1 /* 2 * Copyright (c) 2001, 2014, 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_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp" 27 #include "gc_implementation/parNew/parNewGeneration.hpp" 28 #include "gc_implementation/parNew/parOopClosures.inline.hpp" 29 #include "gc_implementation/shared/adaptiveSizePolicy.hpp" 30 #include "gc_implementation/shared/ageTable.hpp" 31 #include "gc_implementation/shared/copyFailedInfo.hpp" 32 #include "gc_implementation/shared/gcHeapSummary.hpp" 33 #include "gc_implementation/shared/gcTimer.hpp" 34 #include "gc_implementation/shared/gcTrace.hpp" 35 #include "gc_implementation/shared/gcTraceTime.hpp" 36 #include "gc_implementation/shared/parGCAllocBuffer.inline.hpp" 37 #include "gc_implementation/shared/spaceDecorator.hpp" 38 #include "memory/defNewGeneration.inline.hpp" 39 #include "memory/genCollectedHeap.hpp" 40 #include "memory/genOopClosures.inline.hpp" 41 #include "memory/generation.hpp" 42 #include "memory/generation.inline.hpp" 43 #include "memory/referencePolicy.hpp" 44 #include "memory/resourceArea.hpp" 45 #include "memory/sharedHeap.hpp" 46 #include "memory/space.hpp" 47 #include "oops/objArrayOop.hpp" 48 #include "oops/oop.inline.hpp" 49 #include "oops/oop.pcgc.inline.hpp" 50 #include "runtime/handles.hpp" 51 #include "runtime/handles.inline.hpp" 52 #include "runtime/java.hpp" 53 #include "runtime/thread.inline.hpp" 54 #include "utilities/copy.hpp" 55 #include "utilities/globalDefinitions.hpp" 56 #include "utilities/workgroup.hpp" 57 58 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC 59 60 #ifdef _MSC_VER 61 #pragma warning( push ) 62 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list 63 #endif 64 ParScanThreadState::ParScanThreadState(Space* to_space_, 65 ParNewGeneration* gen_, 66 Generation* old_gen_, 67 int thread_num_, 68 ObjToScanQueueSet* work_queue_set_, 69 Stack<oop, mtGC>* overflow_stacks_, 70 size_t desired_plab_sz_, 71 ParallelTaskTerminator& term_) : 72 _to_space(to_space_), _old_gen(old_gen_), _young_gen(gen_), _thread_num(thread_num_), 73 _work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false), 74 _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL), 75 _ageTable(false), // false ==> not the global age table, no perf data. 76 _to_space_alloc_buffer(desired_plab_sz_), 77 _to_space_closure(gen_, this), _old_gen_closure(gen_, this), 78 _to_space_root_closure(gen_, this), _old_gen_root_closure(gen_, this), 79 _older_gen_closure(gen_, this), 80 _evacuate_followers(this, &_to_space_closure, &_old_gen_closure, 81 &_to_space_root_closure, gen_, &_old_gen_root_closure, 82 work_queue_set_, &term_), 83 _is_alive_closure(gen_), _scan_weak_ref_closure(gen_, this), 84 _keep_alive_closure(&_scan_weak_ref_closure), 85 _strong_roots_time(0.0), _term_time(0.0) 86 { 87 #if TASKQUEUE_STATS 88 _term_attempts = 0; 89 _overflow_refills = 0; 90 _overflow_refill_objs = 0; 91 #endif // TASKQUEUE_STATS 92 93 _survivor_chunk_array = 94 (ChunkArray*) old_gen()->get_data_recorder(thread_num()); 95 _hash_seed = 17; // Might want to take time-based random value. 96 _start = os::elapsedTime(); 97 _old_gen_closure.set_generation(old_gen_); 98 _old_gen_root_closure.set_generation(old_gen_); 99 } 100 #ifdef _MSC_VER 101 #pragma warning( pop ) 102 #endif 103 104 void ParScanThreadState::record_survivor_plab(HeapWord* plab_start, 105 size_t plab_word_size) { 106 ChunkArray* sca = survivor_chunk_array(); 107 if (sca != NULL) { 108 // A non-null SCA implies that we want the PLAB data recorded. 109 sca->record_sample(plab_start, plab_word_size); 110 } 111 } 112 113 bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const { 114 return new_obj->is_objArray() && 115 arrayOop(new_obj)->length() > ParGCArrayScanChunk && 116 new_obj != old_obj; 117 } 118 119 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) { 120 assert(old->is_objArray(), "must be obj array"); 121 assert(old->is_forwarded(), "must be forwarded"); 122 assert(Universe::heap()->is_in_reserved(old), "must be in heap."); 123 assert(!old_gen()->is_in(old), "must be in young generation."); 124 125 objArrayOop obj = objArrayOop(old->forwardee()); 126 // Process ParGCArrayScanChunk elements now 127 // and push the remainder back onto queue 128 int start = arrayOop(old)->length(); 129 int end = obj->length(); 130 int remainder = end - start; 131 assert(start <= end, "just checking"); 132 if (remainder > 2 * ParGCArrayScanChunk) { 133 // Test above combines last partial chunk with a full chunk 134 end = start + ParGCArrayScanChunk; 135 arrayOop(old)->set_length(end); 136 // Push remainder. 137 bool ok = work_queue()->push(old); 138 assert(ok, "just popped, push must be okay"); 139 } else { 140 // Restore length so that it can be used if there 141 // is a promotion failure and forwarding pointers 142 // must be removed. 143 arrayOop(old)->set_length(end); 144 } 145 146 // process our set of indices (include header in first chunk) 147 // should make sure end is even (aligned to HeapWord in case of compressed oops) 148 if ((HeapWord *)obj < young_old_boundary()) { 149 // object is in to_space 150 obj->oop_iterate_range(&_to_space_closure, start, end); 151 } else { 152 // object is in old generation 153 obj->oop_iterate_range(&_old_gen_closure, start, end); 154 } 155 } 156 157 158 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(Universe::heap()->is_in_reserved(cur), "Should be in heap"); 205 assert(!old_gen()->is_in_reserved(cur), "Should be in young gen"); 206 assert(Universe::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) { 225 226 // Otherwise, if the object is small enough, try to reallocate the 227 // buffer. 228 HeapWord* obj = NULL; 229 if (!_to_space_full) { 230 ParGCAllocBuffer* const plab = to_space_alloc_buffer(); 231 Space* const sp = to_space(); 232 if (word_sz * 100 < 233 ParallelGCBufferWastePct * plab->word_sz()) { 234 // Is small enough; abandon this buffer and start a new one. 235 plab->retire(false, false); 236 size_t buf_size = plab->word_sz(); 237 HeapWord* buf_space = sp->par_allocate(buf_size); 238 if (buf_space == NULL) { 239 const size_t min_bytes = 240 ParGCAllocBuffer::min_size() << LogHeapWordSize; 241 size_t free_bytes = sp->free(); 242 while(buf_space == NULL && free_bytes >= min_bytes) { 243 buf_size = free_bytes >> LogHeapWordSize; 244 assert(buf_size == (size_t)align_object_size(buf_size), 245 "Invariant"); 246 buf_space = sp->par_allocate(buf_size); 247 free_bytes = sp->free(); 248 } 249 } 250 if (buf_space != NULL) { 251 plab->set_word_size(buf_size); 252 plab->set_buf(buf_space); 253 record_survivor_plab(buf_space, buf_size); 254 obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes); 255 // Note that we cannot compare buf_size < word_sz below 256 // because of AlignmentReserve (see ParGCAllocBuffer::allocate()). 257 assert(obj != NULL || plab->words_remaining() < word_sz, 258 "Else should have been able to allocate"); 259 // It's conceivable that we may be able to use the 260 // buffer we just grabbed for subsequent small requests 261 // even if not for this one. 262 } else { 263 // We're used up. 264 _to_space_full = true; 265 } 266 267 } else { 268 // Too large; allocate the object individually. 