1 /* 2 * Copyright (c) 2001, 2018, 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 "classfile/javaClasses.inline.hpp" 27 #include "classfile/systemDictionary.hpp" 28 #include "gc/shared/collectedHeap.hpp" 29 #include "gc/shared/collectedHeap.inline.hpp" 30 #include "gc/shared/gcTimer.hpp" 31 #include "gc/shared/gcTraceTime.inline.hpp" 32 #include "gc/shared/referencePolicy.hpp" 33 #include "gc/shared/referenceProcessor.inline.hpp" 34 #include "gc/shared/referenceProcessorPhaseTimes.hpp" 35 #include "logging/log.hpp" 36 #include "memory/allocation.inline.hpp" 37 #include "memory/resourceArea.hpp" 38 #include "memory/universe.hpp" 39 #include "oops/access.inline.hpp" 40 #include "oops/oop.inline.hpp" 41 #include "runtime/java.hpp" 42 43 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL; 44 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL; 45 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0; 46 47 void referenceProcessor_init() { 48 ReferenceProcessor::init_statics(); 49 } 50 51 void ReferenceProcessor::init_statics() { 52 // We need a monotonically non-decreasing time in ms but 53 // os::javaTimeMillis() does not guarantee monotonicity. 54 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 55 56 // Initialize the soft ref timestamp clock. 57 _soft_ref_timestamp_clock = now; 58 // Also update the soft ref clock in j.l.r.SoftReference 59 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock); 60 61 _always_clear_soft_ref_policy = new AlwaysClearPolicy(); 62 if (is_server_compilation_mode_vm()) { 63 _default_soft_ref_policy = new LRUMaxHeapPolicy(); 64 } else { 65 _default_soft_ref_policy = new LRUCurrentHeapPolicy(); 66 } 67 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) { 68 vm_exit_during_initialization("Could not allocate reference policy object"); 69 } 70 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || 71 RefDiscoveryPolicy == ReferentBasedDiscovery, 72 "Unrecognized RefDiscoveryPolicy"); 73 } 74 75 void ReferenceProcessor::enable_discovery(bool check_no_refs) { 76 #ifdef ASSERT 77 // Verify that we're not currently discovering refs 78 assert(!_discovering_refs, "nested call?"); 79 80 if (check_no_refs) { 81 // Verify that the discovered lists are empty 82 verify_no_references_recorded(); 83 } 84 #endif // ASSERT 85 86 // Someone could have modified the value of the static 87 // field in the j.l.r.SoftReference class that holds the 88 // soft reference timestamp clock using reflection or 89 // Unsafe between GCs. Unconditionally update the static 90 // field in ReferenceProcessor here so that we use the new 91 // value during reference discovery. 92 93 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); 94 _discovering_refs = true; 95 } 96 97 ReferenceProcessor::ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery, 98 bool mt_processing, 99 uint mt_processing_degree, 100 bool mt_discovery, 101 uint mt_discovery_degree, 102 bool atomic_discovery, 103 BoolObjectClosure* is_alive_non_header, 104 bool adjust_no_of_processing_threads) : 105 _is_subject_to_discovery(is_subject_to_discovery), 106 _discovering_refs(false), 107 _enqueuing_is_done(false), 108 _processing_is_mt(mt_processing), 109 _next_id(0), 110 _adjust_no_of_processing_threads(adjust_no_of_processing_threads), 111 _is_alive_non_header(is_alive_non_header) 112 { 113 assert(is_subject_to_discovery != NULL, "must be set"); 114 115 _discovery_is_atomic = atomic_discovery; 116 _discovery_is_mt = mt_discovery; 117 _num_queues = MAX2(1U, mt_processing_degree); 118 _max_num_queues = MAX2(_num_queues, mt_discovery_degree); 119 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList, 120 _max_num_queues * number_of_subclasses_of_ref(), mtGC); 121 122 if (_discovered_refs == NULL) { 123 vm_exit_during_initialization("Could not allocated RefProc Array"); 124 } 125 _discoveredSoftRefs = &_discovered_refs[0]; 126 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_queues]; 127 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_queues]; 128 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_queues]; 129 130 // Initialize all entries to NULL 131 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) { 132 _discovered_refs[i].clear(); 133 } 134 135 setup_policy(false /* default soft ref policy */); 136 } 137 138 #ifndef PRODUCT 139 void ReferenceProcessor::verify_no_references_recorded() { 140 guarantee(!