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/compactibleFreeListSpace.hpp" 27 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp" 28 #include "gc_implementation/parNew/parNewGeneration.hpp" 29 #include "gc_implementation/parNew/parOopClosures.inline.hpp" 30 #include "gc_implementation/shared/adaptiveSizePolicy.hpp" 31 #include "gc_implementation/shared/ageTable.hpp" 32 #include "gc_implementation/shared/copyFailedInfo.hpp" 33 #include "gc_implementation/shared/gcHeapSummary.hpp" 34 #include "gc_implementation/shared/gcTimer.hpp" 35 #include "gc_implementation/shared/gcTrace.hpp" 36 #include "gc_implementation/shared/gcTraceTime.hpp" 37 #include "gc_implementation/shared/parGCAllocBuffer.inline.hpp" 38 #include "gc_implementation/shared/spaceDecorator.hpp" 39 #include "memory/defNewGeneration.inline.hpp" 40 #include "memory/genCollectedHeap.hpp" 41 #include "memory/genOopClosures.inline.hpp" 42 #include "memory/generation.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 "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 #ifdef _MSC_VER 59 #pragma warning( push ) 60 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list 61 #endif 62 ParScanThreadState::ParScanThreadState(Space* to_space_, 63 ParNewGeneration* gen_, 64 Generation* old_gen_, 65 int thread_num_, 66 ObjToScanQueueSet* work_queue_set_, 67 Stack<oop, mtGC>* overflow_stacks_, 68 size_t desired_plab_sz_, 69 ParallelTaskTerminator& term_) : 70 _to_space(to_space_), _old_gen(old_gen_), _young_gen(gen_), _thread_num(thread_num_), 71 _work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false), 72 _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL), 73 _ageTable(false), // false ==> not the global age table, no perf data. 74 _to_space_alloc_buffer(desired_plab_sz_), 75 _to_space_closure(gen_, this), _old_gen_closure(gen_, this), 76 _to_space_root_closure(gen_, this), _old_gen_root_closure(gen_, this), 77 _older_gen_closure(gen_, this), 78 _evacuate_followers(this, &_to_space_closure, &_old_gen_closure, 79 &_to_space_root_closure, gen_, &_old_gen_root_closure, 80 work_queue_set_, &term_), 81 _is_alive_closure(gen_), _scan_weak_ref_closure(gen_, this), 82 _keep_alive_closure(&_scan_weak_ref_closure), 83 _strong_roots_time(0.0), _term_time(0.0) 84 { 85 #if TASKQUEUE_STATS 86 _term_attempts = 0; 87 _overflow_refills = 0; 88 _overflow_refill_objs = 0; 89 #endif // TASKQUEUE_STATS 90 91 _survivor_chunk_array = 92 (ChunkArray*) old_gen()->get_data_recorder(thread_num()); 93 _hash_seed = 17; // Might want to take time-based random value. 94 _start = os::elapsedTime(); 95 _old_gen_closure.set_generation(old_gen_); 96 _old_gen_root_closure.set_generation(old_gen_); 97 } 98 #ifdef _MSC_VER 99 #pragma warning( pop ) 100 #endif 101 102 void ParScanThreadState::record_survivor_plab(HeapWord* plab_start, 103 size_t plab_word_size) { 104 ChunkArray* sca = survivor_chunk_array(); 105 if (sca != NULL) { 106 // A non-null SCA implies that we want the PLAB data recorded. 107 sca->record_sample(plab_start, plab_word_size); 108 } 109 } 110 111 bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const { 112 return new_obj->is_objArray() && 113 arrayOop(new_obj)->length() > ParGCArrayScanChunk && 114 new_obj != old_obj; 115 } 116 117 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) { 118 assert(old->is_objArray(), "must be obj array"); 119 assert(old->is_forwarded(), "must be forwarded"); 120 assert(Universe::heap()->is_in_reserved(old), "must be in heap."); 121 assert(!old_gen()->is_in(old), "must be in young generation."); 122 123 objArrayOop obj = objArrayOop(old->forwardee()); 124 // Process ParGCArrayScanChunk elements now 125 // and push the remainder back onto queue 126 int start = arrayOop(old)->length(); 127 int end = obj->length(); 128 int remainder = end - start; 129 assert(start <= end, "just checking"); 130 if (remainder > 2 * ParGCArrayScanChunk) { 131 // Test above combines last partial chunk with a full chunk 132 end = start + ParGCArrayScanChunk; 133 arrayOop(old)->set_length(end); 134 // Push remainder. 135 bool ok = work_queue()->push(old); 136 assert(ok, "just popped, push must be okay"); 137 } else { 138 // Restore length so that it can be used if there 139 // is a promotion failure and forwarding pointers 140 // must be removed. 141 arrayOop(old)->set_length(end); 142 } 143 144 // process our set of indices (include header in first chunk) 145 // should make sure end is even (aligned to HeapWord in case of compressed oops) 146 if ((HeapWord *)obj < young_old_boundary()) { 147 // object is in to_space 148 obj->oop_iterate_range(&_to_space_closure, start, end); 149 } else { 150 // object is in old generation 151 obj->oop_iterate_range(&_old_gen_closure, start, end); 152 } 153 } 154 155 156 void ParScanThreadState::trim_queues(int max_size) { 157 ObjToScanQueue* queue = work_queue(); 158 do { 159 while (queue->size() > (juint)max_size) { 160 oop obj_to_scan; 161 if (queue->pop_local(obj_to_scan)) { 162 if ((HeapWord *)obj_to_scan < young_old_boundary()) { 163 if (obj_to_scan->is_objArray() && 164 obj_to_scan->is_forwarded() && 165 obj_to_scan->forwardee() != obj_to_scan) { 166 scan_partial_array_and_push_remainder(obj_to_scan); 167 } else { 168 // object is in to_space 169 obj_to_scan->oop_iterate(&_to_space_closure); 170 } 171 } else { 172 // object is in old generation 173 obj_to_scan->oop_iterate(&_old_gen_closure); 174 } 175 } 176 } 177 // For the case of compressed oops, we have a private, non-shared 178 // overflow stack, so we eagerly drain it so as to more evenly 179 // distribute load early. Note: this may be good to do in 180 // general rather than delay for the final stealing phase. 181 // If applicable, we'll transfer a set of objects over to our 182 // work queue, allowing them to be stolen and draining our 183 // private overflow stack. 184 } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this)); 185 } 186 187 bool ParScanThreadState::take_from_overflow_stack() { 188 assert(ParGCUseLocalOverflow, "Else should not call"); 189 assert(young_gen()->overflow_list() == NULL, "Error"); 190 ObjToScanQueue* queue = work_queue(); 191 Stack<oop, mtGC>* const of_stack = overflow_stack(); 192 const size_t num_overflow_elems = of_stack->size(); 193 const size_t space_available = queue->max_elems() - queue->size(); 194 const size_t num_take_elems = MIN3(space_available / 4, 195 ParGCDesiredObjsFromOverflowList, 196 num_overflow_elems); 197 // Transfer the most recent num_take_elems from the overflow 198 // stack to our work queue. 