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/plab.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/strongRootsScope.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/stack.inline.hpp" 57 #include "utilities/taskqueue.inline.hpp" 58 #include "utilities/workgroup.hpp" 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(GenCollectedHeap::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(GenCollectedHeap::heap()->is_in_reserved(cur), "Should be in heap"); 205 assert(!old_gen()->is_in_reserved(cur), "Should be in young gen"); 206 assert(GenCollectedHeap::heap()->is_in_reserved(obj_to_push), "Should be in heap"); 207 if (should_be_partially_scanned(obj_to_push, cur)) { 208 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 209 obj_to_push = cur; 210 } 211 bool ok = queue->push(obj_to_push); 212 assert(ok, "Should have succeeded"); 213 } 214 assert(young_gen()->overflow_list() == NULL, "Error"); 215 return num_take_elems > 0; // was something transferred? 216 } 217 218 void ParScanThreadState::push_on_overflow_stack(oop p) { 219 assert(ParGCUseLocalOverflow, "Else should not call"); 220 overflow_stack()->push(p); 221 assert(young_gen()->overflow_list() == NULL, "Error"); 222 } 223 224 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) { 225 226 // Otherwise, if the object is small enough, try to reallocate the 227 // buffer. 228 HeapWord* obj = NULL; 229 if (!_to_space_full) { 230 PLAB* 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 PLAB::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 PLAB::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& _old_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), _old_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 _old_gen.par_promote_alloc_done(i); 475 _old_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* old_gen, 578 HeapWord* young_old_boundary, ParScanThreadStateSet* state_set) : 579 AbstractGangTask("ParNewGeneration collection"), 580 _gen(gen), _old_gen(old_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; 601 602 ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id); 603 assert(_state_set->is_valid(worker_id), "Should not have been called"); 604 605 par_scan_state.set_young_old_boundary(_young_old_boundary); 606 607 KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(), 608 gch->rem_set()->klass_rem_set()); 609 CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure, 610 &par_scan_state.to_space_root_closure(), 611 false); 612 613 par_scan_state.start_strong_roots(); 614 gch->gen_process_roots(_gen->level(), 615 true, // Process younger gens, if any, 616 // as strong roots. 617 false, // no scope; this is parallel code 618 GenCollectedHeap::SO_ScavengeCodeCache, 619 GenCollectedHeap::StrongAndWeakRoots, 620 &par_scan_state.to_space_root_closure(), 621 &par_scan_state.older_gen_closure(), 622 &cld_scan_closure); 623 624 par_scan_state.end_strong_roots(); 625 626 // "evacuate followers". 627 par_scan_state.evacuate_followers_closure().do_void(); 628 } 629 630 #ifdef _MSC_VER 631 #pragma warning( push ) 632 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list 633 #endif 634 ParNewGeneration:: 635 ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level) 636 : DefNewGeneration(rs, initial_byte_size, level, "PCopy"), 637 _overflow_list(NULL), 638 _is_alive_closure(this), 639 _plab_stats(YoungPLABSize, PLABWeight) 640 { 641 NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;) 642 NOT_PRODUCT(_num_par_pushes = 0;) 643 _task_queues = new ObjToScanQueueSet(ParallelGCThreads); 644 guarantee(_task_queues != NULL, "task_queues allocation failure."); 645 646 for (uint i1 = 0; i1 < ParallelGCThreads; i1++) { 647 ObjToScanQueue *q = new ObjToScanQueue(); 648 guarantee(q != NULL, "work_queue Allocation failure."); 649 _task_queues->register_queue(i1, q); 650 } 651 652 for (uint i2 = 0; i2 < ParallelGCThreads; i2++) 653 _task_queues->queue(i2)->initialize(); 654 655 _overflow_stacks = NULL; 656 if (ParGCUseLocalOverflow) { 657 658 // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal 