1 /* 2 * Copyright (c) 2001, 2017, 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 "logging/logStream.hpp" 51 #include "memory/resourceArea.hpp" 52 #include "oops/objArrayOop.hpp" 53 #include "oops/oop.inline.hpp" 54 #include "runtime/atomic.hpp" 55 #include "runtime/handles.hpp" 56 #include "runtime/handles.inline.hpp" 57 #include "runtime/java.hpp" 58 #include "runtime/thread.inline.hpp" 59 #include "utilities/copy.hpp" 60 #include "utilities/globalDefinitions.hpp" 61 #include "utilities/stack.inline.hpp" 62 63 ParScanThreadState::ParScanThreadState(Space* to_space_, 64 ParNewGeneration* young_gen_, 65 Generation* old_gen_, 66 int thread_num_, 67 ObjToScanQueueSet* work_queue_set_, 68 Stack<oop, mtGC>* overflow_stacks_, 69 PreservedMarks* preserved_marks_, 70 size_t desired_plab_sz_, 71 ParallelTaskTerminator& term_) : 72 _to_space(to_space_), 73 _old_gen(old_gen_), 74 _young_gen(young_gen_), 75 _thread_num(thread_num_), 76 _work_queue(work_queue_set_->queue(thread_num_)), 77 _to_space_full(false), 78 _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL), 79 _preserved_marks(preserved_marks_), 80 _ageTable(false), // false ==> not the global age table, no perf data. 81 _to_space_alloc_buffer(desired_plab_sz_), 82 _to_space_closure(young_gen_, this), 83 _old_gen_closure(young_gen_, this), 84 _to_space_root_closure(young_gen_, this), 85 _old_gen_root_closure(young_gen_, this), 86 _older_gen_closure(young_gen_, this), 87 _evacuate_followers(this, &_to_space_closure, &_old_gen_closure, 88 &_to_space_root_closure, young_gen_, &_old_gen_root_closure, 89 work_queue_set_, &term_), 90 _is_alive_closure(young_gen_), 91 _scan_weak_ref_closure(young_gen_, this), 92 _keep_alive_closure(&_scan_weak_ref_closure), 93 _strong_roots_time(0.0), 94 _term_time(0.0) 95 { 96 #if TASKQUEUE_STATS 97 _term_attempts = 0; 98 _overflow_refills = 0; 99 _overflow_refill_objs = 0; 100 #endif // TASKQUEUE_STATS 101 102 _survivor_chunk_array = (ChunkArray*) old_gen()->get_data_recorder(thread_num()); 103 _hash_seed = 17; // Might want to take time-based random value. 104 _start = os::elapsedTime(); 105 _old_gen_closure.set_generation(old_gen_); 106 _old_gen_root_closure.set_generation(old_gen_); 107 } 108 109 void ParScanThreadState::record_survivor_plab(HeapWord* plab_start, 110 size_t plab_word_size) { 111 ChunkArray* sca = survivor_chunk_array(); 112 if (sca != NULL) { 113 // A non-null SCA implies that we want the PLAB data recorded. 114 sca->record_sample(plab_start, plab_word_size); 115 } 116 } 117 118 bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const { 119 return new_obj->is_objArray() && 120 arrayOop(new_obj)->length() > ParGCArrayScanChunk && 121 new_obj != old_obj; 122 } 123 124 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) { 125 assert(old->is_objArray(), "must be obj array"); 126 assert(old->is_forwarded(), "must be forwarded"); 127 assert(GenCollectedHeap::heap()->is_in_reserved(old), "must be in heap."); 128 assert(!old_gen()->is_in(old), "must be in young generation."); 129 130 objArrayOop obj = objArrayOop(old->forwardee()); 131 // Process ParGCArrayScanChunk elements now 132 // and push the remainder back onto queue 133 int start = arrayOop(old)->length(); 134 int end = obj->length(); 135 int remainder = end - start; 136 assert(start <= end, "just checking"); 137 if (remainder > 2 * ParGCArrayScanChunk) { 138 // Test above combines last partial chunk with a full chunk 139 end = start + ParGCArrayScanChunk; 140 arrayOop(old)->set_length(end); 141 // Push remainder. 142 bool ok = work_queue()->push(old); 143 assert(ok, "just popped, push must be okay"); 144 } else { 145 // Restore length so that it can be used if there 146 // is a promotion failure and forwarding pointers 147 // must be removed. 148 arrayOop(old)->set_length(end); 149 } 150 151 // process our set of indices (include header in first chunk) 152 // should make sure end is even (aligned to HeapWord in case of compressed oops) 153 if ((HeapWord *)obj < young_old_boundary()) { 154 // object is in to_space 155 obj->oop_iterate_range(&_to_space_closure, start, end); 156 } else { 157 // object is in old generation 158 obj->oop_iterate_range(&_old_gen_closure, start, end); 159 } 160 } 161 162 void ParScanThreadState::trim_queues(int max_size) { 163 ObjToScanQueue* queue = work_queue(); 164 do { 165 while (queue->size() > (juint)max_size) { 166 oop obj_to_scan; 167 if (queue->pop_local(obj_to_scan)) { 168 if ((HeapWord *)obj_to_scan < young_old_boundary()) { 169 if (obj_to_scan->is_objArray() && 170 obj_to_scan->is_forwarded() && 171 obj_to_scan->forwardee() != obj_to_scan) { 172 scan_partial_array_and_push_remainder(obj_to_scan); 173 } else { 174 // object is in to_space 175 obj_to_scan->oop_iterate(&_to_space_closure); 176 } 177 } else { 178 // object is in old generation 179 obj_to_scan->oop_iterate(&_old_gen_closure); 180 } 181 } 182 } 183 // For the case of compressed oops, we have a private, non-shared 184 // overflow stack, so we eagerly drain it so as to more evenly 185 // distribute load early. Note: this may be good to do in 186 // general rather than delay for the final stealing phase. 187 // If applicable, we'll transfer a set of objects over to our 188 // work queue, allowing them to be stolen and draining our 189 // private overflow stack. 190 } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this)); 191 } 192 193 bool ParScanThreadState::take_from_overflow_stack() { 194 assert(ParGCUseLocalOverflow, "Else should not call"); 195 assert(young_gen()->overflow_list() == NULL, "Error"); 196 ObjToScanQueue* queue = work_queue(); 197 Stack<oop, mtGC>* const of_stack = overflow_stack(); 198 const size_t num_overflow_elems = of_stack->size(); 199 const size_t space_available = queue->max_elems() - queue->size(); 200 const size_t num_take_elems = MIN3(space_available / 4, 201 ParGCDesiredObjsFromOverflowList, 202 num_overflow_elems); 203 // Transfer the most recent num_take_elems from the overflow 204 // stack to our work queue. 205 for (size_t i = 0; i != num_take_elems; i++) { 206 oop cur = of_stack->pop(); 207 oop obj_to_push = cur->forwardee(); 208 assert(GenCollectedHeap::heap()->is_in_reserved(cur), "Should be in heap"); 209 assert(!old_gen()->is_in_reserved(cur), "Should be in young gen"); 210 assert(GenCollectedHeap::heap()->is_in_reserved(obj_to_push), "Should be in heap"); 211 if (should_be_partially_scanned(obj_to_push, cur)) { 212 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 213 obj_to_push = cur; 214 } 215 bool ok = queue->push(obj_to_push); 216 assert(ok, "Should have succeeded"); 217 } 218 assert(young_gen()->overflow_list() == NULL, "Error"); 219 return num_take_elems > 0; // was something transferred? 