199 for (size_t i = 0; i != num_take_elems; i++) { 200 oop cur = of_stack->pop(); 201 oop obj_to_push = cur->forwardee(); 202 assert(Universe::heap()->is_in_reserved(cur), "Should be in heap"); 203 assert(!old_gen()->is_in_reserved(cur), "Should be in young gen"); 204 assert(Universe::heap()->is_in_reserved(obj_to_push), "Should be in heap"); 205 if (should_be_partially_scanned(obj_to_push, cur)) { 206 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 207 obj_to_push = cur; 208 } 209 bool ok = queue->push(obj_to_push); 210 assert(ok, "Should have succeeded"); 211 } 212 assert(young_gen()->overflow_list() == NULL, "Error"); 213 return num_take_elems > 0; // was something transferred? 214 } 215 216 void ParScanThreadState::push_on_overflow_stack(oop p) { 217 assert(ParGCUseLocalOverflow, "Else should not call"); 218 overflow_stack()->push(p); 219 assert(young_gen()->overflow_list() == NULL, "Error"); 220 } 221 222 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) { 223 224 // Otherwise, if the object is small enough, try to reallocate the 225 // buffer. 226 HeapWord* obj = NULL; 227 if (!_to_space_full) { 228 ParGCAllocBuffer* const plab = to_space_alloc_buffer(); 229 Space* const sp = to_space(); 230 if (word_sz * 100 < 231 ParallelGCBufferWastePct * plab->word_sz()) { 232 // Is small enough; abandon this buffer and start a new one. 233 plab->retire(); 234 size_t buf_size = plab->word_sz(); 235 HeapWord* buf_space = sp->par_allocate(buf_size); 236 if (buf_space == NULL) { 237 const size_t min_bytes = 238 ParGCAllocBuffer::min_size() << LogHeapWordSize; 239 size_t free_bytes = sp->free(); 240 while(buf_space == NULL && free_bytes >= min_bytes) { 241 buf_size = free_bytes >> LogHeapWordSize; 242 assert(buf_size == (size_t)align_object_size(buf_size), 243 "Invariant"); 244 buf_space = sp->par_allocate(buf_size); 245 free_bytes = sp->free(); 246 } 247 } 248 if (buf_space != NULL) { 249 plab->set_word_size(buf_size); 250 plab->set_buf(buf_space); 251 record_survivor_plab(buf_space, buf_size); 252 obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes); 253 // Note that we cannot compare buf_size < word_sz below 254 // because of AlignmentReserve (see ParGCAllocBuffer::allocate()). 255 assert(obj != NULL || plab->words_remaining() < word_sz, 256 "Else should have been able to allocate"); 257 // It's conceivable that we may be able to use the 258 // buffer we just grabbed for subsequent small requests 259 // even if not for this one. 260 } else { 261 // We're used up. 262 _to_space_full = true; 263 } 264 265 } else { 266 // Too large; allocate the object individually. 267 obj = sp->par_allocate(word_sz); 268 } 269 } 270 return obj; 271 } 272 273 274 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, 275 size_t word_sz) { 276 // Is the alloc in the current alloc buffer? 277 if (to_space_alloc_buffer()->contains(obj)) { 278 assert(to_space_alloc_buffer()->contains(obj + word_sz - 1), 279 "Should contain whole object."); 280 to_space_alloc_buffer()->undo_allocation(obj, word_sz); 281 } else { 282 CollectedHeap::fill_with_object(obj, word_sz); 283 } 284 } 285 286 void ParScanThreadState::print_promotion_failure_size() { 287 if (_promotion_failed_info.has_failed() && PrintPromotionFailure) { 288 gclog_or_tty->print(" (%d: promotion failure size = " SIZE_FORMAT ") ", 289 _thread_num, _promotion_failed_info.first_size()); 290 } 291 } 292 293 class ParScanThreadStateSet: private ResourceArray { 294 public: 295 // Initializes states for the specified number of threads; 296 ParScanThreadStateSet(int num_threads, 297 Space& to_space, 298 ParNewGeneration& gen, 299 Generation& old_gen, 300 ObjToScanQueueSet& queue_set, 301 Stack<oop, mtGC>* overflow_stacks_, 302 size_t desired_plab_sz, 303 ParallelTaskTerminator& term); 304 305 ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); } 306 307 inline ParScanThreadState& thread_state(int i); 308 309 void trace_promotion_failed(const YoungGCTracer* gc_tracer); 310 void reset(int active_workers, bool promotion_failed); 311 void flush(); 312 313 #if TASKQUEUE_STATS 314 static void 315 print_termination_stats_hdr(outputStream* const st = gclog_or_tty); 316 void print_termination_stats(outputStream* const st = gclog_or_tty); 317 static void 318 print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty); 319 void print_taskqueue_stats(outputStream* const st = gclog_or_tty); 320 void reset_stats(); 321 #endif // TASKQUEUE_STATS 322 323 private: 324 ParallelTaskTerminator& _term; 325 ParNewGeneration& _gen; 326 Generation& _old_gen; 327 public: 328 bool is_valid(int id) const { return id < length(); } 329 ParallelTaskTerminator* terminator() { return &_term; } 330 }; 331 332 333 ParScanThreadStateSet::ParScanThreadStateSet( 334 int num_threads, Space& to_space, ParNewGeneration& gen, 335 Generation& old_gen, ObjToScanQueueSet& queue_set, 336 Stack<oop, mtGC>* overflow_stacks, 337 size_t desired_plab_sz, ParallelTaskTerminator& term) 338 : ResourceArray(sizeof(ParScanThreadState), num_threads), 339 _gen(gen), _old_gen(old_gen), _term(term) 340 { 341 assert(num_threads > 0, "sanity check!"); 342 assert(ParGCUseLocalOverflow == (overflow_stacks != NULL), 343 "overflow_stack allocation mismatch"); 344 // Initialize states. 345 for (int i = 0; i < num_threads; ++i) { 346 new ((ParScanThreadState*)_data + i) 347 ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set, 348 overflow_stacks, desired_plab_sz, term); 349 } 350 } 351 352 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i) 353 { 354 assert(i >= 0 && i < length(), "sanity check!"); 355 return ((ParScanThreadState*)_data)[i]; 356 } 357 358 void ParScanThreadStateSet::trace_promotion_failed(const YoungGCTracer* gc_tracer) { 359 for (int i = 0; i < length(); ++i) { 360 if (thread_state(i).promotion_failed()) { 361 gc_tracer->report_promotion_failed(thread_state(i).promotion_failed_info()); 362 thread_state(i).promotion_failed_info().reset(); 363 } 364 } 365 } 366 367 void ParScanThreadStateSet::reset(int active_threads, bool promotion_failed) 368 { 369 _term.reset_for_reuse(active_threads); 370 if (promotion_failed) { 371 for (int i = 0; i < length(); ++i) { 372 thread_state(i).print_promotion_failure_size(); 373 } 374 } 375 } 376 377 #if TASKQUEUE_STATS 378 void 379 ParScanThreadState::reset_stats() 380 { 381 taskqueue_stats().reset(); 382 _term_attempts = 0; 383 _overflow_refills = 0; 384 _overflow_refill_objs = 0; 385 } 386 387 void ParScanThreadStateSet::reset_stats() 388 { 389 for (int i = 0; i < length(); ++i) { 390 thread_state(i).reset_stats(); 391 } 392 } 393 394 void 395 ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st) 396 { 397 st->print_raw_cr("GC Termination Stats"); 398 st->print_raw_cr(" elapsed --strong roots-- " 399 "-------termination-------"); 400 st->print_raw_cr("thr ms ms % " 401 " ms % attempts"); 402 st->print_raw_cr("--- --------- --------- ------ " 403 "--------- ------ --------"); 404 } 405 406 void ParScanThreadStateSet::print_termination_stats(outputStream* const st) 407 { 408 print_termination_stats_hdr(st); 409 410 for (int i = 0; i < length(); ++i) { 411 const ParScanThreadState & pss = thread_state(i); 412 const double elapsed_ms = pss.elapsed_time() * 1000.0; 413 const double s_roots_ms = pss.strong_roots_time() * 1000.0; 414 const double term_ms = pss.term_time() * 1000.0; 415 st->print_cr("%3d %9.2f %9.2f %6.2f " 416 "%9.2f %6.2f " SIZE_FORMAT_W(8), 417 i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms, 418 term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts()); 419 } 420 } 421 422 // Print stats related to work queue activity. 