parNewGeneration.cpp revision 8528:01d947f8d411
1/* 2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25#include "precompiled.hpp" 26#include "gc/cms/compactibleFreeListSpace.hpp" 27#include "gc/cms/concurrentMarkSweepGeneration.hpp" 28#include "gc/cms/parNewGeneration.hpp" 29#include "gc/cms/parOopClosures.inline.hpp" 30#include "gc/serial/defNewGeneration.inline.hpp" 31#include "gc/shared/adaptiveSizePolicy.hpp" 32#include "gc/shared/ageTable.hpp" 33#include "gc/shared/copyFailedInfo.hpp" 34#include "gc/shared/gcHeapSummary.hpp" 35#include "gc/shared/gcTimer.hpp" 36#include "gc/shared/gcTrace.hpp" 37#include "gc/shared/gcTraceTime.hpp" 38#include "gc/shared/genCollectedHeap.hpp" 39#include "gc/shared/genOopClosures.inline.hpp" 40#include "gc/shared/generation.hpp" 41#include "gc/shared/plab.inline.hpp" 42#include "gc/shared/referencePolicy.hpp" 43#include "gc/shared/space.hpp" 44#include "gc/shared/spaceDecorator.hpp" 45#include "gc/shared/strongRootsScope.hpp" 46#include "gc/shared/taskqueue.inline.hpp" 47#include "gc/shared/workgroup.hpp" 48#include "memory/resourceArea.hpp" 49#include "oops/objArrayOop.hpp" 50#include "oops/oop.inline.hpp" 51#include "runtime/atomic.inline.hpp" 52#include "runtime/handles.hpp" 53#include "runtime/handles.inline.hpp" 54#include "runtime/java.hpp" 55#include "runtime/thread.inline.hpp" 56#include "utilities/copy.hpp" 57#include "utilities/globalDefinitions.hpp" 58#include "utilities/stack.inline.hpp" 59 60#ifdef _MSC_VER 61#pragma warning( push ) 62#pragma warning( disable:4355 ) // 'this' : used in base member initializer list 63#endif 64ParScanThreadState::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 104void 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 113bool 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 119void 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 158void 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 189bool 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 218void 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 224HeapWord* 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 276void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, size_t word_sz) { 277 to_space_alloc_buffer()->undo_allocation(obj, word_sz); 278} 279 280void ParScanThreadState::print_promotion_failure_size() { 281 if (_promotion_failed_info.has_failed() && PrintPromotionFailure) { 282 gclog_or_tty->print(" (%d: promotion failure size = " SIZE_FORMAT ") ", 283 _thread_num, _promotion_failed_info.first_size()); 284 } 285} 286 287class ParScanThreadStateSet: private ResourceArray { 288public: 289 // Initializes states for the specified number of threads; 290 ParScanThreadStateSet(int num_threads, 291 Space& to_space, 292 ParNewGeneration& gen, 293 Generation& old_gen, 294 ObjToScanQueueSet& queue_set, 295 Stack<oop, mtGC>* overflow_stacks_, 296 size_t desired_plab_sz, 297 ParallelTaskTerminator& term); 298 299 ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); } 300 301 inline ParScanThreadState& thread_state(int i); 302 303 void trace_promotion_failed(const YoungGCTracer* gc_tracer); 304 void reset(uint active_workers, bool promotion_failed); 305 void flush(); 306 307 #if TASKQUEUE_STATS 308 static void 309 print_termination_stats_hdr(outputStream* const st = gclog_or_tty); 310 void print_termination_stats(outputStream* const st = gclog_or_tty); 311 static void 312 print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty); 313 void print_taskqueue_stats(outputStream* const st = gclog_or_tty); 314 void reset_stats(); 315 #endif // TASKQUEUE_STATS 316 317private: 318 ParallelTaskTerminator& _term; 319 ParNewGeneration& _gen; 320 Generation& _old_gen; 321 public: 322 bool is_valid(int id) const { return id < length(); } 323 ParallelTaskTerminator* terminator() { return &_term; } 324}; 325 326 327ParScanThreadStateSet::ParScanThreadStateSet( 328 int num_threads, Space& to_space, ParNewGeneration& gen, 329 Generation& old_gen, ObjToScanQueueSet& queue_set, 330 Stack<oop, mtGC>* overflow_stacks, 331 size_t desired_plab_sz, ParallelTaskTerminator& term) 332 : ResourceArray(sizeof(ParScanThreadState), num_threads), 333 _gen(gen), _old_gen(old_gen), _term(term) 334{ 335 assert(num_threads > 0, "sanity check!"); 336 assert(ParGCUseLocalOverflow == (overflow_stacks != NULL), 337 "overflow_stack allocation mismatch"); 338 // Initialize states. 339 for (int i = 0; i < num_threads; ++i) { 340 new ((ParScanThreadState*)_data + i) 341 ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set, 342 overflow_stacks, desired_plab_sz, term); 343 } 344} 345 346inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i) 347{ 348 assert(i >= 0 && i < length(), "sanity check!"); 349 return ((ParScanThreadState*)_data)[i]; 350} 351 352void ParScanThreadStateSet::trace_promotion_failed(const YoungGCTracer* gc_tracer) { 353 for (int i = 0; i < length(); ++i) { 354 if (thread_state(i).promotion_failed()) { 355 gc_tracer->report_promotion_failed(thread_state(i).promotion_failed_info()); 356 thread_state(i).promotion_failed_info().reset(); 357 } 358 } 359} 360 361void ParScanThreadStateSet::reset(uint active_threads, bool promotion_failed) 362{ 363 _term.reset_for_reuse(active_threads); 364 if (promotion_failed) { 365 for (int i = 0; i < length(); ++i) { 366 thread_state(i).print_promotion_failure_size(); 367 } 368 } 369} 370 371#if TASKQUEUE_STATS 372void 373ParScanThreadState::reset_stats() 374{ 375 taskqueue_stats().reset(); 376 _term_attempts = 0; 377 _overflow_refills = 0; 378 _overflow_refill_objs = 0; 379} 380 381void ParScanThreadStateSet::reset_stats() 382{ 383 for (int i = 0; i < length(); ++i) { 384 thread_state(i).reset_stats(); 385 } 386} 387 