracer); 296 void reset(uint active_workers, bool promotion_failed); 297 void flush(); 298 299 #if TASKQUEUE_STATS 300 static void 301 print_termination_stats_hdr(outputStream* const st = gclog_or_tty); 302 void print_termination_stats(outputStream* const st = gclog_or_tty); 303 static void 304 print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty); 305 void print_taskqueue_stats(outputStream* const st = gclog_or_tty); 306 void reset_stats(); 307 #endif // TASKQUEUE_STATS 308 309private: 310 ParallelTaskTerminator& _term; 311 ParNewGeneration& _young_gen; 312 Generation& _old_gen; 313 public: 314 bool is_valid(int id) const { return id < length(); } 315 ParallelTaskTerminator* terminator() { return &_term; } 316}; 317 318ParScanThreadStateSet::ParScanThreadStateSet(int num_threads, 319 Space& to_space, 320 ParNewGeneration& young_gen, 321 Generation& old_gen, 322 ObjToScanQueueSet& queue_set, 323 Stack<oop, mtGC>* overflow_stacks, 324 size_t desired_plab_sz, 325 ParallelTaskTerminator& term) 326 : ResourceArray(sizeof(ParScanThreadState), num_threads), 327 _young_gen(young_gen), 328 _old_gen(old_gen), 329 _term(term) 330{ 331 assert(num_threads > 0, "sanity check!"); 332 assert(ParGCUseLocalOverflow == (overflow_stacks != NULL), 333 "overflow_stack allocation mismatch"); 334 // Initialize states. 335 for (int i = 0; i < num_threads; ++i) { 336 new ((ParScanThreadState*)_data + i) 337 ParScanThreadState(&to_space, &young_gen, &old_gen, i, &queue_set, 338 overflow_stacks, desired_plab_sz, term); 339 } 340} 341 342inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i) { 343 assert(i >= 0 && i < length(), "sanity check!"); 344 return ((ParScanThreadState*)_data)[i]; 345} 346 347void ParScanThreadStateSet::trace_promotion_failed(const YoungGCTracer* gc_tracer) { 348 for (int i = 0; i < length(); ++i) { 349 if (thread_state(i).promotion_failed()) { 350 gc_tracer->report_promotion_failed(thread_state(i).promotion_failed_info()); 351 thread_state(i).promotion_failed_info().reset(); 352 } 353 } 354} 355 356void ParScanThreadStateSet::reset(uint active_threads, bool promotion_failed) { 357 _term.reset_for_reuse(active_threads); 358 if (promotion_failed) { 359 for (int i = 0; i < length(); ++i) { 360 thread_state(i).print_promotion_failure_size(); 361 } 362 } 363} 364 365#if TASKQUEUE_STATS 366void ParScanThreadState::reset_stats() { 367 taskqueue_stats().reset(); 368 _term_attempts = 0; 369 _overflow_refills = 0; 370 _overflow_refill_objs = 0; 371} 372 373void ParScanThreadStateSet::reset_stats() { 374 for (int i = 0; i < length(); ++i) { 375 thread_state(i).reset_stats(); 376 } 377} 378 379void ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st) { 380 st->print_raw_cr("GC Termination Stats"); 381 st->print_raw_cr(" elapsed --strong roots-- -------termination-------"); 382 st->print_raw_cr("thr ms ms % ms % attempts"); 383 st->print_raw_cr("--- --------- --------- ------ --------- ------ --------"); 384} 385 386void ParScanThreadStateSet::print_termination_stats(outputStream* const st) { 387 print_termination_stats_hdr(st); 388 389 for (int i = 0; i < length(); ++i) { 390 const ParScanThreadState & pss = thread_state(i); 391 const double elapsed_ms = pss.elapsed_time() * 1000.0; 392 const double s_roots_ms = pss.strong_roots_time() * 1000.0; 393 const double term_ms = pss.term_time() * 1000.0; 394 st->print_cr("%3d %9.2f %9.2f %6.2f %9.2f %6.2f " SIZE_FORMAT_W(8), 395 i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms, 396 term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts()); 397 } 398} 399 400// Print stats related to work queue activity. 401void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st) { 402 st->print_raw_cr("GC Task Stats"); 403 st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr(); 404 st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr(); 405} 406 407void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st) { 408 print_taskqueue_stats_hdr(st); 409 410 TaskQueueStats totals; 411 for (int i = 0; i < length(); ++i) { 412 const ParScanThreadState & pss = thread_state(i); 413 const TaskQueueStats & stats = pss.taskqueue_stats(); 414 st->print("%3d ", i); stats.print(st); st->cr(); 415 totals += stats; 416 417 if (pss.overflow_refills() > 0) { 418 st->print_cr(" " SIZE_FORMAT_W(10) " overflow refills " 419 SIZE_FORMAT_W(10) " overflow objects", 420 pss.overflow_refills(), pss.overflow_refill_objs()); 421 } 422 } 423 st->print("tot "); totals.print(st); st->cr(); 424 425 DEBUG_ONLY(totals.verify()); 426} 427#endif // TASKQUEUE_STATS 428 429void ParScanThreadStateSet::flush() { 430 // Work in this loop should be kept as lightweight as 431 // possible since this might otherwise become a bottleneck 432 // to scaling. Should we add heavy-weight work into this 433 // loop, consider parallelizing the loop into the worker threads. 434 for (int i = 0; i < length(); ++i) { 435 ParScanThreadState& par_scan_state = thread_state(i); 436 437 // Flush stats related to To-space PLAB activity and 438 // retire the last buffer. 