423 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st) 424 { 425 st->print_raw_cr("GC Task Stats"); 426 st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr(); 427 st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr(); 428 } 429 430 void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st) 431 { 432 print_taskqueue_stats_hdr(st); 433 434 TaskQueueStats totals; 435 for (int i = 0; i < length(); ++i) { 436 const ParScanThreadState & pss = thread_state(i); 437 const TaskQueueStats & stats = pss.taskqueue_stats(); 438 st->print("%3d ", i); stats.print(st); st->cr(); 439 totals += stats; 440 441 if (pss.overflow_refills() > 0) { 442 st->print_cr(" " SIZE_FORMAT_W(10) " overflow refills " 443 SIZE_FORMAT_W(10) " overflow objects", 444 pss.overflow_refills(), pss.overflow_refill_objs()); 445 } 446 } 447 st->print("tot "); totals.print(st); st->cr(); 448 449 DEBUG_ONLY(totals.verify()); 450 } 451 #endif // TASKQUEUE_STATS 452 453 void ParScanThreadStateSet::flush() 454 { 455 // Work in this loop should be kept as lightweight as 456 // possible since this might otherwise become a bottleneck 457 // to scaling. Should we add heavy-weight work into this 458 // loop, consider parallelizing the loop into the worker threads. 459 for (int i = 0; i < length(); ++i) { 460 ParScanThreadState& par_scan_state = thread_state(i); 461 462 // Flush stats related to To-space PLAB activity and 463 // retire the last buffer. 464 par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_gen.plab_stats()); 465 466 // Every thread has its own age table. We need to merge 467 // them all into one. 468 ageTable *local_table = par_scan_state.age_table(); 469 _gen.age_table()->merge(local_table); 470 471 // Inform old gen that we're done. 472 _old_gen.par_promote_alloc_done(i); 473 _old_gen.par_oop_since_save_marks_iterate_done(i); 474 } 475 476 if (UseConcMarkSweepGC) { 477 // We need to call this even when ResizeOldPLAB is disabled 478 // so as to avoid breaking some asserts. While we may be able 479 // to avoid this by reorganizing the code a bit, I am loathe 480 // to do that unless we find cases where ergo leads to bad 481 // performance. 482 CFLS_LAB::compute_desired_plab_size(); 483 } 484 } 485 486 ParScanClosure::ParScanClosure(ParNewGeneration* g, 487 ParScanThreadState* par_scan_state) : 488 OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g) 489 { 490 assert(_g->level() == 0, "Optimized for youngest generation"); 491 _boundary = _g->reserved().end(); 492 } 493 494 void ParScanWithBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, false); } 495 void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); } 496 497 void ParScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, false); } 498 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); } 499 500 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); } 501 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); } 502 503 void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); } 504 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); } 505 506 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g, 507 ParScanThreadState* par_scan_state) 508 : ScanWeakRefClosure(g), _par_scan_state(par_scan_state) 509 {} 510 511 void ParScanWeakRefClosure::do_oop(oop* p) { ParScanWeakRefClosure::do_oop_work(p); } 512 void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); } 513 514 #ifdef WIN32 515 #pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */ 516 #endif 517 518 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure( 519 ParScanThreadState* par_scan_state_, 520 ParScanWithoutBarrierClosure* to_space_closure_, 521 ParScanWithBarrierClosure* old_gen_closure_, 522 ParRootScanWithoutBarrierClosure* to_space_root_closure_, 523 ParNewGeneration* par_gen_, 524 ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_, 525 ObjToScanQueueSet* task_queues_, 526 ParallelTaskTerminator* terminator_) : 527 528 _par_scan_state(par_scan_state_), 529 _to_space_closure(to_space_closure_), 530 _old_gen_closure(old_gen_closure_), 531 _to_space_root_closure(to_space_root_closure_), 532 _old_gen_root_closure(old_gen_root_closure_), 533 _par_gen(par_gen_), 534 _task_queues(task_queues_), 535 _terminator(terminator_) 536 {} 537 538 void ParEvacuateFollowersClosure::do_void() { 539 ObjToScanQueue* work_q = par_scan_state()->work_queue(); 540 541 while (true) { 542 543 // Scan to-space and old-gen objs until we run out of both. 544 oop obj_to_scan; 545 par_scan_state()->trim_queues(0); 546 547 // We have no local work, attempt to steal from other threads. 548 549 // attempt to steal work from promoted. 550 if (task_queues()->steal(par_scan_state()->thread_num(), 551 par_scan_state()->hash_seed(), 552 obj_to_scan)) { 553 bool res = work_q->push(obj_to_scan); 554 assert(res, "Empty queue should have room for a push."); 555 556 // if successful, goto Start. 557 continue; 558 559 // try global overflow list. 560 } else if (par_gen()->take_from_overflow_list(par_scan_state())) { 561 continue; 562 } 563 564 // Otherwise, offer termination. 565 par_scan_state()->start_term_time(); 566 if (terminator()->offer_termination()) break; 567 par_scan_state()->end_term_time(); 568 } 569 assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0, 570 "Broken overflow list?"); 571 // Finish the last termination pause. 572 par_scan_state()->end_term_time(); 573 } 574 575 ParNewGenTask::ParNewGenTask(ParNewGeneration* gen, Generation* old_gen, 576 HeapWord* young_old_boundary, ParScanThreadStateSet* state_set) : 577 AbstractGangTask("ParNewGeneration collection"), 578 _gen(gen), _old_gen(old_gen), 579 _young_old_boundary(young_old_boundary), 580 _state_set(state_set) 581 {} 582 583 // Reset the terminator for the given number of 584 // active threads. 585 void ParNewGenTask::set_for_termination(int active_workers) { 586 _state_set->reset(active_workers, _gen->promotion_failed()); 587 // Should the heap be passed in? There's only 1 for now so 588 // grab it instead. 