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_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/referencePolicy.hpp" 43 #include "memory/resourceArea.hpp" 44 #include "memory/sharedHeap.hpp" 45 #include "memory/space.hpp" 46 #include "oops/objArrayOop.hpp" 47 #include "oops/oop.inline.hpp" 48 #include "oops/oop.pcgc.inline.hpp" 49 #include "runtime/atomic.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(); 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(const 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(const 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()->flush_and_retire_stats(_gen.plab_stats()); 467 468 // Every thread has its own age table. We need to merge 469 // them all into one. 470 ageTable *local_table = par_scan_state.age_table(); 471 _gen.age_table()->merge(local_table); 472 473 // Inform old gen that we're done. 474 _next_gen.par_promote_alloc_done(i); 475 _next_gen.par_oop_since_save_marks_iterate_done(i); 476 } 477 478 if (UseConcMarkSweepGC) { 479 // We need to call this even when ResizeOldPLAB is disabled 480 // so as to avoid breaking some asserts. While we may be able 481 // to avoid this by reorganizing the code a bit, I am loathe 482 // to do that unless we find cases where ergo leads to bad 483 // performance. 484 CFLS_LAB::compute_desired_plab_size(); 485 } 486 } 487 488 ParScanClosure::ParScanClosure(ParNewGeneration* g, 489 ParScanThreadState* par_scan_state) : 490 OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g) 491 { 492 assert(_g->level() == 0, "Optimized for youngest generation"); 493 _boundary = _g->reserved().end(); 494 } 495 496 void ParScanWithBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, false); } 497 void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); } 498 499 void ParScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, false); } 500 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); } 501 502 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); } 503 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); } 504 505 void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); } 506 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); } 507 508 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g, 509 ParScanThreadState* par_scan_state) 510 : ScanWeakRefClosure(g), _par_scan_state(par_scan_state) 511 {} 512 513 void ParScanWeakRefClosure::do_oop(oop* p) { ParScanWeakRefClosure::do_oop_work(p); } 514 void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); } 515 516 #ifdef WIN32 517 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */ 518 #endif 519 520 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure( 521 ParScanThreadState* par_scan_state_, 522 ParScanWithoutBarrierClosure* to_space_closure_, 523 ParScanWithBarrierClosure* old_gen_closure_, 524 ParRootScanWithoutBarrierClosure* to_space_root_closure_, 525 ParNewGeneration* par_gen_, 526 ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_, 527 ObjToScanQueueSet* task_queues_, 528 ParallelTaskTerminator* terminator_) : 529 530 _par_scan_state(par_scan_state_), 531 _to_space_closure(to_space_closure_), 532 _old_gen_closure(old_gen_closure_), 533 _to_space_root_closure(to_space_root_closure_), 534 _old_gen_root_closure(old_gen_root_closure_), 535 _par_gen(par_gen_), 536 _task_queues(task_queues_), 537 _terminator(terminator_) 538 {} 539 540 void ParEvacuateFollowersClosure::do_void() { 541 ObjToScanQueue* work_q = par_scan_state()->work_queue(); 542 543 while (true) { 544 545 // Scan to-space and old-gen objs until we run out of both. 546 oop obj_to_scan; 547 par_scan_state()->trim_queues(0); 548 549 // We have no local work, attempt to steal from other threads. 550 551 // attempt to steal work from promoted. 552 if (task_queues()->steal(par_scan_state()->thread_num(), 553 par_scan_state()->hash_seed(), 554 obj_to_scan)) { 555 bool res = work_q->push(obj_to_scan); 556 assert(res, "Empty queue should have room for a push."); 557 558 // if successful, goto Start. 559 continue; 560 561 // try global overflow list. 562 } else if (par_gen()->take_from_overflow_list(par_scan_state())) { 563 continue; 564 } 565 566 // Otherwise, offer termination. 567 par_scan_state()->start_term_time(); 568 if (terminator()->offer_termination()) break; 569 par_scan_state()->end_term_time(); 570 } 571 assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0, 572 "Broken overflow list?"); 573 // Finish the last termination pause. 574 par_scan_state()->end_term_time(); 575 } 576 577 ParNewGenTask::ParNewGenTask(ParNewGeneration* gen, Generation* next_gen, 578 HeapWord* young_old_boundary, ParScanThreadStateSet* state_set) : 579 AbstractGangTask("ParNewGeneration collection"), 580 _gen(gen), _next_gen(next_gen), 581 _young_old_boundary(young_old_boundary), 582 _state_set(state_set) 583 {} 584 585 // Reset the terminator for the given number of 586 // active threads. 