439 par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_young_gen.plab_stats()); 440 441 // Every thread has its own age table. We need to merge 442 // them all into one. 443 ageTable *local_table = par_scan_state.age_table(); 444 _young_gen.age_table()->merge(local_table); 445 446 // Inform old gen that we're done. 447 _old_gen.par_promote_alloc_done(i); 448 _old_gen.par_oop_since_save_marks_iterate_done(i); 449 } 450 451 if (UseConcMarkSweepGC) { 452 // We need to call this even when ResizeOldPLAB is disabled 453 // so as to avoid breaking some asserts. While we may be able 454 // to avoid this by reorganizing the code a bit, I am loathe 455 // to do that unless we find cases where ergo leads to bad 456 // performance. 457 CFLS_LAB::compute_desired_plab_size(); 458 } 459} 460 461ParScanClosure::ParScanClosure(ParNewGeneration* g, 462 ParScanThreadState* par_scan_state) : 463 OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g) { 464 _boundary = _g->reserved().end(); 465} 466 467void ParScanWithBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, false); } 468void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); } 469 470void ParScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, false); } 471void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); } 472 473void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); } 474void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); } 475 476void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); } 477void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); } 478 479ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g, 480 ParScanThreadState* par_scan_state) 481 : ScanWeakRefClosure(g), _par_scan_state(par_scan_state) 482{} 483 484void ParScanWeakRefClosure::do_oop(oop* p) { ParScanWeakRefClosure::do_oop_work(p); } 485void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); } 486 487#ifdef WIN32 488#pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */ 489#endif 490 491ParEvacuateFollowersClosure::ParEvacuateFollowersClosure( 492 ParScanThreadState* par_scan_state_, 493 ParScanWithoutBarrierClosure* to_space_closure_, 494 ParScanWithBarrierClosure* old_gen_closure_, 495 ParRootScanWithoutBarrierClosure* to_space_root_closure_, 496 ParNewGeneration* par_gen_, 497 ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_, 498 ObjToScanQueueSet* task_queues_, 499 ParallelTaskTerminator* terminator_) : 500 501 _par_scan_state(par_scan_state_), 502 _to_space_closure(to_space_closure_), 503 _old_gen_closure(old_gen_closure_), 504 _to_space_root_closure(to_space_root_closure_), 505 _old_gen_root_closure(old_gen_root_closure_), 506 _par_gen(par_gen_), 507 _task_queues(task_queues_), 508 _terminator(terminator_) 509{} 510 511void ParEvacuateFollowersClosure::do_void() { 512 ObjToScanQueue* work_q = par_scan_state()->work_queue(); 513 514 while (true) { 515 // Scan to-space and old-gen objs until we run out of both. 516 oop obj_to_scan; 517 par_scan_state()->trim_queues(0); 518 519 // We have no local work, attempt to steal from other threads. 520 521 // Attempt to steal work from promoted. 522 if (task_queues()->steal(par_scan_state()->thread_num(), 523 par_scan_state()->hash_seed(), 524 obj_to_scan)) { 525 bool res = work_q->push(obj_to_scan); 526 assert(res, "Empty queue should have room for a push."); 527 528 // If successful, goto Start. 529 continue; 530 531 // Try global overflow list. 532 } else if (par_gen()->take_from_overflow_list(par_scan_state())) { 533 continue; 534 } 535 536 // Otherwise, offer termination. 537 par_scan_state()->start_term_time(); 538 if (terminator()->offer_termination()) break; 539 par_scan_state()->end_term_time(); 540 } 541 assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0, 542 "Broken overflow list?"); 543 // Finish the last termination pause. 544 par_scan_state()->end_term_time(); 545} 546 547ParNewGenTask::ParNewGenTask(ParNewGeneration* young_gen, 548 Generation* old_gen, 549 HeapWord* young_old_boundary, 550 ParScanThreadStateSet* state_set, 551 StrongRootsScope* strong_roots_scope) : 552 AbstractGangTask("ParNewGeneration collection"), 553 _young_gen(young_gen), _old_gen(old_gen), 554 _young_old_boundary(young_old_boundary), 555 _state_set(state_set), 556 _strong_roots_scope(strong_roots_scope) 557{} 558 559void ParNewGenTask::work(uint worker_id) { 560 GenCollectedHeap* gch = GenCollectedHeap::heap(); 561 // Since this is being done in a separate thread, need new resource 562 // and handle marks. 563 ResourceMark rm; 564 HandleMark hm; 565 566 ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id); 567 assert(_state_set->is_valid(worker_id), "Should not have been called"); 568 569 par_scan_state.set_young_old_boundary(_young_old_boundary); 570 571 KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(), 572 gch->rem_set()->klass_rem_set()); 573 CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure, 574 &par_scan_state.to_space_root_closure(), 575 false); 576 577 par_scan_state.start_strong_roots(); 578 gch->gen_process_roots(_strong_roots_scope, 579 GenCollectedHeap::YoungGen, 580 true, // Process younger gens, if any, as strong roots. 581 GenCollectedHeap::SO_ScavengeCodeCache, 582 GenCollectedHeap::StrongAndWeakRoots, 583 &par_scan_state.to_space_root_closure(), 584 &par_scan_state.older_gen_closure(), 585 &cld_scan_closure); 586 587 par_scan_state.end_strong_roots(); 588 589 // "evacuate followers". 