269 obj = sp->par_allocate(word_sz); 270 } 271 } 272 return obj; 273 } 274 275 276 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, 277 size_t word_sz) { 278 // Is the alloc in the current alloc buffer? 279 if (to_space_alloc_buffer()->contains(obj)) { 280 assert(to_space_alloc_buffer()->contains(obj + word_sz - 1), 281 "Should contain whole object."); 282 to_space_alloc_buffer()->undo_allocation(obj, word_sz); 283 } else { 284 CollectedHeap::fill_with_object(obj, word_sz); 285 } 286 } 287 288 void ParScanThreadState::print_promotion_failure_size() { 289 if (_promotion_failed_info.has_failed() && PrintPromotionFailure) { 290 gclog_or_tty->print(" (%d: promotion failure size = " SIZE_FORMAT ") ", 291 _thread_num, _promotion_failed_info.first_size()); 292 } 293 } 294 295 class ParScanThreadStateSet: private ResourceArray { 296 public: 297 // Initializes states for the specified number of threads; 298 ParScanThreadStateSet(int num_threads, 299 Space& to_space, 300 ParNewGeneration& gen, 301 Generation& old_gen, 302 ObjToScanQueueSet& queue_set, 303 Stack<oop, mtGC>* overflow_stacks_, 304 size_t desired_plab_sz, 305 ParallelTaskTerminator& term); 306 307 ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); } 308 309 inline ParScanThreadState& thread_state(int i); 310 311 void trace_promotion_failed(YoungGCTracer& gc_tracer); 312 void reset(int active_workers, bool promotion_failed); 313 void flush(); 314 315 #if TASKQUEUE_STATS 316 static void 317 print_termination_stats_hdr(outputStream* const st = gclog_or_tty); 318 void print_termination_stats(outputStream* const st = gclog_or_tty); 319 static void 320 print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty); 321 void print_taskqueue_stats(outputStream* const st = gclog_or_tty); 322 void reset_stats(); 323 #endif // TASKQUEUE_STATS 324 325 private: 326 ParallelTaskTerminator& _term; 327 ParNewGeneration& _gen; 328 Generation& _next_gen; 329 public: 330 bool is_valid(int id) const { return id < length(); } 331 ParallelTaskTerminator* terminator() { return &_term; } 332 }; 333 334 335 ParScanThreadStateSet::ParScanThreadStateSet( 336 int num_threads, Space& to_space, ParNewGeneration& gen, 337 Generation& old_gen, ObjToScanQueueSet& queue_set, 338 Stack<oop, mtGC>* overflow_stacks, 339 size_t desired_plab_sz, ParallelTaskTerminator& term) 340 : ResourceArray(sizeof(ParScanThreadState), num_threads), 341 _gen(gen), _next_gen(old_gen), _term(term) 342 { 343 assert(num_threads > 0, "sanity check!"); 344 assert(ParGCUseLocalOverflow == (overflow_stacks != NULL), 345 "overflow_stack allocation mismatch"); 346 // Initialize states. 347 for (int i = 0; i < num_threads; ++i) { 348 new ((ParScanThreadState*)_data + i) 349 ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set, 350 overflow_stacks, desired_plab_sz, term); 351 } 352 } 353 354 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i) 355 { 356 assert(i >= 0 && i < length(), "sanity check!"); 357 return ((ParScanThreadState*)_data)[i]; 358 } 359 360 void ParScanThreadStateSet::trace_promotion_failed(YoungGCTracer& gc_tracer) { 361 for (int i = 0; i < length(); ++i) { 362 if (thread_state(i).promotion_failed()) { 363 gc_tracer.report_promotion_failed(thread_state(i).promotion_failed_info()); 364 thread_state(i).promotion_failed_info().reset(); 365 } 366 } 367 } 368 369 void ParScanThreadStateSet::reset(int active_threads, bool promotion_failed) 370 { 371 _term.reset_for_reuse(active_threads); 372 if (promotion_failed) { 373 for (int i = 0; i < length(); ++i) { 374 thread_state(i).print_promotion_failure_size(); 375 } 376 } 377 } 378 379 #if TASKQUEUE_STATS 380 void 381 ParScanThreadState::reset_stats() 382 { 383 taskqueue_stats().reset(); 384 _term_attempts = 0; 385 _overflow_refills = 0; 386 _overflow_refill_objs = 0; 387 } 388 389 void ParScanThreadStateSet::reset_stats() 390 { 391 for (int i = 0; i < length(); ++i) { 392 thread_state(i).reset_stats(); 393 } 394 } 395 396 void 397 ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st) 398 { 399 st->print_raw_cr("GC Termination Stats"); 400 st->print_raw_cr(" elapsed --strong roots-- " 401 "-------termination-------"); 402 st->print_raw_cr("thr ms ms % " 403 " ms % attempts"); 404 st->print_raw_cr("--- --------- --------- ------ " 405 "--------- ------ --------"); 406 } 407 408 void ParScanThreadStateSet::print_termination_stats(outputStream* const st) 409 { 410 print_termination_stats_hdr(st); 411 412 for (int i = 0; i < length(); ++i) { 413 const ParScanThreadState & pss = thread_state(i); 414 const double elapsed_ms = pss.elapsed_time() * 1000.0; 415 const double s_roots_ms = pss.strong_roots_time() * 1000.0; 416 const double term_ms = pss.term_time() * 1000.0; 417 st->print_cr("%3d %9.2f %9.2f %6.2f " 418 "%9.2f %6.2f " SIZE_FORMAT_W(8), 419 i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms, 420 term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts()); 421 } 422 } 423 424 // Print stats related to work queue activity. 425 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st) 426 { 427 st->print_raw_cr("GC Task Stats"); 428 st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr(); 429 st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr(); 430 } 431 432 void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st) 433 { 434 print_taskqueue_stats_hdr(st); 435 436 TaskQueueStats totals; 437 for (int i = 0; i < length(); ++i) { 438 const ParScanThreadState & pss = thread_state(i); 439 const TaskQueueStats & stats = pss.taskqueue_stats(); 440 st->print("%3d ", i); stats.print(st); st->cr(); 441 totals += stats; 442 443 if (pss.overflow_refills() > 0) { 444 st->print_cr(" " SIZE_FORMAT_W(10) " overflow refills " 445 SIZE_FORMAT_W(10) " overflow objects", 446 pss.overflow_refills(), pss.overflow_refill_objs()); 447 } 448 } 449 st->print("tot "); totals.print(st); st->cr(); 450 451 DEBUG_ONLY(totals.verify()); 452 } 453 #endif // TASKQUEUE_STATS 454 455 void ParScanThreadStateSet::flush() 456 { 457 // Work in this loop should be kept as lightweight as 458 // possible since this might otherwise become a bottleneck 459 // to scaling. Should we add heavy-weight work into this 460 // loop, consider parallelizing the loop into the worker threads. 461 for (int i = 0; i < length(); ++i) { 462 ParScanThreadState& par_scan_state = thread_state(i); 463 464 // Flush stats related to To-space PLAB activity and 465 // retire the last buffer. 466 par_scan_state.to_space_alloc_buffer()-> 467 flush_stats_and_retire(_gen.plab_stats(), 468 true /* end_of_gc */, 469 false /* retain */); 470 471 // Every thread has its own age table. We need to merge 472 // them all into one. 473 ageTable *local_table = par_scan_state.age_table(); 474 _gen.age_table()->merge(local_table); 475 476 // Inform old gen that we're done. 477 _next_gen.par_promote_alloc_done(i); 478 _next_gen.par_oop_since_save_marks_iterate_done(i); 479 } 480 481 if (UseConcMarkSweepGC && ParallelGCThreads > 0) { 482 // We need to call this even when ResizeOldPLAB is disabled 483 // so as to avoid breaking some asserts. While we may be able 484 // to avoid this by reorganizing the code a bit, I am loathe 485 // to do that unless we find cases where ergo leads to bad 486 // performance. 