220 } 221 222 void ParScanThreadState::push_on_overflow_stack(oop p) { 223 assert(ParGCUseLocalOverflow, "Else should not call"); 224 overflow_stack()->push(p); 225 assert(young_gen()->overflow_list() == NULL, "Error"); 226 } 227 228 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) { 229 // If the object is small enough, try to reallocate the buffer. 230 HeapWord* obj = NULL; 231 if (!_to_space_full) { 232 PLAB* const plab = to_space_alloc_buffer(); 233 Space* const sp = to_space(); 234 if (word_sz * 100 < ParallelGCBufferWastePct * plab->word_sz()) { 235 // Is small enough; abandon this buffer and start a new one. 236 plab->retire(); 237 // The minimum size has to be twice SurvivorAlignmentInBytes to 238 // allow for padding used in the alignment of 1 word. A padding 239 // of 1 is too small for a filler word so the padding size will 240 // be increased by SurvivorAlignmentInBytes. 241 size_t min_usable_size = 2 * static_cast<size_t>(SurvivorAlignmentInBytes >> LogHeapWordSize); 242 size_t buf_size = MAX2(plab->word_sz(), min_usable_size); 243 HeapWord* buf_space = sp->par_allocate(buf_size); 244 if (buf_space == NULL) { 245 const size_t min_bytes = MAX2(PLAB::min_size(), min_usable_size) << LogHeapWordSize; 246 size_t free_bytes = sp->free(); 247 while(buf_space == NULL && free_bytes >= min_bytes) { 248 buf_size = free_bytes >> LogHeapWordSize; 249 assert(buf_size == (size_t)align_object_size(buf_size), "Invariant"); 250 buf_space = sp->par_allocate(buf_size); 251 free_bytes = sp->free(); 252 } 253 } 254 if (buf_space != NULL) { 255 plab->set_buf(buf_space, buf_size); 256 record_survivor_plab(buf_space, buf_size); 257 obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes); 258 // Note that we cannot compare buf_size < word_sz below 259 // because of AlignmentReserve (see PLAB::allocate()). 260 assert(obj != NULL || plab->words_remaining() < word_sz, 261 "Else should have been able to allocate requested object size " 262 SIZE_FORMAT ", PLAB size " SIZE_FORMAT ", SurvivorAlignmentInBytes " 263 SIZE_FORMAT ", words_remaining " SIZE_FORMAT, 264 word_sz, buf_size, SurvivorAlignmentInBytes, plab->words_remaining()); 265 // It's conceivable that we may be able to use the 266 // buffer we just grabbed for subsequent small requests 267 // even if not for this one. 268 } else { 269 // We're used up. 270 _to_space_full = true; 271 } 272 } else { 273 // Too large; allocate the object individually. 274 obj = sp->par_allocate(word_sz); 275 } 276 } 277 return obj; 278 } 279 280 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, size_t word_sz) { 281 to_space_alloc_buffer()->undo_allocation(obj, word_sz); 282 } 283 284 void ParScanThreadState::print_promotion_failure_size() { 285 if (_promotion_failed_info.has_failed()) { 286 log_trace(gc, promotion)(" (%d: promotion failure size = " SIZE_FORMAT ") ", 287 _thread_num, _promotion_failed_info.first_size()); 288 } 289 } 290 291 class ParScanThreadStateSet: StackObj { 292 public: 293 // Initializes states for the specified number of threads; 294 ParScanThreadStateSet(int num_threads, 295 Space& to_space, 296 ParNewGeneration& young_gen, 297 Generation& old_gen, 298 ObjToScanQueueSet& queue_set, 299 Stack<oop, mtGC>* overflow_stacks_, 300 PreservedMarksSet& preserved_marks_set, 301 size_t desired_plab_sz, 302 ParallelTaskTerminator& term); 303 304 ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); } 305 306 inline ParScanThreadState& thread_state(int i); 307 308 void trace_promotion_failed(const YoungGCTracer* gc_tracer); 309 void reset(uint active_workers, bool promotion_failed); 310 void flush(); 311 312 #if TASKQUEUE_STATS 313 static void 314 print_termination_stats_hdr(outputStream* const st); 315 void print_termination_stats(); 316 static void 317 print_taskqueue_stats_hdr(outputStream* const st); 318 void print_taskqueue_stats(); 319 void reset_stats(); 320 #endif // TASKQUEUE_STATS 321 322 private: 323 ParallelTaskTerminator& _term; 324 ParNewGeneration& _young_gen; 325 Generation& _old_gen; 326 ParScanThreadState* _per_thread_states; 327 const int _num_threads; 328 public: 329 bool is_valid(int id) const { return id < _num_threads; } 330 ParallelTaskTerminator* terminator() { return &_term; } 331 }; 332 333 ParScanThreadStateSet::ParScanThreadStateSet(int num_threads, 334 Space& to_space, 335 ParNewGeneration& young_gen, 336 Generation& old_gen, 337 ObjToScanQueueSet& queue_set, 338 Stack<oop, mtGC>* overflow_stacks, 339 PreservedMarksSet& preserved_marks_set, 340 size_t desired_plab_sz, 341 ParallelTaskTerminator& term) 342 : _young_gen(young_gen), 343 _old_gen(old_gen), 344 _term(term), 345 _per_thread_states(NEW_RESOURCE_ARRAY(ParScanThreadState, num_threads)), 346 _num_threads(num_threads) 347 { 348 assert(num_threads > 0, "sanity check!"); 349 assert(ParGCUseLocalOverflow == (overflow_stacks != NULL), 350 "overflow_stack allocation mismatch"); 351 // Initialize states. 352 for (int i = 0; i < num_threads; ++i) { 353 new(_per_thread_states + i) 354 ParScanThreadState(&to_space, &young_gen, &old_gen, i, &queue_set, 355 overflow_stacks, preserved_marks_set.get(i), 356 desired_plab_sz, term); 357 } 358 } 359 360 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i) { 361 assert(i >= 0 && i < _num_threads, "sanity check!"); 362 return _per_thread_states[i]; 363 } 364 365 void ParScanThreadStateSet::trace_promotion_failed(const YoungGCTracer* gc_tracer) { 366 for (int i = 0; i < _num_threads; ++i) { 367 if (thread_state(i).promotion_failed()) { 368 gc_tracer->report_promotion_failed(thread_state(i).promotion_failed_info()); 369 thread_state(i).promotion_failed_info().reset(); 370 } 371 } 372 } 373 374 void ParScanThreadStateSet::reset(uint active_threads, bool promotion_failed) { 375 _term.reset_for_reuse(active_threads); 376 if (promotion_failed) { 377 for (int i = 0; i < _num_threads; ++i) { 378 thread_state(i).print_promotion_failure_size(); 379 } 380 } 381 } 382 383 #if TASKQUEUE_STATS 384 void ParScanThreadState::reset_stats() { 385 taskqueue_stats().reset(); 386 _term_attempts = 0; 387 _overflow_refills = 0; 388 _overflow_refill_objs = 0; 389 } 390 391 void ParScanThreadStateSet::reset_stats() { 392 for (int i = 0; i < _num_threads; ++i) { 393 thread_state(i).reset_stats(); 394 } 395 } 396 397 void ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st) { 398 st->print_raw_cr("GC Termination Stats"); 399 st->print_raw_cr(" elapsed --strong roots-- -------termination-------"); 400 st->print_raw_cr("thr ms ms % ms % attempts"); 401 st->print_raw_cr("--- --------- --------- ------ --------- ------ --------"); 402 } 403 404 void ParScanThreadStateSet::print_termination_stats() { 405 Log(gc, task, stats) log; 406 if (!log.is_debug()) { 407 return; 408 } 409 410 ResourceMark rm; 411 LogStream ls(log.debug()); 412 outputStream* st = &ls; 413 414 print_termination_stats_hdr(st); 415 416 for (int i = 0; i < _num_threads; ++i) { 417 const ParScanThreadState & pss = thread_state(i); 418 const double elapsed_ms = pss.elapsed_time() * 1000.0; 419 const double s_roots_ms = pss.strong_roots_time() * 1000.0; 420 const double term_ms = pss.term_time() * 1000.0; 421 st->print_cr("%3d %9.2f %9.2f %6.2f %9.2f %6.2f " SIZE_FORMAT_W(8), 422 i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms, 423 term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts()); 424 } 425 } 426 427 // Print stats related to work queue activity. 