_discovering_refs, "Discovering refs?"); 141 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) { 142 guarantee(_discovered_refs[i].is_empty(), 143 "Found non-empty discovered list at %u", i); 144 } 145 } 146 #endif 147 148 void ReferenceProcessor::weak_oops_do(OopClosure* f) { 149 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) { 150 if (UseCompressedOops) { 151 f->do_oop((narrowOop*)_discovered_refs[i].adr_head()); 152 } else { 153 f->do_oop((oop*)_discovered_refs[i].adr_head()); 154 } 155 } 156 } 157 158 void ReferenceProcessor::update_soft_ref_master_clock() { 159 // Update (advance) the soft ref master clock field. This must be done 160 // after processing the soft ref list. 161 162 // We need a monotonically non-decreasing time in ms but 163 // os::javaTimeMillis() does not guarantee monotonicity. 164 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 165 jlong soft_ref_clock = java_lang_ref_SoftReference::clock(); 166 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync"); 167 168 NOT_PRODUCT( 169 if (now < _soft_ref_timestamp_clock) { 170 log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, 171 _soft_ref_timestamp_clock, now); 172 } 173 ) 174 // The values of now and _soft_ref_timestamp_clock are set using 175 // javaTimeNanos(), which is guaranteed to be monotonically 176 // non-decreasing provided the underlying platform provides such 177 // a time source (and it is bug free). 178 // In product mode, however, protect ourselves from non-monotonicity. 179 if (now > _soft_ref_timestamp_clock) { 180 _soft_ref_timestamp_clock = now; 181 java_lang_ref_SoftReference::set_clock(now); 182 } 183 // Else leave clock stalled at its old value until time progresses 184 // past clock value. 185 } 186 187 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) const { 188 size_t total = 0; 189 for (uint i = 0; i < _max_num_queues; ++i) { 190 total += lists[i].length(); 191 } 192 return total; 193 } 194 195 #ifdef ASSERT 196 void ReferenceProcessor::verify_total_count_zero(DiscoveredList lists[], const char* type) { 197 size_t count = total_count(lists); 198 assert(count == 0, "%ss must be empty but has " SIZE_FORMAT " elements", type, count); 199 } 200 #endif 201 202 ReferenceProcessorStats ReferenceProcessor::process_discovered_references( 203 BoolObjectClosure* is_alive, 204 OopClosure* keep_alive, 205 VoidClosure* complete_gc, 206 AbstractRefProcTaskExecutor* task_executor, 207 ReferenceProcessorPhaseTimes* phase_times) { 208 209 double start_time = os::elapsedTime(); 210 211 assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); 212 // Stop treating discovered references specially. 213 disable_discovery(); 214 215 // If discovery was concurrent, someone could have modified 216 // the value of the static field in the j.l.r.SoftReference 217 // class that holds the soft reference timestamp clock using 218 // reflection or Unsafe between when discovery was enabled and 219 // now. Unconditionally update the static field in ReferenceProcessor 220 // here so that we use the new value during processing of the 221 // discovered soft refs. 222 223 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); 224 225 ReferenceProcessorStats stats(total_count(_discoveredSoftRefs), 226 total_count(_discoveredWeakRefs), 227 total_count(_discoveredFinalRefs), 228 total_count(_discoveredPhantomRefs)); 229 230 { 231 RefProcTotalPhaseTimesTracker tt(RefPhase1, phase_times, this); 232 process_soft_ref_reconsider(is_alive, keep_alive, complete_gc, 233 task_executor, phase_times); 234 } 235 236 update_soft_ref_master_clock(); 237 238 { 239 RefProcTotalPhaseTimesTracker tt(RefPhase2, phase_times, this); 240 process_soft_weak_final_refs(is_alive, keep_alive, complete_gc, task_executor, phase_times); 241 } 242 243 { 244 RefProcTotalPhaseTimesTracker tt(RefPhase3, phase_times, this); 245 process_final_keep_alive(keep_alive, complete_gc, task_executor, phase_times); 246 } 247 248 { 249 RefProcTotalPhaseTimesTracker tt(RefPhase4, phase_times, this); 250 process_phantom_refs(is_alive, keep_alive, complete_gc, task_executor, phase_times); 251 } 252 253 if (task_executor != NULL) { 254 // Record the work done by the parallel workers. 