590 par_scan_state.evacuate_followers_closure().do_void(); 591} 592 593ParNewGeneration::ParNewGeneration(ReservedSpace rs, size_t initial_byte_size) 594 : DefNewGeneration(rs, initial_byte_size, "PCopy"), 595 _overflow_list(NULL), 596 _is_alive_closure(this), 597 _plab_stats(YoungPLABSize, PLABWeight) 598{ 599 NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;) 600 NOT_PRODUCT(_num_par_pushes = 0;) 601 _task_queues = new ObjToScanQueueSet(ParallelGCThreads); 602 guarantee(_task_queues != NULL, "task_queues allocation failure."); 603 604 for (uint i = 0; i < ParallelGCThreads; i++) { 605 ObjToScanQueue *q = new ObjToScanQueue(); 606 guarantee(q != NULL, "work_queue Allocation failure."); 607 _task_queues->register_queue(i, q); 608 } 609 610 for (uint i = 0; i < ParallelGCThreads; i++) { 611 _task_queues->queue(i)->initialize(); 612 } 613 614 _overflow_stacks = NULL; 615 if (ParGCUseLocalOverflow) { 616 // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal with ',' 617 typedef Stack<oop, mtGC> GCOopStack; 618 619 _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC); 620 for (size_t i = 0; i < ParallelGCThreads; ++i) { 621 new (_overflow_stacks + i) Stack<oop, mtGC>(); 622 } 623 } 624 625 if (UsePerfData) { 626 EXCEPTION_MARK; 627 ResourceMark rm; 628 629 const char* cname = 630 PerfDataManager::counter_name(_gen_counters->name_space(), "threads"); 631 PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None, 632 ParallelGCThreads, CHECK); 633 } 634} 635 636// ParNewGeneration:: 637ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) : 638 DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {} 639 640template <class T> 641void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) { 642#ifdef ASSERT 643 { 644 assert(!oopDesc::is_null(*p), "expected non-null ref"); 645 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 646 // We never expect to see a null reference being processed 647 // as a weak reference. 648 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 649 } 650#endif // ASSERT 651 652 _par_cl->do_oop_nv(p); 653 654 if (GenCollectedHeap::heap()->is_in_reserved(p)) { 655 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 656 _rs->write_ref_field_gc_par(p, obj); 657 } 658} 659 660void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); } 661void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); } 662 663// ParNewGeneration:: 664KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) : 665 DefNewGeneration::KeepAliveClosure(cl) {} 666 667template <class T> 668void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) { 669#ifdef ASSERT 670 { 671 assert(!oopDesc::is_null(*p), "expected non-null ref"); 672 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 673 // We never expect to see a null reference being processed 674 // as a weak reference. 675 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 676 } 677#endif // ASSERT 678 679 _cl->do_oop_nv(p); 680 681 if (GenCollectedHeap::heap()->is_in_reserved(p)) { 682 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 683 _rs->write_ref_field_gc_par(p, obj); 684 } 685} 686 687void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); } 688void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); } 689 690template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) { 691 T heap_oop = oopDesc::load_heap_oop(p); 692 if (!oopDesc::is_null(heap_oop)) { 693 oop obj = oopDesc::decode_heap_oop_not_null(heap_oop); 694 if ((HeapWord*)obj < _boundary) { 695 assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?"); 696 oop new_obj = obj->is_forwarded() 697 ? obj->forwardee() 698 : _g->DefNewGeneration::copy_to_survivor_space(obj); 699 oopDesc::encode_store_heap_oop_not_null(p, new_obj); 700 } 701 if (_gc_barrier) { 702 // If p points to a younger generation, mark the card. 703 if ((HeapWord*)obj < _gen_boundary) { 704 _rs->write_ref_field_gc_par(p, obj); 705 } 706 } 707 } 708} 709 710void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 711void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 712 713class ParNewRefProcTaskProxy: public AbstractGangTask { 714 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; 715public: 716 ParNewRefProcTaskProxy(ProcessTask& task, 717 ParNewGeneration& young_gen, 718 Generation& old_gen, 719 HeapWord* young_old_boundary, 720 ParScanThreadStateSet& state_set); 721 722private: 723 virtual void work(uint worker_id); 724private: 725 ParNewGeneration& _young_gen; 726 ProcessTask& _task; 727 Generation& _old_gen; 728 HeapWord* _young_old_boundary; 729 ParScanThreadStateSet& _state_set; 730}; 731 732ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task, 733 ParNewGeneration& young_gen, 734 Generation& old_gen, 735 HeapWord* young_old_boundary, 736 ParScanThreadStateSet& state_set) 737 : AbstractGangTask("ParNewGeneration parallel reference processing"), 738 _young_gen(young_gen), 739 _task(task), 740 _old_gen(old_gen), 741 _young_old_boundary(young_old_boundary), 742 _state_set(state_set) 743{ } 744 745void ParNewRefProcTaskProxy::work(uint worker_id) { 746 ResourceMark rm; 747 HandleMark hm; 748 ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id); 749 par_scan_state.set_young_old_boundary(_young_old_boundary); 750 _task.work(worker_id, par_scan_state.is_alive_closure(), 751 par_scan_state.keep_alive_closure(), 752 par_scan_state.evacuate_followers_closure()); 