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