587 void ParNewGenTask::set_for_termination(int active_workers) { 588 _state_set->reset(active_workers, _gen->promotion_failed()); 589 // Should the heap be passed in? There's only 1 for now so 590 // grab it instead. 591 GenCollectedHeap* gch = GenCollectedHeap::heap(); 592 gch->set_n_termination(active_workers); 593 } 594 595 void ParNewGenTask::work(uint worker_id) { 596 GenCollectedHeap* gch = GenCollectedHeap::heap(); 597 // Since this is being done in a separate thread, need new resource 598 // and handle marks. 599 ResourceMark rm; 600 HandleMark hm; 601 // We would need multiple old-gen queues otherwise. 602 assert(gch->n_gens() == 2, "Par young collection currently only works with one older gen."); 603 604 Generation* old_gen = gch->next_gen(_gen); 605 606 ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id); 607 assert(_state_set->is_valid(worker_id), "Should not have been called"); 608 609 par_scan_state.set_young_old_boundary(_young_old_boundary); 610 611 KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(), 612 gch->rem_set()->klass_rem_set()); 613 CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure, 614 &par_scan_state.to_space_root_closure(), 615 false); 616 617 par_scan_state.start_strong_roots(); 618 gch->gen_process_roots(_gen->level(), 619 true, // Process younger gens, if any, 620 // as strong roots. 621 false, // no scope; this is parallel code 622 SharedHeap::SO_ScavengeCodeCache, 623 GenCollectedHeap::StrongAndWeakRoots, 624 &par_scan_state.to_space_root_closure(), 625 &par_scan_state.older_gen_closure(), 626 &cld_scan_closure); 627 628 par_scan_state.end_strong_roots(); 629 630 // "evacuate followers". 631 par_scan_state.evacuate_followers_closure().do_void(); 632 } 633 634 #ifdef _MSC_VER 635 #pragma warning( push ) 636 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list 637 #endif 638 ParNewGeneration:: 639 ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level) 640 : DefNewGeneration(rs, initial_byte_size, level, "PCopy"), 641 _overflow_list(NULL), 642 _is_alive_closure(this), 643 _plab_stats(YoungPLABSize, PLABWeight) 644 { 645 NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;) 646 NOT_PRODUCT(_num_par_pushes = 0;) 647 _task_queues = new ObjToScanQueueSet(ParallelGCThreads); 648 guarantee(_task_queues != NULL, "task_queues allocation failure."); 649 650 for (uint i1 = 0; i1 < ParallelGCThreads; i1++) { 651 ObjToScanQueue *q = new ObjToScanQueue(); 652 guarantee(q != NULL, "work_queue Allocation failure."); 653 _task_queues->register_queue(i1, q); 654 } 655 656 for (uint i2 = 0; i2 < ParallelGCThreads; i2++) 657 _task_queues->queue(i2)->initialize(); 658 659 _overflow_stacks = NULL; 660 if (ParGCUseLocalOverflow) { 661 662 // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal 663 // with ',' 664 typedef Stack<oop, mtGC> GCOopStack; 665 666 _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC); 667 for (size_t i = 0; i < ParallelGCThreads; ++i) { 668 new (_overflow_stacks + i) Stack<oop, mtGC>(); 669 } 670 } 671 672 if (UsePerfData) { 673 EXCEPTION_MARK; 674 ResourceMark rm; 675 676 const char* cname = 677 PerfDataManager::counter_name(_gen_counters->name_space(), "threads"); 678 PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None, 679 ParallelGCThreads, CHECK); 680 } 681 } 682 #ifdef _MSC_VER 683 #pragma warning( pop ) 684 #endif 685 686 // ParNewGeneration:: 687 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) : 688 DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {} 689 690 template <class T> 691 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) { 692 #ifdef ASSERT 693 { 694 assert(!oopDesc::is_null(*p), "expected non-null ref"); 695 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 696 // We never expect to see a null reference being processed 697 // as a weak reference. 698 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 699 } 700 #endif // ASSERT 701 702 _par_cl->do_oop_nv(p); 703 704 if (Universe::heap()->is_in_reserved(p)) { 705 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 706 _rs->write_ref_field_gc_par(p, obj); 707 } 708 } 709 710 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); } 711 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); } 712 713 // ParNewGeneration:: 714 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) : 715 DefNewGeneration::KeepAliveClosure(cl) {} 716 717 template <class T> 718 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) { 719 #ifdef ASSERT 720 { 721 assert(!oopDesc::is_null(*p), "expected non-null ref"); 722 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 723 // We never expect to see a null reference being processed 724 // as a weak reference. 