753} 754 755class ParNewRefEnqueueTaskProxy: public AbstractGangTask { 756 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; 757 EnqueueTask& _task; 758 759public: 760 ParNewRefEnqueueTaskProxy(EnqueueTask& task) 761 : AbstractGangTask("ParNewGeneration parallel reference enqueue"), 762 _task(task) 763 { } 764 765 virtual void work(uint worker_id) { 766 _task.work(worker_id); 767 } 768}; 769 770void ParNewRefProcTaskExecutor::execute(ProcessTask& task) { 771 GenCollectedHeap* gch = GenCollectedHeap::heap(); 772 WorkGang* workers = gch->workers(); 773 assert(workers != NULL, "Need parallel worker threads."); 774 _state_set.reset(workers->active_workers(), _young_gen.promotion_failed()); 775 ParNewRefProcTaskProxy rp_task(task, _young_gen, _old_gen, 776 _young_gen.reserved().end(), _state_set); 777 workers->run_task(&rp_task); 778 _state_set.reset(0 /* bad value in debug if not reset */, 779 _young_gen.promotion_failed()); 780} 781 782void ParNewRefProcTaskExecutor::execute(EnqueueTask& task) { 783 GenCollectedHeap* gch = GenCollectedHeap::heap(); 784 WorkGang* workers = gch->workers(); 785 assert(workers != NULL, "Need parallel worker threads."); 786 ParNewRefEnqueueTaskProxy enq_task(task); 787 workers->run_task(&enq_task); 788} 789 790void ParNewRefProcTaskExecutor::set_single_threaded_mode() { 791 _state_set.flush(); 792 GenCollectedHeap* gch = GenCollectedHeap::heap(); 793 gch->save_marks(); 794} 795 796ScanClosureWithParBarrier:: 797ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) : 798 ScanClosure(g, gc_barrier) 799{ } 800 801EvacuateFollowersClosureGeneral:: 802EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, 803 OopsInGenClosure* cur, 804 OopsInGenClosure* older) : 805 _gch(gch), 806 _scan_cur_or_nonheap(cur), _scan_older(older) 807{ } 808 809void EvacuateFollowersClosureGeneral::do_void() { 810 do { 811 // Beware: this call will lead to closure applications via virtual 812 // calls. 813 _gch->oop_since_save_marks_iterate(GenCollectedHeap::YoungGen, 814 _scan_cur_or_nonheap, 815 _scan_older); 816 } while (!_gch->no_allocs_since_save_marks()); 817} 818 819// A Generation that does parallel young-gen collection. 820 821void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set) { 822 assert(_promo_failure_scan_stack.is_empty(), "post condition"); 823 _promo_failure_scan_stack.clear(true); // Clear cached segments. 824 825 remove_forwarding_pointers(); 826 if (PrintGCDetails) { 827 gclog_or_tty->print(" (promotion failed)"); 828 } 829 // All the spaces are in play for mark-sweep. 830 swap_spaces(); // Make life simpler for CMS || rescan; see 6483690. 831 from()->set_next_compaction_space(to()); 832 gch->set_incremental_collection_failed(); 833 // Inform the next generation that a promotion failure occurred. 834 _old_gen->promotion_failure_occurred(); 835 836 // Trace promotion failure in the parallel GC threads 837 thread_state_set.trace_promotion_failed(gc_tracer()); 838 // Single threaded code may have reported promotion failure to the global state 839 if (_promotion_failed_info.has_failed()) { 840 _gc_tracer.report_promotion_failed(_promotion_failed_info); 841 } 842 // Reset the PromotionFailureALot counters. 843 NOT_PRODUCT(gch->reset_promotion_should_fail();) 844} 845 846void ParNewGeneration::collect(bool full, 847 bool clear_all_soft_refs, 848 size_t size, 849 bool is_tlab) { 850 assert(full || size > 0, "otherwise we don't want to collect"); 851 852 GenCollectedHeap* gch = GenCollectedHeap::heap(); 853 854 _gc_timer->register_gc_start(); 855 856 AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy(); 857 WorkGang* workers = gch->workers(); 858 assert(workers != NULL, "Need workgang for parallel work"); 859 uint active_workers = 860 AdaptiveSizePolicy::calc_active_workers(workers->total_workers(), 861 workers->active_workers(), 862 Threads::number_of_non_daemon_threads()); 863 workers->set_active_workers(active_workers); 864 _old_gen = gch->old_gen(); 865 866 // If the next generation is too full to accommodate worst-case promotion 867 // from this generation, pass on collection; let the next generation 868 // do it. 869 if (!collection_attempt_is_safe()) { 870 gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one 871 return; 872 } 873 assert(to()->is_empty(), "Else not collection_attempt_is_safe"); 874 875 _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start()); 876 gch->trace_heap_before_gc(gc_tracer()); 877 878 init_assuming_no_promotion_failure(); 879 880 if (UseAdaptiveSizePolicy) { 881 set_survivor_overflow(false); 882 size_policy->minor_collection_begin(); 883 } 884 885 GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL); 886 // Capture heap used before collection (for printing). 887 size_t gch_prev_used = gch->used(); 888 889 age_table()->clear(); 890 to()->clear(SpaceDecorator::Mangle); 891 892 gch->save_marks(); 893 894 // Set the correct parallelism (number of queues) in the reference processor 895 ref_processor()->set_active_mt_degree(active_workers); 896 897 // Always set the terminator for the active number of workers 898 // because only those workers go through the termination protocol. 