388void 389ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st) 390{ 391 st->print_raw_cr("GC Termination Stats"); 392 st->print_raw_cr(" elapsed --strong roots-- " 393 "-------termination-------"); 394 st->print_raw_cr("thr ms ms % " 395 " ms % attempts"); 396 st->print_raw_cr("--- --------- --------- ------ " 397 "--------- ------ --------"); 398} 399 400void ParScanThreadStateSet::print_termination_stats(outputStream* const st) 401{ 402 print_termination_stats_hdr(st); 403 404 for (int i = 0; i < length(); ++i) { 405 const ParScanThreadState & pss = thread_state(i); 406 const double elapsed_ms = pss.elapsed_time() * 1000.0; 407 const double s_roots_ms = pss.strong_roots_time() * 1000.0; 408 const double term_ms = pss.term_time() * 1000.0; 409 st->print_cr("%3d %9.2f %9.2f %6.2f " 410 "%9.2f %6.2f " SIZE_FORMAT_W(8), 411 i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms, 412 term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts()); 413 } 414} 415 416// Print stats related to work queue activity. 417void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st) 418{ 419 st->print_raw_cr("GC Task Stats"); 420 st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr(); 421 st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr(); 422} 423 424void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st) 425{ 426 print_taskqueue_stats_hdr(st); 427 428 TaskQueueStats totals; 429 for (int i = 0; i < length(); ++i) { 430 const ParScanThreadState & pss = thread_state(i); 431 const TaskQueueStats & stats = pss.taskqueue_stats(); 432 st->print("%3d ", i); stats.print(st); st->cr(); 433 totals += stats; 434 435 if (pss.overflow_refills() > 0) { 436 st->print_cr(" " SIZE_FORMAT_W(10) " overflow refills " 437 SIZE_FORMAT_W(10) " overflow objects", 438 pss.overflow_refills(), pss.overflow_refill_objs()); 439 } 440 } 441 st->print("tot "); totals.print(st); st->cr(); 442 443 DEBUG_ONLY(totals.verify()); 444} 445#endif // TASKQUEUE_STATS 446 447void ParScanThreadStateSet::flush() 448{ 449 // Work in this loop should be kept as lightweight as 450 // possible since this might otherwise become a bottleneck 451 // to scaling. Should we add heavy-weight work into this 452 // loop, consider parallelizing the loop into the worker threads. 453 for (int i = 0; i < length(); ++i) { 454 ParScanThreadState& par_scan_state = thread_state(i); 455 456 // Flush stats related to To-space PLAB activity and 457 // retire the last buffer. 458 par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_gen.plab_stats()); 459 460 // Every thread has its own age table. We need to merge 461 // them all into one. 462 ageTable *local_table = par_scan_state.age_table(); 463 _gen.age_table()->merge(local_table); 464 465 // Inform old gen that we're done. 466 _old_gen.par_promote_alloc_done(i); 467 _old_gen.par_oop_since_save_marks_iterate_done(i); 468 } 469 470 if (UseConcMarkSweepGC) { 471 // We need to call this even when ResizeOldPLAB is disabled 472 // so as to avoid breaking some asserts. While we may be able 473 // to avoid this by reorganizing the code a bit, I am loathe 474 // to do that unless we find cases where ergo leads to bad 475 // performance. 476 CFLS_LAB::compute_desired_plab_size(); 477 } 478} 479 480ParScanClosure::ParScanClosure(ParNewGeneration* g, 481 ParScanThreadState* par_scan_state) : 482 OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g) 483{ 484 assert(_g->level() == 0, "Optimized for youngest generation"); 485 _boundary = _g->reserved().end(); 486} 487 488void ParScanWithBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, false); } 489void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); } 490 491void ParScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, false); } 492void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); } 493 494void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); } 495void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); } 496 497void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); } 498void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); } 499 500ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g, 501 ParScanThreadState* par_scan_state) 502 : ScanWeakRefClosure(g), _par_scan_state(par_scan_state) 503{} 504 505void ParScanWeakRefClosure::do_oop(oop* p) { ParScanWeakRefClosure::do_oop_work(p); } 506void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); } 507 508#ifdef WIN32 509#pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */ 510#endif 511 512ParEvacuateFollowersClosure::ParEvacuateFollowersClosure( 513 ParScanThreadState* par_scan_state_, 514 ParScanWithoutBarrierClosure* to_space_closure_, 515 ParScanWithBarrierClosure* old_gen_closure_, 516 ParRootScanWithoutBarrierClosure* to_space_root_closure_, 517 ParNewGeneration* par_gen_, 518 ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_, 519 ObjToScanQueueSet* task_queues_, 520 ParallelTaskTerminator* terminator_) : 521 522 _par_scan_state(par_scan_state_), 523 _to_space_closure(to_space_closure_), 524 _old_gen_closure(old_gen_closure_), 525 _to_space_root_closure(to_space_root_closure_), 526 _old_gen_root_closure(old_gen_root_closure_), 527 _par_gen(par_gen_), 528 _task_queues(task_queues_), 529 _terminator(terminator_) 530{} 531 532void ParEvacuateFollowersClosure::do_void() { 533 ObjToScanQueue* work_q = par_scan_state()->work_queue(); 534 535 while (true) { 536 537 // Scan to-space and old-gen objs until we run out of both. 538 oop obj_to_scan; 539 par_scan_state()->trim_queues(0); 540 541 // We have no local work, attempt to steal from other threads. 542 543 // attempt to steal work from promoted. 