255 task_executor->set_single_threaded_mode(); 256 } 257 258 phase_times->set_total_time_ms((os::elapsedTime() - start_time) * 1000); 259 260 return stats; 261 } 262 263 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { 264 _current_discovered_addr = java_lang_ref_Reference::discovered_addr_raw(_current_discovered); 265 oop discovered = java_lang_ref_Reference::discovered(_current_discovered); 266 assert(_current_discovered_addr && oopDesc::is_oop_or_null(discovered), 267 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)); 268 _next_discovered = discovered; 269 270 _referent_addr = java_lang_ref_Reference::referent_addr_raw(_current_discovered); 271 _referent = java_lang_ref_Reference::referent(_current_discovered); 272 assert(Universe::heap()->is_in_reserved_or_null(_referent), 273 "Wrong oop found in java.lang.Reference object"); 274 assert(allow_null_referent ? 275 oopDesc::is_oop_or_null(_referent) 276 : oopDesc::is_oop(_referent), 277 "Expected an oop%s for referent field at " PTR_FORMAT, 278 (allow_null_referent ? " or NULL" : ""), 279 p2i(_referent)); 280 } 281 282 void DiscoveredListIterator::remove() { 283 assert(oopDesc::is_oop(_current_discovered), "Dropping a bad reference"); 284 RawAccess<>::oop_store(_current_discovered_addr, oop(NULL)); 285 286 // First _prev_next ref actually points into DiscoveredList (gross). 287 oop new_next; 288 if (oopDesc::equals_raw(_next_discovered, _current_discovered)) { 289 // At the end of the list, we should make _prev point to itself. 290 // If _ref is the first ref, then _prev_next will be in the DiscoveredList, 291 // and _prev will be NULL. 292 new_next = _prev_discovered; 293 } else { 294 new_next = _next_discovered; 295 } 296 // Remove Reference object from discovered list. Note that G1 does not need a 297 // pre-barrier here because we know the Reference has already been found/marked, 298 // that's how it ended up in the discovered list in the first place. 299 RawAccess<>::oop_store(_prev_discovered_addr, new_next); 300 _removed++; 301 _refs_list.dec_length(1); 302 } 303 304 void DiscoveredListIterator::clear_referent() { 305 RawAccess<>::oop_store(_referent_addr, oop(NULL)); 306 } 307 308 void DiscoveredListIterator::enqueue() { 309 HeapAccess<AS_NO_KEEPALIVE>::oop_store_at(_current_discovered, 310 java_lang_ref_Reference::discovered_offset, 311 _next_discovered); 312 } 313 314 void DiscoveredListIterator::complete_enqueue() { 315 if (_prev_discovered != NULL) { 316 // This is the last object. 317 // Swap refs_list into pending list and set obj's 318 // discovered to what we read from the pending list. 319 oop old = Universe::swap_reference_pending_list(_refs_list.head()); 320 HeapAccess<AS_NO_KEEPALIVE>::oop_store_at(_prev_discovered, java_lang_ref_Reference::discovered_offset, old); 321 } 322 } 323 324 inline void log_dropped_ref(const DiscoveredListIterator& iter, const char* reason) { 325 if (log_develop_is_enabled(Trace, gc, ref)) { 326 ResourceMark rm; 327 log_develop_trace(gc, ref)("Dropping %s reference " PTR_FORMAT ": %s", 328 reason, p2i(iter.obj()), 329 iter.obj()->klass()->internal_name()); 330 } 331 } 332 333 inline void log_enqueued_ref(const DiscoveredListIterator& iter, const char* reason) { 334 if (log_develop_is_enabled(Trace, gc, ref)) { 335 ResourceMark rm; 336 log_develop_trace(gc, ref)("Enqueue %s reference (" INTPTR_FORMAT ": %s)", 337 reason, p2i(iter.obj()), iter.obj()->klass()->internal_name()); 338 } 339 assert(oopDesc::is_oop(iter.obj(), UseConcMarkSweepGC), "Adding a bad reference"); 340 } 341 342 size_t ReferenceProcessor::process_soft_ref_reconsider_work(DiscoveredList& refs_list, 343 ReferencePolicy* policy, 344 BoolObjectClosure* is_alive, 345 OopClosure* keep_alive, 346 VoidClosure* complete_gc) { 347 assert(policy != NULL, "Must have a non-NULL policy"); 348 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 349 // Decide which softly reachable refs should be kept alive. 