487 CFLS_LAB::compute_desired_plab_size(); 488 } 489 } 490 491 ParScanClosure::ParScanClosure(ParNewGeneration* g, 492 ParScanThreadState* par_scan_state) : 493 OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g) 494 { 495 assert(_g->level() == 0, "Optimized for youngest generation"); 496 _boundary = _g->reserved().end(); 497 } 498 499 void ParScanWithBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, false); } 500 void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); } 501 502 void ParScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, false); } 503 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); } 504 505 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); } 506 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); } 507 508 void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); } 509 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); } 510 511 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g, 512 ParScanThreadState* par_scan_state) 513 : ScanWeakRefClosure(g), _par_scan_state(par_scan_state) 514 {} 515 516 void ParScanWeakRefClosure::do_oop(oop* p) { ParScanWeakRefClosure::do_oop_work(p); } 517 void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); } 518 519 #ifdef WIN32 520 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */ 521 #endif 522 523 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure( 524 ParScanThreadState* par_scan_state_, 525 ParScanWithoutBarrierClosure* to_space_closure_, 526 ParScanWithBarrierClosure* old_gen_closure_, 527 ParRootScanWithoutBarrierClosure* to_space_root_closure_, 528 ParNewGeneration* par_gen_, 529 ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_, 530 ObjToScanQueueSet* task_queues_, 531 ParallelTaskTerminator* terminator_) : 532 533 _par_scan_state(par_scan_state_), 534 _to_space_closure(to_space_closure_), 535 _old_gen_closure(old_gen_closure_), 536 _to_space_root_closure(to_space_root_closure_), 537 _old_gen_root_closure(old_gen_root_closure_), 538 _par_gen(par_gen_), 539 _task_queues(task_queues_), 540 _terminator(terminator_) 541 {} 542 543 void ParEvacuateFollowersClosure::do_void() { 544 ObjToScanQueue* work_q = par_scan_state()->work_queue(); 545 546 while (true) { 547 548 // 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* gen, Generation* next_gen, 581 HeapWord* young_old_boundary, ParScanThreadStateSet* state_set) : 582 AbstractGangTask("ParNewGeneration collection"), 583 _gen(gen), _next_gen(next_gen), 584 _young_old_boundary(young_old_boundary), 585 _state_set(state_set) 586 {} 587 588 // Reset the terminator for the given number of 589 // active threads. 590 void ParNewGenTask::set_for_termination(int active_workers) { 591 _state_set->reset(active_workers, _gen->promotion_failed()); 592 // Should the heap be passed in? There's only 1 for now so 593 // grab it instead. 594 GenCollectedHeap* gch = GenCollectedHeap::heap(); 595 gch->set_n_termination(active_workers); 596 } 597 598 void ParNewGenTask::work(uint worker_id) { 599 GenCollectedHeap* gch = GenCollectedHeap::heap(); 600 // Since this is being done in a separate thread, need new resource 601 // and handle marks. 602 ResourceMark rm; 603 HandleMark hm; 604 // We would need multiple old-gen queues otherwise. 605 assert(gch->n_gens() == 2, "Par young collection currently only works with one older gen."); 606 607 Generation* old_gen = gch->next_gen(_gen); 608 609 ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id); 610 assert(_state_set->is_valid(worker_id), "Should not have been called"); 611 612 par_scan_state.set_young_old_boundary(_young_old_boundary); 613 614 KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(), 615 gch->rem_set()->klass_rem_set()); 616 CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure, 617 &par_scan_state.to_space_root_closure(), 618 false); 619 620 par_scan_state.start_strong_roots(); 621 gch->gen_process_roots(_gen->level(), 622 true, // Process younger gens, if any, 623 // as strong roots. 624 false, // no scope; this is parallel code 625 GenCollectedHeap::SO_ScavengeCodeCache, 626 GenCollectedHeap::StrongAndWeakRoots, 627 &par_scan_state.to_space_root_closure(), 628 &par_scan_state.older_gen_closure(), 629 &cld_scan_closure); 630 631 par_scan_state.end_strong_roots(); 632 633 // "evacuate followers". 634 par_scan_state.evacuate_followers_closure().do_void(); 635 } 636 637 #ifdef _MSC_VER 638 #pragma warning( push ) 639 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list 640 #endif 641 ParNewGeneration:: 642 ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level) 643 : DefNewGeneration(rs, initial_byte_size, level, "PCopy"), 644 _overflow_list(NULL), 645 _is_alive_closure(this), 646 _plab_stats(YoungPLABSize, PLABWeight) 647 { 648 NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;) 649 NOT_PRODUCT(_num_par_pushes = 0;) 650 _task_queues = new ObjToScanQueueSet(ParallelGCThreads); 651 guarantee(_task_queues != NULL, "task_queues allocation failure."); 652 653 for (uint i1 = 0; i1 < ParallelGCThreads; i1++) { 654 ObjToScanQueue *q = new ObjToScanQueue(); 655 guarantee(q != NULL, "work_queue Allocation failure."); 656 _task_queues->register_queue(i1, q); 657 } 658 659 for (uint i2 = 0; i2 < ParallelGCThreads; i2++) 660 _task_queues->queue(i2)->initialize(); 661 662 _overflow_stacks = NULL; 663 if (ParGCUseLocalOverflow) { 664 665 // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal 666 // with ',' 667 typedef Stack<oop, mtGC> GCOopStack; 668 669 _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC); 670 for (size_t i = 0; i < ParallelGCThreads; ++i) { 671 new (_overflow_stacks + i) Stack<oop, mtGC>(); 672 } 673 } 674 675 if (UsePerfData) { 676 EXCEPTION_MARK; 677 ResourceMark rm; 678 679 const char* cname = 680 PerfDataManager::counter_name(_gen_counters->name_space(), "threads"); 681 PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None, 682 ParallelGCThreads, CHECK); 683 } 684 } 685 #ifdef _MSC_VER 686 #pragma warning( pop ) 687 #endif 688 689 // ParNewGeneration:: 690 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) : 691 DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {} 692 693 template <class T> 694 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) { 695 #ifdef ASSERT 696 { 697 assert(!oopDesc::is_null(*p), "expected non-null ref"); 698 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 699 // We never expect to see a null reference being processed 700 // as a weak reference. 