428 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st) { 429 st->print_raw_cr("GC Task Stats"); 430 st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr(); 431 st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr(); 432 } 433 434 void ParScanThreadStateSet::print_taskqueue_stats() { 435 if (!log_develop_is_enabled(Trace, gc, task, stats)) { 436 return; 437 } 438 Log(gc, task, stats) log; 439 ResourceMark rm; 440 LogStream ls(log.trace()); 441 outputStream* st = &ls; 442 print_taskqueue_stats_hdr(st); 443 444 TaskQueueStats totals; 445 for (int i = 0; i < _num_threads; ++i) { 446 const ParScanThreadState & pss = thread_state(i); 447 const TaskQueueStats & stats = pss.taskqueue_stats(); 448 st->print("%3d ", i); stats.print(st); st->cr(); 449 totals += stats; 450 451 if (pss.overflow_refills() > 0) { 452 st->print_cr(" " SIZE_FORMAT_W(10) " overflow refills " 453 SIZE_FORMAT_W(10) " overflow objects", 454 pss.overflow_refills(), pss.overflow_refill_objs()); 455 } 456 } 457 st->print("tot "); totals.print(st); st->cr(); 458 459 DEBUG_ONLY(totals.verify()); 460 } 461 #endif // TASKQUEUE_STATS 462 463 void ParScanThreadStateSet::flush() { 464 // Work in this loop should be kept as lightweight as 465 // possible since this might otherwise become a bottleneck 466 // to scaling. Should we add heavy-weight work into this 467 // loop, consider parallelizing the loop into the worker threads. 468 for (int i = 0; i < _num_threads; ++i) { 469 ParScanThreadState& par_scan_state = thread_state(i); 470 471 // Flush stats related to To-space PLAB activity and 472 // retire the last buffer. 473 par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_young_gen.plab_stats()); 474 475 // Every thread has its own age table. We need to merge 476 // them all into one. 477 AgeTable *local_table = par_scan_state.age_table(); 478 _young_gen.age_table()->merge(local_table); 479 480 // Inform old gen that we're done. 481 _old_gen.par_promote_alloc_done(i); 482 } 483 484 if (UseConcMarkSweepGC) { 485 // We need to call this even when ResizeOldPLAB is disabled 486 // so as to avoid breaking some asserts. While we may be able 487 // to avoid this by reorganizing the code a bit, I am loathe 488 // to do that unless we find cases where ergo leads to bad 489 // performance. 490 CompactibleFreeListSpaceLAB::compute_desired_plab_size(); 491 } 492 } 493 494 ParScanClosure::ParScanClosure(ParNewGeneration* g, 495 ParScanThreadState* par_scan_state) : 496 OopsInClassLoaderDataOrGenClosure(g), _par_scan_state(par_scan_state), _g(g) { 497 _boundary = _g->reserved().end(); 498 } 499 500 void ParScanWithBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, false); } 501 void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); } 502 503 void ParScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, false); } 504 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); } 505 506 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); } 507 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); } 508 509 void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); } 510 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); } 511 512 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g, 513 ParScanThreadState* par_scan_state) 514 : ScanWeakRefClosure(g), _par_scan_state(par_scan_state) 515 {} 516 517 void ParScanWeakRefClosure::do_oop(oop* p) { ParScanWeakRefClosure::do_oop_work(p); } 518 void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); } 519 520 #ifdef WIN32 521 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */ 522 #endif 523 524 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure( 525 ParScanThreadState* par_scan_state_, 526 ParScanWithoutBarrierClosure* to_space_closure_, 527 ParScanWithBarrierClosure* old_gen_closure_, 528 ParRootScanWithoutBarrierClosure* to_space_root_closure_, 529 ParNewGeneration* par_gen_, 530 ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_, 531 ObjToScanQueueSet* task_queues_, 532 ParallelTaskTerminator* terminator_) : 533 534 _par_scan_state(par_scan_state_), 535 _to_space_closure(to_space_closure_), 536 _old_gen_closure(old_gen_closure_), 537 _to_space_root_closure(to_space_root_closure_), 538 _old_gen_root_closure(old_gen_root_closure_), 539 _par_gen(par_gen_), 540 _task_queues(task_queues_), 541 _terminator(terminator_) 542 {} 543 544 void ParEvacuateFollowersClosure::do_void() { 545 ObjToScanQueue* work_q = par_scan_state()->work_queue(); 546 547 while (true) { 548 // Scan to-space and old-gen objs until we run out of both. 549 oop obj_to_scan; 550 par_scan_state()->trim_queues(0); 551 552 // We have no local work, attempt to steal from other threads. 553 554 // Attempt to steal work from promoted. 555 if (task_queues()->steal(par_scan_state()->thread_num(), 556 par_scan_state()->hash_seed(), 557 obj_to_scan)) { 558 bool res = work_q->push(obj_to_scan); 559 assert(res, "Empty queue should have room for a push."); 560 561 // If successful, goto Start. 562 continue; 563 564 // Try global overflow list. 565 } else if (par_gen()->take_from_overflow_list(par_scan_state())) { 566 continue; 567 } 568 569 // Otherwise, offer termination. 570 par_scan_state()->start_term_time(); 571 if (terminator()->offer_termination()) break; 572 par_scan_state()->end_term_time(); 573 } 574 assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0, 575 "Broken overflow list?"); 576 // Finish the last termination pause. 577 par_scan_state()->end_term_time(); 578 } 579 580 ParNewGenTask::ParNewGenTask(ParNewGeneration* young_gen, 581 Generation* old_gen, 582 HeapWord* young_old_boundary, 583 ParScanThreadStateSet* state_set, 584 StrongRootsScope* strong_roots_scope) : 585 AbstractGangTask("ParNewGeneration collection"), 586 _young_gen(young_gen), _old_gen(old_gen), 587 _young_old_boundary(young_old_boundary), 588 _state_set(state_set), 589 _strong_roots_scope(strong_roots_scope) 590 {} 591 592 void ParNewGenTask::work(uint worker_id) { 593 GenCollectedHeap* gch = GenCollectedHeap::heap(); 594 // Since this is being done in a separate thread, need new resource 595 // and handle marks. 