589 GenCollectedHeap* gch = GenCollectedHeap::heap(); 590 gch->set_n_termination(active_workers); 591 } 592 593 void ParNewGenTask::work(uint worker_id) { 594 GenCollectedHeap* gch = GenCollectedHeap::heap(); 595 // Since this is being done in a separate thread, need new resource 596 // and handle marks. 597 ResourceMark rm; 598 HandleMark hm; 599 600 ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id); 601 assert(_state_set->is_valid(worker_id), "Should not have been called"); 602 603 par_scan_state.set_young_old_boundary(_young_old_boundary); 604 605 KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(), 606 gch->rem_set()->klass_rem_set()); 607 CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure, 608 &par_scan_state.to_space_root_closure(), 609 false); 610 611 par_scan_state.start_strong_roots(); 612 gch->gen_process_roots(_gen->level(), 613 true, // Process younger gens, if any, 614 // as strong roots. 615 false, // no scope; this is parallel code 616 GenCollectedHeap::SO_ScavengeCodeCache, 617 GenCollectedHeap::StrongAndWeakRoots, 618 &par_scan_state.to_space_root_closure(), 619 &par_scan_state.older_gen_closure(), 620 &cld_scan_closure); 621 622 par_scan_state.end_strong_roots(); 623 624 // "evacuate followers". 625 par_scan_state.evacuate_followers_closure().do_void(); 626 } 627 628 #ifdef _MSC_VER 629 #pragma warning( push ) 630 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list 631 #endif 632 ParNewGeneration:: 633 ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level) 634 : DefNewGeneration(rs, initial_byte_size, level, "PCopy"), 635 _overflow_list(NULL), 636 _is_alive_closure(this), 637 _plab_stats(YoungPLABSize, PLABWeight) 638 { 639 NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;) 640 NOT_PRODUCT(_num_par_pushes = 0;) 641 _task_queues = new ObjToScanQueueSet(ParallelGCThreads); 642 guarantee(_task_queues != NULL, "task_queues allocation failure."); 643 644 for (uint i1 = 0; i1 < ParallelGCThreads; i1++) { 645 ObjToScanQueue *q = new ObjToScanQueue(); 646 guarantee(q != NULL, "work_queue Allocation failure."); 647 _task_queues->register_queue(i1, q); 648 } 649 650 for (uint i2 = 0; i2 < ParallelGCThreads; i2++) 651 _task_queues->queue(i2)->initialize(); 652 653 _overflow_stacks = NULL; 654 if (ParGCUseLocalOverflow) { 655 656 // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal 657 // with ',' 658 typedef Stack<oop, mtGC> GCOopStack; 659 660 _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC); 661 for (size_t i = 0; i < ParallelGCThreads; ++i) { 662 new (_overflow_stacks + i) Stack<oop, mtGC>(); 663 } 664 } 665 666 if (UsePerfData) { 667 EXCEPTION_MARK; 668 ResourceMark rm; 669 670 const char* cname = 671 PerfDataManager::counter_name(_gen_counters->name_space(), "threads"); 672 PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None, 673 ParallelGCThreads, CHECK); 674 } 675 } 676 #ifdef _MSC_VER 677 #pragma warning( pop ) 678 #endif 679 680 // ParNewGeneration:: 681 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) : 682 DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {} 683 684 template <class T> 685 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) { 686 #ifdef ASSERT 687 { 688 assert(!oopDesc::is_null(*p), "expected non-null ref"); 689 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 690 // We never expect to see a null reference being processed 691 // as a weak reference. 692 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 693 } 694 #endif // ASSERT 695 696 _par_cl->do_oop_nv(p); 697 698 if (Universe::heap()->is_in_reserved(p)) { 699 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 700 _rs->write_ref_field_gc_par(p, obj); 701 } 702 } 703 704 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); } 705 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); } 706 707 // ParNewGeneration:: 708 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) : 709 DefNewGeneration::KeepAliveClosure(cl) {} 710 711 template <class T> 712 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) { 713 #ifdef ASSERT 714 { 715 assert(!oopDesc::is_null(*p), "expected non-null ref"); 716 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 717 // We never expect to see a null reference being processed 718 // as a weak reference. 719 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 720 } 721 #endif // ASSERT 722 723 _cl->do_oop_nv(p); 724 725 if (Universe::heap()->is_in_reserved(p)) { 726 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 727 _rs->write_ref_field_gc_par(p, obj); 728 } 729 } 730 731 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); } 732 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); } 733 734 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) { 735 T heap_oop = oopDesc::load_heap_oop(p); 736 if (!oopDesc::is_null(heap_oop)) { 737 oop obj = oopDesc::decode_heap_oop_not_null(heap_oop); 738 if ((HeapWord*)obj < _boundary) { 739 assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?"); 740 oop new_obj = obj->is_forwarded() 741 ? obj->forwardee() 742 : _g->DefNewGeneration::copy_to_survivor_space(obj); 743 oopDesc::encode_store_heap_oop_not_null(p, new_obj); 744 } 745 if (_gc_barrier) { 746 // If p points to a younger generation, mark the card. 747 if ((HeapWord*)obj < _gen_boundary) { 748 _rs->write_ref_field_gc_par(p, obj); 749 } 750 } 751 } 752 } 753 754 void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 755 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 756 757 class ParNewRefProcTaskProxy: public AbstractGangTask { 758 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; 759 public: 760 ParNewRefProcTaskProxy(ProcessTask& task, 761 ParNewGeneration& gen, 762 Generation& old_gen, 763 HeapWord* young_old_boundary, 764 ParScanThreadStateSet& state_set); 765 766 private: 767 virtual void work(uint worker_id); 768 virtual void set_for_termination(int active_workers) { 769 _state_set.terminator()->reset_for_reuse(active_workers); 770 } 771 private: 772 ParNewGeneration& _gen; 773 ProcessTask& _task; 774 Generation& _old_gen; 775 HeapWord* _young_old_boundary; 776 ParScanThreadStateSet& _state_set; 777 }; 778 779 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task, 780 ParNewGeneration& gen, 781 Generation& old_gen, 782 HeapWord* young_old_boundary, 783 ParScanThreadStateSet& state_set) 784 : AbstractGangTask("ParNewGeneration parallel reference processing"), 785 _gen(gen), 786 _task(task), 787 _old_gen(old_gen), 788 _young_old_boundary(young_old_boundary), 789 _state_set(state_set) 790 { 791 } 792 793 void ParNewRefProcTaskProxy::work(uint worker_id) 794 { 795 ResourceMark rm; 796 HandleMark hm; 797 ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id); 798 par_scan_state.set_young_old_boundary(_young_old_boundary); 799 _task.work(worker_id, par_scan_state.is_alive_closure(), 800 