725 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 726 } 727 #endif // ASSERT 728 729 _cl->do_oop_nv(p); 730 731 if (Universe::heap()->is_in_reserved(p)) { 732 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 733 _rs->write_ref_field_gc_par(p, obj); 734 } 735 } 736 737 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); } 738 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); } 739 740 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) { 741 T heap_oop = oopDesc::load_heap_oop(p); 742 if (!oopDesc::is_null(heap_oop)) { 743 oop obj = oopDesc::decode_heap_oop_not_null(heap_oop); 744 if ((HeapWord*)obj < _boundary) { 745 assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?"); 746 oop new_obj = obj->is_forwarded() 747 ? obj->forwardee() 748 : _g->DefNewGeneration::copy_to_survivor_space(obj); 749 oopDesc::encode_store_heap_oop_not_null(p, new_obj); 750 } 751 if (_gc_barrier) { 752 // If p points to a younger generation, mark the card. 753 if ((HeapWord*)obj < _gen_boundary) { 754 _rs->write_ref_field_gc_par(p, obj); 755 } 756 } 757 } 758 } 759 760 void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 761 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 762 763 class ParNewRefProcTaskProxy: public AbstractGangTask { 764 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; 765 public: 766 ParNewRefProcTaskProxy(ProcessTask& task, ParNewGeneration& gen, 767 Generation& next_gen, 768 HeapWord* young_old_boundary, 769 ParScanThreadStateSet& state_set); 770 771 private: 772 virtual void work(uint worker_id); 773 virtual void set_for_termination(int active_workers) { 774 _state_set.terminator()->reset_for_reuse(active_workers); 775 } 776 private: 777 ParNewGeneration& _gen; 778 ProcessTask& _task; 779 Generation& _next_gen; 780 HeapWord* _young_old_boundary; 781 ParScanThreadStateSet& _state_set; 782 }; 783 784 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy( 785 ProcessTask& task, ParNewGeneration& gen, 786 Generation& next_gen, 787 HeapWord* young_old_boundary, 788 ParScanThreadStateSet& state_set) 789 : AbstractGangTask("ParNewGeneration parallel reference processing"), 790 _gen(gen), 791 _task(task), 792 _next_gen(next_gen), 793 _young_old_boundary(young_old_boundary), 794 _state_set(state_set) 795 { 796 } 797 798 void ParNewRefProcTaskProxy::work(uint worker_id) 799 { 800 ResourceMark rm; 801 HandleMark hm; 802 ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id); 803 par_scan_state.set_young_old_boundary(_young_old_boundary); 804 _task.work(worker_id, par_scan_state.is_alive_closure(), 805 par_scan_state.keep_alive_closure(), 806 par_scan_state.evacuate_followers_closure()); 807 } 808 809 class ParNewRefEnqueueTaskProxy: public AbstractGangTask { 810 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; 811 EnqueueTask& _task; 812 813 public: 814 ParNewRefEnqueueTaskProxy(EnqueueTask& task) 815 : AbstractGangTask("ParNewGeneration parallel reference enqueue"), 816 _task(task) 817 { } 818 819 virtual void work(uint worker_id) 820 { 821 _task.work(worker_id); 822 } 823 }; 824 825 826 void ParNewRefProcTaskExecutor::execute(ProcessTask& task) 827 { 828 GenCollectedHeap* gch = GenCollectedHeap::heap(); 829 assert(gch->kind() == CollectedHeap::GenCollectedHeap, 830 "not a generational heap"); 831 FlexibleWorkGang* workers = gch->workers(); 832 assert(workers != NULL, "Need parallel worker threads."); 833 _state_set.reset(workers->active_workers(), _generation.promotion_failed()); 834 ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(), 835 _generation.reserved().end(), _state_set); 836 workers->run_task(&rp_task); 837 _state_set.reset(0 /* bad value in debug if not reset */, 838 _generation.promotion_failed()); 839 } 840 841 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task) 842 { 843 GenCollectedHeap* gch = GenCollectedHeap::heap(); 844 FlexibleWorkGang* workers = gch->workers(); 845 assert(workers != NULL, "Need parallel worker threads."); 846 ParNewRefEnqueueTaskProxy enq_task(task); 847 workers->run_task(&enq_task); 848 } 849 850 void ParNewRefProcTaskExecutor::set_single_threaded_mode() 851 { 852 _state_set.flush(); 853 GenCollectedHeap* gch = GenCollectedHeap::heap(); 854 gch->set_par_threads(0); // 0 ==> non-parallel. 855 gch->save_marks(); 856 } 857 858 ScanClosureWithParBarrier:: 859 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) : 860 ScanClosure(g, gc_barrier) {} 861 862 EvacuateFollowersClosureGeneral:: 863 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, int level, 864 OopsInGenClosure* cur, 865 OopsInGenClosure* older) : 866 _gch(gch), _level(level), 867 _scan_cur_or_nonheap(cur), _scan_older(older) 868 {} 869 870 void EvacuateFollowersClosureGeneral::do_void() { 871 do { 872 // Beware: this call will lead to closure applications via virtual 873 // calls. 874 _gch->oop_since_save_marks_iterate(_level, 875 _scan_cur_or_nonheap, 876 _scan_older); 877 } while (!_gch->no_allocs_since_save_marks(_level)); 878 } 879 880 881 // A Generation that does parallel young-gen collection. 882 883 void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set) { 884 assert(_promo_failure_scan_stack.is_empty(), "post condition"); 885 _promo_failure_scan_stack.clear(true); // Clear cached segments. 