596 ResourceMark rm; 597 HandleMark hm; 598 599 ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id); 600 assert(_state_set->is_valid(worker_id), "Should not have been called"); 601 602 par_scan_state.set_young_old_boundary(_young_old_boundary); 603 604 CLDScanClosure cld_scan_closure(&par_scan_state.to_space_root_closure(), 605 gch->rem_set()->cld_rem_set()->accumulate_modified_oops()); 606 607 par_scan_state.start_strong_roots(); 608 gch->young_process_roots(_strong_roots_scope, 609 &par_scan_state.to_space_root_closure(), 610 &par_scan_state.older_gen_closure(), 611 &cld_scan_closure); 612 613 par_scan_state.end_strong_roots(); 614 615 // "evacuate followers". 616 par_scan_state.evacuate_followers_closure().do_void(); 617 618 // This will collapse this worker's promoted object list that's 619 // created during the main ParNew parallel phase of ParNew. This has 620 // to be called after all workers have finished promoting objects 621 // and scanning promoted objects. It should be safe calling it from 622 // here, given that we can only reach here after all thread have 623 // offered termination, i.e., after there is no more work to be 624 // done. It will also disable promotion tracking for the rest of 625 // this GC as it's not necessary to be on during reference processing. 626 _old_gen->par_oop_since_save_marks_iterate_done((int) worker_id); 627 } 628 629 ParNewGeneration::ParNewGeneration(ReservedSpace rs, size_t initial_byte_size) 630 : DefNewGeneration(rs, initial_byte_size, "PCopy"), 631 _overflow_list(NULL), 632 _is_alive_closure(this), 633 _plab_stats("Young", YoungPLABSize, PLABWeight) 634 { 635 NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;) 636 NOT_PRODUCT(_num_par_pushes = 0;) 637 _task_queues = new ObjToScanQueueSet(ParallelGCThreads); 638 guarantee(_task_queues != NULL, "task_queues allocation failure."); 639 640 for (uint i = 0; i < ParallelGCThreads; i++) { 641 ObjToScanQueue *q = new ObjToScanQueue(); 642 guarantee(q != NULL, "work_queue Allocation failure."); 643 _task_queues->register_queue(i, q); 644 } 645 646 for (uint i = 0; i < ParallelGCThreads; i++) { 647 _task_queues->queue(i)->initialize(); 648 } 649 650 _overflow_stacks = NULL; 651 if (ParGCUseLocalOverflow) { 652 // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal with ',' 653 typedef Stack<oop, mtGC> GCOopStack; 654 655 _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC); 656 for (size_t i = 0; i < ParallelGCThreads; ++i) { 657 new (_overflow_stacks + i) Stack<oop, mtGC>(); 658 } 659 } 660 661 if (UsePerfData) { 662 EXCEPTION_MARK; 663 ResourceMark rm; 664 665 const char* cname = 666 PerfDataManager::counter_name(_gen_counters->name_space(), "threads"); 667 PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None, 668 ParallelGCThreads, CHECK); 669 } 670 } 671 672 // ParNewGeneration:: 673 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) : 674 DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {} 675 676 template <class T> 677 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) { 678 #ifdef ASSERT 679 { 680 assert(!oopDesc::is_null(*p), "expected non-null ref"); 681 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 682 // We never expect to see a null reference being processed 683 // as a weak reference. 684 assert(oopDesc::is_oop(obj), "expected an oop while scanning weak refs"); 685 } 686 #endif // ASSERT 687 688 _par_cl->do_oop_nv(p); 689 690 if (GenCollectedHeap::heap()->is_in_reserved(p)) { 691 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 692 _rs->write_ref_field_gc_par(p, obj); 693 } 694 } 695 696 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); } 697 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); } 698 699 // ParNewGeneration:: 700 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) : 701 DefNewGeneration::KeepAliveClosure(cl) {} 702 703 template <class T> 704 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) { 705 #ifdef ASSERT 706 { 707 assert(!oopDesc::is_null(*p), "expected non-null ref"); 708 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 709 // We never expect to see a null reference being processed 710 // as a weak reference. 711 assert(oopDesc::is_oop(obj), "expected an oop while scanning weak refs"); 712 } 713 #endif // ASSERT 714 715 _cl->do_oop_nv(p); 716 717 if (GenCollectedHeap::heap()->is_in_reserved(p)) { 718 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 719 _rs->write_ref_field_gc_par(p, obj); 720 } 721 } 722 723 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); } 724 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); } 725 726 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) { 727 T heap_oop = oopDesc::load_heap_oop(p); 728 if (!oopDesc::is_null(heap_oop)) { 729 oop obj = oopDesc::decode_heap_oop_not_null(heap_oop); 730 if ((HeapWord*)obj < _boundary) { 731 assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?"); 732 oop new_obj = obj->is_forwarded() 733 ? obj->forwardee() 734 : _g->DefNewGeneration::copy_to_survivor_space(obj); 735 oopDesc::encode_store_heap_oop_not_null(p, new_obj); 736 } 737 if (_gc_barrier) { 738 // If p points to a younger generation, mark the card. 739 if ((HeapWord*)obj < _gen_boundary) { 740 _rs->write_ref_field_gc_par(p, obj); 741 } 742 } 743 } 744 } 745 746 void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 747 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 748 749 class ParNewRefProcTaskProxy: public AbstractGangTask { 750 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; 751 public: 752 ParNewRefProcTaskProxy(ProcessTask& task, 753 ParNewGeneration& young_gen, 754 Generation& old_gen, 755 HeapWord* young_old_boundary, 756 ParScanThreadStateSet& state_set); 757 758 private: 759 virtual void work(uint worker_id); 760 private: 761 ParNewGeneration& _young_gen; 762 ProcessTask& _task; 763 Generation& _old_gen; 764 HeapWord* _young_old_boundary; 765 ParScanThreadStateSet& _state_set; 766 }; 767 768 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task, 769 ParNewGeneration& young_gen, 770 Generation& old_gen, 771 HeapWord* young_old_boundary, 772 ParScanThreadStateSet& state_set) 773 : AbstractGangTask("ParNewGeneration parallel reference processing"), 774 _young_gen(young_gen), 775 _task(task), 776 _old_gen(old_gen), 777 _young_old_boundary(young_old_boundary), 778 _state_set(state_set) 779 { } 780 781 void ParNewRefProcTaskProxy::work(uint worker_id) { 782 ResourceMark rm; 783 HandleMark hm; 784 ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id); 785 par_scan_state.set_young_old_boundary(_young_old_boundary); 