544 if (task_queues()->steal(par_scan_state()->thread_num(), 545 par_scan_state()->hash_seed(), 546 obj_to_scan)) { 547 bool res = work_q->push(obj_to_scan); 548 assert(res, "Empty queue should have room for a push."); 549 550 // if successful, goto Start. 551 continue; 552 553 // try global overflow list. 554 } else if (par_gen()->take_from_overflow_list(par_scan_state())) { 555 continue; 556 } 557 558 // Otherwise, offer termination. 559 par_scan_state()->start_term_time(); 560 if (terminator()->offer_termination()) break; 561 par_scan_state()->end_term_time(); 562 } 563 assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0, 564 "Broken overflow list?"); 565 // Finish the last termination pause. 566 par_scan_state()->end_term_time(); 567} 568 569ParNewGenTask::ParNewGenTask(ParNewGeneration* gen, Generation* old_gen, 570 HeapWord* young_old_boundary, ParScanThreadStateSet* state_set, 571 StrongRootsScope* strong_roots_scope) : 572 AbstractGangTask("ParNewGeneration collection"), 573 _gen(gen), _old_gen(old_gen), 574 _young_old_boundary(young_old_boundary), 575 _state_set(state_set), 576 _strong_roots_scope(strong_roots_scope) 577 {} 578 579void ParNewGenTask::work(uint worker_id) { 580 GenCollectedHeap* gch = GenCollectedHeap::heap(); 581 // Since this is being done in a separate thread, need new resource 582 // and handle marks. 583 ResourceMark rm; 584 HandleMark hm; 585 586 ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id); 587 assert(_state_set->is_valid(worker_id), "Should not have been called"); 588 589 par_scan_state.set_young_old_boundary(_young_old_boundary); 590 591 KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(), 592 gch->rem_set()->klass_rem_set()); 593 CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure, 594 &par_scan_state.to_space_root_closure(), 595 false); 596 597 par_scan_state.start_strong_roots(); 598 gch->gen_process_roots(_strong_roots_scope, 599 _gen->level(), 600 true, // Process younger gens, if any, 601 // as strong roots. 602 GenCollectedHeap::SO_ScavengeCodeCache, 603 GenCollectedHeap::StrongAndWeakRoots, 604 &par_scan_state.to_space_root_closure(), 605 &par_scan_state.older_gen_closure(), 606 &cld_scan_closure); 607 608 par_scan_state.end_strong_roots(); 609 610 // "evacuate followers". 611 par_scan_state.evacuate_followers_closure().do_void(); 612} 613 614#ifdef _MSC_VER 615#pragma warning( push ) 616#pragma warning( disable:4355 ) // 'this' : used in base member initializer list 617#endif 618ParNewGeneration:: 619ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level) 620 : DefNewGeneration(rs, initial_byte_size, level, "PCopy"), 621 _overflow_list(NULL), 622 _is_alive_closure(this), 623 _plab_stats(YoungPLABSize, PLABWeight) 624{ 625 NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;) 626 NOT_PRODUCT(_num_par_pushes = 0;) 627 _task_queues = new ObjToScanQueueSet(ParallelGCThreads); 628 guarantee(_task_queues != NULL, "task_queues allocation failure."); 629 630 for (uint i1 = 0; i1 < ParallelGCThreads; i1++) { 631 ObjToScanQueue *q = new ObjToScanQueue(); 632 guarantee(q != NULL, "work_queue Allocation failure."); 633 _task_queues->register_queue(i1, q); 634 } 635 636 for (uint i2 = 0; i2 < ParallelGCThreads; i2++) 637 _task_queues->queue(i2)->initialize(); 638 639 _overflow_stacks = NULL; 640 if (ParGCUseLocalOverflow) { 641 642 // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal 643 // with ',' 644 typedef Stack<oop, mtGC> GCOopStack; 645 646 _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC); 647 for (size_t i = 0; i < ParallelGCThreads; ++i) { 648 new (_overflow_stacks + i) Stack<oop, mtGC>(); 649 } 650 } 651 652 if (UsePerfData) { 653 EXCEPTION_MARK; 654 ResourceMark rm; 655 656 const char* cname = 657 PerfDataManager::counter_name(_gen_counters->name_space(), "threads"); 658 PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None, 659 ParallelGCThreads, CHECK); 660 } 661} 662#ifdef _MSC_VER 663#pragma warning( pop ) 664#endif 665 666// ParNewGeneration:: 667ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) : 668 DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {} 669 670template <class T> 671void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) { 672#ifdef ASSERT 673 { 674 assert(!oopDesc::is_null(*p), "expected non-null ref"); 675 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 676 // We never expect to see a null reference being processed 677 // as a weak reference. 678 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 679 } 680#endif // ASSERT 681 682 _par_cl->do_oop_nv(p); 683 684 if (GenCollectedHeap::heap()->is_in_reserved(p)) { 685 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 686 _rs->write_ref_field_gc_par(p, obj); 687 } 688} 689 690void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); } 691void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); } 692 693// ParNewGeneration:: 694KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) : 695 DefNewGeneration::KeepAliveClosure(cl) {} 696 697template <class T> 698void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) { 699#ifdef ASSERT 700 { 701 assert(!oopDesc::is_null(*p), "expected non-null ref"); 702 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 703 // We never expect to see a null reference being processed 704 // as a weak reference. 