659 // with ',' 660 typedef Stack<oop, mtGC> GCOopStack; 661 662 _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC); 663 for (size_t i = 0; i < ParallelGCThreads; ++i) { 664 new (_overflow_stacks + i) Stack<oop, mtGC>(); 665 } 666 } 667 668 if (UsePerfData) { 669 EXCEPTION_MARK; 670 ResourceMark rm; 671 672 const char* cname = 673 PerfDataManager::counter_name(_gen_counters->name_space(), "threads"); 674 PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None, 675 ParallelGCThreads, CHECK); 676 } 677 } 678 #ifdef _MSC_VER 679 #pragma warning( pop ) 680 #endif 681 682 // ParNewGeneration:: 683 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) : 684 DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {} 685 686 template <class T> 687 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) { 688 #ifdef ASSERT 689 { 690 assert(!oopDesc::is_null(*p), "expected non-null ref"); 691 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 692 // We never expect to see a null reference being processed 693 // as a weak reference. 694 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 695 } 696 #endif // ASSERT 697 698 _par_cl->do_oop_nv(p); 699 700 if (GenCollectedHeap::heap()->is_in_reserved(p)) { 701 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 702 _rs->write_ref_field_gc_par(p, obj); 703 } 704 } 705 706 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); } 707 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); } 708 709 // ParNewGeneration:: 710 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) : 711 DefNewGeneration::KeepAliveClosure(cl) {} 712 713 template <class T> 714 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) { 715 #ifdef ASSERT 716 { 717 assert(!oopDesc::is_null(*p), "expected non-null ref"); 718 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 719 // We never expect to see a null reference being processed 720 // as a weak reference. 721 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 722 } 723 #endif // ASSERT 724 725 _cl->do_oop_nv(p); 726 727 if (GenCollectedHeap::heap()->is_in_reserved(p)) { 728 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 729 _rs->write_ref_field_gc_par(p, obj); 730 } 731 } 732 733 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); } 734 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); } 735 736 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) { 737 T heap_oop = oopDesc::load_heap_oop(p); 738 if (!oopDesc::is_null(heap_oop)) { 739 oop obj = oopDesc::decode_heap_oop_not_null(heap_oop); 740 if ((HeapWord*)obj < _boundary) { 741 assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?"); 742 oop new_obj = obj->is_forwarded() 743 ? obj->forwardee() 744 : _g->DefNewGeneration::copy_to_survivor_space(obj); 745 oopDesc::encode_store_heap_oop_not_null(p, new_obj); 746 } 747 if (_gc_barrier) { 748 // If p points to a younger generation, mark the card. 749 if ((HeapWord*)obj < _gen_boundary) { 750 _rs->write_ref_field_gc_par(p, obj); 751 } 752 } 753 } 754 } 755 756 void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 757 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 758 759 class ParNewRefProcTaskProxy: public AbstractGangTask { 760 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; 761 public: 762 ParNewRefProcTaskProxy(ProcessTask& task, 763 ParNewGeneration& gen, 764 Generation& old_gen, 765 HeapWord* young_old_boundary, 766 ParScanThreadStateSet& state_set); 767 768 private: 769 virtual void work(uint worker_id); 770 virtual void set_for_termination(int active_workers) { 771 _state_set.terminator()->reset_for_reuse(active_workers); 772 } 773 private: 774 ParNewGeneration& _gen; 775 ProcessTask& _task; 776 Generation& _old_gen; 777 HeapWord* _young_old_boundary; 778 ParScanThreadStateSet& _state_set; 779 }; 780 781 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task, 782 ParNewGeneration& gen, 783 Generation& old_gen, 784 HeapWord* young_old_boundary, 785 ParScanThreadStateSet& state_set) 786 : AbstractGangTask("ParNewGeneration