par_scan_state.keep_alive_closure(), 801 par_scan_state.evacuate_followers_closure()); 802 } 803 804 class ParNewRefEnqueueTaskProxy: public AbstractGangTask { 805 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; 806 EnqueueTask& _task; 807 808 public: 809 ParNewRefEnqueueTaskProxy(EnqueueTask& task) 810 : AbstractGangTask("ParNewGeneration parallel reference enqueue"), 811 _task(task) 812 { } 813 814 virtual void work(uint worker_id) 815 { 816 _task.work(worker_id); 817 } 818 }; 819 820 821 void ParNewRefProcTaskExecutor::execute(ProcessTask& task) 822 { 823 GenCollectedHeap* gch = GenCollectedHeap::heap(); 824 assert(gch->kind() == CollectedHeap::GenCollectedHeap, 825 "not a generational heap"); 826 FlexibleWorkGang* workers = gch->workers(); 827 assert(workers != NULL, "Need parallel worker threads."); 828 _state_set.reset(workers->active_workers(), _generation.promotion_failed()); 829 ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(), 830 _generation.reserved().end(), _state_set); 831 workers->run_task(&rp_task); 832 _state_set.reset(0 /* bad value in debug if not reset */, 833 _generation.promotion_failed()); 834 } 835 836 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task) 837 { 838 GenCollectedHeap* gch = GenCollectedHeap::heap(); 839 FlexibleWorkGang* workers = gch->workers(); 840 assert(workers != NULL, "Need parallel worker threads."); 841 ParNewRefEnqueueTaskProxy enq_task(task); 842 workers->run_task(&enq_task); 843 } 844 845 void ParNewRefProcTaskExecutor::set_single_threaded_mode() 846 { 847 _state_set.flush(); 848 GenCollectedHeap* gch = GenCollectedHeap::heap(); 849 gch->set_par_threads(0); // 0 ==> non-parallel. 850 gch->save_marks(); 851 } 852 853 ScanClosureWithParBarrier:: 854 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) : 855 ScanClosure(g, gc_barrier) {} 856 857 EvacuateFollowersClosureGeneral:: 858 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, int level, 859 OopsInGenClosure* cur, 860 OopsInGenClosure* older) : 861 _gch(gch), _level(level), 862 _scan_cur_or_nonheap(cur), _scan_older(older) 863 {} 864 865 void EvacuateFollowersClosureGeneral::do_void() { 866 do { 867 // Beware: this call will lead to closure applications via virtual 868 // calls. 869 _gch->oop_since_save_marks_iterate(_level, 870 _scan_cur_or_nonheap, 871 _scan_older); 872 } while (!_gch->no_allocs_since_save_marks(_level)); 873 } 874 875 876 // A Generation that does parallel young-gen collection. 877 878 void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set) { 879 assert(_promo_failure_scan_stack.is_empty(), "post condition"); 880 _promo_failure_scan_stack.clear(true); // Clear cached segments. 881 882 remove_forwarding_pointers(); 883 if (PrintGCDetails) { 884 gclog_or_tty->print(" (promotion failed)"); 885 } 886 // All the spaces are in play for mark-sweep. 887 swap_spaces(); // Make life simpler for CMS || rescan; see 6483690. 888 from()->set_next_compaction_space(to()); 889 gch->set_incremental_collection_failed(); 890 // Inform the next generation that a promotion failure occurred. 891 _old_gen->promotion_failure_occurred(); 892 893 // Trace promotion failure in the parallel GC threads 894 thread_state_set.trace_promotion_failed(gc_tracer()); 895 // Single threaded code may have reported promotion failure to the global state 896 if (_promotion_failed_info.has_failed()) { 897 _gc_tracer.report_promotion_failed(_promotion_failed_info); 898 } 899 // Reset the PromotionFailureALot counters. 900 NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();) 901 } 902 903 void ParNewGeneration::collect(bool full, 904 bool clear_all_soft_refs, 905 size_t size, 906 bool is_tlab) { 907 assert(full || size > 0, "otherwise we don't want to collect"); 908 909 GenCollectedHeap* gch = GenCollectedHeap::heap(); 910 911 _gc_timer->register_gc_start(); 912 913 assert(gch->kind() == CollectedHeap::GenCollectedHeap, 914 "not a CMS generational heap"); 915 AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy(); 916 FlexibleWorkGang* workers = gch->workers(); 917 assert(workers != NULL, "Need workgang for parallel work"); 918 int active_workers = 919 AdaptiveSizePolicy::calc_active_workers(workers->total_workers(), 920 workers->active_workers(), 921 Threads::number_of_non_daemon_threads()); 922 workers->set_active_workers(active_workers); 923 _old_gen = gch->old_gen(); 924 925 // If the next generation is too full to accommodate worst-case promotion 926 // from this generation, pass on collection; let the next generation 927 // do it. 928 if (!collection_attempt_is_safe()) { 929 gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one 930 return; 931 } 932 assert(to()->is_empty(), "Else not collection_attempt_is_safe"); 933 934 _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start()); 935 gch->trace_heap_before_gc(gc_tracer()); 936 937 init_assuming_no_promotion_failure(); 938 939 if (UseAdaptiveSizePolicy) { 940 set_survivor_overflow(false); 941 size_policy->minor_collection_begin(); 942 } 943 944 GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, _gc_tracer.gc_id()); 945 // Capture heap used before collection (for printing). 946 size_t gch_prev_used = gch->used(); 947 948 age_table()->clear(); 949 to()->clear(SpaceDecorator::Mangle); 950 951 gch->save_marks(); 952 assert(workers != NULL, "Need parallel worker threads."); 953 int n_workers = active_workers; 954 955 // Set the correct parallelism (number of queues) in the reference processor 956 ref_processor()->set_active_mt_degree(n_workers); 957 958 // Always set the terminator for the active number of workers 959 // because only those workers go through the termination protocol. 960 ParallelTaskTerminator _term(n_workers, task_queues()); 961 ParScanThreadStateSet thread_state_set(workers->active_workers(), 962 *to(), *this, *_old_gen, *task_queues(), 963 _overflow_stacks, desired_plab_sz(), _term); 964 965 ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set); 966 gch->set_par_threads(n_workers); 967 gch->rem_set()->prepare_for_younger_refs_iterate(true); 968 // It turns out that even when we're using 1 thread, doing the work in a 969 // separate thread causes wide variance in run times. We can't help this 970 // in the multi-threaded case, but we special-case n=1 here to get 971 // repeatable measurements of the 1-thread overhead of the parallel code. 972 if (n_workers > 1) { 973 GenCollectedHeap::StrongRootsScope srs(gch); 974 workers->run_task(&tsk); 975 } else { 976 GenCollectedHeap::StrongRootsScope srs(gch); 977 tsk.work(0); 978 } 979 thread_state_set.reset(0 /* Bad value in debug if not reset */, 980 promotion_failed()); 981 982 // Trace and reset failed promotion info. 983 if (promotion_failed()) { 984 thread_state_set.trace_promotion_failed(gc_tracer()); 985 } 986 987 // Process (weak) reference objects found during scavenge. 