786 _task.work(worker_id, par_scan_state.is_alive_closure(), 787 par_scan_state.keep_alive_closure(), 788 par_scan_state.evacuate_followers_closure()); 789 } 790 791 class ParNewRefEnqueueTaskProxy: public AbstractGangTask { 792 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; 793 EnqueueTask& _task; 794 795 public: 796 ParNewRefEnqueueTaskProxy(EnqueueTask& task) 797 : AbstractGangTask("ParNewGeneration parallel reference enqueue"), 798 _task(task) 799 { } 800 801 virtual void work(uint worker_id) { 802 _task.work(worker_id); 803 } 804 }; 805 806 void ParNewRefProcTaskExecutor::execute(ProcessTask& task) { 807 GenCollectedHeap* gch = GenCollectedHeap::heap(); 808 WorkGang* workers = gch->workers(); 809 assert(workers != NULL, "Need parallel worker threads."); 810 _state_set.reset(workers->active_workers(), _young_gen.promotion_failed()); 811 ParNewRefProcTaskProxy rp_task(task, _young_gen, _old_gen, 812 _young_gen.reserved().end(), _state_set); 813 workers->run_task(&rp_task); 814 _state_set.reset(0 /* bad value in debug if not reset */, 815 _young_gen.promotion_failed()); 816 } 817 818 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task) { 819 GenCollectedHeap* gch = GenCollectedHeap::heap(); 820 WorkGang* workers = gch->workers(); 821 assert(workers != NULL, "Need parallel worker threads."); 822 ParNewRefEnqueueTaskProxy enq_task(task); 823 workers->run_task(&enq_task); 824 } 825 826 void ParNewRefProcTaskExecutor::set_single_threaded_mode() { 827 _state_set.flush(); 828 GenCollectedHeap* gch = GenCollectedHeap::heap(); 829 gch->save_marks(); 830 } 831 832 ScanClosureWithParBarrier:: 833 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) : 834 ScanClosure(g, gc_barrier) 835 { } 836 837 EvacuateFollowersClosureGeneral:: 838 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, 839 OopsInGenClosure* cur, 840 OopsInGenClosure* older) : 841 _gch(gch), 842 _scan_cur_or_nonheap(cur), _scan_older(older) 843 { } 844 845 void EvacuateFollowersClosureGeneral::do_void() { 846 do { 847 // Beware: this call will lead to closure applications via virtual 848 // calls. 849 _gch->oop_since_save_marks_iterate(GenCollectedHeap::YoungGen, 850 _scan_cur_or_nonheap, 851 _scan_older); 852 } while (!_gch->no_allocs_since_save_marks()); 853 } 854 855 // A Generation that does parallel young-gen collection. 856 857 void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set) { 858 assert(_promo_failure_scan_stack.is_empty(), "post condition"); 859 _promo_failure_scan_stack.clear(true); // Clear cached segments. 860 861 remove_forwarding_pointers(); 862 log_info(gc, promotion)("Promotion failed"); 863 // All the spaces are in play for mark-sweep. 864 swap_spaces(); // Make life simpler for CMS || rescan; see 6483690. 865 from()->set_next_compaction_space(to()); 866 gch->set_incremental_collection_failed(); 867 // Inform the next generation that a promotion failure occurred. 868 _old_gen->promotion_failure_occurred(); 869 870 // Trace promotion failure in the parallel GC threads 871 thread_state_set.trace_promotion_failed(gc_tracer()); 872 // Single threaded code may have reported promotion failure to the global state 873 if (_promotion_failed_info.has_failed()) { 874 _gc_tracer.report_promotion_failed(_promotion_failed_info); 875 } 876 // Reset the PromotionFailureALot counters. 877 NOT_PRODUCT(gch->reset_promotion_should_fail();) 878 } 879 880 void ParNewGeneration::collect(bool full, 881 bool clear_all_soft_refs, 882 size_t size, 883 bool is_tlab) { 884 assert(full || size > 0, "otherwise we don't want to collect"); 885 886 GenCollectedHeap* gch = GenCollectedHeap::heap(); 887 888 _gc_timer->register_gc_start(); 889 890 AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy(); 891 WorkGang* workers = gch->workers(); 892 assert(workers != NULL, "Need workgang for parallel work"); 893 uint active_workers = 894 AdaptiveSizePolicy::calc_active_workers(workers->total_workers(), 895 workers->active_workers(), 896 Threads::number_of_non_daemon_threads()); 897 active_workers = workers->update_active_workers(active_workers); 898 log_info(gc,task)("Using %u workers of %u for evacuation", active_workers, workers->total_workers()); 899 900 _old_gen = gch->old_gen(); 901 902 // If the next generation is too full to accommodate worst-case promotion 903 // from this generation, pass on collection; let the next generation 904 // do it. 905 if (!collection_attempt_is_safe()) { 906 gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one 907 return; 908 } 909 assert(to()->is_empty(), "Else not collection_attempt_is_safe"); 910 911 _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start()); 912 gch->trace_heap_before_gc(gc_tracer()); 913 914 init_assuming_no_promotion_failure(); 915 916 if (UseAdaptiveSizePolicy) { 917 set_survivor_overflow(false); 918 size_policy->minor_collection_begin(); 919 } 920 921 GCTraceTime(Trace, gc, phases) t1("ParNew", NULL, gch->gc_cause()); 922 923 age_table()->clear(); 924 to()->clear(SpaceDecorator::Mangle); 925 926 gch->save_marks(); 927 928 // Set the correct parallelism (number of queues) in the reference processor 929 ref_processor()->set_active_mt_degree(active_workers); 930 931 // Need to initialize the preserved marks before the ThreadStateSet c'tor. 932 _preserved_marks_set.init(active_workers); 933 934 // Always set the terminator for the active number of workers 935 // because only those workers go through the termination protocol. 936 ParallelTaskTerminator _term(active_workers, task_queues()); 937 ParScanThreadStateSet thread_state_set(active_workers, 938 *to(), *this, *_old_gen, *task_queues(), 939 _overflow_stacks, _preserved_marks_set, 940 desired_plab_sz(), _term); 941 942 thread_state_set.reset(active_workers, promotion_failed()); 943 944 { 945 StrongRootsScope srs(active_workers); 946 947 ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set, &srs); 948 gch->rem_set()->prepare_for_younger_refs_iterate(true); 949 // It turns out that even when we're using 1 thread, doing the work in a 950 // separate thread causes wide variance in run times. We can't help this 951 // in the multi-threaded case, but we special-case n=1 here to get 952 // repeatable measurements of the 1-thread overhead of the parallel code. 953 // Might multiple workers ever be used? If yes, initialization 954 // has been done such that the single threaded path should not be used. 955 if (workers->total_workers() > 1) { 956 workers->run_task(&tsk); 957 } else { 958 tsk.work(0); 959 } 960 } 961 962 thread_state_set.reset(0 /* Bad value in debug if not reset */, 963 promotion_failed()); 964 965 // Trace and reset failed promotion info. 966 if (promotion_failed()) { 967 thread_state_set.trace_promotion_failed(gc_tracer()); 968 } 969 970 // Process (weak) reference objects found during scavenge. 