parallel reference processing"), 787 _gen(gen), 788 _task(task), 789 _old_gen(old_gen), 790 _young_old_boundary(young_old_boundary), 791 _state_set(state_set) 792 { 793 } 794 795 void ParNewRefProcTaskProxy::work(uint worker_id) 796 { 797 ResourceMark rm; 798 HandleMark hm; 799 ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id); 800 par_scan_state.set_young_old_boundary(_young_old_boundary); 801 _task.work(worker_id, par_scan_state.is_alive_closure(), 802 par_scan_state.keep_alive_closure(), 803 par_scan_state.evacuate_followers_closure()); 804 } 805 806 class ParNewRefEnqueueTaskProxy: public AbstractGangTask { 807 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; 808 EnqueueTask& _task; 809 810 public: 811 ParNewRefEnqueueTaskProxy(EnqueueTask& task) 812 : AbstractGangTask("ParNewGeneration parallel reference enqueue"), 813 _task(task) 814 { } 815 816 virtual void work(uint worker_id) 817 { 818 _task.work(worker_id); 819 } 820 }; 821 822 823 void ParNewRefProcTaskExecutor::execute(ProcessTask& task) 824 { 825 GenCollectedHeap* gch = GenCollectedHeap::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(gch->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 AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy(); 914 FlexibleWorkGang* workers = gch->workers(); 915 assert(workers != NULL, "Need workgang for parallel work"); 916 int active_workers = 917 AdaptiveSizePolicy::calc_active_workers(workers->total_workers(), 918 workers->active_workers(), 919 Threads::number_of_non_daemon_threads()); 920 workers->set_active_workers(active_workers); 921 _old_gen = gch->old_gen(); 922 923 // If the next generation is too full to accommodate worst-case promotion 924 // from this generation, pass on collection; let the next generation 925 // do it. 926 if (!collection_attempt_is_safe()) { 927 gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one 928 return; 929 } 930 assert(to()->is_empty(), "Else not collection_attempt_is_safe"); 931 932 _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start()); 933 gch->trace_heap_before_gc(gc_tracer()); 934 935 init_assuming_no_promotion_failure(); 936 937 if (UseAdaptiveSizePolicy) { 938 set_survivor_overflow(false); 939 size_policy->minor_collection_begin(); 940 } 941 942 GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, _gc_tracer.gc_id()); 943 // Capture heap used before collection (for printing). 944 size_t gch_prev_used = gch->used(); 945 946 age_table()->clear(); 947 to()->clear(SpaceDecorator::Mangle); 948 949 gch->save_marks(); 950 assert(workers != NULL, "Need parallel worker threads."); 951 int n_workers = active_workers; 952 953 // Set the correct parallelism (number of queues) in the reference processor 954 ref_processor()->set_active_mt_degree(n_workers); 955 956 // Always set the terminator for the active number of workers 957 // because only those workers go through the termination protocol. 958 ParallelTaskTerminator _term(n_workers, task_queues()); 959 ParScanThreadStateSet thread_state_set(workers->active_workers(), 960 *to(), *this, *_old_gen, *task_queues(), 961 _overflow_stacks, desired_plab_sz(), _term); 962 963 ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set); 964 gch->set_par_threads(n_workers); 965 gch->rem_set()->prepare_for_younger_refs_iterate(true); 966 // It turns out that even when we're using 1 thread, doing the work in a 967 // separate thread causes wide variance in run times. We can't help this 968 // in the multi-threaded case, but we special-case n=1 here to get 969 // repeatable measurements of the 1-thread overhead of the parallel code. 970 if (n_workers > 1) { 971 StrongRootsScope srs; 972 workers->run_task(&tsk); 973 } else { 974 StrongRootsScope srs; 975 tsk.work(0); 976 } 977 thread_state_set.reset(0 /* Bad value in debug if not reset */, 978 promotion_failed()); 979 980 // Trace and reset failed promotion info. 981 if (promotion_failed()) { 982 thread_state_set.trace_promotion_failed(gc_tracer()); 983 } 984 985 // Process (weak) reference objects found during scavenge. 