705 assert(obj->is_oop(), "expected an oop while scanning weak refs"); 706 } 707#endif // ASSERT 708 709 _cl->do_oop_nv(p); 710 711 if (GenCollectedHeap::heap()->is_in_reserved(p)) { 712 oop obj = oopDesc::load_decode_heap_oop_not_null(p); 713 _rs->write_ref_field_gc_par(p, obj); 714 } 715} 716 717void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); } 718void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); } 719 720template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) { 721 T heap_oop = oopDesc::load_heap_oop(p); 722 if (!oopDesc::is_null(heap_oop)) { 723 oop obj = oopDesc::decode_heap_oop_not_null(heap_oop); 724 if ((HeapWord*)obj < _boundary) { 725 assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?"); 726 oop new_obj = obj->is_forwarded() 727 ? obj->forwardee() 728 : _g->DefNewGeneration::copy_to_survivor_space(obj); 729 oopDesc::encode_store_heap_oop_not_null(p, new_obj); 730 } 731 if (_gc_barrier) { 732 // If p points to a younger generation, mark the card. 733 if ((HeapWord*)obj < _gen_boundary) { 734 _rs->write_ref_field_gc_par(p, obj); 735 } 736 } 737 } 738} 739 740void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 741void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); } 742 743class ParNewRefProcTaskProxy: public AbstractGangTask { 744 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; 745public: 746 ParNewRefProcTaskProxy(ProcessTask& task, 747 ParNewGeneration& gen, 748 Generation& old_gen, 749 HeapWord* young_old_boundary, 750 ParScanThreadStateSet& state_set); 751 752private: 753 virtual void work(uint worker_id); 754private: 755 ParNewGeneration& _gen; 756 ProcessTask& _task; 757 Generation& _old_gen; 758 HeapWord* _young_old_boundary; 759 ParScanThreadStateSet& _state_set; 760}; 761 762ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task, 763 ParNewGeneration& gen, 764 Generation& old_gen, 765 HeapWord* young_old_boundary, 766 ParScanThreadStateSet& state_set) 767 : AbstractGangTask("ParNewGeneration parallel reference processing"), 768 _gen(gen), 769 _task(task), 770 _old_gen(old_gen), 771 _young_old_boundary(young_old_boundary), 772 _state_set(state_set) 773{ 774} 775 776void ParNewRefProcTaskProxy::work(uint worker_id) 777{ 778 ResourceMark rm; 779 HandleMark hm; 780 ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id); 781 par_scan_state.set_young_old_boundary(_young_old_boundary); 782 _task.work(worker_id, par_scan_state.is_alive_closure(), 783 par_scan_state.keep_alive_closure(), 784 par_scan_state.evacuate_followers_closure()); 785} 786 787class ParNewRefEnqueueTaskProxy: public AbstractGangTask { 788 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; 789 EnqueueTask& _task; 790 791public: 792 ParNewRefEnqueueTaskProxy(EnqueueTask& task) 793 : AbstractGangTask("ParNewGeneration parallel reference enqueue"), 794 _task(task) 795 { } 796 797 virtual void work(uint worker_id) 798 { 799 _task.work(worker_id); 800 } 801}; 802 803 804void ParNewRefProcTaskExecutor::execute(ProcessTask& task) 805{ 806 GenCollectedHeap* gch = GenCollectedHeap::heap(); 807 FlexibleWorkGang* workers = gch->workers(); 808 assert(workers != NULL, "Need parallel worker threads."); 809 _state_set.reset(workers->active_workers(), _generation.promotion_failed()); 810 ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(), 811 _generation.reserved().end(), _state_set); 812 workers->run_task(&rp_task); 813 _state_set.reset(0 /* bad value in debug if not reset */, 814 _generation.promotion_failed()); 815} 816 817void ParNewRefProcTaskExecutor::execute(EnqueueTask& task) 818{ 819 GenCollectedHeap* gch = GenCollectedHeap::heap(); 820 FlexibleWorkGang* workers = gch->workers(); 821 assert(workers != NULL, "Need parallel worker threads."); 822 ParNewRefEnqueueTaskProxy enq_task(task); 823 workers->run_task(&enq_task); 824} 825 826void ParNewRefProcTaskExecutor::set_single_threaded_mode() 827{ 828 _state_set.flush(); 829 GenCollectedHeap* gch = GenCollectedHeap::heap(); 830 gch->save_marks(); 831} 832 833ScanClosureWithParBarrier:: 834ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) : 835 ScanClosure(g, gc_barrier) {} 836 837EvacuateFollowersClosureGeneral:: 838EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, int level, 839 OopsInGenClosure* cur, 840 OopsInGenClosure* older) : 841 _gch(gch), _level(level), 842 _scan_cur_or_nonheap(cur), _scan_older(older) 843{} 844 845void EvacuateFollowersClosureGeneral::do_void() { 846 do { 847 // Beware: this call will lead to closure applications via virtual 848 // calls. 849 _gch->oop_since_save_marks_iterate(_level, 850 _scan_cur_or_nonheap, 851 _scan_older); 852 } while (!_gch->no_allocs_since_save_marks(_level)); 853} 854 855 856// A Generation that does parallel young-gen collection. 857 858void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set) { 859 assert(_promo_failure_scan_stack.is_empty(), "post condition"); 860 _promo_failure_scan_stack.clear(true); // Clear cached segments. 861 862 remove_forwarding_pointers(); 863 if (PrintGCDetails) { 864 gclog_or_tty->print(" (promotion failed)"); 865 } 866 // All the spaces are in play for mark-sweep. 867 swap_spaces(); // Make life simpler for CMS || rescan; see 6483690. 868 from()->set_next_compaction_space(to()); 869 gch->set_incremental_collection_failed(); 870 // Inform the next generation that a promotion failure occurred. 871 _old_gen->promotion_failure_occurred(); 872 873 // Trace promotion failure in the parallel GC threads 874 thread_state_set.trace_promotion_failed(gc_tracer()); 875 // Single threaded code may have reported promotion failure to the global state 876 if (_promotion_failed_info.has_failed()) { 877 _gc_tracer.report_promotion_failed(_promotion_failed_info); 878 } 879 // Reset the PromotionFailureALot counters. 