701 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 702 } 703 #endif // ASSERT 704 705 _par_cl->do_oop_nv(p); 706 707 if (Universe::heap()->is_in_reserved(p)) { 708 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 709 _rs->write_ref_field_gc_par(p, obj); 710 } 711 } 712 713 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); } 714 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); } 715 716 // ParNewGeneration:: 717 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) : 718 DefNewGeneration::KeepAliveClosure(cl) {} 719 720 template <class T> 721 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) { 722 #ifdef ASSERT 723 { 724 assert(!oopDesc::is_null(*p), "expected non-null ref"); 725 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 726 // We never expect to see a null reference being processed 727 // as a weak reference. 728 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 729 } 730 #endif // ASSERT 731 732 _cl->do_oop_nv(p); 733 734 if (Universe::heap()->is_in_reserved(p)) { 735 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 736 _rs->write_ref_field_gc_par(p, obj); 737 } 738 } 739 740 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); } 741 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); } 742 743 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) { 744 T heap_oop = oopDesc::load_heap_oop(p); 745 if (!oopDesc::is_null(heap_oop)) { 746 oop obj = oopDesc::decode_heap_oop_not_null(heap_oop); 747 if ((HeapWord*)obj < _boundary) { 748 assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?"); 749 oop new_obj = obj->is_forwarded() 750 ? obj->forwardee() 751 : _g->DefNewGeneration::copy_to_survivor_space(obj); 752 oopDesc::encode_store_heap_oop_not_null(p, new_obj); 753 } 754 if (_gc_barrier) { 755 // If p points to a younger generation, mark the card. 756 if ((HeapWord*)obj < _gen_boundary) { 757 _rs->write_ref_field_gc_par(p, obj); 758 } 759 } 760 } 761 } 762 763 void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 764 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 765 766 class ParNewRefProcTaskProxy: public AbstractGangTask { 767 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; 768 public: 769 ParNewRefProcTaskProxy(ProcessTask& task, ParNewGeneration& gen, 770 Generation& next_gen, 771 HeapWord* young_old_boundary, 772 ParScanThreadStateSet& state_set); 773 774 private: 775 virtual void work(uint worker_id); 776 virtual void set_for_termination(int active_workers) { 777 _state_set.terminator()->reset_for_reuse(active_workers); 778 } 779 private: 780 ParNewGeneration& _gen; 781 ProcessTask& _task; 782 Generation& _next_gen; 783 HeapWord* _young_old_boundary; 784 ParScanThreadStateSet& _state_set; 785 }; 786 787 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy( 788 ProcessTask& task, ParNewGeneration& gen, 789 Generation& next_gen, 790 HeapWord* young_old_boundary, 791 ParScanThreadStateSet& state_set) 792 : AbstractGangTask("ParNewGeneration parallel reference processing"), 793 _gen(gen), 794 _task(task), 795 _next_gen(next_gen), 796 _young_old_boundary(young_old_boundary), 797 _state_set(state_set) 798 { 799 } 800 801 void ParNewRefProcTaskProxy::work(uint worker_id) 802 { 803 ResourceMark rm; 804 HandleMark hm; 805 ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id); 806 par_scan_state.set_young_old_boundary(_young_old_boundary); 807 _task.work(worker_id, par_scan_state.is_alive_closure(), 808 par_scan_state.keep_alive_closure(), 809 par_scan_state.evacuate_followers_closure()); 810 } 811 812 class ParNewRefEnqueueTaskProxy: public AbstractGangTask { 813 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; 814 EnqueueTask& _task; 815 816 public: 817 ParNewRefEnqueueTaskProxy(EnqueueTask& task) 818 : AbstractGangTask("ParNewGeneration parallel reference enqueue"), 819 _task(task) 820 { } 821 822 virtual void work(uint worker_id) 823 { 824 _task.work(worker_id); 825 } 826 }; 827 828 829 void ParNewRefProcTaskExecutor::execute(ProcessTask& task) 830 { 831 GenCollectedHeap* gch = GenCollectedHeap::heap(); 832 assert(gch->kind() == CollectedHeap::GenCollectedHeap, 833 "not a generational heap"); 834 FlexibleWorkGang* workers = gch->workers(); 835 assert(workers != NULL, "Need parallel worker threads."); 836 _state_set.reset(workers->active_workers(), _generation.promotion_failed()); 837 ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(), 838 _generation.reserved().end(), _state_set); 839 workers->run_task(&rp_task); 840 _state_set.reset(0 /* bad value in debug if not reset */, 841 _generation.promotion_failed()); 842 } 843 844 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task) 845 { 846 GenCollectedHeap* gch = GenCollectedHeap::heap(); 847 FlexibleWorkGang* workers = gch->workers(); 848 assert(workers != NULL, "Need parallel worker threads."); 849 ParNewRefEnqueueTaskProxy enq_task(task); 850 workers->run_task(&enq_task); 851 } 852 853 void ParNewRefProcTaskExecutor::set_single_threaded_mode() 854 { 855 _state_set.flush(); 856 GenCollectedHeap* gch = GenCollectedHeap::heap(); 857 gch->set_par_threads(0); // 0 ==> non-parallel. 858 gch->save_marks(); 859 } 860 861 ScanClosureWithParBarrier:: 862 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) : 863 ScanClosure(g, gc_barrier) {} 864 865 EvacuateFollowersClosureGeneral:: 866 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, int level, 867 OopsInGenClosure* cur, 868 OopsInGenClosure* older) : 869 _gch(gch), _level(level), 870 _scan_cur_or_nonheap(cur), _scan_older(older) 871 {} 872 873 void EvacuateFollowersClosureGeneral::do_void() { 874 do { 875 // Beware: this call will lead to closure applications via virtual 876 // calls. 877 _gch->oop_since_save_marks_iterate(_level, 878 _scan_cur_or_nonheap, 879 _scan_older); 880 } while (!_gch->no_allocs_since_save_marks(_level)); 881 } 882 883 884 // A Generation that does parallel young-gen collection. 885 886 bool ParNewGeneration::_avoid_promotion_undo = false; 887 888 void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set, ParNewTracer& gc_tracer) { 889 assert(_promo_failure_scan_stack.is_empty(), "post condition"); 890 _promo_failure_scan_stack.clear(true); // Clear cached segments. 891 892 remove_forwarding_pointers(); 893 if (PrintGCDetails) { 894 gclog_or_tty->print(" (promotion failed)"); 895 } 896 // All the spaces are in play for mark-sweep. 897 swap_spaces(); // Make life simpler for CMS || rescan; see 6483690. 898 from()->set_next_compaction_space(to()); 899 gch->set_incremental_collection_failed(); 900 // Inform the next generation that a promotion failure occurred. 901 _next_gen->promotion_failure_occurred(); 902 903 // Trace promotion failure in the parallel GC threads 904 thread_state_set.trace_promotion_failed(gc_tracer); 905 // Single threaded code may have reported promotion failure to the global state 906 if (_promotion_failed_info.has_failed()) { 907 gc_tracer.report_promotion_failed(_promotion_failed_info); 908 } 909 // Reset the PromotionFailureALot counters. 