350 while (iter.has_next()) { 351 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); 352 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); 353 if (referent_is_dead && 354 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) { 355 log_dropped_ref(iter, "by policy"); 356 // Remove Reference object from list 357 iter.remove(); 358 // keep the referent around 359 iter.make_referent_alive(); 360 iter.move_to_next(); 361 } else { 362 iter.next(); 363 } 364 } 365 // Close the reachable set 366 complete_gc->do_void(); 367 368 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT, 369 iter.removed(), iter.processed(), p2i(&refs_list)); 370 return iter.removed(); 371 } 372 373 size_t ReferenceProcessor::process_soft_weak_final_refs_work(DiscoveredList& refs_list, 374 BoolObjectClosure* is_alive, 375 OopClosure* keep_alive, 376 bool do_enqueue_and_clear) { 377 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 378 while (iter.has_next()) { 379 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); 380 if (iter.referent() == NULL) { 381 // Reference has been cleared since discovery; only possible if 382 // discovery is not atomic (checked by load_ptrs). Remove 383 // reference from list. 384 log_dropped_ref(iter, "cleared"); 385 iter.remove(); 386 iter.move_to_next(); 387 } else if (iter.is_referent_alive()) { 388 // The referent is reachable after all. 389 // Remove reference from list. 390 log_dropped_ref(iter, "reachable"); 391 iter.remove(); 392 // Update the referent pointer as necessary. Note that this 393 // should not entail any recursive marking because the 394 // referent must already have been traversed. 395 iter.make_referent_alive(); 396 iter.move_to_next(); 397 } else { 398 if (do_enqueue_and_clear) { 399 iter.clear_referent(); 400 iter.enqueue(); 401 log_enqueued_ref(iter, "cleared"); 402 } 403 // Keep in discovered list 404 iter.next(); 405 } 406 } 407 if (do_enqueue_and_clear) { 408 iter.complete_enqueue(); 409 refs_list.clear(); 410 } 411 412 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT 413 " Refs in discovered list " INTPTR_FORMAT, 414 iter.removed(), iter.processed(), p2i(&refs_list)); 415 return iter.removed(); 416 } 417 418 size_t ReferenceProcessor::process_final_keep_alive_work(DiscoveredList& refs_list, 419 OopClosure* keep_alive, 420 VoidClosure* complete_gc) { 421 DiscoveredListIterator iter(refs_list, keep_alive, NULL); 422 while (iter.has_next()) { 423 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); 424 // keep the referent and followers around 425 iter.make_referent_alive(); 426 427 // Self-loop next, to mark the FinalReference not active. 428 assert(java_lang_ref_Reference::next(iter.obj()) == NULL, "enqueued FinalReference"); 429 java_lang_ref_Reference::set_next_raw(iter.obj(), iter.obj()); 430 431 iter.enqueue(); 432 log_enqueued_ref(iter, "Final"); 433 iter.next(); 434 } 435 iter.complete_enqueue(); 436 // Close the reachable set 437 complete_gc->do_void(); 438 refs_list.clear(); 439 440 assert(iter.removed() == 0, "This phase does not remove anything."); 441 return iter.removed(); 442 } 443 444 size_t ReferenceProcessor::process_phantom_refs_work(DiscoveredList& refs_list, 445 BoolObjectClosure* is_alive, 446 OopClosure* keep_alive, 447 VoidClosure* complete_gc) { 448 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 449 while (iter.has_next()) { 450 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); 451 452 oop const referent = iter.referent(); 453 454 if (referent == NULL || iter.is_referent_alive()) { 455 