971 ReferenceProcessor* rp = ref_processor(); 972 IsAliveClosure is_alive(this); 973 ScanWeakRefClosure scan_weak_ref(this); 974 KeepAliveClosure keep_alive(&scan_weak_ref); 975 ScanClosure scan_without_gc_barrier(this, false); 976 ScanClosureWithParBarrier scan_with_gc_barrier(this, true); 977 set_promo_failure_scan_stack_closure(&scan_without_gc_barrier); 978 EvacuateFollowersClosureGeneral evacuate_followers(gch, 979 &scan_without_gc_barrier, &scan_with_gc_barrier); 980 rp->setup_policy(clear_all_soft_refs); 981 // Can the mt_degree be set later (at run_task() time would be best)? 982 rp->set_active_mt_degree(active_workers); 983 ReferenceProcessorStats stats; 984 ReferenceProcessorPhaseTimes pt(_gc_timer, rp->num_q()); 985 if (rp->processing_is_mt()) { 986 ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set); 987 stats = rp->process_discovered_references(&is_alive, &keep_alive, 988 &evacuate_followers, &task_executor, 989 &pt); 990 } else { 991 thread_state_set.flush(); 992 gch->save_marks(); 993 stats = rp->process_discovered_references(&is_alive, &keep_alive, 994 &evacuate_followers, NULL, 995 &pt); 996 } 997 _gc_tracer.report_gc_reference_stats(stats); 998 _gc_tracer.report_tenuring_threshold(tenuring_threshold()); 999 pt.print_all_references(); 1000 1001 if (!promotion_failed()) { 1002 // Swap the survivor spaces. 1003 eden()->clear(SpaceDecorator::Mangle); 1004 from()->clear(SpaceDecorator::Mangle); 1005 if (ZapUnusedHeapArea) { 1006 // This is now done here because of the piece-meal mangling which 1007 // can check for valid mangling at intermediate points in the 1008 // collection(s). When a young collection fails to collect 1009 // sufficient space resizing of the young generation can occur 1010 // and redistribute the spaces in the young generation. Mangle 1011 // here so that unzapped regions don't get distributed to 1012 // other spaces. 1013 to()->mangle_unused_area(); 1014 } 1015 swap_spaces(); 1016 1017 // A successful scavenge should restart the GC time limit count which is 1018 // for full GC's. 1019 size_policy->reset_gc_overhead_limit_count(); 1020 1021 assert(to()->is_empty(), "to space should be empty now"); 1022 1023 adjust_desired_tenuring_threshold(); 1024 } else { 1025 handle_promotion_failed(gch, thread_state_set); 1026 } 1027 _preserved_marks_set.reclaim(); 1028 // set new iteration safe limit for the survivor spaces 1029 from()->set_concurrent_iteration_safe_limit(from()->top()); 1030 to()->set_concurrent_iteration_safe_limit(to()->top()); 1031 1032 plab_stats()->adjust_desired_plab_sz(); 1033 1034 TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats()); 1035 TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats()); 1036 1037 if (UseAdaptiveSizePolicy) { 1038 size_policy->minor_collection_end(gch->gc_cause()); 1039 size_policy->avg_survived()->sample(from()->used()); 1040 } 1041 1042 // We need to use a monotonically non-decreasing time in ms 1043 // or we will see time-warp warnings and os::javaTimeMillis() 1044 // does not guarantee monotonicity. 1045 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 1046 update_time_of_last_gc(now); 1047 1048 rp->set_enqueuing_is_done(true); 1049 if (rp->processing_is_mt()) { 1050 ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set); 1051 rp->enqueue_discovered_references(&task_executor, &pt); 1052 } else { 1053 rp->enqueue_discovered_references(NULL, &pt); 1054 } 1055 rp->verify_no_references_recorded(); 1056 1057 gch->trace_heap_after_gc(gc_tracer()); 1058 1059 pt.print_enqueue_phase(); 1060 1061 _gc_timer->register_gc_end(); 1062 1063 _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions()); 1064 } 1065 1066 size_t ParNewGeneration::desired_plab_sz() { 1067 return _plab_stats.desired_plab_sz(GenCollectedHeap::heap()->workers()->active_workers()); 1068 } 1069 1070 static int sum; 1071 void ParNewGeneration::waste_some_time() { 1072 for (int i = 0; i < 100; i++) { 1073 sum += i; 1074 } 1075 } 1076 1077 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4); 1078 1079 // Because of concurrency, there are times where an object for which 1080 // "is_forwarded()" is true contains an "interim" forwarding pointer 1081 // value. Such a value will soon be overwritten with a real value. 1082 // This method requires "obj" to have a forwarding pointer, and waits, if 1083 // necessary for a real one to be inserted, and returns it. 1084 1085 oop ParNewGeneration::real_forwardee(oop obj) { 1086 oop forward_ptr = obj->forwardee(); 1087 if (forward_ptr != ClaimedForwardPtr) { 1088 return forward_ptr; 1089 } else { 1090 return real_forwardee_slow(obj); 1091 } 1092 } 1093 1094 oop ParNewGeneration::real_forwardee_slow(oop obj) { 1095 // Spin-read if it is claimed but not yet written by another thread. 1096 oop forward_ptr = obj->forwardee(); 1097 while (forward_ptr == ClaimedForwardPtr) { 1098 waste_some_time(); 1099 assert(obj->is_forwarded(), "precondition"); 1100 forward_ptr = obj->forwardee(); 1101 } 1102 return forward_ptr; 1103 } 1104 1105 // Multiple GC threads may try to promote an object. If the object 1106 // is successfully promoted, a forwarding pointer will be installed in 1107 // the object in the young generation. This method claims the right 1108 // to install the forwarding pointer before it copies the object, 1109 // thus avoiding the need to undo the copy as in 1110 // copy_to_survivor_space_avoiding_with_undo. 1111 1112 oop ParNewGeneration::copy_to_survivor_space(ParScanThreadState* par_scan_state, 1113 oop old, 1114 size_t sz, 1115 markOop m) { 1116 // In the sequential version, this assert also says that the object is 1117 // not forwarded. That might not be the case here. It is the case that 1118 // the caller observed it to be not forwarded at some time in the past. 1119 assert(is_in_reserved(old), "shouldn't be scavenging this oop"); 1120 1121 // The sequential code read "old->age()" below. That doesn't work here, 1122 // since the age is in the mark word, and that might be overwritten with 1123 // a forwarding pointer by a parallel thread. So we must save the mark 1124 // word in a local and then analyze it. 1125 oopDesc dummyOld; 1126 dummyOld.set_mark(m); 1127 assert(!dummyOld.is_forwarded(), 1128 "should not be called with forwarding pointer mark word."); 1129 1130 oop new_obj = NULL; 1131 oop forward_ptr; 1132 1133 // Try allocating obj in to-space (unless too old) 1134 if (dummyOld.age() < tenuring_threshold()) { 1135 new_obj = (oop)par_scan_state->alloc_in_to_space(sz); 1136 if (new_obj == NULL) { 1137 set_survivor_overflow(true); 1138 } 1139 } 1140 1141 if (new_obj == NULL) { 1142 // Either to-space is full or we decided to promote try allocating obj tenured 1143 1144 // Attempt to install a null forwarding pointer (atomically), 1145 // to claim the right to install the real forwarding pointer. 