988 ReferenceProcessor* rp = ref_processor(); 989 IsAliveClosure is_alive(this); 990 ScanWeakRefClosure scan_weak_ref(this); 991 KeepAliveClosure keep_alive(&scan_weak_ref); 992 ScanClosure scan_without_gc_barrier(this, false); 993 ScanClosureWithParBarrier scan_with_gc_barrier(this, true); 994 set_promo_failure_scan_stack_closure(&scan_without_gc_barrier); 995 EvacuateFollowersClosureGeneral evacuate_followers(gch, _level, 996 &scan_without_gc_barrier, &scan_with_gc_barrier); 997 rp->setup_policy(clear_all_soft_refs); 998 // Can the mt_degree be set later (at run_task() time would be best)? 999 rp->set_active_mt_degree(active_workers); 1000 ReferenceProcessorStats stats; 1001 if (rp->processing_is_mt()) { 1002 ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); 1003 stats = rp->process_discovered_references(&is_alive, &keep_alive, 1004 &evacuate_followers, &task_executor, 1005 _gc_timer, _gc_tracer.gc_id()); 1006 } else { 1007 thread_state_set.flush(); 1008 gch->set_par_threads(0); // 0 ==> non-parallel. 1009 gch->save_marks(); 1010 stats = rp->process_discovered_references(&is_alive, &keep_alive, 1011 &evacuate_followers, NULL, 1012 _gc_timer, _gc_tracer.gc_id()); 1013 } 1014 _gc_tracer.report_gc_reference_stats(stats); 1015 if (!promotion_failed()) { 1016 // Swap the survivor spaces. 1017 eden()->clear(SpaceDecorator::Mangle); 1018 from()->clear(SpaceDecorator::Mangle); 1019 if (ZapUnusedHeapArea) { 1020 // This is now done here because of the piece-meal mangling which 1021 // can check for valid mangling at intermediate points in the 1022 // collection(s). When a minor collection fails to collect 1023 // sufficient space resizing of the young generation can occur 1024 // an redistribute the spaces in the young generation. Mangle 1025 // here so that unzapped regions don't get distributed to 1026 // other spaces. 1027 to()->mangle_unused_area(); 1028 } 1029 swap_spaces(); 1030 1031 // A successful scavenge should restart the GC time limit count which is 1032 // for full GC's. 1033 size_policy->reset_gc_overhead_limit_count(); 1034 1035 assert(to()->is_empty(), "to space should be empty now"); 1036 1037 adjust_desired_tenuring_threshold(); 1038 } else { 1039 handle_promotion_failed(gch, thread_state_set); 1040 } 1041 // set new iteration safe limit for the survivor spaces 1042 from()->set_concurrent_iteration_safe_limit(from()->top()); 1043 to()->set_concurrent_iteration_safe_limit(to()->top()); 1044 1045 if (ResizePLAB) { 1046 plab_stats()->adjust_desired_plab_sz(n_workers); 1047 } 1048 1049 if (PrintGC && !PrintGCDetails) { 1050 gch->print_heap_change(gch_prev_used); 1051 } 1052 1053 TASKQUEUE_STATS_ONLY(if (PrintTerminationStats) thread_state_set.print_termination_stats()); 1054 TASKQUEUE_STATS_ONLY(if (PrintTaskqueue) thread_state_set.print_taskqueue_stats()); 1055 1056 if (UseAdaptiveSizePolicy) { 1057 size_policy->minor_collection_end(gch->gc_cause()); 1058 size_policy->avg_survived()->sample(from()->used()); 1059 } 1060 1061 // We need to use a monotonically non-decreasing time in ms 1062 // or we will see time-warp warnings and os::javaTimeMillis() 1063 // does not guarantee monotonicity. 1064 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 1065 update_time_of_last_gc(now); 1066 1067 rp->set_enqueuing_is_done(true); 1068 if (rp->processing_is_mt()) { 1069 ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); 1070 rp->enqueue_discovered_references(&task_executor); 1071 } else { 1072 rp->enqueue_discovered_references(NULL); 1073 } 1074 rp->verify_no_references_recorded(); 1075 1076 gch->trace_heap_after_gc(gc_tracer()); 1077 _gc_tracer.report_tenuring_threshold(tenuring_threshold()); 1078 1079 _gc_timer->register_gc_end(); 1080 1081 _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions()); 1082 } 1083 1084 static int sum; 1085 void ParNewGeneration::waste_some_time() { 1086 for (int i = 0; i < 100; i++) { 1087 sum += i; 1088 } 1089 } 1090 1091 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4); 1092 1093 // Because of concurrency, there are times where an object for which 1094 // "is_forwarded()" is true contains an "interim" forwarding pointer 1095 // value. Such a value will soon be overwritten with a real value. 1096 // This method requires "obj" to have a forwarding pointer, and waits, if 1097 // necessary for a real one to be inserted, and returns it. 1098 1099 oop ParNewGeneration::real_forwardee(oop obj) { 1100 oop forward_ptr = obj->forwardee(); 1101 if (forward_ptr != ClaimedForwardPtr) { 1102 return forward_ptr; 1103 } else { 1104 return real_forwardee_slow(obj); 1105 } 1106 } 1107 1108 oop ParNewGeneration::real_forwardee_slow(oop obj) { 1109 // Spin-read if it is claimed but not yet written by another thread. 1110 oop forward_ptr = obj->forwardee(); 1111 while (forward_ptr == ClaimedForwardPtr) { 1112 waste_some_time(); 1113 assert(obj->is_forwarded(), "precondition"); 1114 forward_ptr = obj->forwardee(); 1115 } 1116 return forward_ptr; 1117 } 1118 1119 void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) { 1120 if (m->must_be_preserved_for_promotion_failure(obj)) { 1121 // We should really have separate per-worker stacks, rather 1122 // than use locking of a common pair of stacks. 1123 MutexLocker ml(ParGCRareEvent_lock); 1124 preserve_mark(obj, m); 1125 } 1126 } 1127 1128 // Multiple GC threads may try to promote an object. If the object 1129 // is successfully promoted, a forwarding pointer will be installed in 1130 // the object in the young generation. This method claims the right 1131 // to install the forwarding pointer before it copies the object, 1132 // thus avoiding the need to undo the copy as in 1133 // copy_to_survivor_space_avoiding_with_undo. 1134 1135 oop ParNewGeneration::copy_to_survivor_space( 1136 ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) { 1137 // In the sequential version, this assert also says that the object is 1138 // not forwarded. That might not be the case here. It is the case that 1139 // the caller observed it to be not forwarded at some time in the past. 1140 assert(is_in_reserved(old), "shouldn't be scavenging this oop"); 1141 1142 // The sequential code read "old->age()" below. That doesn't work here, 1143 // since the age is in the mark word, and that might be overwritten with 1144 // a forwarding pointer by a parallel thread. So we must save the mark 1145 // word in a local and then analyze it. 1146 oopDesc dummyOld; 1147 dummyOld.set_mark(m); 1148 assert(!dummyOld.is_forwarded(), 1149 "should not be called with forwarding pointer mark word."); 1150 1151 oop new_obj = NULL; 1152 oop forward_ptr; 1153 1154 // Try allocating obj in to-space (unless too old) 1155 if (dummyOld.age() < tenuring_threshold()) { 1156 new_obj = (oop)par_scan_state->alloc_in_to_space(sz); 1157 if (new_obj == NULL) { 1158 set_survivor_overflow(true); 1159 } 1160 } 1161 1162 if (new_obj == NULL) { 1163 // Either to-space is full or we decided to promote 1164 // try allocating obj tenured 1165 1166 // Attempt to install a null forwarding pointer (atomically), 1167 // to claim the right to install the real forwarding pointer. 