986 ReferenceProcessor* rp = ref_processor(); 987 IsAliveClosure is_alive(this); 988 ScanWeakRefClosure scan_weak_ref(this); 989 KeepAliveClosure keep_alive(&scan_weak_ref); 990 ScanClosure scan_without_gc_barrier(this, false); 991 ScanClosureWithParBarrier scan_with_gc_barrier(this, true); 992 set_promo_failure_scan_stack_closure(&scan_without_gc_barrier); 993 EvacuateFollowersClosureGeneral evacuate_followers(gch, _level, 994 &scan_without_gc_barrier, &scan_with_gc_barrier); 995 rp->setup_policy(clear_all_soft_refs); 996 // Can the mt_degree be set later (at run_task() time would be best)? 997 rp->set_active_mt_degree(active_workers); 998 ReferenceProcessorStats stats; 999 if (rp->processing_is_mt()) { 1000 ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); 1001 stats = rp->process_discovered_references(&is_alive, &keep_alive, 1002 &evacuate_followers, &task_executor, 1003 _gc_timer, _gc_tracer.gc_id()); 1004 } else { 1005 thread_state_set.flush(); 1006 gch->set_par_threads(0); // 0 ==> non-parallel. 1007 gch->save_marks(); 1008 stats = rp->process_discovered_references(&is_alive, &keep_alive, 1009 &evacuate_followers, NULL, 1010 _gc_timer, _gc_tracer.gc_id()); 1011 } 1012 _gc_tracer.report_gc_reference_stats(stats); 1013 if (!promotion_failed()) { 1014 // Swap the survivor spaces. 1015 eden()->clear(SpaceDecorator::Mangle); 1016 from()->clear(SpaceDecorator::Mangle); 1017 if (ZapUnusedHeapArea) { 1018 // This is now done here because of the piece-meal mangling which 1019 // can check for valid mangling at intermediate points in the 1020 // collection(s). When a minor collection fails to collect 1021 // sufficient space resizing of the young generation can occur 1022 // an redistribute the spaces in the young generation. Mangle 1023 // here so that unzapped regions don't get distributed to 1024 // other spaces. 1025 to()->mangle_unused_area(); 1026 } 1027 swap_spaces(); 1028 1029 // A successful scavenge should restart the GC time limit count which is 1030 // for full GC's. 1031 size_policy->reset_gc_overhead_limit_count(); 1032 1033 assert(to()->is_empty(), "to space should be empty now"); 1034 1035 adjust_desired_tenuring_threshold(); 1036 } else { 1037 handle_promotion_failed(gch, thread_state_set); 1038 } 1039 // set new iteration safe limit for the survivor spaces 1040 from()->set_concurrent_iteration_safe_limit(from()->top()); 1041 to()->set_concurrent_iteration_safe_limit(to()->top()); 1042 1043 if (ResizePLAB) { 1044 plab_stats()->adjust_desired_plab_sz(n_workers); 1045 } 1046 1047 if (PrintGC && !PrintGCDetails) { 1048 gch->print_heap_change(gch_prev_used); 1049 } 1050 1051 TASKQUEUE_STATS_ONLY(if (PrintTerminationStats) thread_state_set.print_termination_stats()); 1052 TASKQUEUE_STATS_ONLY(if (PrintTaskqueue) thread_state_set.print_taskqueue_stats()); 1053 1054 if (UseAdaptiveSizePolicy) { 1055 size_policy->minor_collection_end(gch->gc_cause()); 1056 size_policy->avg_survived()->sample(from()->used()); 1057 } 1058 1059 // We need to use a monotonically non-decreasing time in ms 1060 // or we will see time-warp warnings and os::javaTimeMillis() 1061 // does not guarantee monotonicity. 1062 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 1063 update_time_of_last_gc(now); 1064 1065 rp->set_enqueuing_is_done(true); 1066 if (rp->processing_is_mt()) { 1067 ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); 1068 rp->enqueue_discovered_references(&task_executor); 1069 } else { 1070 rp->enqueue_discovered_references(NULL); 1071 } 1072 rp->verify_no_references_recorded(); 1073 1074 gch->trace_heap_after_gc(gc_tracer()); 1075 _gc_tracer.report_tenuring_threshold(tenuring_threshold()); 1076 1077 _gc_timer->register_gc_end(); 1078 1079 _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions()); 1080 } 1081 1082 static int sum; 1083 void ParNewGeneration::waste_some_time() { 1084 for (int i = 0; i < 100; i++) { 1085 sum += i; 1086 } 1087 } 1088 1089 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4); 1090 1091 // Because of concurrency, there are times where an object for which 1092 // "is_forwarded()" is true contains an "interim" forwarding pointer 1093 // value. Such a value will soon be overwritten with a real value. 