886 887 remove_forwarding_pointers(); 888 if (PrintGCDetails) { 889 gclog_or_tty->print(" (promotion failed)"); 890 } 891 // All the spaces are in play for mark-sweep. 892 swap_spaces(); // Make life simpler for CMS || rescan; see 6483690. 893 from()->set_next_compaction_space(to()); 894 gch->set_incremental_collection_failed(); 895 // Inform the next generation that a promotion failure occurred. 896 _next_gen->promotion_failure_occurred(); 897 898 // Trace promotion failure in the parallel GC threads 899 thread_state_set.trace_promotion_failed(gc_tracer()); 900 // Single threaded code may have reported promotion failure to the global state 901 if (_promotion_failed_info.has_failed()) { 902 _gc_tracer.report_promotion_failed(_promotion_failed_info); 903 } 904 // Reset the PromotionFailureALot counters. 905 NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();) 906 } 907 908 void ParNewGeneration::collect(bool full, 909 bool clear_all_soft_refs, 910 size_t size, 911 bool is_tlab) { 912 assert(full || size > 0, "otherwise we don't want to collect"); 913 914 GenCollectedHeap* gch = GenCollectedHeap::heap(); 915 916 _gc_timer->register_gc_start(); 917 918 assert(gch->kind() == CollectedHeap::GenCollectedHeap, 919 "not a CMS generational heap"); 920 AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy(); 921 FlexibleWorkGang* workers = gch->workers(); 922 assert(workers != NULL, "Need workgang for parallel work"); 923 int active_workers = 924 AdaptiveSizePolicy::calc_active_workers(workers->total_workers(), 925 workers->active_workers(), 926 Threads::number_of_non_daemon_threads()); 927 workers->set_active_workers(active_workers); 928 assert(gch->n_gens() == 2, 929 "Par collection currently only works with single older gen."); 930 _next_gen = gch->next_gen(this); 931 932 // If the next generation is too full to accommodate worst-case promotion 933 // from this generation, pass on collection; let the next generation 934 // do it. 935 if (!collection_attempt_is_safe()) { 936 gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one 937 return; 938 } 939 assert(to()->is_empty(), "Else not collection_attempt_is_safe"); 940 941 _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start()); 942 gch->trace_heap_before_gc(gc_tracer()); 943 944 init_assuming_no_promotion_failure(); 945 946 if (UseAdaptiveSizePolicy) { 947 set_survivor_overflow(false); 948 size_policy->minor_collection_begin(); 949 } 950 951 GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, _gc_tracer.gc_id()); 952 // Capture heap used before collection (for printing). 953 size_t gch_prev_used = gch->used(); 954 955 SpecializationStats::clear(); 956 957 age_table()->clear(); 958 to()->clear(SpaceDecorator::Mangle); 959 960 gch->save_marks(); 961 assert(workers != NULL, "Need parallel worker threads."); 962 int n_workers = active_workers; 963 964 // Set the correct parallelism (number of queues) in the reference processor 965 ref_processor()->set_active_mt_degree(n_workers); 966 967 // Always set the terminator for the active number of workers 968 // because only those workers go through the termination protocol. 969 ParallelTaskTerminator _term(n_workers, task_queues()); 970 ParScanThreadStateSet thread_state_set(workers->active_workers(), 971 *to(), *this, *_next_gen, *task_queues(), 972 _overflow_stacks, desired_plab_sz(), _term); 973 974 ParNewGenTask tsk(this, _next_gen, reserved().end(), &thread_state_set); 975 gch->set_par_threads(n_workers); 976 gch->rem_set()->prepare_for_younger_refs_iterate(true); 977 // It turns out that even when we're using 1 thread, doing the work in a 978 // separate thread causes wide variance in run times. We can't help this 979 // in the multi-threaded case, but we special-case n=1 here to get 980 // repeatable measurements of the 1-thread overhead of the parallel code. 981 if (n_workers > 1) { 982 GenCollectedHeap::StrongRootsScope srs(gch); 983 workers->run_task(&tsk); 984 } else { 985 GenCollectedHeap::StrongRootsScope srs(gch); 986 tsk.work(0); 987 } 988 thread_state_set.reset(0 /* Bad value in debug if not reset */, 989 promotion_failed()); 990 991 // Trace and reset failed promotion info. 992 if (promotion_failed()) { 993 thread_state_set.trace_promotion_failed(gc_tracer()); 994 } 995 996 // Process (weak) reference objects found during scavenge. 997 ReferenceProcessor* rp = ref_processor(); 998 IsAliveClosure is_alive(this); 999 ScanWeakRefClosure scan_weak_ref(this); 1000 KeepAliveClosure keep_alive(&scan_weak_ref); 1001 ScanClosure scan_without_gc_barrier(this, false); 1002 ScanClosureWithParBarrier scan_with_gc_barrier(this, true); 1003 set_promo_failure_scan_stack_closure(&scan_without_gc_barrier); 1004 EvacuateFollowersClosureGeneral evacuate_followers(gch, _level, 1005 &scan_without_gc_barrier, &scan_with_gc_barrier); 1006 rp->setup_policy(clear_all_soft_refs); 1007 // Can the mt_degree be set later (at run_task() time would be best)? 