1168 forward_ptr = old->forward_to_atomic(ClaimedForwardPtr); 1169 if (forward_ptr != NULL) { 1170 // someone else beat us to it. 1171 return real_forwardee(old); 1172 } 1173 1174 if (!_promotion_failed) { 1175 new_obj = _old_gen->par_promote(par_scan_state->thread_num(), 1176 old, m, sz); 1177 } 1178 1179 if (new_obj == NULL) { 1180 // promotion failed, forward to self 1181 _promotion_failed = true; 1182 new_obj = old; 1183 1184 preserve_mark_if_necessary(old, m); 1185 par_scan_state->register_promotion_failure(sz); 1186 } 1187 1188 old->forward_to(new_obj); 1189 forward_ptr = NULL; 1190 } else { 1191 // Is in to-space; do copying ourselves. 1192 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz); 1193 assert(Universe::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value."); 1194 forward_ptr = old->forward_to_atomic(new_obj); 1195 // Restore the mark word copied above. 1196 new_obj->set_mark(m); 1197 // Increment age if obj still in new generation 1198 new_obj->incr_age(); 1199 par_scan_state->age_table()->add(new_obj, sz); 1200 } 1201 assert(new_obj != NULL, "just checking"); 1202 1203 #ifndef PRODUCT 1204 // This code must come after the CAS test, or it will print incorrect 1205 // information. 1206 if (TraceScavenge) { 1207 gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}", 1208 is_in_reserved(new_obj) ? "copying" : "tenuring", 1209 new_obj->klass()->internal_name(), p2i(old), p2i(new_obj), new_obj->size()); 1210 } 1211 #endif 1212 1213 if (forward_ptr == NULL) { 1214 oop obj_to_push = new_obj; 1215 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) { 1216 // Length field used as index of next element to be scanned. 1217 // Real length can be obtained from real_forwardee() 1218 arrayOop(old)->set_length(0); 1219 obj_to_push = old; 1220 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push, 1221 "push forwarded object"); 1222 } 1223 // Push it on one of the queues of to-be-scanned objects. 1224 bool simulate_overflow = false; 1225 NOT_PRODUCT( 1226 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) { 1227 // simulate a stack overflow 1228 simulate_overflow = true; 1229 } 1230 ) 1231 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) { 1232 // Add stats for overflow pushes. 1233 if (Verbose && PrintGCDetails) { 1234 gclog_or_tty->print("queue overflow!\n"); 1235 } 1236 push_on_overflow_list(old, par_scan_state); 1237 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0)); 1238 } 1239 1240 return new_obj; 1241 } 1242 1243 // Oops. Someone beat us to it. Undo the allocation. Where did we 1244 // allocate it? 1245 if (is_in_reserved(new_obj)) { 1246 // Must be in to_space. 1247 assert(to()->is_in_reserved(new_obj), "Checking"); 1248 if (forward_ptr == ClaimedForwardPtr) { 1249 // Wait to get the real forwarding pointer value. 1250 forward_ptr = real_forwardee(old); 1251 } 1252 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz); 1253 } 1254 1255 return forward_ptr; 1256 } 1257 1258 #ifndef PRODUCT 1259 // It's OK to call this multi-threaded; the worst thing 1260 // that can happen is that we'll get a bunch of closely 1261 // spaced simulated overflows, but that's OK, in fact 1262 // probably good as it would exercise the overflow code 1263 // under contention. 1264 bool ParNewGeneration::should_simulate_overflow() { 1265 if (_overflow_counter-- <= 0) { // just being defensive 1266 _overflow_counter = ParGCWorkQueueOverflowInterval; 1267 return true; 1268 } else { 1269 return false; 1270 } 1271 } 1272 #endif 1273 1274 // In case we are using compressed oops, we need to be careful. 1275 // If the object being pushed is an object array, then its length 1276 // field keeps track of the "grey boundary" at which the next 1277 // incremental scan will be done (see ParGCArrayScanChunk). 1278 // When using compressed oops, this length field is kept in the 1279 // lower 32 bits of the erstwhile klass word and cannot be used 1280 // for the overflow chaining pointer (OCP below). As such the OCP 1281 // would itself need to be compressed into the top 32-bits in this 1282 // case. Unfortunately, see below, in the event that we have a 1283 // promotion failure, the node to be pushed on the list can be 1284 // outside of the Java heap, so the heap-based pointer compression 1285 // would not work (we would have potential aliasing between C-heap 1286 // and Java-heap pointers). For this reason, when using compressed 1287 // oops, we simply use a worker-thread-local, non-shared overflow 1288 // list in the form of a growable array, with a slightly different 1289 // overflow stack draining strategy. If/when we start using fat 1290 // stacks here, we can go back to using (fat) pointer chains 1291 // (although some performance comparisons would be useful since 1292 // single global lists have their own performance disadvantages 1293 // as we were made painfully aware not long ago, see 6786503). 1294 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff)) 1295 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) { 1296 assert(is_in_reserved(from_space_obj), "Should be from this generation"); 1297 if (ParGCUseLocalOverflow) { 1298 // In the case of compressed oops, we use a private, not-shared 1299 // overflow stack. 1300 par_scan_state->push_on_overflow_stack(from_space_obj); 1301 } else { 1302 assert(!UseCompressedOops, "Error"); 1303 // if the object has been forwarded to itself, then we cannot 1304 // use the klass pointer for the linked list. Instead we have 1305 // to allocate an oopDesc in the C-Heap and use that for the linked list. 1306 // XXX This is horribly inefficient when a promotion failure occurs 1307 // and should be fixed. XXX FIX ME !!! 