899 ParallelTaskTerminator _term(active_workers, task_queues()); 900 ParScanThreadStateSet thread_state_set(active_workers, 901 *to(), *this, *_old_gen, *task_queues(), 902 _overflow_stacks, desired_plab_sz(), _term); 903 904 thread_state_set.reset(active_workers, promotion_failed()); 905 906 { 907 StrongRootsScope srs(active_workers); 908 909 ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set, &srs); 910 gch->rem_set()->prepare_for_younger_refs_iterate(true); 911 // It turns out that even when we're using 1 thread, doing the work in a 912 // separate thread causes wide variance in run times. We can't help this 913 // in the multi-threaded case, but we special-case n=1 here to get 914 // repeatable measurements of the 1-thread overhead of the parallel code. 915 if (active_workers > 1) { 916 workers->run_task(&tsk); 917 } else { 918 tsk.work(0); 919 } 920 } 921 922 thread_state_set.reset(0 /* Bad value in debug if not reset */, 923 promotion_failed()); 924 925 // Trace and reset failed promotion info. 926 if (promotion_failed()) { 927 thread_state_set.trace_promotion_failed(gc_tracer()); 928 } 929 930 // Process (weak) reference objects found during scavenge. 931 ReferenceProcessor* rp = ref_processor(); 932 IsAliveClosure is_alive(this); 933 ScanWeakRefClosure scan_weak_ref(this); 934 KeepAliveClosure keep_alive(&scan_weak_ref); 935 ScanClosure scan_without_gc_barrier(this, false); 936 ScanClosureWithParBarrier scan_with_gc_barrier(this, true); 937 set_promo_failure_scan_stack_closure(&scan_without_gc_barrier); 938 EvacuateFollowersClosureGeneral evacuate_followers(gch, 939 &scan_without_gc_barrier, &scan_with_gc_barrier); 940 rp->setup_policy(clear_all_soft_refs); 941 // Can the mt_degree be set later (at run_task() time would be best)? 942 rp->set_active_mt_degree(active_workers); 943 ReferenceProcessorStats stats; 944 if (rp->processing_is_mt()) { 945 ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set); 946 stats = rp->process_discovered_references(&is_alive, &keep_alive, 947 &evacuate_followers, &task_executor, 948 _gc_timer); 949 } else { 950 thread_state_set.flush(); 951 gch->save_marks(); 952 stats = rp->process_discovered_references(&is_alive, &keep_alive, 953 &evacuate_followers, NULL, 954 _gc_timer); 955 } 956 _gc_tracer.report_gc_reference_stats(stats); 957 _gc_tracer.report_tenuring_threshold(tenuring_threshold()); 958 959 if (!promotion_failed()) { 960 // Swap the survivor spaces. 961 eden()->clear(SpaceDecorator::Mangle); 962 from()->clear(SpaceDecorator::Mangle); 963 if (ZapUnusedHeapArea) { 964 // This is now done here because of the piece-meal mangling which 965 // can check for valid mangling at intermediate points in the 966 // collection(s). When a young collection fails to collect 967 // sufficient space resizing of the young generation can occur 968 // and redistribute the spaces in the young generation. Mangle 969 // here so that unzapped regions don't get distributed to 970 // other spaces. 971 to()->mangle_unused_area(); 972 } 973 swap_spaces(); 974 975 // A successful scavenge should restart the GC time limit count which is 976 // for full GC's. 977 size_policy->reset_gc_overhead_limit_count(); 978 979 assert(to()->is_empty(), "to space should be empty now"); 980 981 adjust_desired_tenuring_threshold(); 982 } else { 983 handle_promotion_failed(gch, thread_state_set); 984 } 985 // set new iteration safe limit for the survivor spaces 986 from()->set_concurrent_iteration_safe_limit(from()->top()); 987 to()->set_concurrent_iteration_safe_limit(to()->top()); 988 989 if (ResizePLAB) { 990 plab_stats()->adjust_desired_plab_sz(); 991 } 992 993 if (PrintGC && !PrintGCDetails) { 994 gch->print_heap_change(gch_prev_used); 995 } 996 997 TASKQUEUE_STATS_ONLY(if (PrintTerminationStats) thread_state_set.print_termination_stats()); 998 TASKQUEUE_STATS_ONLY(if (PrintTaskqueue) thread_state_set.print_taskqueue_stats()); 999 1000 if (UseAdaptiveSizePolicy) { 1001 size_policy->minor_collection_end(gch->gc_cause()); 1002 size_policy->avg_survived()->sample(from()->used()); 1003 } 1004 1005 // We need to use a monotonically non-decreasing time in ms 1006 // or we will see time-warp warnings and os::javaTimeMillis() 1007 // does not guarantee monotonicity. 1008 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 1009 update_time_of_last_gc(now); 1010 1011 rp->set_enqueuing_is_done(true); 1012 if (rp->processing_is_mt()) { 1013 ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set); 1014 rp->enqueue_discovered_references(&task_executor); 1015 } else { 1016 rp->enqueue_discovered_references(NULL); 1017 } 1018 rp->verify_no_references_recorded(); 1019 1020 gch->trace_heap_after_gc(gc_tracer()); 1021 1022 _gc_timer->register_gc_end(); 1023 1024 _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions()); 1025} 1026 1027size_t ParNewGeneration::desired_plab_sz() { 1028 return _plab_stats.desired_plab_sz(GenCollectedHeap::heap()->workers()->active_workers()); 1029} 1030 1031static int sum; 1032void ParNewGeneration::waste_some_time() { 1033 for (int i = 0; i < 100; i++) { 1034 sum += i; 1035 } 1036} 1037 1038static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4); 1039 1040// Because of concurrency, there are times where an object for which 1041// "is_forwarded()" is true contains an "interim" forwarding pointer 1042// value. Such a value will soon be overwritten with a real value. 