1008 rp->set_active_mt_degree(active_workers); 1009 ReferenceProcessorStats stats; 1010 if (rp->processing_is_mt()) { 1011 ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); 1012 stats = rp->process_discovered_references(&is_alive, &keep_alive, 1013 &evacuate_followers, &task_executor, 1014 _gc_timer, _gc_tracer.gc_id()); 1015 } else { 1016 thread_state_set.flush(); 1017 gch->set_par_threads(0); // 0 ==> non-parallel. 1018 gch->save_marks(); 1019 stats = rp->process_discovered_references(&is_alive, &keep_alive, 1020 &evacuate_followers, NULL, 1021 _gc_timer, _gc_tracer.gc_id()); 1022 } 1023 _gc_tracer.report_gc_reference_stats(stats); 1024 if (!promotion_failed()) { 1025 // Swap the survivor spaces. 1026 eden()->clear(SpaceDecorator::Mangle); 1027 from()->clear(SpaceDecorator::Mangle); 1028 if (ZapUnusedHeapArea) { 1029 // This is now done here because of the piece-meal mangling which 1030 // can check for valid mangling at intermediate points in the 1031 // collection(s). When a minor collection fails to collect 1032 // sufficient space resizing of the young generation can occur 1033 // an redistribute the spaces in the young generation. Mangle 1034 // here so that unzapped regions don't get distributed to 1035 // other spaces. 1036 to()->mangle_unused_area(); 1037 } 1038 swap_spaces(); 1039 1040 // A successful scavenge should restart the GC time limit count which is 1041 // for full GC's. 1042 size_policy->reset_gc_overhead_limit_count(); 1043 1044 assert(to()->is_empty(), "to space should be empty now"); 1045 1046 adjust_desired_tenuring_threshold(); 1047 } else { 1048 handle_promotion_failed(gch, thread_state_set); 1049 } 1050 // set new iteration safe limit for the survivor spaces 1051 from()->set_concurrent_iteration_safe_limit(from()->top()); 1052 to()->set_concurrent_iteration_safe_limit(to()->top()); 1053 1054 if (ResizePLAB) { 1055 plab_stats()->adjust_desired_plab_sz(n_workers); 1056 } 1057 1058 if (PrintGC && !PrintGCDetails) { 1059 gch->print_heap_change(gch_prev_used); 1060 } 1061 1062 TASKQUEUE_STATS_ONLY(if (PrintTerminationStats) thread_state_set.print_termination_stats()); 1063 TASKQUEUE_STATS_ONLY(if (PrintTaskqueue) thread_state_set.print_taskqueue_stats()); 1064 1065 if (UseAdaptiveSizePolicy) { 1066 size_policy->minor_collection_end(gch->gc_cause()); 1067 size_policy->avg_survived()->sample(from()->used()); 1068 } 1069 1070 // We need to use a monotonically non-decreasing time in ms 1071 // or we will see time-warp warnings and os::javaTimeMillis() 1072 // does not guarantee monotonicity. 1073 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 1074 update_time_of_last_gc(now); 1075 1076 SpecializationStats::print(); 1077 1078 rp->set_enqueuing_is_done(true); 1079 if (rp->processing_is_mt()) { 1080 ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); 1081 rp->enqueue_discovered_references(&task_executor); 1082 } else { 1083 rp->enqueue_discovered_references(NULL); 1084 } 1085 rp->verify_no_references_recorded(); 1086 1087 gch->trace_heap_after_gc(gc_tracer()); 1088 _gc_tracer.report_tenuring_threshold(tenuring_threshold()); 1089 1090 _gc_timer->register_gc_end(); 1091 1092 _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions()); 1093 } 1094 1095 static int sum; 1096 void ParNewGeneration::waste_some_time() { 1097 for (int i = 0; i < 100; i++) { 1098 sum += i; 1099 } 1100 } 1101 1102 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4); 1103 1104 // Because of concurrency, there are times where an object for which 1105 // "is_forwarded()" is true contains an "interim" forwarding pointer 1106 // value. Such a value will soon be overwritten with a real value. 1107 // This method requires "obj" to have a forwarding pointer, and waits, if 1108 // necessary for a real one to be inserted, and returns it. 1109 1110 oop ParNewGeneration::real_forwardee(oop obj) { 1111 oop forward_ptr = obj->forwardee(); 1112 if (forward_ptr != ClaimedForwardPtr) { 1113 return forward_ptr; 1114 } else { 1115 return real_forwardee_slow(obj); 1116 } 1117 } 1118 1119 oop ParNewGeneration::real_forwardee_slow(oop obj) { 1120 // Spin-read if it is claimed but not yet written by another thread. 1121 oop forward_ptr = obj->forwardee(); 1122 while (forward_ptr == ClaimedForwardPtr) { 1123 waste_some_time(); 1124 assert(obj->is_forwarded(), "precondition"); 1125 forward_ptr = obj->forwardee(); 1126 } 1127 return forward_ptr; 1128 } 1129 1130 #ifdef ASSERT 1131 bool ParNewGeneration::is_legal_forward_ptr(oop p) { 1132 return 1133 (p == ClaimedForwardPtr) 1134 || Universe::heap()->is_in_reserved(p); 1135 } 1136 #endif 1137 1138 void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) { 1139 if (m->must_be_preserved_for_promotion_failure(obj)) { 1140 // We should really have separate per-worker stacks, rather 1141 // than use locking of a common pair of stacks. 