910 NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();) 911 } 912 913 void ParNewGeneration::collect(bool full, 914 bool clear_all_soft_refs, 915 size_t size, 916 bool is_tlab) { 917 assert(full || size > 0, "otherwise we don't want to collect"); 918 919 GenCollectedHeap* gch = GenCollectedHeap::heap(); 920 921 _gc_timer->register_gc_start(); 922 923 assert(gch->kind() == CollectedHeap::GenCollectedHeap, 924 "not a CMS generational heap"); 925 AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy(); 926 FlexibleWorkGang* workers = gch->workers(); 927 assert(workers != NULL, "Need workgang for parallel work"); 928 int active_workers = 929 AdaptiveSizePolicy::calc_active_workers(workers->total_workers(), 930 workers->active_workers(), 931 Threads::number_of_non_daemon_threads()); 932 workers->set_active_workers(active_workers); 933 assert(gch->n_gens() == 2, 934 "Par collection currently only works with single older gen."); 935 _next_gen = gch->next_gen(this); 936 // Do we have to avoid promotion_undo? 937 if (gch->collector_policy()->is_concurrent_mark_sweep_policy()) { 938 set_avoid_promotion_undo(true); 939 } 940 941 // If the next generation is too full to accommodate worst-case promotion 942 // from this generation, pass on collection; let the next generation 943 // do it. 944 if (!collection_attempt_is_safe()) { 945 gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one 946 return; 947 } 948 assert(to()->is_empty(), "Else not collection_attempt_is_safe"); 949 950 ParNewTracer gc_tracer; 951 gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start()); 952 gch->trace_heap_before_gc(&gc_tracer); 953 954 init_assuming_no_promotion_failure(); 955 956 if (UseAdaptiveSizePolicy) { 957 set_survivor_overflow(false); 958 size_policy->minor_collection_begin(); 959 } 960 961 GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, gc_tracer.gc_id()); 962 // Capture heap used before collection (for printing). 963 size_t gch_prev_used = gch->used(); 964 965 SpecializationStats::clear(); 966 967 age_table()->clear(); 968 to()->clear(SpaceDecorator::Mangle); 969 970 gch->save_marks(); 971 assert(workers != NULL, "Need parallel worker threads."); 972 int n_workers = active_workers; 973 974 // Set the correct parallelism (number of queues) in the reference processor 975 ref_processor()->set_active_mt_degree(n_workers); 976 977 // Always set the terminator for the active number of workers 978 // because only those workers go through the termination protocol. 979 ParallelTaskTerminator _term(n_workers, task_queues()); 980 ParScanThreadStateSet thread_state_set(workers->active_workers(), 981 *to(), *this, *_next_gen, *task_queues(), 982 _overflow_stacks, desired_plab_sz(), _term); 983 984 ParNewGenTask tsk(this, _next_gen, reserved().end(), &thread_state_set); 985 gch->set_par_threads(n_workers); 986 gch->rem_set()->prepare_for_younger_refs_iterate(true); 987 // It turns out that even when we're using 1 thread, doing the work in a 988 // separate thread causes wide variance in run times. We can't help this 989 // in the multi-threaded case, but we special-case n=1 here to get 990 // repeatable measurements of the 1-thread overhead of the parallel code. 991 if (n_workers > 1) { 992 GenCollectedHeap::StrongRootsScope srs(gch); 993 workers->run_task(&tsk); 994 } else { 995 GenCollectedHeap::StrongRootsScope srs(gch); 996 tsk.work(0); 997 } 998 thread_state_set.reset(0 /* Bad value in debug if not reset */, 999 promotion_failed()); 1000 1001 // Process (weak) reference objects found during scavenge. 1002 ReferenceProcessor* rp = ref_processor(); 1003 IsAliveClosure is_alive(this); 1004 ScanWeakRefClosure scan_weak_ref(this); 1005 KeepAliveClosure keep_alive(&scan_weak_ref); 1006 ScanClosure scan_without_gc_barrier(this, false); 1007 ScanClosureWithParBarrier scan_with_gc_barrier(this, true); 1008 set_promo_failure_scan_stack_closure(&scan_without_gc_barrier); 1009 EvacuateFollowersClosureGeneral evacuate_followers(gch, _level, 1010 &scan_without_gc_barrier, &scan_with_gc_barrier); 1011 rp->setup_policy(clear_all_soft_refs); 1012 // Can the mt_degree be set later (at run_task() time would be best)? 1013 rp->set_active_mt_degree(active_workers); 1014 ReferenceProcessorStats stats; 1015 if (rp->processing_is_mt()) { 1016 ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); 1017 stats = rp->process_discovered_references(&is_alive, &keep_alive, 1018 &evacuate_followers, &task_executor, 1019 _gc_timer, gc_tracer.gc_id()); 1020 } else { 1021 thread_state_set.flush(); 1022 gch->set_par_threads(0); // 0 ==> non-parallel. 1023 gch->save_marks(); 1024 stats = rp->process_discovered_references(&is_alive, &keep_alive, 1025 &evacuate_followers, NULL, 1026 _gc_timer, gc_tracer.gc_id()); 1027 } 1028 gc_tracer.report_gc_reference_stats(stats); 1029 if (!promotion_failed()) { 1030 // Swap the survivor spaces. 1031 eden()->clear(SpaceDecorator::Mangle); 1032 from()->clear(SpaceDecorator::Mangle); 1033 if (ZapUnusedHeapArea) { 1034 // This is now done here because of the piece-meal mangling which 1035 // can check for valid mangling at intermediate points in the 1036 // collection(s). When a minor collection fails to collect 1037 // sufficient space resizing of the young generation can occur 1038 // an redistribute the spaces in the young generation. Mangle 1039 // here so that unzapped regions don't get distributed to 1040 // other spaces. 1041 to()->mangle_unused_area(); 1042 } 1043 swap_spaces(); 1044 1045 // A successful scavenge should restart the GC time limit count which is 1046 // for full GC's. 1047 size_policy->reset_gc_overhead_limit_count(); 1048 1049 assert(to()->is_empty(), "to space should be empty now"); 1050 1051 adjust_desired_tenuring_threshold(); 1052 } else { 1053 handle_promotion_failed(gch, thread_state_set, gc_tracer); 1054 } 1055 // set new iteration safe limit for the survivor spaces 1056 from()->set_concurrent_iteration_safe_limit(from()->top()); 1057 to()->set_concurrent_iteration_safe_limit(to()->top()); 1058 1059 if (ResizePLAB) { 1060 plab_stats()->adjust_desired_plab_sz(n_workers); 1061 } 1062 1063 if (PrintGC && !PrintGCDetails) { 1064 gch->print_heap_change(gch_prev_used); 1065 } 1066 1067 if (PrintGCDetails && ParallelGCVerbose) { 1068 TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats()); 1069 TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats()); 1070 } 1071 1072 if (UseAdaptiveSizePolicy) { 1073 size_policy->minor_collection_end(gch->gc_cause()); 1074 size_policy->avg_survived()->sample(from()->used()); 1075 } 1076 1077 // We need to use a monotonically non-deccreasing time in ms 1078 // or we will see time-warp warnings and os::javaTimeMillis() 1079 // does not guarantee monotonicity. 1080 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 1081 update_time_of_last_gc(now); 1082 1083 SpecializationStats::print(); 1084 1085 rp->set_enqueuing_is_done(true); 1086 if (rp->processing_is_mt()) { 1087 ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); 1088 rp->enqueue_discovered_references(&task_executor); 1089 } else { 1090 rp->enqueue_discovered_references(NULL); 1091 } 1092 rp->verify_no_references_recorded(); 1093 1094 gch->trace_heap_after_gc(&gc_tracer); 1095 gc_tracer.report_tenuring_threshold(tenuring_threshold()); 1096 1097 _gc_timer->register_gc_end(); 1098 1099 gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions()); 1100 } 1101 1102 static int sum; 1103 void ParNewGeneration::waste_some_time() { 1104 for (int i = 0; i < 100; i++) { 1105 sum += i; 1106 } 1107 } 1108 1109 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4); 1110 1111 // Because of concurrency, there are times where an object for which 1112 // "is_forwarded()" is true contains an "interim" forwarding pointer 1113 // value. Such a value will soon be overwritten with a real value. 