1094 // This method requires "obj" to have a forwarding pointer, and waits, if 1095 // necessary for a real one to be inserted, and returns it. 1096 1097 oop ParNewGeneration::real_forwardee(oop obj) { 1098 oop forward_ptr = obj->forwardee(); 1099 if (forward_ptr != ClaimedForwardPtr) { 1100 return forward_ptr; 1101 } else { 1102 return real_forwardee_slow(obj); 1103 } 1104 } 1105 1106 oop ParNewGeneration::real_forwardee_slow(oop obj) { 1107 // Spin-read if it is claimed but not yet written by another thread. 1108 oop forward_ptr = obj->forwardee(); 1109 while (forward_ptr == ClaimedForwardPtr) { 1110 waste_some_time(); 1111 assert(obj->is_forwarded(), "precondition"); 1112 forward_ptr = obj->forwardee(); 1113 } 1114 return forward_ptr; 1115 } 1116 1117 void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) { 1118 if (m->must_be_preserved_for_promotion_failure(obj)) { 1119 // We should really have separate per-worker stacks, rather 1120 // than use locking of a common pair of stacks. 1121 MutexLocker ml(ParGCRareEvent_lock); 1122 preserve_mark(obj, m); 1123 } 1124 } 1125 1126 // Multiple GC threads may try to promote an object. If the object 1127 // is successfully promoted, a forwarding pointer will be installed in 1128 // the object in the young generation. This method claims the right 1129 // to install the forwarding pointer before it copies the object, 1130 // thus avoiding the need to undo the copy as in 1131 // copy_to_survivor_space_avoiding_with_undo. 1132 1133 oop ParNewGeneration::copy_to_survivor_space( 1134 ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) { 1135 // In the sequential version, this assert also says that the object is 1136 // not forwarded. That might not be the case here. It is the case that 1137 // the caller observed it to be not forwarded at some time in the past. 1138 assert(is_in_reserved(old), "shouldn't be scavenging this oop"); 1139 1140 // The sequential code read "old->age()" below. That doesn't work here, 1141 // since the age is in the mark word, and that might be overwritten with 1142 // a forwarding pointer by a parallel thread. So we must save the mark 1143 // word in a local and then analyze it. 1144 oopDesc dummyOld; 1145 dummyOld.set_mark(m); 1146 assert(!dummyOld.is_forwarded(), 1147 "should not be called with forwarding pointer mark word."); 1148 1149 oop new_obj = NULL; 1150 oop forward_ptr; 1151 1152 // Try allocating obj in to-space (unless too old) 1153 if (dummyOld.age() < tenuring_threshold()) { 1154 new_obj = (oop)par_scan_state->alloc_in_to_space(sz); 1155 if (new_obj == NULL) { 1156 set_survivor_overflow(true); 1157 } 1158 } 1159 1160 if (new_obj == NULL) { 1161 // Either to-space is full or we decided to promote 1162 // try allocating obj tenured 1163 1164 // Attempt to install a null forwarding pointer (atomically), 1165 // to claim the right to install the real forwarding pointer. 1166 forward_ptr = old->forward_to_atomic(ClaimedForwardPtr); 1167 if (forward_ptr != NULL) { 1168 // someone else beat us to it. 1169 return real_forwardee(old); 1170 } 1171 1172 if (!_promotion_failed) { 1173 new_obj = _old_gen->par_promote(par_scan_state->thread_num(), 1174 old, m, sz); 1175 } 1176 1177 if (new_obj == NULL) { 1178 // promotion failed, forward to self 1179 _promotion_failed = true; 1180 new_obj = old; 1181 1182 preserve_mark_if_necessary(old, m); 1183 par_scan_state->register_promotion_failure(sz); 1184 } 1185 1186 old->forward_to(new_obj); 1187 forward_ptr = NULL; 1188 } else { 1189 // Is in to-space; do copying ourselves. 1190 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz); 1191 assert(GenCollectedHeap::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value."); 1192 forward_ptr = old->forward_to_atomic(new_obj); 1193 // Restore the mark word copied above. 