1142 MutexLocker ml(ParGCRareEvent_lock); 1143 preserve_mark(obj, m); 1144 } 1145 } 1146 1147 // Multiple GC threads may try to promote an object. If the object 1148 // is successfully promoted, a forwarding pointer will be installed in 1149 // the object in the young generation. This method claims the right 1150 // to install the forwarding pointer before it copies the object, 1151 // thus avoiding the need to undo the copy as in 1152 // copy_to_survivor_space_avoiding_with_undo. 1153 1154 oop ParNewGeneration::copy_to_survivor_space( 1155 ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) { 1156 // In the sequential version, this assert also says that the object is 1157 // not forwarded. That might not be the case here. It is the case that 1158 // the caller observed it to be not forwarded at some time in the past. 1159 assert(is_in_reserved(old), "shouldn't be scavenging this oop"); 1160 1161 // The sequential code read "old->age()" below. That doesn't work here, 1162 // since the age is in the mark word, and that might be overwritten with 1163 // a forwarding pointer by a parallel thread. So we must save the mark 1164 // word in a local and then analyze it. 1165 oopDesc dummyOld; 1166 dummyOld.set_mark(m); 1167 assert(!dummyOld.is_forwarded(), 1168 "should not be called with forwarding pointer mark word."); 1169 1170 oop new_obj = NULL; 1171 oop forward_ptr; 1172 1173 // Try allocating obj in to-space (unless too old) 1174 if (dummyOld.age() < tenuring_threshold()) { 1175 new_obj = (oop)par_scan_state->alloc_in_to_space(sz); 1176 if (new_obj == NULL) { 1177 set_survivor_overflow(true); 1178 } 1179 } 1180 1181 if (new_obj == NULL) { 1182 // Either to-space is full or we decided to promote 1183 // try allocating obj tenured 1184 1185 // Attempt to install a null forwarding pointer (atomically), 1186 // to claim the right to install the real forwarding pointer. 1187 forward_ptr = old->forward_to_atomic(ClaimedForwardPtr); 1188 if (forward_ptr != NULL) { 1189 // someone else beat us to it. 1190 return real_forwardee(old); 1191 } 1192 1193 if (!_promotion_failed) { 1194 new_obj = _next_gen->par_promote(par_scan_state->thread_num(), 1195 old, m, sz); 1196 } 1197 1198 if (new_obj == NULL) { 1199 // promotion failed, forward to self 1200 _promotion_failed = true; 1201 new_obj = old; 1202 1203 preserve_mark_if_necessary(old, m); 1204 par_scan_state->register_promotion_failure(sz); 1205 } 1206 1207 old->forward_to(new_obj); 1208 forward_ptr = NULL; 1209 } else { 1210 // Is in to-space; do copying ourselves. 1211 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz); 1212 forward_ptr = old->forward_to_atomic(new_obj); 1213 // Restore the mark word copied above. 1214 new_obj->set_mark(m); 1215 // Increment age if obj still in new generation 1216 new_obj->incr_age(); 1217 par_scan_state->age_table()->add(new_obj, sz); 1218 } 1219 assert(new_obj != NULL, "just checking"); 1220 1221 #ifndef PRODUCT 1222 // This code must come after the CAS test, or it will print incorrect 1223 // information. 1224 if (TraceScavenge) { 1225 gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}", 1226 is_in_reserved(new_obj) ? "copying" : "tenuring", 1227 new_obj->klass()->internal_name(), (void *)old, (void *)new_obj, new_obj->size()); 1228 } 1229 #endif 1230 1231 if (forward_ptr == NULL) { 1232 oop obj_to_push = new_obj; 1233 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) { 1234 // Length field used as index of next element to be scanned. 1235 // Real length can be obtained from real_forwardee() 1236 arrayOop(old)->set_length(0); 1237 obj_to_push = old; 1238 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push, 1239 "push forwarded object"); 1240 } 1241 // Push it on one of the queues of to-be-scanned objects. 1242 bool simulate_overflow = false; 1243 NOT_PRODUCT( 1244 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) { 1245 // simulate a stack overflow 1246 simulate_overflow = true; 1247 } 1248 ) 1249 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) { 1250 // Add stats for overflow pushes. 1251 if (Verbose && PrintGCDetails) { 1252 gclog_or_tty->print("queue overflow!\n"); 1253 } 1254 push_on_overflow_list(old, par_scan_state); 1255 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0)); 1256 } 1257 1258 return new_obj; 1259 } 1260 1261 // Oops. Someone beat us to it. Undo the allocation. Where did we 1262 // allocate it? 1263 if (is_in_reserved(new_obj)) { 1264 // Must be in to_space. 1265 assert(to()->is_in_reserved(new_obj), "Checking"); 1266 if (forward_ptr == ClaimedForwardPtr) { 1267 // Wait to get the real forwarding pointer value. 1268 forward_ptr = real_forwardee(old); 1269 } 1270 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz); 1271 } 1272 1273 return forward_ptr; 1274 } 1275 1276 #ifndef PRODUCT 1277 // It's OK to call this multi-threaded; the worst thing 1278 // that can happen is that we'll get a bunch of closely 1279 // spaced simulated overflows, but that's OK, in fact 1280 // probably good as it would exercise the overflow code 1281 // under contention. 