1114 // This method requires "obj" to have a forwarding pointer, and waits, if 1115 // necessary for a real one to be inserted, and returns it. 1116 1117 oop ParNewGeneration::real_forwardee(oop obj) { 1118 oop forward_ptr = obj->forwardee(); 1119 if (forward_ptr != ClaimedForwardPtr) { 1120 return forward_ptr; 1121 } else { 1122 return real_forwardee_slow(obj); 1123 } 1124 } 1125 1126 oop ParNewGeneration::real_forwardee_slow(oop obj) { 1127 // Spin-read if it is claimed but not yet written by another thread. 1128 oop forward_ptr = obj->forwardee(); 1129 while (forward_ptr == ClaimedForwardPtr) { 1130 waste_some_time(); 1131 assert(obj->is_forwarded(), "precondition"); 1132 forward_ptr = obj->forwardee(); 1133 } 1134 return forward_ptr; 1135 } 1136 1137 #ifdef ASSERT 1138 bool ParNewGeneration::is_legal_forward_ptr(oop p) { 1139 return 1140 (_avoid_promotion_undo && p == ClaimedForwardPtr) 1141 || Universe::heap()->is_in_reserved(p); 1142 } 1143 #endif 1144 1145 void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) { 1146 if (m->must_be_preserved_for_promotion_failure(obj)) { 1147 // We should really have separate per-worker stacks, rather 1148 // than use locking of a common pair of stacks. 1149 MutexLocker ml(ParGCRareEvent_lock); 1150 preserve_mark(obj, m); 1151 } 1152 } 1153 1154 // Multiple GC threads may try to promote an object. If the object 1155 // is successfully promoted, a forwarding pointer will be installed in 1156 // the object in the young generation. This method claims the right 1157 // to install the forwarding pointer before it copies the object, 1158 // thus avoiding the need to undo the copy as in 1159 // copy_to_survivor_space_avoiding_with_undo. 1160 1161 oop ParNewGeneration::copy_to_survivor_space_avoiding_promotion_undo( 1162 ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) { 1163 // In the sequential version, this assert also says that the object is 1164 // not forwarded. That might not be the case here. It is the case that 1165 // the caller observed it to be not forwarded at some time in the past. 1166 assert(is_in_reserved(old), "shouldn't be scavenging this oop"); 1167 1168 // The sequential code read "old->age()" below. That doesn't work here, 1169 // since the age is in the mark word, and that might be overwritten with 1170 // a forwarding pointer by a parallel thread. So we must save the mark 1171 // word in a local and then analyze it. 1172 oopDesc dummyOld; 1173 dummyOld.set_mark(m); 1174 assert(!dummyOld.is_forwarded(), 1175 "should not be called with forwarding pointer mark word."); 1176 1177 oop new_obj = NULL; 1178 oop forward_ptr; 1179 1180 // Try allocating obj in to-space (unless too old) 1181 if (dummyOld.age() < tenuring_threshold()) { 1182 new_obj = (oop)par_scan_state->alloc_in_to_space(sz); 1183 if (new_obj == NULL) { 1184 set_survivor_overflow(true); 1185 } 1186 } 1187 1188 if (new_obj == NULL) { 1189 // Either to-space is full or we decided to promote 1190 // try allocating obj tenured 1191 1192 // Attempt to install a null forwarding pointer (atomically), 1193 // to claim the right to install the real forwarding pointer. 1194 forward_ptr = old->forward_to_atomic(ClaimedForwardPtr); 1195 if (forward_ptr != NULL) { 1196 // someone else beat us to it. 1197 return real_forwardee(old); 1198 } 1199 1200 new_obj = _next_gen->par_promote(par_scan_state->thread_num(), 1201 old, m, sz); 1202 1203 if (new_obj == NULL) { 1204 // promotion failed, forward to self 1205 _promotion_failed = true; 1206 new_obj = old; 1207 1208 preserve_mark_if_necessary(old, m); 1209 par_scan_state->register_promotion_failure(sz); 1210 } 1211 1212 old->forward_to(new_obj); 1213 forward_ptr = NULL; 1214 } else { 1215 // Is in to-space; do copying ourselves. 1216 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz); 1217 forward_ptr = old->forward_to_atomic(new_obj); 1218 // Restore the mark word copied above. 1219 new_obj->set_mark(m); 1220 // Increment age if obj still in new generation 1221 new_obj->incr_age(); 1222 par_scan_state->age_table()->add(new_obj, sz); 1223 } 1224 assert(new_obj != NULL, "just checking"); 1225 1226 #ifndef PRODUCT 1227 // This code must come after the CAS test, or it will print incorrect 1228 // information. 1229 if (TraceScavenge) { 1230 gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}", 1231 is_in_reserved(new_obj) ? "copying" : "tenuring", 1232 new_obj->klass()->internal_name(), (void *)old, (void *)new_obj, new_obj->size()); 1233 } 1234 #endif 1235 1236 if (forward_ptr == NULL) { 1237 oop obj_to_push = new_obj; 1238 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) { 1239 // Length field used as index of next element to be scanned. 1240 // Real length can be obtained from real_forwardee() 1241 arrayOop(old)->set_length(0); 1242 obj_to_push = old; 1243 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push, 1244 "push forwarded object"); 1245 } 1246 // Push it on one of the queues of to-be-scanned objects. 1247 bool simulate_overflow = false; 1248 NOT_PRODUCT( 1249 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) { 1250 // simulate a stack overflow 1251 simulate_overflow = true; 1252 } 1253 ) 1254 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) { 1255 // Add stats for overflow pushes. 1256 if (Verbose && PrintGCDetails) { 1257 gclog_or_tty->print("queue overflow!\n"); 1258 } 1259 push_on_overflow_list(old, par_scan_state); 1260 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0)); 1261 } 1262 1263 return new_obj; 1264 } 1265 1266 // Oops. Someone beat us to it. Undo the allocation. Where did we 1267 // allocate it? 1268 if (is_in_reserved(new_obj)) { 1269 // Must be in to_space. 1270 assert(to()->is_in_reserved(new_obj), "Checking"); 1271 if (forward_ptr == ClaimedForwardPtr) { 1272 // Wait to get the real forwarding pointer value. 