1146 forward_ptr = old->forward_to_atomic(ClaimedForwardPtr); 1147 if (forward_ptr != NULL) { 1148 // someone else beat us to it. 1149 return real_forwardee(old); 1150 } 1151 1152 if (!_promotion_failed) { 1153 new_obj = _old_gen->par_promote(par_scan_state->thread_num(), 1154 old, m, sz); 1155 } 1156 1157 if (new_obj == NULL) { 1158 // promotion failed, forward to self 1159 _promotion_failed = true; 1160 new_obj = old; 1161 1162 par_scan_state->preserved_marks()->push_if_necessary(old, m); 1163 par_scan_state->register_promotion_failure(sz); 1164 } 1165 1166 old->forward_to(new_obj); 1167 forward_ptr = NULL; 1168 } else { 1169 // Is in to-space; do copying ourselves. 1170 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz); 1171 assert(GenCollectedHeap::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value."); 1172 forward_ptr = old->forward_to_atomic(new_obj); 1173 // Restore the mark word copied above. 1174 new_obj->set_mark(m); 1175 // Increment age if obj still in new generation 1176 new_obj->incr_age(); 1177 par_scan_state->age_table()->add(new_obj, sz); 1178 } 1179 assert(new_obj != NULL, "just checking"); 1180 1181 // This code must come after the CAS test, or it will print incorrect 1182 // information. 1183 log_develop_trace(gc, scavenge)("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}", 1184 is_in_reserved(new_obj) ? "copying" : "tenuring", 1185 new_obj->klass()->internal_name(), p2i(old), p2i(new_obj), new_obj->size()); 1186 1187 if (forward_ptr == NULL) { 1188 oop obj_to_push = new_obj; 1189 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) { 1190 // Length field used as index of next element to be scanned. 1191 // Real length can be obtained from real_forwardee() 1192 arrayOop(old)->set_length(0); 1193 obj_to_push = old; 1194 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push, 1195 "push forwarded object"); 1196 } 1197 // Push it on one of the queues of to-be-scanned objects. 1198 bool simulate_overflow = false; 1199 NOT_PRODUCT( 1200 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) { 1201 // simulate a stack overflow 1202 simulate_overflow = true; 1203 } 1204 ) 1205 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) { 1206 // Add stats for overflow pushes. 1207 log_develop_trace(gc)("Queue Overflow"); 1208 push_on_overflow_list(old, par_scan_state); 1209 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0)); 1210 } 1211 1212 return new_obj; 1213 } 1214 1215 // Oops. Someone beat us to it. Undo the allocation. Where did we 1216 // allocate it? 1217 if (is_in_reserved(new_obj)) { 1218 // Must be in to_space. 1219 assert(to()->is_in_reserved(new_obj), "Checking"); 1220 if (forward_ptr == ClaimedForwardPtr) { 1221 // Wait to get the real forwarding pointer value. 1222 forward_ptr = real_forwardee(old); 1223 } 1224 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz); 1225 } 1226 1227 return forward_ptr; 1228 } 1229 1230 #ifndef PRODUCT 1231 // It's OK to call this multi-threaded; the worst thing 1232 // that can happen is that we'll get a bunch of closely 1233 // spaced simulated overflows, but that's OK, in fact 1234 // probably good as it would exercise the overflow code 1235 // under contention. 1236 bool ParNewGeneration::should_simulate_overflow() { 1237 if (_overflow_counter-- <= 0) { // just being defensive 1238 _overflow_counter = ParGCWorkQueueOverflowInterval; 1239 return true; 1240 } else { 1241 return false; 1242 } 1243 } 1244 #endif 1245 1246 // In case we are using compressed oops, we need to be careful. 1247 // If the object being pushed is an object array, then its length 1248 // field keeps track of the "grey boundary" at which the next 1249 // incremental scan will be done (see ParGCArrayScanChunk). 1250 // When using compressed oops, this length field is kept in the 1251 // lower 32 bits of the erstwhile klass word and cannot be used 1252 // for the overflow chaining pointer (OCP below). As such the OCP 1253 // would itself need to be compressed into the top 32-bits in this 1254 // case. Unfortunately, see below, in the event that we have a 1255 // promotion failure, the node to be pushed on the list can be 1256 // outside of the Java heap, so the heap-based pointer compression 1257 // would not work (we would have potential aliasing between C-heap 1258 // and Java-heap pointers). For this reason, when using compressed 1259 // oops, we simply use a worker-thread-local, non-shared overflow 1260 // list in the form of a growable array, with a slightly different 1261 // overflow stack draining strategy. If/when we start using fat 1262 // stacks here, we can go back to using (fat) pointer chains 1263 // (although some performance comparisons would be useful since 1264 // single global lists have their own performance disadvantages 1265 // as we were made painfully aware not long ago, see 6786503). 1266 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff)) 1267 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) { 1268 assert(is_in_reserved(from_space_obj), "Should be from this generation"); 1269 if (ParGCUseLocalOverflow) { 1270 // In the case of compressed oops, we use a private, not-shared 1271 // overflow stack. 1272 par_scan_state->push_on_overflow_stack(from_space_obj); 1273 } else { 1274 assert(!UseCompressedOops, "Error"); 1275 // if the object has been forwarded to itself, then we cannot 1276 // use the klass pointer for the linked list. Instead we have 1277 // to allocate an oopDesc in the C-Heap and use that for the linked list. 1278 // XXX This is horribly inefficient when a promotion failure occurs 1279 // and should be fixed. XXX FIX ME !!! 1280 #ifndef PRODUCT 1281 Atomic::inc(&_num_par_pushes); 1282 assert(_num_par_pushes > 0, "Tautology"); 1283 #endif 1284 if (from_space_obj->forwardee() == from_space_obj) { 1285 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC); 1286 listhead->forward_to(from_space_obj); 1287 from_space_obj = listhead; 1288 } 1289 oop observed_overflow_list = _overflow_list; 1290 oop cur_overflow_list; 1291 do { 1292 cur_overflow_list = observed_overflow_list; 1293 if (cur_overflow_list != BUSY) { 1294 from_space_obj->set_klass_to_list_ptr(cur_overflow_list); 1295 } else { 1296 from_space_obj->set_klass_to_list_ptr(NULL); 1297 } 1298 observed_overflow_list = 1299 Atomic::cmpxchg((oopDesc*)from_space_obj, &_overflow_list, (oopDesc*)cur_overflow_list); 1300 } while (cur_overflow_list != observed_overflow_list); 1301 } 1302 } 1303 1304 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) { 1305 bool res; 1306 1307 if (ParGCUseLocalOverflow) { 1308 res = par_scan_state->take_from_overflow_stack(); 1309 } else { 1310 assert(!UseCompressedOops, "Error"); 1311 res = take_from_overflow_list_work(par_scan_state); 1312 } 1313 return res; 1314 } 1315 1316 1317 // *NOTE*: The overflow list manipulation code here and 1318 // in CMSCollector:: are very similar in shape, 1319 // except that in the CMS case we thread the objects 1320 // directly into the list via their mark word, and do 1321 // not need to deal with special cases below related 1322 // to chunking of object arrays and promotion failure 1323 // handling. 