1194 new_obj->set_mark(m); 1195 // Increment age if obj still in new generation 1196 new_obj->incr_age(); 1197 par_scan_state->age_table()->add(new_obj, sz); 1198 } 1199 assert(new_obj != NULL, "just checking"); 1200 1201 #ifndef PRODUCT 1202 // This code must come after the CAS test, or it will print incorrect 1203 // information. 1204 if (TraceScavenge) { 1205 gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}", 1206 is_in_reserved(new_obj) ? "copying" : "tenuring", 1207 new_obj->klass()->internal_name(), p2i(old), p2i(new_obj), new_obj->size()); 1208 } 1209 #endif 1210 1211 if (forward_ptr == NULL) { 1212 oop obj_to_push = new_obj; 1213 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) { 1214 // Length field used as index of next element to be scanned. 1215 // Real length can be obtained from real_forwardee() 1216 arrayOop(old)->set_length(0); 1217 obj_to_push = old; 1218 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push, 1219 "push forwarded object"); 1220 } 1221 // Push it on one of the queues of to-be-scanned objects. 1222 bool simulate_overflow = false; 1223 NOT_PRODUCT( 1224 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) { 1225 // simulate a stack overflow 1226 simulate_overflow = true; 1227 } 1228 ) 1229 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) { 1230 // Add stats for overflow pushes. 1231 if (Verbose && PrintGCDetails) { 1232 gclog_or_tty->print("queue overflow!\n"); 1233 } 1234 push_on_overflow_list(old, par_scan_state); 1235 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0)); 1236 } 1237 1238 return new_obj; 1239 } 1240 1241 // Oops. Someone beat us to it. Undo the allocation. Where did we 1242 // allocate it? 1243 if (is_in_reserved(new_obj)) { 1244 // Must be in to_space. 1245 assert(to()->is_in_reserved(new_obj), "Checking"); 1246 if (forward_ptr == ClaimedForwardPtr) { 1247 // Wait to get the real forwarding pointer value. 1248 forward_ptr = real_forwardee(old); 1249 } 1250 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz); 1251 } 1252 1253 return forward_ptr; 1254 } 1255 1256 #ifndef PRODUCT 1257 // It's OK to call this multi-threaded; the worst thing 1258 // that can happen is that we'll get a bunch of closely 1259 // spaced simulated overflows, but that's OK, in fact 1260 // probably good as it would exercise the overflow code 1261 // under contention. 1262 bool ParNewGeneration::should_simulate_overflow() { 1263 if (_overflow_counter-- <= 0) { // just being defensive 1264 _overflow_counter = ParGCWorkQueueOverflowInterval; 1265 return true; 1266 } else { 1267 return false; 1268 } 1269 } 1270 #endif 1271 1272 // In case we are using compressed oops, we need to be careful. 1273 // If the object being pushed is an object array, then its length 1274 // field keeps track of the "grey boundary" at which the next 1275 // incremental scan will be done (see ParGCArrayScanChunk). 1276 // When using compressed oops, this length field is kept in the 1277 // lower 32 bits of the erstwhile klass word and cannot be used 1278 // for the overflow chaining pointer (OCP below). As such the OCP 1279 // would itself need to be compressed into the top 32-bits in this 1280 // case. Unfortunately, see below, in the event that we have a 1281 // promotion failure, the node to be pushed on the list can be 1282 // outside of the Java heap, so the heap-based pointer compression 1283 // would not work (we would have potential aliasing between C-heap 1284 // and Java-heap pointers). For this reason, when using compressed 1285 // oops, we simply use a worker-thread-local, non-shared overflow 1286 // list in the form of a growable array, with a slightly different 1287 // overflow stack draining strategy. If/when we start using fat 1288 // stacks here, we can go back to using (fat) pointer chains 1289 // (although some performance comparisons would be useful since 1290 // single global lists have their own performance disadvantages 1291 // as we were made painfully aware not long ago, see 6786503). 