1273 forward_ptr = real_forwardee(old); 1274 } 1275 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz); 1276 } 1277 1278 return forward_ptr; 1279 } 1280 1281 1282 // Multiple GC threads may try to promote the same object. If two 1283 // or more GC threads copy the object, only one wins the race to install 1284 // the forwarding pointer. The other threads have to undo their copy. 1285 1286 oop ParNewGeneration::copy_to_survivor_space_with_undo( 1287 ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) { 1288 1289 // In the sequential version, this assert also says that the object is 1290 // not forwarded. That might not be the case here. It is the case that 1291 // the caller observed it to be not forwarded at some time in the past. 1292 assert(is_in_reserved(old), "shouldn't be scavenging this oop"); 1293 1294 // The sequential code read "old->age()" below. That doesn't work here, 1295 // since the age is in the mark word, and that might be overwritten with 1296 // a forwarding pointer by a parallel thread. So we must save the mark 1297 // word here, install it in a local oopDesc, and then analyze it. 1298 oopDesc dummyOld; 1299 dummyOld.set_mark(m); 1300 assert(!dummyOld.is_forwarded(), 1301 "should not be called with forwarding pointer mark word."); 1302 1303 bool failed_to_promote = false; 1304 oop new_obj = NULL; 1305 oop forward_ptr; 1306 1307 // Try allocating obj in to-space (unless too old) 1308 if (dummyOld.age() < tenuring_threshold()) { 1309 new_obj = (oop)par_scan_state->alloc_in_to_space(sz); 1310 if (new_obj == NULL) { 1311 set_survivor_overflow(true); 1312 } 1313 } 1314 1315 if (new_obj == NULL) { 1316 // Either to-space is full or we decided to promote 1317 // try allocating obj tenured 1318 new_obj = _next_gen->par_promote(par_scan_state->thread_num(), 1319 old, m, sz); 1320 1321 if (new_obj == NULL) { 1322 // promotion failed, forward to self 1323 forward_ptr = old->forward_to_atomic(old); 1324 new_obj = old; 1325 1326 if (forward_ptr != NULL) { 1327 return forward_ptr; // someone else succeeded 1328 } 1329 1330 _promotion_failed = true; 1331 failed_to_promote = true; 1332 1333 preserve_mark_if_necessary(old, m); 1334 par_scan_state->register_promotion_failure(sz); 1335 } 1336 } else { 1337 // Is in to-space; do copying ourselves. 1338 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz); 1339 // Restore the mark word copied above. 1340 new_obj->set_mark(m); 1341 // Increment age if new_obj still in new generation 1342 new_obj->incr_age(); 1343 par_scan_state->age_table()->add(new_obj, sz); 1344 } 1345 assert(new_obj != NULL, "just checking"); 1346 1347 #ifndef PRODUCT 1348 // This code must come after the CAS test, or it will print incorrect 1349 // information. 1350 if (TraceScavenge) { 1351 gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}", 1352 is_in_reserved(new_obj) ? "copying" : "tenuring", 1353 new_obj->klass()->internal_name(), (void *)old, (void *)new_obj, new_obj->size()); 1354 } 1355 #endif 1356 1357 // Now attempt to install the forwarding pointer (atomically). 1358 // We have to copy the mark word before overwriting with forwarding 1359 // ptr, so we can restore it below in the copy. 1360 if (!failed_to_promote) { 1361 forward_ptr = old->forward_to_atomic(new_obj); 1362 } 1363 1364 if (forward_ptr == NULL) { 1365 oop obj_to_push = new_obj; 1366 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) { 1367 // Length field used as index of next element to be scanned. 1368 // Real length can be obtained from real_forwardee() 1369 arrayOop(old)->set_length(0); 1370 obj_to_push = old; 1371 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push, 1372 "push forwarded object"); 1373 } 1374 // Push it on one of the queues of to-be-scanned objects. 1375 bool simulate_overflow = false; 1376 NOT_PRODUCT( 1377 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) { 1378 // simulate a stack overflow 1379 simulate_overflow = true; 1380 } 1381 ) 1382 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) { 1383 // Add stats for overflow pushes. 1384 push_on_overflow_list(old, par_scan_state); 1385 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0)); 1386 } 1387 1388 return new_obj; 1389 } 1390 1391 // Oops. Someone beat us to it. Undo the allocation. Where did we 1392 // allocate it? 1393 if (is_in_reserved(new_obj)) { 1394 // Must be in to_space. 1395 assert(to()->is_in_reserved(new_obj), "Checking"); 1396 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz); 1397 } else { 1398 assert(!_avoid_promotion_undo, "Should not be here if avoiding."); 1399 _next_gen->par_promote_alloc_undo(par_scan_state->thread_num(), 1400 (HeapWord*)new_obj, sz); 1401 } 1402 1403 return forward_ptr; 1404 } 1405 1406 #ifndef PRODUCT 1407 // It's OK to call this multi-threaded; the worst thing 1408 // that can happen is that we'll get a bunch of closely 1409 // spaced simulated oveflows, but that's OK, in fact 1410 // probably good as it would exercise the overflow code 1411 // under contention. 1412 bool ParNewGeneration::should_simulate_overflow() { 1413 if (_overflow_counter-- <= 0) { // just being defensive 1414 _overflow_counter = ParGCWorkQueueOverflowInterval; 1415 return true; 1416 } else { 1417 return false; 1418 } 1419 } 1420 #endif 1421 1422 // In case we are using compressed oops, we need to be careful. 1423 // If the object being pushed is an object array, then its length 1424 // field keeps track of the "grey boundary" at which the next 1425 // incremental scan will be done (see ParGCArrayScanChunk). 1426 // When using compressed oops, this length field is kept in the 1427 // lower 32 bits of the erstwhile klass word and cannot be used 1428 // for the overflow chaining pointer (OCP below). As such the OCP 1429 // would itself need to be compressed into the top 32-bits in this 1430 // case. Unfortunately, see below, in the event that we have a 1431 // promotion failure, the node to be pushed on the list can be 1432 // outside of the Java heap, so the heap-based pointer compression 1433 // would not work (we would have potential aliasing between C-heap 1434 // and Java-heap pointers). For this reason, when using compressed 1435 // oops, we simply use a worker-thread-local, non-shared overflow 1436 // list in the form of a growable array, with a slightly different 1437 // overflow stack draining strategy. If/when we start using fat 1438 // stacks here, we can go back to using (fat) pointer chains 1439 // (although some performance comparisons would be useful since 1440 // single global lists have their own performance disadvantages 1441 // as we were made painfully aware not long ago, see 6786503). 1442 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff)) 1443 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) { 1444 assert(is_in_reserved(from_space_obj), "Should be from this generation"); 1445 if (ParGCUseLocalOverflow) { 1446 // In the case of compressed oops, we use a private, not-shared 1447 // overflow stack. 1448 par_scan_state->push_on_overflow_stack(from_space_obj); 1449 } else { 1450 assert(!UseCompressedOops, "Error"); 1451 // if the object has been forwarded to itself, then we cannot 1452 // use the klass pointer for the linked list. Instead we have 1453 // to allocate an oopDesc in the C-Heap and use that for the linked list. 1454 // XXX This is horribly inefficient when a promotion failure occurs 1455 // and should be fixed. XXX FIX ME !!! 