1043// This method requires "obj" to have a forwarding pointer, and waits, if 1044// necessary for a real one to be inserted, and returns it. 1045 1046oop ParNewGeneration::real_forwardee(oop obj) { 1047 oop forward_ptr = obj->forwardee(); 1048 if (forward_ptr != ClaimedForwardPtr) { 1049 return forward_ptr; 1050 } else { 1051 return real_forwardee_slow(obj); 1052 } 1053} 1054 1055oop ParNewGeneration::real_forwardee_slow(oop obj) { 1056 // Spin-read if it is claimed but not yet written by another thread. 1057 oop forward_ptr = obj->forwardee(); 1058 while (forward_ptr == ClaimedForwardPtr) { 1059 waste_some_time(); 1060 assert(obj->is_forwarded(), "precondition"); 1061 forward_ptr = obj->forwardee(); 1062 } 1063 return forward_ptr; 1064} 1065 1066void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) { 1067 if (m->must_be_preserved_for_promotion_failure(obj)) { 1068 // We should really have separate per-worker stacks, rather 1069 // than use locking of a common pair of stacks. 1070 MutexLocker ml(ParGCRareEvent_lock); 1071 preserve_mark(obj, m); 1072 } 1073} 1074 1075// Multiple GC threads may try to promote an object. If the object 1076// is successfully promoted, a forwarding pointer will be installed in 1077// the object in the young generation. This method claims the right 1078// to install the forwarding pointer before it copies the object, 1079// thus avoiding the need to undo the copy as in 1080// copy_to_survivor_space_avoiding_with_undo. 1081 1082oop ParNewGeneration::copy_to_survivor_space(ParScanThreadState* par_scan_state, 1083 oop old, 1084 size_t sz, 1085 markOop m) { 1086 // In the sequential version, this assert also says that the object is 1087 // not forwarded. That might not be the case here. It is the case that 1088 // the caller observed it to be not forwarded at some time in the past. 1089 assert(is_in_reserved(old), "shouldn't be scavenging this oop"); 1090 1091 // The sequential code read "old->age()" below. That doesn't work here, 1092 // since the age is in the mark word, and that might be overwritten with 1093 // a forwarding pointer by a parallel thread. So we must save the mark 1094 // word in a local and then analyze it. 1095 oopDesc dummyOld; 1096 dummyOld.set_mark(m); 1097 assert(!dummyOld.is_forwarded(), 1098 "should not be called with forwarding pointer mark word."); 1099 1100 oop new_obj = NULL; 1101 oop forward_ptr; 1102 1103 // Try allocating obj in to-space (unless too old) 1104 if (dummyOld.age() < tenuring_threshold()) { 1105 new_obj = (oop)par_scan_state->alloc_in_to_space(sz); 1106 if (new_obj == NULL) { 1107 set_survivor_overflow(true); 1108 } 1109 } 1110 1111 if (new_obj == NULL) { 1112 // Either to-space is full or we decided to promote try allocating obj tenured 1113 1114 // Attempt to install a null forwarding pointer (atomically), 1115 // to claim the right to install the real forwarding pointer. 1116 forward_ptr = old->forward_to_atomic(ClaimedForwardPtr); 1117 if (forward_ptr != NULL) { 1118 // someone else beat us to it. 1119 return real_forwardee(old); 1120 } 1121 1122 if (!_promotion_failed) { 1123 new_obj = _old_gen->par_promote(par_scan_state->thread_num(), 1124 old, m, sz); 1125 } 1126 1127 if (new_obj == NULL) { 1128 // promotion failed, forward to self 1129 _promotion_failed = true; 1130 new_obj = old; 1131 1132 preserve_mark_if_necessary(old, m); 1133 par_scan_state->register_promotion_failure(sz); 1134 } 1135 1136 old->forward_to(new_obj); 1137 forward_ptr = NULL; 1138 } else { 1139 // Is in to-space; do copying ourselves. 1140 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz); 1141 assert(GenCollectedHeap::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value."); 1142 forward_ptr = old->forward_to_atomic(new_obj); 1143 // Restore the mark word copied above. 1144 new_obj->set_mark(m); 1145 // Increment age if obj still in new generation 1146 new_obj->incr_age(); 1147 par_scan_state->age_table()->add(new_obj, sz); 1148 } 1149 assert(new_obj != NULL, "just checking"); 1150 1151 // This code must come after the CAS test, or it will print incorrect 1152 // information. 1153 if (TraceScavenge) { 1154 gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}", 1155 is_in_reserved(new_obj) ? "copying" : "tenuring", 1156 new_obj->klass()->internal_name(), p2i(old), p2i(new_obj), new_obj->size()); 1157 } 1158 1159 if (forward_ptr == NULL) { 1160 oop obj_to_push = new_obj; 1161 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) { 1162 // Length field used as index of next element to be scanned. 1163 // Real length can be obtained from real_forwardee() 1164 arrayOop(old)->set_length(0); 1165 obj_to_push = old; 1166 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push, 1167 "push forwarded object"); 1168 } 1169 // Push it on one of the queues of to-be-scanned objects. 1170 bool simulate_overflow = false; 1171 NOT_PRODUCT( 1172 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) { 1173 // simulate a stack overflow 1174 simulate_overflow = true; 1175 } 1176 ) 1177 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) { 1178 // Add stats for overflow pushes. 1179 if (Verbose && PrintGCDetails) { 1180 gclog_or_tty->print("queue overflow!