1324 // CR 6797058 has been filed to attempt consolidation of 1325 // the common code. 1326 // Because of the common code, if you make any changes in 1327 // the code below, please check the CMS version to see if 1328 // similar changes might be needed. 1329 // See CMSCollector::par_take_from_overflow_list() for 1330 // more extensive documentation comments. 1331 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) { 1332 ObjToScanQueue* work_q = par_scan_state->work_queue(); 1333 // How many to take? 1334 size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 1335 (size_t)ParGCDesiredObjsFromOverflowList); 1336 1337 assert(!UseCompressedOops, "Error"); 1338 assert(par_scan_state->overflow_stack() == NULL, "Error"); 1339 if (_overflow_list == NULL) return false; 1340 1341 // Otherwise, there was something there; try claiming the list. 1342 oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list)); 1343 // Trim off a prefix of at most objsFromOverflow items 1344 Thread* tid = Thread::current(); 1345 size_t spin_count = ParallelGCThreads; 1346 size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100); 1347 for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) { 1348 // someone grabbed it before we did ... 1349 // ... we spin for a short while... 1350 os::sleep(tid, sleep_time_millis, false); 1351 if (_overflow_list == NULL) { 1352 // nothing left to take 1353 return false; 1354 } else if (_overflow_list != BUSY) { 1355 // try and grab the prefix 1356 prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list)); 1357 } 1358 } 1359 if (prefix == NULL || prefix == BUSY) { 1360 // Nothing to take or waited long enough 1361 if (prefix == NULL) { 1362 // Write back the NULL in case we overwrote it with BUSY above 1363 // and it is still the same value. 1364 (void) Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY); 1365 } 1366 return false; 1367 } 1368 assert(prefix != NULL && prefix != BUSY, "Error"); 1369 oop cur = prefix; 1370 for (size_t i = 1; i < objsFromOverflow; ++i) { 1371 oop next = cur->list_ptr_from_klass(); 1372 if (next == NULL) break; 1373 cur = next; 1374 } 1375 assert(cur != NULL, "Loop postcondition"); 1376 1377 // Reattach remaining (suffix) to overflow list 1378 oop suffix = cur->list_ptr_from_klass(); 1379 if (suffix == NULL) { 1380 // Write back the NULL in lieu of the BUSY we wrote 1381 // above and it is still the same value. 1382 if (_overflow_list == BUSY) { 1383 (void) Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY); 1384 } 1385 } else { 1386 assert(suffix != BUSY, "Error"); 1387 // suffix will be put back on global list 1388 cur->set_klass_to_list_ptr(NULL); // break off suffix 1389 // It's possible that the list is still in the empty(busy) state 1390 // we left it in a short while ago; in that case we may be 1391 // able to place back the suffix. 1392 oop observed_overflow_list = _overflow_list; 1393 oop cur_overflow_list = observed_overflow_list; 1394 bool attached = false; 1395 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { 1396 observed_overflow_list = 1397 Atomic::cmpxchg((oopDesc*)suffix, &_overflow_list, (oopDesc*)cur_overflow_list); 1398 if (cur_overflow_list == observed_overflow_list) { 1399 attached = true; 1400 break; 1401 } else cur_overflow_list = observed_overflow_list; 1402 } 1403 if (!attached) { 1404 // Too bad, someone else got in in between; we'll need to do a splice. 1405 // Find the last item of suffix list 1406 oop last = suffix; 1407 while (true) { 1408 oop next = last->list_ptr_from_klass(); 1409 if (next == NULL) break; 1410 last = next; 1411 } 1412 // Atomically prepend suffix to current overflow list 1413 observed_overflow_list = _overflow_list; 1414 do { 1415 cur_overflow_list = observed_overflow_list; 1416 if (cur_overflow_list != BUSY) { 1417 // Do the splice ... 1418 last->set_klass_to_list_ptr(cur_overflow_list); 1419 } else { // cur_overflow_list == BUSY 1420 last->set_klass_to_list_ptr(NULL); 1421 } 1422 observed_overflow_list = 1423 Atomic::cmpxchg((oopDesc*)suffix, &_overflow_list, (oopDesc*)cur_overflow_list); 1424 } while (cur_overflow_list != observed_overflow_list); 1425 } 1426 } 1427 1428 // Push objects on prefix list onto this thread's work queue 1429 assert(prefix != NULL && prefix != BUSY, "program logic"); 1430 cur = prefix; 1431 ssize_t n = 0; 1432 while (cur != NULL) { 1433 oop obj_to_push = cur->forwardee(); 1434 oop next = cur->list_ptr_from_klass(); 1435 cur->set_klass(obj_to_push->klass()); 1436 // This may be an array object that is self-forwarded. In that case, the list pointer 1437 // space, cur, is not in the Java heap, but rather in the C-heap and should be freed. 1438 if (!is_in_reserved(cur)) { 1439 // This can become a scaling bottleneck when there is work queue overflow coincident 1440 // with promotion failure. 1441 oopDesc* f = cur; 1442 FREE_C_HEAP_ARRAY(oopDesc, f); 1443 } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) { 1444 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 1445 obj_to_push = cur; 1446 } 1447 bool ok = work_q->push(obj_to_push); 1448 assert(ok, "Should have succeeded"); 1449 cur = next; 1450 n++; 1451 } 1452 TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n)); 1453 #ifndef PRODUCT 1454 assert(_num_par_pushes >= n, "Too many pops?"); 1455 Atomic::add(-n, &_num_par_pushes); 1456 #endif 1457 return true; 1458 } 1459 #undef BUSY 1460 1461 void ParNewGeneration::ref_processor_init() { 1462 if (_ref_processor == NULL) { 1463 // Allocate and initialize a reference processor 1464 _ref_processor = 1465 new ReferenceProcessor(_reserved, // span 1466 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing 1467 ParallelGCThreads, // mt processing degree 1468 refs_discovery_is_mt(), // mt discovery 1469 ParallelGCThreads, // mt discovery degree 1470 refs_discovery_is_atomic(), // atomic_discovery 1471 NULL); // is_alive_non_header 1472 } 1473 } 1474 1475 const char* ParNewGeneration::name() const { 1476 return "par new generation"; 1477 }