1456 #ifndef PRODUCT 1457 Atomic::inc_ptr(&_num_par_pushes); 1458 assert(_num_par_pushes > 0, "Tautology"); 1459 #endif 1460 if (from_space_obj->forwardee() == from_space_obj) { 1461 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC); 1462 listhead->forward_to(from_space_obj); 1463 from_space_obj = listhead; 1464 } 1465 oop observed_overflow_list = _overflow_list; 1466 oop cur_overflow_list; 1467 do { 1468 cur_overflow_list = observed_overflow_list; 1469 if (cur_overflow_list != BUSY) { 1470 from_space_obj->set_klass_to_list_ptr(cur_overflow_list); 1471 } else { 1472 from_space_obj->set_klass_to_list_ptr(NULL); 1473 } 1474 observed_overflow_list = 1475 (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list); 1476 } while (cur_overflow_list != observed_overflow_list); 1477 } 1478 } 1479 1480 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) { 1481 bool res; 1482 1483 if (ParGCUseLocalOverflow) { 1484 res = par_scan_state->take_from_overflow_stack(); 1485 } else { 1486 assert(!UseCompressedOops, "Error"); 1487 res = take_from_overflow_list_work(par_scan_state); 1488 } 1489 return res; 1490 } 1491 1492 1493 // *NOTE*: The overflow list manipulation code here and 1494 // in CMSCollector:: are very similar in shape, 1495 // except that in the CMS case we thread the objects 1496 // directly into the list via their mark word, and do 1497 // not need to deal with special cases below related 1498 // to chunking of object arrays and promotion failure 1499 // handling. 1500 // CR 6797058 has been filed to attempt consolidation of 1501 // the common code. 1502 // Because of the common code, if you make any changes in 1503 // the code below, please check the CMS version to see if 1504 // similar changes might be needed. 1505 // See CMSCollector::par_take_from_overflow_list() for 1506 // more extensive documentation comments. 1507 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) { 1508 ObjToScanQueue* work_q = par_scan_state->work_queue(); 1509 // How many to take? 1510 size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 1511 (size_t)ParGCDesiredObjsFromOverflowList); 1512 1513 assert(!UseCompressedOops, "Error"); 1514 assert(par_scan_state->overflow_stack() == NULL, "Error"); 1515 if (_overflow_list == NULL) return false; 1516 1517 // Otherwise, there was something there; try claiming the list. 1518 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1519 // Trim off a prefix of at most objsFromOverflow items 1520 Thread* tid = Thread::current(); 1521 size_t spin_count = (size_t)ParallelGCThreads; 1522 size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100); 1523 for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) { 1524 // someone grabbed it before we did ... 1525 // ... we spin for a short while... 1526 os::sleep(tid, sleep_time_millis, false); 1527 if (_overflow_list == NULL) { 1528 // nothing left to take 1529 return false; 1530 } else if (_overflow_list != BUSY) { 1531 // try and grab the prefix 1532 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1533 } 1534 } 1535 if (prefix == NULL || prefix == BUSY) { 1536 // Nothing to take or waited long enough 1537 if (prefix == NULL) { 1538 // Write back the NULL in case we overwrote it with BUSY above 1539 // and it is still the same value. 1540 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1541 } 1542 return false; 1543 } 1544 assert(prefix != NULL && prefix != BUSY, "Error"); 1545 size_t i = 1; 1546 oop cur = prefix; 1547 while (i < objsFromOverflow && cur->klass_or_null() != NULL) { 1548 i++; cur = cur->list_ptr_from_klass(); 1549 } 1550 1551 // Reattach remaining (suffix) to overflow list 1552 if (cur->klass_or_null() == NULL) { 1553 // Write back the NULL in lieu of the BUSY we wrote 1554 // above and it is still the same value. 1555 if (_overflow_list == BUSY) { 1556 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1557 } 1558 } else { 1559 assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error"); 1560 oop suffix = cur->list_ptr_from_klass(); // suffix will be put back on global list 1561 cur->set_klass_to_list_ptr(NULL); // break off suffix 1562 // It's possible that the list is still in the empty(busy) state 1563 // we left it in a short while ago; in that case we may be 1564 // able to place back the suffix. 1565 oop observed_overflow_list = _overflow_list; 1566 oop cur_overflow_list = observed_overflow_list; 1567 bool attached = false; 1568 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { 1569 observed_overflow_list = 1570 (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1571 if (cur_overflow_list == observed_overflow_list) { 1572 attached = true; 1573 break; 1574 } else cur_overflow_list = observed_overflow_list; 1575 } 1576 if (!attached) { 1577 // Too bad, someone else got in in between; we'll need to do a splice. 1578 // Find the last item of suffix list 1579 oop last = suffix; 1580 while (last->klass_or_null() != NULL) { 1581 last = last->list_ptr_from_klass(); 1582 } 1583 // Atomically prepend suffix to current overflow list 1584 observed_overflow_list = _overflow_list; 1585 do { 1586 cur_overflow_list = observed_overflow_list; 1587 if (cur_overflow_list != BUSY) { 1588 // Do the splice ... 1589 last->set_klass_to_list_ptr(cur_overflow_list); 1590 } else { // cur_overflow_list == BUSY 1591 last->set_klass_to_list_ptr(NULL); 1592 } 1593 observed_overflow_list = 1594 (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1595 } while (cur_overflow_list != observed_overflow_list); 1596 } 1597 } 1598 1599 // Push objects on prefix list onto this thread's work queue 1600 assert(prefix != NULL && prefix != BUSY, "program logic"); 1601 cur = prefix; 1602 ssize_t n = 0; 1603 while (cur != NULL) { 1604 oop obj_to_push = cur->forwardee(); 1605 oop next = cur->list_ptr_from_klass(); 1606 cur->set_klass(obj_to_push->klass()); 1607 // This may be an array object that is self-forwarded. In that case, the list pointer 1608 // space, cur, is not in the Java heap, but rather in the C-heap and should be freed. 1609 if (!is_in_reserved(cur)) { 1610 // This can become a scaling bottleneck when there is work queue overflow coincident 1611 // with promotion failure. 1612 oopDesc* f = cur; 1613 FREE_C_HEAP_ARRAY(oopDesc, f, mtGC); 1614 } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) { 1615 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 1616 obj_to_push = cur; 1617 } 1618 bool ok = work_q->push(obj_to_push); 1619 assert(ok, "Should have succeeded"); 1620 cur = next; 1621 n++; 1622 } 1623 TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n)); 1624 #ifndef PRODUCT 1625 assert(_num_par_pushes >= n, "Too many pops?"); 1626 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes); 1627 #endif 1628 return true; 1629 } 1630 #undef BUSY 1631 1632 void ParNewGeneration::ref_processor_init() { 1633 if (_ref_processor == NULL) { 1634 // Allocate and initialize a reference processor 1635 _ref_processor = 1636 new ReferenceProcessor(_reserved, // span 1637 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing 1638 (int) ParallelGCThreads, // mt processing degree 1639 refs_discovery_is_mt(), // mt discovery 1640 (int) ParallelGCThreads, // mt discovery degree 1641 refs_discovery_is_atomic(), // atomic_discovery 1642 NULL); // is_alive_non_header 1643 } 1644 } 1645 1646 const char* ParNewGeneration::name() const { 1647 return "par new generation"; 1648 }