880 NOT_PRODUCT(gch->reset_promotion_should_fail();) 881} 882 883void ParNewGeneration::collect(bool full, 884 bool clear_all_soft_refs, 885 size_t size, 886 bool is_tlab) { 887 assert(full || size > 0, "otherwise we don't want to collect"); 888 889 GenCollectedHeap* gch = GenCollectedHeap::heap(); 890 891 _gc_timer->register_gc_start(); 892 893 AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy(); 894 FlexibleWorkGang* workers = gch->workers(); 895 assert(workers != NULL, "Need workgang for parallel work"); 896 uint active_workers = 897 AdaptiveSizePolicy::calc_active_workers(workers->total_workers(), 898 workers->active_workers(), 899 Threads::number_of_non_daemon_threads()); 900 workers->set_active_workers(active_workers); 901 _old_gen = gch->old_gen(); 902 903 // If the next generation is too full to accommodate worst-case promotion 904 // from this generation, pass on collection; let the next generation 905 // do it. 906 if (!collection_attempt_is_safe()) { 907 gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one 908 return; 909 } 910 assert(to()->is_empty(), "Else not collection_attempt_is_safe"); 911 912 _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start()); 913 gch->trace_heap_before_gc(gc_tracer()); 914 915 init_assuming_no_promotion_failure(); 916 917 if (UseAdaptiveSizePolicy) { 918 set_survivor_overflow(false); 919 size_policy->minor_collection_begin(); 920 } 921 922 GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, _gc_tracer.gc_id()); 923 // Capture heap used before collection (for printing). 924 size_t gch_prev_used = gch->used(); 925 926 age_table()->clear(); 927 to()->clear(SpaceDecorator::Mangle); 928 929 gch->save_marks(); 930 931 // Set the correct parallelism (number of queues) in the reference processor 932 ref_processor()->set_active_mt_degree(active_workers); 933 934 // Always set the terminator for the active number of workers 935 // because only those workers go through the termination protocol. 936 ParallelTaskTerminator _term(active_workers, task_queues()); 937 ParScanThreadStateSet thread_state_set(active_workers, 938 *to(), *this, *_old_gen, *task_queues(), 939 _overflow_stacks, desired_plab_sz(), _term); 940 941 thread_state_set.reset(active_workers, promotion_failed()); 942 943 { 944 StrongRootsScope srs(active_workers); 945 946 ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set, &srs); 947 gch->rem_set()->prepare_for_younger_refs_iterate(true); 948 // It turns out that even when we're using 1 thread, doing the work in a 949 // separate thread causes wide variance in run times. We can't help this 950 // in the multi-threaded case, but we special-case n=1 here to get 951 // repeatable measurements of the 1-thread overhead of the parallel code. 952 if (active_workers > 1) { 953 workers->run_task(&tsk); 954 } else { 955 tsk.work(0); 956 } 957 } 958 959 thread_state_set.reset(0 /* Bad value in debug if not reset */, 960 promotion_failed()); 961 962 // Trace and reset failed promotion info. 963 if (promotion_failed()) { 964 thread_state_set.trace_promotion_failed(gc_tracer()); 965 } 966 967 // Process (weak) reference objects found during scavenge. 968 ReferenceProcessor* rp = ref_processor(); 969 IsAliveClosure is_alive(this); 970 ScanWeakRefClosure scan_weak_ref(this); 971 KeepAliveClosure keep_alive(&scan_weak_ref); 972 ScanClosure scan_without_gc_barrier(this, false); 973 ScanClosureWithParBarrier scan_with_gc_barrier(this, true); 974 set_promo_failure_scan_stack_closure(&scan_without_gc_barrier); 975 EvacuateFollowersClosureGeneral evacuate_followers(gch, _level, 976 &scan_without_gc_barrier, &scan_with_gc_barrier); 977 rp->setup_policy(clear_all_soft_refs); 978 // Can the mt_degree be set later (at run_task() time would be best)? 979 rp->set_active_mt_degree(active_workers); 980 ReferenceProcessorStats stats; 981 if (rp->processing_is_mt()) { 982 ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); 983 stats = rp->process_discovered_references(&is_alive, &keep_alive, 984 &evacuate_followers, &task_executor, 985 _gc_timer, _gc_tracer.gc_id()); 986 } else { 987 thread_state_set.flush(); 988 gch->save_marks(); 989 stats = rp->process_discovered_references(&is_alive, &keep_alive, 990 &evacuate_followers, NULL, 991 _gc_timer, _gc_tracer.gc_id()); 992 } 993 _gc_tracer.report_gc_reference_stats(stats); 994 if (!promotion_failed()) { 995 // Swap the survivor spaces. 996 eden()->clear(SpaceDecorator::Mangle); 997 from()->clear(SpaceDecorator::Mangle); 998 if (ZapUnusedHeapArea) { 999 // This is now done here because of the piece-meal mangling which 1000 // can check for valid mangling at intermediate points in the 1001 // collection(s). When a minor collection fails to collect 1002 // sufficient space resizing of the young generation can occur 1003 // an redistribute the spaces in the young generation. Mangle 1004 // here so that unzapped regions don't get distributed to 1005 // other spaces. 1006 to()->mangle_unused_area(); 1007 } 1008 swap_spaces(); 1009 1010 // A successful scavenge should restart the GC time limit count which is 1011 // for full GC's. 1012 size_policy->reset_gc_overhead_limit_count(); 1013 1014 assert(to()->is_empty(), "to space should be empty now"); 1015 1016 adjust_desired_tenuring_threshold(); 1017 } else { 1018 handle_promotion_failed(gch, thread_state_set); 1019 } 1020 // set new iteration safe limit for the survivor spaces 1021 from()->set_concurrent_iteration_safe_limit(from()->top()); 1022 to()->set_concurrent_iteration_safe_limit(to()->top()); 1023 1024 if (ResizePLAB) { 1025 plab_stats()->adjust_desired_plab_sz(active_workers); 1026 } 1027 1028 if (PrintGC && !PrintGCDetails) { 1029 gch->print_heap_change(gch_prev_used); 1030 } 1031 1032 TASKQUEUE_STATS_ONLY(if (PrintTerminationStats) thread_state_set.print_termination_stats()); 1033 TASKQUEUE_STATS_ONLY(if (PrintTaskqueue) thread_state_set.print_taskqueue_stats()); 1034 1035 if (UseAdaptiveSizePolicy) { 1036 size_policy->minor_collection_end(gch->gc_cause()); 1037 size_policy->avg_survived()->sample(from()->used()); 1038 } 1039 1040 // We need to use a monotonically non-decreasing time in ms 1041 // or we will see time-warp warnings and os::javaTimeMillis() 1042 // does not guarantee monotonicity. 