1292 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff)) 1293 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) { 1294 assert(is_in_reserved(from_space_obj), "Should be from this generation"); 1295 if (ParGCUseLocalOverflow) { 1296 // In the case of compressed oops, we use a private, not-shared 1297 // overflow stack. 1298 par_scan_state->push_on_overflow_stack(from_space_obj); 1299 } else { 1300 assert(!UseCompressedOops, "Error"); 1301 // if the object has been forwarded to itself, then we cannot 1302 // use the klass pointer for the linked list. Instead we have 1303 // to allocate an oopDesc in the C-Heap and use that for the linked list. 1304 // XXX This is horribly inefficient when a promotion failure occurs 1305 // and should be fixed. XXX FIX ME !!! 1306 #ifndef PRODUCT 1307 Atomic::inc_ptr(&_num_par_pushes); 1308 assert(_num_par_pushes > 0, "Tautology"); 1309 #endif 1310 if (from_space_obj->forwardee() == from_space_obj) { 1311 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC); 1312 listhead->forward_to(from_space_obj); 1313 from_space_obj = listhead; 1314 } 1315 oop observed_overflow_list = _overflow_list; 1316 oop cur_overflow_list; 1317 do { 1318 cur_overflow_list = observed_overflow_list; 1319 if (cur_overflow_list != BUSY) { 1320 from_space_obj->set_klass_to_list_ptr(cur_overflow_list); 1321 } else { 1322 from_space_obj->set_klass_to_list_ptr(NULL); 1323 } 1324 observed_overflow_list = 1325 (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list); 1326 } while (cur_overflow_list != observed_overflow_list); 1327 } 1328 } 1329 1330 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) { 1331 bool res; 1332 1333 if (ParGCUseLocalOverflow) { 1334 res = par_scan_state->take_from_overflow_stack(); 1335 } else { 1336 assert(!UseCompressedOops, "Error"); 1337 res = take_from_overflow_list_work(par_scan_state); 1338 } 1339 return res; 1340 } 1341 1342 1343 // *NOTE*: The overflow list manipulation code here and 1344 // in CMSCollector:: are very similar in shape, 1345 // except that in the CMS case we thread the objects 1346 // directly into the list via their mark word, and do 1347 // not need to deal with special cases below related 1348 // to chunking of object arrays and promotion failure 1349 // handling. 1350 // CR 6797058 has been filed to attempt consolidation of 1351 // the common code. 1352 // Because of the common code, if you make any changes in 1353 // the code below, please check the CMS version to see if 1354 // similar changes might be needed. 1355 // See CMSCollector::par_take_from_overflow_list() for 1356 // more extensive documentation comments. 1357 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) { 1358 ObjToScanQueue* work_q = par_scan_state->work_queue(); 1359 // How many to take? 1360 size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 1361 (size_t)ParGCDesiredObjsFromOverflowList); 1362 1363 assert(!UseCompressedOops, "Error"); 1364 assert(par_scan_state->overflow_stack() == NULL, "Error"); 1365 if (_overflow_list == NULL) return false; 1366 1367 // Otherwise, there was something there; try claiming the list. 1368 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1369 // Trim off a prefix of at most objsFromOverflow items 1370 Thread* tid = Thread::current(); 1371 size_t spin_count = (size_t)ParallelGCThreads; 1372 size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100); 1373 for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) { 1374 // someone grabbed it before we did ... 1375 // ... we spin for a short while... 1376 os::sleep(tid, sleep_time_millis, false); 1377 if (_overflow_list == NULL) { 1378 // nothing left to take 1379 return false; 1380 } else if (_overflow_list != BUSY) { 1381 // try and grab the prefix 1382 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1383 } 1384 } 1385 if (prefix == NULL || prefix == BUSY) { 1386 // Nothing to take or waited long enough 1387 if (prefix == NULL) { 1388 // Write back the NULL in case we overwrote it with BUSY above 1389 // and it is still the same value. 