1308 #ifndef PRODUCT 1309 Atomic::inc_ptr(&_num_par_pushes); 1310 assert(_num_par_pushes > 0, "Tautology"); 1311 #endif 1312 if (from_space_obj->forwardee() == from_space_obj) { 1313 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC); 1314 listhead->forward_to(from_space_obj); 1315 from_space_obj = listhead; 1316 } 1317 oop observed_overflow_list = _overflow_list; 1318 oop cur_overflow_list; 1319 do { 1320 cur_overflow_list = observed_overflow_list; 1321 if (cur_overflow_list != BUSY) { 1322 from_space_obj->set_klass_to_list_ptr(cur_overflow_list); 1323 } else { 1324 from_space_obj->set_klass_to_list_ptr(NULL); 1325 } 1326 observed_overflow_list = 1327 (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list); 1328 } while (cur_overflow_list != observed_overflow_list); 1329 } 1330 } 1331 1332 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) { 1333 bool res; 1334 1335 if (ParGCUseLocalOverflow) { 1336 res = par_scan_state->take_from_overflow_stack(); 1337 } else { 1338 assert(!UseCompressedOops, "Error"); 1339 res = take_from_overflow_list_work(par_scan_state); 1340 } 1341 return res; 1342 } 1343 1344 1345 // *NOTE*: The overflow list manipulation code here and 1346 // in CMSCollector:: are very similar in shape, 1347 // except that in the CMS case we thread the objects 1348 // directly into the list via their mark word, and do 1349 // not need to deal with special cases below related 1350 // to chunking of object arrays and promotion failure 1351 // handling. 1352 // CR 6797058 has been filed to attempt consolidation of 1353 // the common code. 1354 // Because of the common code, if you make any changes in 1355 // the code below, please check the CMS version to see if 1356 // similar changes might be needed. 1357 // See CMSCollector::par_take_from_overflow_list() for 1358 // more extensive documentation comments. 1359 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) { 1360 ObjToScanQueue* work_q = par_scan_state->work_queue(); 1361 // How many to take? 1362 size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 1363 (size_t)ParGCDesiredObjsFromOverflowList); 1364 1365 assert(!UseCompressedOops, "Error"); 1366 assert(par_scan_state->overflow_stack() == NULL, "Error"); 1367 if (_overflow_list == NULL) return false; 1368 1369 // Otherwise, there was something there; try claiming the list. 1370 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1371 // Trim off a prefix of at most objsFromOverflow items 1372 Thread* tid = Thread::current(); 1373 size_t spin_count = (size_t)ParallelGCThreads; 1374 size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100); 1375 for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) { 1376 // someone grabbed it before we did ... 1377 // ... we spin for a short while... 1378 os::sleep(tid, sleep_time_millis, false); 1379 if (_overflow_list == NULL) { 1380 // nothing left to take 1381 return false; 1382 } else if (_overflow_list != BUSY) { 1383 // try and grab the prefix 1384 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1385 } 1386 } 1387 if (prefix == NULL || prefix == BUSY) { 1388 // Nothing to take or waited long enough 1389 if (prefix == NULL) { 1390 // Write back the NULL in case we overwrote it with BUSY above 1391 // and it is still the same value. 1392 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1393 } 1394 return false; 1395 } 1396 assert(prefix != NULL && prefix != BUSY, "Error"); 1397 size_t i = 1; 1398 oop cur = prefix; 1399 while (i < objsFromOverflow && cur->klass_or_null() != NULL) { 1400 i++; cur = cur->list_ptr_from_klass(); 1401 } 1402 1403 // Reattach remaining (suffix) to overflow list 1404 if (cur->klass_or_null() == NULL) { 1405 // Write back the NULL in lieu of the BUSY we wrote 1406 // above and it is still the same value. 1407 if (_overflow_list == BUSY) { 1408 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1409 } 1410 } else { 1411 assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error"); 1412 oop suffix = cur->list_ptr_from_klass(); // suffix will be put back on global list 1413 cur->set_klass_to_list_ptr(NULL); // break off suffix 1414 // It's possible that the list is still in the empty(busy) state 1415 // we left it in a short while ago; in that case we may be 1416 // able to place back the suffix. 1417 oop observed_overflow_list = _overflow_list; 1418 oop cur_overflow_list = observed_overflow_list; 1419 bool attached = false; 1420 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { 1421 observed_overflow_list = 1422 (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1423 if (cur_overflow_list == observed_overflow_list) { 1424 attached = true; 1425 break; 1426 } else cur_overflow_list = observed_overflow_list; 1427 } 1428 if (!attached) { 1429 // Too bad, someone else got in in between; we'll need to do a splice. 1430 // Find the last item of suffix list 1431 oop last = suffix; 1432 while (last->klass_or_null() != NULL) { 1433 last = last->list_ptr_from_klass(); 1434 } 1435 // Atomically prepend suffix to current overflow list 1436 observed_overflow_list = _overflow_list; 1437 do { 1438 cur_overflow_list = observed_overflow_list; 1439 if (cur_overflow_list != BUSY) { 1440 // Do the splice ... 1441 last->set_klass_to_list_ptr(cur_overflow_list); 1442 } else { // cur_overflow_list == BUSY 1443 last->set_klass_to_list_ptr(NULL); 1444 } 1445 observed_overflow_list = 1446 (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1447 } while (cur_overflow_list != observed_overflow_list); 1448 } 1449 } 1450 1451 // Push objects on prefix list onto this thread's work queue 1452 assert(prefix != NULL && prefix != BUSY, "program logic"); 1453 cur = prefix; 1454 ssize_t n = 0; 1455 while (cur != NULL) { 1456 oop obj_to_push = cur->forwardee(); 1457 oop next = cur->list_ptr_from_klass(); 1458 cur->set_klass(obj_to_push->klass()); 1459 // This may be an array object that is self-forwarded. In that case, the list pointer 1460 // space, cur, is not in the Java heap, but rather in the C-heap and should be freed. 1461 if (!is_in_reserved(cur)) { 1462 // This can become a scaling bottleneck when there is work queue overflow coincident 1463 // with promotion failure. 1464 oopDesc* f = cur; 1465 FREE_C_HEAP_ARRAY(oopDesc, f); 1466 } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) { 1467 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 1468 obj_to_push = cur; 1469 } 1470 bool ok = work_q->push(obj_to_push); 1471 assert(ok, "Should have succeeded"); 1472 cur = next; 1473 n++; 1474 } 1475 TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n)); 1476 #ifndef PRODUCT 1477 assert(_num_par_pushes >= n, "Too many pops?"); 1478 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes); 1479 #endif 1480 return true; 1481 } 1482 #undef BUSY 1483 1484 void ParNewGeneration::ref_processor_init() { 1485 if (_ref_processor == NULL) { 1486 // Allocate and initialize a reference processor 1487 _ref_processor = 1488 new ReferenceProcessor(_reserved, // span 1489 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing 1490 (int) ParallelGCThreads, // mt processing degree 1491 refs_discovery_is_mt(), // mt discovery 1492 (int) ParallelGCThreads, // mt discovery degree 1493 refs_discovery_is_atomic(), // atomic_discovery 1494 NULL); // is_alive_non_header 1495 } 1496 } 1497 1498 const char* ParNewGeneration::name() const { 1499 return "par new generation"; 1500 }