1043 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 1044 update_time_of_last_gc(now); 1045 1046 rp->set_enqueuing_is_done(true); 1047 if (rp->processing_is_mt()) { 1048 ParNewRefProcTaskExecutor task_executor(*this, thread_state_set); 1049 rp->enqueue_discovered_references(&task_executor); 1050 } else { 1051 rp->enqueue_discovered_references(NULL); 1052 } 1053 rp->verify_no_references_recorded(); 1054 1055 gch->trace_heap_after_gc(gc_tracer()); 1056 _gc_tracer.report_tenuring_threshold(tenuring_threshold()); 1057 1058 _gc_timer->register_gc_end(); 1059 1060 _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions()); 1061} 1062 1063static int sum; 1064void ParNewGeneration::waste_some_time() { 1065 for (int i = 0; i < 100; i++) { 1066 sum += i; 1067 } 1068} 1069 1070static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4); 1071 1072// Because of concurrency, there are times where an object for which 1073// "is_forwarded()" is true contains an "interim" forwarding pointer 1074// value. Such a value will soon be overwritten with a real value. 1075// This method requires "obj" to have a forwarding pointer, and waits, if 1076// necessary for a real one to be inserted, and returns it. 1077 1078oop ParNewGeneration::real_forwardee(oop obj) { 1079 oop forward_ptr = obj->forwardee(); 1080 if (forward_ptr != ClaimedForwardPtr) { 1081 return forward_ptr; 1082 } else { 1083 return real_forwardee_slow(obj); 1084 } 1085} 1086 1087oop ParNewGeneration::real_forwardee_slow(oop obj) { 1088 // Spin-read if it is claimed but not yet written by another thread. 1089 oop forward_ptr = obj->forwardee(); 1090 while (forward_ptr == ClaimedForwardPtr) { 1091 waste_some_time(); 1092 assert(obj->is_forwarded(), "precondition"); 1093 forward_ptr = obj->forwardee(); 1094 } 1095 return forward_ptr; 1096} 1097 1098void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) { 1099 if (m->must_be_preserved_for_promotion_failure(obj)) { 1100 // We should really have separate per-worker stacks, rather 1101 // than use locking of a common pair of stacks. 1102 MutexLocker ml(ParGCRareEvent_lock); 1103 preserve_mark(obj, m); 1104 } 1105} 1106 1107// Multiple GC threads may try to promote an object. If the object 1108// is successfully promoted, a forwarding pointer will be installed in 1109// the object in the young generation. This method claims the right 1110// to install the forwarding pointer before it copies the object, 1111// thus avoiding the need to undo the copy as in 1112// copy_to_survivor_space_avoiding_with_undo. 1113 1114oop ParNewGeneration::copy_to_survivor_space( 1115 ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) { 1116 // In the sequential version, this assert also says that the object is 1117 // not forwarded. That might not be the case here. It is the case that 1118 // the caller observed it to be not forwarded at some time in the past. 1119 assert(is_in_reserved(old), "shouldn't be scavenging this oop"); 1120 1121 // The sequential code read "old->age()" below. That doesn't work here, 1122 // since the age is in the mark word, and that might be overwritten with 1123 // a forwarding pointer by a parallel thread. So we must save the mark 1124 // word in a local and then analyze it. 1125 oopDesc dummyOld; 1126 dummyOld.set_mark(m); 1127 assert(!dummyOld.is_forwarded(), 1128 "should not be called with forwarding pointer mark word."); 1129 1130 oop new_obj = NULL; 1131 oop forward_ptr; 1132 1133 // Try allocating obj in to-space (unless too old) 1134 if (dummyOld.age() < tenuring_threshold()) { 1135 new_obj = (oop)par_scan_state->alloc_in_to_space(sz); 1136 if (new_obj == NULL) { 1137 set_survivor_overflow(true); 1138 } 1139 } 1140 1141 if (new_obj == NULL) { 1142 // Either to-space is full or we decided to promote 1143 // try allocating obj tenured 1144 1145 // Attempt to install a null forwarding pointer (atomically), 1146 // to claim the right to install the real forwarding pointer. 1147 forward_ptr = old->forward_to_atomic(ClaimedForwardPtr); 1148 if (forward_ptr != NULL) { 1149 // someone else beat us to it. 1150 return real_forwardee(old); 1151 } 1152 1153 if (!_promotion_failed) { 1154 new_obj = _old_gen->par_promote(par_scan_state->thread_num(), 1155 old, m, sz); 1156 } 1157 1158 if (new_obj == NULL) { 1159 // promotion failed, forward to self 1160 _promotion_failed = true; 1161 new_obj = old; 1162 1163 preserve_mark_if_necessary(old, m); 1164 par_scan_state->register_promotion_failure(sz); 1165 } 1166 1167 old->forward_to(new_obj); 1168 forward_ptr = NULL; 1169 } else { 1170 // Is in to-space; do copying ourselves. 1171 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz); 1172 assert(GenCollectedHeap::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value."); 1173 forward_ptr = old->forward_to_atomic(new_obj); 1174 // Restore the mark word copied above. 1175 new_obj->set_mark(m); 1176 // Increment age if obj still in new generation 1177 new_obj->incr_age(); 1178 par_scan_state->age_table()->add(new_obj, sz); 1179 } 1180 assert(new_obj != NULL, "just checking"); 1181 1182#ifndef PRODUCT 1183 // This code must come after the CAS test, or it will print incorrect 1184 // information. 1185 if (TraceScavenge) { 1186 gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}", 1187 is_in_reserved(new_obj) ? "copying" : "tenuring", 1188 new_obj->klass()->internal_name(), p2i(old), p2i(new_obj), new_obj->size()); 1189 } 1190#endif 1191 1192 if (forward_ptr == NULL) { 1193 oop obj_to_push = new_obj; 1194 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) { 1195 // Length field used as index of next element to be scanned. 