1282 bool ParNewGeneration::should_simulate_overflow() { 1283 if (_overflow_counter-- <= 0) { // just being defensive 1284 _overflow_counter = ParGCWorkQueueOverflowInterval; 1285 return true; 1286 } else { 1287 return false; 1288 } 1289 } 1290 #endif 1291 1292 // In case we are using compressed oops, we need to be careful. 1293 // If the object being pushed is an object array, then its length 1294 // field keeps track of the "grey boundary" at which the next 1295 // incremental scan will be done (see ParGCArrayScanChunk). 1296 // When using compressed oops, this length field is kept in the 1297 // lower 32 bits of the erstwhile klass word and cannot be used 1298 // for the overflow chaining pointer (OCP below). As such the OCP 1299 // would itself need to be compressed into the top 32-bits in this 1300 // case. Unfortunately, see below, in the event that we have a 1301 // promotion failure, the node to be pushed on the list can be 1302 // outside of the Java heap, so the heap-based pointer compression 1303 // would not work (we would have potential aliasing between C-heap 1304 // and Java-heap pointers). For this reason, when using compressed 1305 // oops, we simply use a worker-thread-local, non-shared overflow 1306 // list in the form of a growable array, with a slightly different 1307 // overflow stack draining strategy. If/when we start using fat 1308 // stacks here, we can go back to using (fat) pointer chains 1309 // (although some performance comparisons would be useful since 1310 // single global lists have their own performance disadvantages 1311 // as we were made painfully aware not long ago, see 6786503). 1312 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff)) 1313 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) { 1314 assert(is_in_reserved(from_space_obj), "Should be from this generation"); 1315 if (ParGCUseLocalOverflow) { 1316 // In the case of compressed oops, we use a private, not-shared 1317 // overflow stack. 1318 par_scan_state->push_on_overflow_stack(from_space_obj); 1319 } else { 1320 assert(!UseCompressedOops, "Error"); 1321 // if the object has been forwarded to itself, then we cannot 1322 // use the klass pointer for the linked list. Instead we have 1323 // to allocate an oopDesc in the C-Heap and use that for the linked list. 1324 // XXX This is horribly inefficient when a promotion failure occurs 1325 // and should be fixed. XXX FIX ME !!! 1326 #ifndef PRODUCT 1327 Atomic::inc_ptr(&_num_par_pushes); 1328 assert(_num_par_pushes > 0, "Tautology"); 1329 #endif 1330 if (from_space_obj->forwardee() == from_space_obj) { 1331 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC); 1332 listhead->forward_to(from_space_obj); 1333 from_space_obj = listhead; 1334 } 1335 oop observed_overflow_list = _overflow_list; 1336 oop cur_overflow_list; 1337 do { 1338 cur_overflow_list = observed_overflow_list; 1339 if (cur_overflow_list != BUSY) { 1340 from_space_obj->set_klass_to_list_ptr(cur_overflow_list); 1341 } else { 1342 from_space_obj->set_klass_to_list_ptr(NULL); 1343 } 1344 observed_overflow_list = 1345 (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list); 1346 } while (cur_overflow_list != observed_overflow_list); 1347 } 1348 } 1349 1350 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) { 1351 bool res; 1352 1353 if (ParGCUseLocalOverflow) { 1354 res = par_scan_state->take_from_overflow_stack(); 1355 } else { 1356 assert(!UseCompressedOops, "Error"); 1357 res = take_from_overflow_list_work(par_scan_state); 1358 } 1359 return res; 1360 } 1361 1362 1363 // *NOTE*: The overflow list manipulation code here and 1364 // in CMSCollector:: are very similar in shape, 1365 // except that in the CMS case we thread the objects 1366 // directly into the list via their mark word, and do 1367 // not need to deal with special cases below related 1368 // to chunking of object arrays and promotion failure 1369 // handling. 1370 // CR 6797058 has been filed to attempt consolidation of 1371 // the common code. 1372 // Because of the common code, if you make any changes in 1373 // the code below, please check the CMS version to see if 1374 // similar changes might be needed. 1375 // See CMSCollector::par_take_from_overflow_list() for 1376 // more extensive documentation comments. 1377 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) { 1378 ObjToScanQueue* work_q = par_scan_state->work_queue(); 1379 // How many to take? 1380 size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 1381 (size_t)ParGCDesiredObjsFromOverflowList); 1382 1383 assert(!UseCompressedOops, "Error"); 1384 assert(par_scan_state->overflow_stack() == NULL, "Error"); 1385 if (_overflow_list == NULL) return false; 1386 1387 // Otherwise, there was something there; try claiming the list. 1388 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1389 // Trim off a prefix of at most objsFromOverflow items 1390 Thread* tid = Thread::current(); 1391 size_t spin_count = (size_t)ParallelGCThreads; 1392 size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100); 1393 for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) { 1394 // someone grabbed it before we did ... 