\n"); 1181 } 1182 push_on_overflow_list(old, par_scan_state); 1183 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0)); 1184 } 1185 1186 return new_obj; 1187 } 1188 1189 // Oops. Someone beat us to it. Undo the allocation. Where did we 1190 // allocate it? 1191 if (is_in_reserved(new_obj)) { 1192 // Must be in to_space. 1193 assert(to()->is_in_reserved(new_obj), "Checking"); 1194 if (forward_ptr == ClaimedForwardPtr) { 1195 // Wait to get the real forwarding pointer value. 1196 forward_ptr = real_forwardee(old); 1197 } 1198 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz); 1199 } 1200 1201 return forward_ptr; 1202} 1203 1204#ifndef PRODUCT 1205// It's OK to call this multi-threaded; the worst thing 1206// that can happen is that we'll get a bunch of closely 1207// spaced simulated overflows, but that's OK, in fact 1208// probably good as it would exercise the overflow code 1209// under contention. 1210bool ParNewGeneration::should_simulate_overflow() { 1211 if (_overflow_counter-- <= 0) { // just being defensive 1212 _overflow_counter = ParGCWorkQueueOverflowInterval; 1213 return true; 1214 } else { 1215 return false; 1216 } 1217} 1218#endif 1219 1220// In case we are using compressed oops, we need to be careful. 1221// If the object being pushed is an object array, then its length 1222// field keeps track of the "grey boundary" at which the next 1223// incremental scan will be done (see ParGCArrayScanChunk). 1224// When using compressed oops, this length field is kept in the 1225// lower 32 bits of the erstwhile klass word and cannot be used 1226// for the overflow chaining pointer (OCP below). As such the OCP 1227// would itself need to be compressed into the top 32-bits in this 1228// case. Unfortunately, see below, in the event that we have a 1229// promotion failure, the node to be pushed on the list can be 1230// outside of the Java heap, so the heap-based pointer compression 1231// would not work (we would have potential aliasing between C-heap 1232// and Java-heap pointers). For this reason, when using compressed 1233// oops, we simply use a worker-thread-local, non-shared overflow 1234// list in the form of a growable array, with a slightly different 1235// overflow stack draining strategy. If/when we start using fat 1236// stacks here, we can go back to using (fat) pointer chains 1237// (although some performance comparisons would be useful since 1238// single global lists have their own performance disadvantages 1239// as we were made painfully aware not long ago, see 6786503). 1240#define BUSY (cast_to_oop<intptr_t>(0x1aff1aff)) 1241void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) { 1242 assert(is_in_reserved(from_space_obj), "Should be from this generation"); 1243 if (ParGCUseLocalOverflow) { 1244 // In the case of compressed oops, we use a private, not-shared 1245 // overflow stack. 1246 par_scan_state->push_on_overflow_stack(from_space_obj); 1247 } else { 1248 assert(!UseCompressedOops, "Error"); 1249 // if the object has been forwarded to itself, then we cannot 1250 // use the klass pointer for the linked list. Instead we have 1251 // to allocate an oopDesc in the C-Heap and use that for the linked list. 1252 // XXX This is horribly inefficient when a promotion failure occurs 1253 // and should be fixed. XXX FIX ME !!! 1254#ifndef PRODUCT 1255 Atomic::inc_ptr(&_num_par_pushes); 1256 assert(_num_par_pushes > 0, "Tautology"); 1257#endif 1258 if (from_space_obj->forwardee() == from_space_obj) { 1259 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC); 1260 listhead->forward_to(from_space_obj); 1261 from_space_obj = listhead; 1262 } 1263 oop observed_overflow_list = _overflow_list; 1264 oop cur_overflow_list; 1265 do { 1266 cur_overflow_list = observed_overflow_list; 1267 if (cur_overflow_list != BUSY) { 1268 from_space_obj->set_klass_to_list_ptr(cur_overflow_list); 1269 } else { 1270 from_space_obj->set_klass_to_list_ptr(NULL); 1271 } 1272 observed_overflow_list = 1273 (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list); 1274 } while (cur_overflow_list != observed_overflow_list); 1275 } 1276} 1277 1278bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) { 1279 bool res; 1280 1281 if (ParGCUseLocalOverflow) { 1282 res = par_scan_state->take_from_overflow_stack(); 1283 } else { 1284 assert(!UseCompressedOops, "Error"); 1285 res = take_from_overflow_list_work(par_scan_state); 1286 } 1287 return res; 1288} 1289 1290 1291// *NOTE*: The overflow list manipulation code here and 1292// in CMSCollector:: are very similar in shape, 1293// except that in the CMS case we thread the objects 1294// directly into the list via their mark word, and do 1295// not need to deal with special cases below related 1296// to chunking of object arrays and promotion failure 1297// handling. 1298// CR 6797058 has been filed to attempt consolidation of 1299// the common code. 1300// Because of the common code, if you make any changes in 1301// the code below, please check the CMS version to see if 1302// similar changes might be needed. 1303// See CMSCollector::par_take_from_overflow_list() for 1304// more extensive documentation comments. 