1196 // Real length can be obtained from real_forwardee() 1197 arrayOop(old)->set_length(0); 1198 obj_to_push = old; 1199 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push, 1200 "push forwarded object"); 1201 } 1202 // Push it on one of the queues of to-be-scanned objects. 1203 bool simulate_overflow = false; 1204 NOT_PRODUCT( 1205 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) { 1206 // simulate a stack overflow 1207 simulate_overflow = true; 1208 } 1209 ) 1210 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) { 1211 // Add stats for overflow pushes. 1212 if (Verbose && PrintGCDetails) { 1213 gclog_or_tty->print("queue overflow!\n"); 1214 } 1215 push_on_overflow_list(old, par_scan_state); 1216 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0)); 1217 } 1218 1219 return new_obj; 1220 } 1221 1222 // Oops. Someone beat us to it. Undo the allocation. Where did we 1223 // allocate it? 1224 if (is_in_reserved(new_obj)) { 1225 // Must be in to_space. 1226 assert(to()->is_in_reserved(new_obj), "Checking"); 1227 if (forward_ptr == ClaimedForwardPtr) { 1228 // Wait to get the real forwarding pointer value. 1229 forward_ptr = real_forwardee(old); 1230 } 1231 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz); 1232 } 1233 1234 return forward_ptr; 1235} 1236 1237#ifndef PRODUCT 1238// It's OK to call this multi-threaded; the worst thing 1239// that can happen is that we'll get a bunch of closely 1240// spaced simulated overflows, but that's OK, in fact 1241// probably good as it would exercise the overflow code 1242// under contention. 1243bool ParNewGeneration::should_simulate_overflow() { 1244 if (_overflow_counter-- <= 0) { // just being defensive 1245 _overflow_counter = ParGCWorkQueueOverflowInterval; 1246 return true; 1247 } else { 1248 return false; 1249 } 1250} 1251#endif 1252 1253// In case we are using compressed oops, we need to be careful. 1254// If the object being pushed is an object array, then its length 1255// field keeps track of the "grey boundary" at which the next 1256// incremental scan will be done (see ParGCArrayScanChunk). 1257// When using compressed oops, this length field is kept in the 1258// lower 32 bits of the erstwhile klass word and cannot be used 1259// for the overflow chaining pointer (OCP below). As such the OCP 1260// would itself need to be compressed into the top 32-bits in this 1261// case. Unfortunately, see below, in the event that we have a 1262// promotion failure, the node to be pushed on the list can be 1263// outside of the Java heap, so the heap-based pointer compression 1264// would not work (we would have potential aliasing between C-heap 1265// and Java-heap pointers). For this reason, when using compressed 1266// oops, we simply use a worker-thread-local, non-shared overflow 1267// list in the form of a growable array, with a slightly different 1268// overflow stack draining strategy. If/when we start using fat 1269// stacks here, we can go back to using (fat) pointer chains 1270// (although some performance comparisons would be useful since 1271// single global lists have their own performance disadvantages 1272// as we were made painfully aware not long ago, see 6786503). 1273#define BUSY (cast_to_oop<intptr_t>(0x1aff1aff)) 1274void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) { 1275 assert(is_in_reserved(from_space_obj), "Should be from this generation"); 1276 if (ParGCUseLocalOverflow) { 1277 // In the case of compressed oops, we use a private, not-shared 1278 // overflow stack. 1279 par_scan_state->push_on_overflow_stack(from_space_obj); 1280 } else { 1281 assert(!UseCompressedOops, "Error"); 1282 // if the object has been forwarded to itself, then we cannot 1283 // use the klass pointer for the linked list. Instead we have 1284 // to allocate an oopDesc in the C-Heap and use that for the linked list. 1285 // XXX This is horribly inefficient when a promotion failure occurs 1286 // and should be fixed. XXX FIX ME !!! 1287#ifndef PRODUCT 1288 Atomic::inc_ptr(&_num_par_pushes); 1289 assert(_num_par_pushes > 0, "Tautology"); 1290#endif 1291 if (from_space_obj->forwardee() == from_space_obj) { 1292 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC); 1293 listhead->forward_to(from_space_obj); 1294 from_space_obj = listhead; 1295 } 1296 oop observed_overflow_list = _overflow_list; 1297 oop cur_overflow_list; 1298 do { 1299 cur_overflow_list = observed_overflow_list; 1300 if (cur_overflow_list != BUSY) { 1301 from_space_obj->set_klass_to_list_ptr(cur_overflow_list); 1302 } else { 1303 from_space_obj->set_klass_to_list_ptr(NULL); 1304 } 1305 observed_overflow_list = 1306 (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list); 1307 } while (cur_overflow_list != observed_overflow_list); 1308 } 1309} 1310 1311bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) { 1312 bool res; 1313 1314 if (ParGCUseLocalOverflow) { 1315 res = par_scan_state->take_from_overflow_stack(); 1316 } else { 1317 assert(!UseCompressedOops, "Error"); 1318 res = take_from_overflow_list_work(par_scan_state); 1319 } 1320 return res; 1321} 1322 1323 1324// *NOTE*: The overflow list manipulation code here and 1325// in CMSCollector:: are very similar in shape, 1326// except that in the CMS case we thread the objects 1327// directly into the list via their mark word, and do 1328// not need to deal with special cases below related 1329// to chunking of object arrays and promotion failure 1330// handling. 1331// CR 6797058 has been filed to attempt consolidation of 1332// the common code. 1333// Because of the common code, if you make any changes in 1334// the code below, please check the CMS version to see if 1335// similar changes might be needed. 