1390 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1391 } 1392 return false; 1393 } 1394 assert(prefix != NULL && prefix != BUSY, "Error"); 1395 size_t i = 1; 1396 oop cur = prefix; 1397 while (i < objsFromOverflow && cur->klass_or_null() != NULL) { 1398 i++; cur = cur->list_ptr_from_klass(); 1399 } 1400 1401 // Reattach remaining (suffix) to overflow list 1402 if (cur->klass_or_null() == NULL) { 1403 // Write back the NULL in lieu of the BUSY we wrote 1404 // above and it is still the same value. 1405 if (_overflow_list == BUSY) { 1406 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1407 } 1408 } else { 1409 assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error"); 1410 oop suffix = cur->list_ptr_from_klass(); // suffix will be put back on global list 1411 cur->set_klass_to_list_ptr(NULL); // break off suffix 1412 // It's possible that the list is still in the empty(busy) state 1413 // we left it in a short while ago; in that case we may be 1414 // able to place back the suffix. 1415 oop observed_overflow_list = _overflow_list; 1416 oop cur_overflow_list = observed_overflow_list; 1417 bool attached = false; 1418 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { 1419 observed_overflow_list = 1420 (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1421 if (cur_overflow_list == observed_overflow_list) { 1422 attached = true; 1423 break; 1424 } else cur_overflow_list = observed_overflow_list; 1425 } 1426 if (!attached) { 1427 // Too bad, someone else got in in between; we'll need to do a splice. 1428 // Find the last item of suffix list 1429 oop last = suffix; 1430 while (last->klass_or_null() != NULL) { 1431 last = last->list_ptr_from_klass(); 1432 } 1433 // Atomically prepend suffix to current overflow list 1434 observed_overflow_list = _overflow_list; 1435 do { 1436 cur_overflow_list = observed_overflow_list; 1437 if (cur_overflow_list != BUSY) { 1438 // Do the splice ... 1439 last->set_klass_to_list_ptr(cur_overflow_list); 1440 } else { // cur_overflow_list == BUSY 1441 last->set_klass_to_list_ptr(NULL); 1442 } 1443 observed_overflow_list = 1444 (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1445 } while (cur_overflow_list != observed_overflow_list); 1446 } 1447 } 1448 1449 // Push objects on prefix list onto this thread's work queue 1450 assert(prefix != NULL && prefix != BUSY, "program logic"); 1451 cur = prefix; 1452 ssize_t n = 0; 1453 while (cur != NULL) { 1454 oop obj_to_push = cur->forwardee(); 1455 oop next = cur->list_ptr_from_klass(); 1456 cur->set_klass(obj_to_push->klass()); 1457 // This may be an array object that is self-forwarded. In that case, the list pointer 1458 // space, cur, is not in the Java heap, but rather in the C-heap and should be freed. 1459 if (!is_in_reserved(cur)) { 1460 // This can become a scaling bottleneck when there is work queue overflow coincident 1461 // with promotion failure. 1462 oopDesc* f = cur; 1463 FREE_C_HEAP_ARRAY(oopDesc, f); 1464 } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) { 1465 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 1466 obj_to_push = cur; 1467 } 1468 bool ok = work_q->push(obj_to_push); 1469 assert(ok, "Should have succeeded"); 1470 cur = next; 1471 n++; 1472 } 1473 TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n)); 1474 #ifndef PRODUCT 1475 assert(_num_par_pushes >= n, "Too many pops?"); 1476 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes); 1477 #endif 1478 return true; 1479 } 1480 #undef BUSY 1481 1482 void ParNewGeneration::ref_processor_init() { 1483 if (_ref_processor == NULL) { 1484 // Allocate and initialize a reference processor 1485 _ref_processor = 1486 new ReferenceProcessor(_reserved, // span 1487 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing 1488 (int) ParallelGCThreads, // mt processing degree 1489 refs_discovery_is_mt(), // mt discovery 1490 (int) ParallelGCThreads, // mt discovery degree 1491 refs_discovery_is_atomic(), // atomic_discovery 1492 NULL); // is_alive_non_header 1493 } 1494 } 1495 1496 const char* ParNewGeneration::name() const { 1497 return "par new generation"; 1498 }