1305bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) { 1306 ObjToScanQueue* work_q = par_scan_state->work_queue(); 1307 // How many to take? 1308 size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 1309 (size_t)ParGCDesiredObjsFromOverflowList); 1310 1311 assert(!UseCompressedOops, "Error"); 1312 assert(par_scan_state->overflow_stack() == NULL, "Error"); 1313 if (_overflow_list == NULL) return false; 1314 1315 // Otherwise, there was something there; try claiming the list. 1316 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1317 // Trim off a prefix of at most objsFromOverflow items 1318 Thread* tid = Thread::current(); 1319 size_t spin_count = ParallelGCThreads; 1320 size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100); 1321 for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) { 1322 // someone grabbed it before we did ... 1323 // ... we spin for a short while... 1324 os::sleep(tid, sleep_time_millis, false); 1325 if (_overflow_list == NULL) { 1326 // nothing left to take 1327 return false; 1328 } else if (_overflow_list != BUSY) { 1329 // try and grab the prefix 1330 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1331 } 1332 } 1333 if (prefix == NULL || prefix == BUSY) { 1334 // Nothing to take or waited long enough 1335 if (prefix == NULL) { 1336 // Write back the NULL in case we overwrote it with BUSY above 1337 // and it is still the same value. 1338 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1339 } 1340 return false; 1341 } 1342 assert(prefix != NULL && prefix != BUSY, "Error"); 1343 size_t i = 1; 1344 oop cur = prefix; 1345 while (i < objsFromOverflow && cur->klass_or_null() != NULL) { 1346 i++; cur = cur->list_ptr_from_klass(); 1347 } 1348 1349 // Reattach remaining (suffix) to overflow list 1350 if (cur->klass_or_null() == NULL) { 1351 // Write back the NULL in lieu of the BUSY we wrote 1352 // above and it is still the same value. 1353 if (_overflow_list == BUSY) { 1354 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1355 } 1356 } else { 1357 assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error"); 1358 oop suffix = cur->list_ptr_from_klass(); // suffix will be put back on global list 1359 cur->set_klass_to_list_ptr(NULL); // break off suffix 1360 // It's possible that the list is still in the empty(busy) state 1361 // we left it in a short while ago; in that case we may be 1362 // able to place back the suffix. 1363 oop observed_overflow_list = _overflow_list; 1364 oop cur_overflow_list = observed_overflow_list; 1365 bool attached = false; 1366 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { 1367 observed_overflow_list = 1368 (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1369 if (cur_overflow_list == observed_overflow_list) { 1370 attached = true; 1371 break; 1372 } else cur_overflow_list = observed_overflow_list; 1373 } 1374 if (!attached) { 1375 // Too bad, someone else got in in between; we'll need to do a splice. 1376 // Find the last item of suffix list 1377 oop last = suffix; 1378 while (last->klass_or_null() != NULL) { 1379 last = last->list_ptr_from_klass(); 1380 } 1381 // Atomically prepend suffix to current overflow list 1382 observed_overflow_list = _overflow_list; 1383 do { 1384 cur_overflow_list = observed_overflow_list; 1385 if (cur_overflow_list != BUSY) { 1386 // Do the splice ... 1387 last->set_klass_to_list_ptr(cur_overflow_list); 1388 } else { // cur_overflow_list == BUSY 1389 last->set_klass_to_list_ptr(NULL); 1390 } 1391 observed_overflow_list = 1392 (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1393 } while (cur_overflow_list != observed_overflow_list); 1394 } 1395 } 1396 1397 // Push objects on prefix list onto this thread's work queue 1398 assert(prefix != NULL && prefix != BUSY, "program logic"); 1399 cur = prefix; 1400 ssize_t n = 0; 1401 while (cur != NULL) { 1402 oop obj_to_push = cur->forwardee(); 1403 oop next = cur->list_ptr_from_klass(); 1404 cur->set_klass(obj_to_push->klass()); 1405 // This may be an array object that is self-forwarded. In that case, the list pointer 1406 // space, cur, is not in the Java heap, but rather in the C-heap and should be freed. 1407 if (!is_in_reserved(cur)) { 1408 // This can become a scaling bottleneck when there is work queue overflow coincident 1409 // with promotion failure. 1410 oopDesc* f = cur; 1411 FREE_C_HEAP_ARRAY(oopDesc, f); 1412 } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) { 1413 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 1414 obj_to_push = cur; 1415 } 1416 bool ok = work_q->push(obj_to_push); 1417 assert(ok, "Should have succeeded"); 1418 cur = next; 1419 n++; 1420 } 1421 TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n)); 1422#ifndef PRODUCT 1423 assert(_num_par_pushes >= n, "Too many pops?"); 1424 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes); 1425#endif 1426 return true; 1427} 1428#undef BUSY 1429 1430void ParNewGeneration::ref_processor_init() { 1431 if (_ref_processor == NULL) { 1432 // Allocate and initialize a reference processor 1433 _ref_processor = 1434 new ReferenceProcessor(_reserved, // span 1435 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing 1436 ParallelGCThreads, // mt processing degree 1437 refs_discovery_is_mt(), // mt discovery 1438 ParallelGCThreads, // mt discovery degree 1439 refs_discovery_is_atomic(), // atomic_discovery 1440 NULL); // is_alive_non_header 1441 } 1442} 1443 1444const char* ParNewGeneration::name() const { 1445 return "par new generation"; 1446} 1447