1336// See CMSCollector::par_take_from_overflow_list() for 1337// more extensive documentation comments. 1338bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) { 1339 ObjToScanQueue* work_q = par_scan_state->work_queue(); 1340 // How many to take? 1341 size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 1342 (size_t)ParGCDesiredObjsFromOverflowList); 1343 1344 assert(!UseCompressedOops, "Error"); 1345 assert(par_scan_state->overflow_stack() == NULL, "Error"); 1346 if (_overflow_list == NULL) return false; 1347 1348 // Otherwise, there was something there; try claiming the list. 1349 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1350 // Trim off a prefix of at most objsFromOverflow items 1351 Thread* tid = Thread::current(); 1352 size_t spin_count = ParallelGCThreads; 1353 size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100); 1354 for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) { 1355 // someone grabbed it before we did ... 1356 // ... we spin for a short while... 1357 os::sleep(tid, sleep_time_millis, false); 1358 if (_overflow_list == NULL) { 1359 // nothing left to take 1360 return false; 1361 } else if (_overflow_list != BUSY) { 1362 // try and grab the prefix 1363 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list)); 1364 } 1365 } 1366 if (prefix == NULL || prefix == BUSY) { 1367 // Nothing to take or waited long enough 1368 if (prefix == NULL) { 1369 // Write back the NULL in case we overwrote it with BUSY above 1370 // and it is still the same value. 1371 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1372 } 1373 return false; 1374 } 1375 assert(prefix != NULL && prefix != BUSY, "Error"); 1376 size_t i = 1; 1377 oop cur = prefix; 1378 while (i < objsFromOverflow && cur->klass_or_null() != NULL) { 1379 i++; cur = cur->list_ptr_from_klass(); 1380 } 1381 1382 // Reattach remaining (suffix) to overflow list 1383 if (cur->klass_or_null() == NULL) { 1384 // Write back the NULL in lieu of the BUSY we wrote 1385 // above and it is still the same value. 1386 if (_overflow_list == BUSY) { 1387 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 1388 } 1389 } else { 1390 assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error"); 1391 oop suffix = cur->list_ptr_from_klass(); // suffix will be put back on global list 1392 cur->set_klass_to_list_ptr(NULL); // break off suffix 1393 // It's possible that the list is still in the empty(busy) state 1394 // we left it in a short while ago; in that case we may be 1395 // able to place back the suffix. 1396 oop observed_overflow_list = _overflow_list; 1397 oop cur_overflow_list = observed_overflow_list; 1398 bool attached = false; 1399 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { 1400 observed_overflow_list = 1401 (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1402 if (cur_overflow_list == observed_overflow_list) { 1403 attached = true; 1404 break; 1405 } else cur_overflow_list = observed_overflow_list; 1406 } 1407 if (!attached) { 1408 // Too bad, someone else got in in between; we'll need to do a splice. 1409 // Find the last item of suffix list 1410 oop last = suffix; 1411 while (last->klass_or_null() != NULL) { 1412 last = last->list_ptr_from_klass(); 1413 } 1414 // Atomically prepend suffix to current overflow list 1415 observed_overflow_list = _overflow_list; 1416 do { 1417 cur_overflow_list = observed_overflow_list; 1418 if (cur_overflow_list != BUSY) { 1419 // Do the splice ... 1420 last->set_klass_to_list_ptr(cur_overflow_list); 1421 } else { // cur_overflow_list == BUSY 1422 last->set_klass_to_list_ptr(NULL); 1423 } 1424 observed_overflow_list = 1425 (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list); 1426 } while (cur_overflow_list != observed_overflow_list); 1427 } 1428 } 1429 1430 // Push objects on prefix list onto this thread's work queue 1431 assert(prefix != NULL && prefix != BUSY, "program logic"); 1432 cur = prefix; 1433 ssize_t n = 0; 1434 while (cur != NULL) { 1435 oop obj_to_push = cur->forwardee(); 1436 oop next = cur->list_ptr_from_klass(); 1437 cur->set_klass(obj_to_push->klass()); 1438 // This may be an array object that is self-forwarded. In that case, the list pointer 1439 // space, cur, is not in the Java heap, but rather in the C-heap and should be freed. 1440 if (!is_in_reserved(cur)) { 1441 // This can become a scaling bottleneck when there is work queue overflow coincident 1442 // with promotion failure. 1443 oopDesc* f = cur; 1444 FREE_C_HEAP_ARRAY(oopDesc, f); 1445 } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) { 1446 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned"); 1447 obj_to_push = cur; 1448 } 1449 bool ok = work_q->push(obj_to_push); 1450 assert(ok, "Should have succeeded"); 1451 cur = next; 1452 n++; 1453 } 1454 TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n)); 1455#ifndef PRODUCT 1456 assert(_num_par_pushes >= n, "Too many pops?"); 1457 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes); 1458#endif 1459 return true; 1460} 1461#undef BUSY 1462 1463void ParNewGeneration::ref_processor_init() { 1464 if (_ref_processor == NULL) { 1465 // Allocate and initialize a reference processor 1466 _ref_processor = 1467 new ReferenceProcessor(_reserved, // span 1468 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing 1469 ParallelGCThreads, // mt processing degree 1470 refs_discovery_is_mt(), // mt discovery 1471 ParallelGCThreads, // mt discovery degree 1472 refs_discovery_is_atomic(), // atomic_discovery 1473 NULL); // is_alive_non_header 1474 } 1475} 1476 1477const char* ParNewGeneration::name() const { 1478 return "par new generation"; 1479} 1480