1395 // ... we spin for a short while... 1396 os::sleep(tid, sleep_time_millis, false); 1397 if (_overflow_list == NULL) { 1398 // nothing left to take 1399 return false; 1400 } else if (_overflow_list != BUSY) { 1401 // try and grab the prefix 1402 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1403 } 1404 } 1405 if (prefix == NULL || prefix == BUSY) { 1406 // Nothing to take or waited long enough 1407 if (prefix == NULL) { 1408 // Write back the NULL in case we overwrote it with BUSY above 1409 // and it is still the same value. 1410 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1411 } 1412 return false; 1413 } 1414 assert(prefix != NULL && prefix != BUSY, "Error"); 1415 size_t i = 1; 1416 oop cur = prefix; 1417 while (i < objsFromOverflow && cur->klass_or_null() != NULL) { 1418 i++; cur = cur->list_ptr_from_klass(); 1419 } 1420 1421 // Reattach remaining (suffix) to overflow list 1422 if (cur->klass_or_null() == NULL) { 1423 // Write back the NULL in lieu of the BUSY we wrote 1424 // above and it is still the same value. 1425 if (_overflow_list == BUSY) { 1426 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1427 } 1428 } else { 1429 assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error"); 1430 oop suffix = cur->list_ptr_from_klass(); // suffix will be put back on global list 1431 cur->set_klass_to_list_ptr(NULL); // break off suffix 1432 // It's possible that the list is still in the empty(busy) state 1433 // we left it in a short while ago; in that case we may be 1434 // able to place back the suffix. 1435 oop observed_overflow_list = _overflow_list; 1436 oop cur_overflow_list = observed_overflow_list; 1437 bool attached = false; 1438 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { 1439 observed_overflow_list = 1440 (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1441 if (cur_overflow_list == observed_overflow_list) { 1442 attached = true; 1443 break; 1444 } else cur_overflow_list = observed_overflow_list; 1445 } 1446 if (!attached) { 1447 // Too bad, someone else got in in between; we'll need to do a splice. 1448 // Find the last item of suffix list 1449 oop last = suffix; 1450 while (last->klass_or_null() != NULL) { 1451 last = last->list_ptr_from_klass(); 1452 } 1453 // Atomically prepend suffix to current overflow list 1454 observed_overflow_list = _overflow_list; 1455 do { 1456 cur_overflow_list = observed_overflow_list; 1457 if (cur_overflow_list != BUSY) { 1458 // Do the splice ... 1459 last->set_klass_to_list_ptr(cur_overflow_list); 1460 } else { // cur_overflow_list == BUSY 1461 last->set_klass_to_list_ptr(NULL); 1462 } 1463 observed_overflow_list = 1464 (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1465 } while (cur_overflow_list != observed_overflow_list); 1466 } 1467 } 1468 1469 // Push objects on prefix list onto this thread's work queue 1470 assert(prefix != NULL && prefix != BUSY, "program logic"); 1471 cur = prefix; 1472 ssize_t n = 0; 1473 while (cur != NULL) { 1474 oop obj_to_push = cur->forwardee(); 1475 oop next = cur->list_ptr_from_klass(); 1476 cur->set_klass(obj_to_push->klass()); 1477 // This may be an array object that is self-forwarded. In that case, the list pointer 1478 // space, cur, is not in the Java heap, but rather in the C-heap and should be freed. 1479 if (!is_in_reserved(cur)) { 1480 // This can become a scaling bottleneck when there is work queue overflow coincident 1481 // with promotion failure. 1482 oopDesc* f = cur; 1483 FREE_C_HEAP_ARRAY(oopDesc, f); 1484 } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) { 1485 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 1486 obj_to_push = cur; 1487 } 1488 bool ok = work_q->push(obj_to_push); 1489 assert(ok, "Should have succeeded"); 1490 cur = next; 1491 n++; 1492 } 1493 TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n)); 1494 #ifndef PRODUCT 1495 assert(_num_par_pushes >= n, "Too many pops?"); 1496 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes); 1497 #endif 1498 return true; 1499 } 1500 #undef BUSY 1501 1502 void ParNewGeneration::ref_processor_init() { 1503 if (_ref_processor == NULL) { 1504 // Allocate and initialize a reference processor 1505 _ref_processor = 1506 new ReferenceProcessor(_reserved, // span 1507 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing 1508 (int) ParallelGCThreads, // mt processing degree 1509 refs_discovery_is_mt(), // mt discovery 1510 (int) ParallelGCThreads, // mt discovery degree 1511 refs_discovery_is_atomic(), // atomic_discovery 1512 NULL); // is_alive_non_header 1513 } 1514 } 1515 1516 const char* ParNewGeneration::name() const { 1517 return "par new generation"; 1518 }