iter.make_referent_alive(); 456 iter.remove(); 457 iter.move_to_next(); 458 } else { 459 iter.clear_referent(); 460 iter.enqueue(); 461 log_enqueued_ref(iter, "cleared Phantom"); 462 iter.next(); 463 } 464 } 465 iter.complete_enqueue(); 466 // Close the reachable set; needed for collectors which keep_alive_closure do 467 // not immediately complete their work. 468 complete_gc->do_void(); 469 refs_list.clear(); 470 471 return iter.removed(); 472 } 473 474 void 475 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) { 476 oop obj = NULL; 477 oop next = refs_list.head(); 478 while (!oopDesc::equals_raw(next, obj)) { 479 obj = next; 480 next = java_lang_ref_Reference::discovered(obj); 481 java_lang_ref_Reference::set_discovered_raw(obj, NULL); 482 } 483 refs_list.clear(); 484 } 485 486 void ReferenceProcessor::abandon_partial_discovery() { 487 // loop over the lists 488 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) { 489 if ((i % _max_num_queues) == 0) { 490 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i)); 491 } 492 clear_discovered_references(_discovered_refs[i]); 493 } 494 } 495 496 size_t ReferenceProcessor::total_reference_count(ReferenceType type) const { 497 DiscoveredList* list = NULL; 498 499 switch (type) { 500 case REF_SOFT: 501 list = _discoveredSoftRefs; 502 break; 503 case REF_WEAK: 504 list = _discoveredWeakRefs; 505 break; 506 case REF_FINAL: 507 list = _discoveredFinalRefs; 508 break; 509 case REF_PHANTOM: 510 list = _discoveredPhantomRefs; 511 break; 512 case REF_OTHER: 513 case REF_NONE: 514 default: 515 ShouldNotReachHere(); 516 } 517 return total_count(list); 518 } 519 520 class RefProcPhase1Task : public AbstractRefProcTaskExecutor::ProcessTask { 521 public: 522 RefProcPhase1Task(ReferenceProcessor& ref_processor, 523 ReferenceProcessorPhaseTimes* phase_times, 524 ReferencePolicy* policy) 525 : ProcessTask(ref_processor, true /* marks_oops_alive */, phase_times), 526 _policy(policy) { } 527 528 virtual void work(uint worker_id, 529 BoolObjectClosure& is_alive, 530 OopClosure& keep_alive, 531 VoidClosure& complete_gc) 532 { 533 RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::SoftRefSubPhase1, _phase_times, worker_id); 534 size_t const removed = _ref_processor.process_soft_ref_reconsider_work(_ref_processor._discoveredSoftRefs[worker_id], 535 _policy, 536 &is_alive, 537 &keep_alive, 538 &complete_gc); 539 _phase_times->add_ref_cleared(REF_SOFT, removed); 540 } 541 private: 542 ReferencePolicy* _policy; 543 }; 544 545 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { 546 void run_phase2(uint worker_id, 547 DiscoveredList list[], 548 BoolObjectClosure& is_alive, 549 OopClosure& keep_alive, 550 bool do_enqueue_and_clear, 551 ReferenceType ref_type) { 552 size_t const removed = _ref_processor.process_soft_weak_final_refs_work(list[worker_id], 553 &is_alive, 554 &keep_alive, 555 do_enqueue_and_clear); 556 _phase_times->add_ref_cleared(ref_type, removed); 557 } 558 559 public: 560 RefProcPhase2Task(ReferenceProcessor& ref_processor, 561 ReferenceProcessorPhaseTimes* phase_times) 562 : ProcessTask(ref_processor, false /* marks_oops_alive */, phase_times) { } 563 564 virtual void work(uint worker_id, 565 BoolObjectClosure& is_alive, 566 OopClosure& keep_alive, 567 VoidClosure& complete_gc) { 568 RefProcWorkerTimeTracker t(_phase_times->phase2_worker_time_sec(), worker_id); 569 { 570 RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::SoftRefSubPhase2, _phase_times, worker_id); 571 run_phase2(worker_id, _ref_processor._discoveredSoftRefs, is_alive, keep_alive, true /* do_enqueue_and_clear */, REF_SOFT); 572 } 573 { 574 RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::WeakRefSubPhase2, _phase_times, worker_id); 575 run_phase2(worker_id, _ref_processor._discoveredWeakRefs, is_alive, keep_alive, true /* do_enqueue_and_clear */, REF_WEAK); 576 } 577 { 578 RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::FinalRefSubPhase2, _phase_times, worker_id); 579 run_phase2(worker_id, _ref_processor._discoveredFinalRefs, is_alive, keep_alive, false /* do_enqueue_and_clear */, REF_FINAL); 580 } 581 // Close the reachable set; needed for collectors which keep_alive_closure do 582 // not immediately complete their work. 583 complete_gc.do_void(); 584 } 585 }; 586 587 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { 588 public: 589 RefProcPhase3Task(ReferenceProcessor& ref_processor, 590 ReferenceProcessorPhaseTimes* phase_times) 591 : ProcessTask(ref_processor, true /* marks_oops_alive */, phase_times) { } 592 593 virtual void work(uint worker_id, 594 BoolObjectClosure& is_alive, 595 OopClosure& keep_alive, 596 VoidClosure& complete_gc) 597 { 598 RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::FinalRefSubPhase3, _phase_times, worker_id); 599 _ref_processor.process_final_keep_alive_work(_ref_processor._discoveredFinalRefs[worker_id], &keep_alive, &complete_gc); 600 } 601 }; 602 603 class RefProcPhase4Task: public AbstractRefProcTaskExecutor::ProcessTask { 604 public: 605 RefProcPhase4Task(ReferenceProcessor& ref_processor, 606 ReferenceProcessorPhaseTimes* phase_times) 607 : ProcessTask(ref_processor, false /* marks_oops_alive */, phase_times) { } 608 609 virtual void work(uint worker_id, 610 BoolObjectClosure& is_alive, 611 OopClosure& keep_alive, 612 VoidClosure& complete_gc) 613 { 614 RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::PhantomRefSubPhase4, _phase_times, worker_id); 615 size_t const removed = _ref_processor.process_phantom_refs_work(_ref_processor._discoveredPhantomRefs[worker_id], 616 &is_alive, 617 &keep_alive, 618 &complete_gc); 619 _phase_times->add_ref_cleared(REF_PHANTOM, removed); 620 } 621 }; 622 623 void ReferenceProcessor::log_reflist(const char* prefix, DiscoveredList list[], uint num_active_queues) { 624 LogTarget(Trace, gc, ref) lt; 625 626 if (!lt.is_enabled()) { 627 return; 628 } 629 630 size_t total = 0; 631 632 LogStream ls(lt); 633 ls.print("%s", prefix); 634 for (uint i = 0; i < num_active_queues; i++) { 635 ls.print(SIZE_FORMAT " ", list[i].length()); 636 total += list[i].length(); 637 } 638 ls.print_cr("(" SIZE_FORMAT ")", total); 639 } 640 641 #ifndef PRODUCT 642 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint num_active_queues) { 643 if (!log_is_enabled(Trace, gc, ref)) { 644 return; 645 } 646 647 log_reflist("", ref_lists, num_active_queues); 648 #ifdef ASSERT 649 for (uint i = num_active_queues; i < _max_num_queues; i++) { 650 assert(ref_lists[i].length() == 0, SIZE_FORMAT " unexpected References in %u", 651 ref_lists[i].length(), i); 652 } 653 #endif 654 } 655 #endif 656 657 void ReferenceProcessor::set_active_mt_degree(uint v) { 658 _num_queues = v; 659 _next_id = 0; 660 } 661 662 bool ReferenceProcessor::need_balance_queues(DiscoveredList refs_lists[]) { 663 assert(_processing_is_mt, "why balance non-mt processing?"); 664 // _num_queues is the processing degree. Only list entries up to 665 // _num_queues will be processed, so any non-empty lists beyond 666 // that must be redistributed to lists in that range. Even if not 667 // needed for that, balancing may be desirable to eliminate poor 668 // distribution of references among the lists. 669 if (ParallelRefProcBalancingEnabled) { 670 return true; // Configuration says do it. 671 } else { 672 // Configuration says don't balance, but if there are non-empty 673 // lists beyond the processing degree, then must ignore the 674 // configuration and balance anyway. 675 for (uint i = _num_queues; i < _max_num_queues; ++i) { 676 if (!refs_lists[i].is_empty()) { 677 return true; // Must balance despite configuration. 678 } 679 } 680 return false; // Safe to obey configuration and not balance. 681 } 682 } 683 684 void ReferenceProcessor::maybe_balance_queues(DiscoveredList refs_lists[]) { 685 assert(_processing_is_mt, "Should not call this otherwise"); 686 if (need_balance_queues(refs_lists)) { 687 balance_queues(refs_lists); 688 } 689 } 690 691 // Balances reference queues. 692 // Move entries from all queues[0, 1, ..., _max_num_q-1] to 693 // queues[0, 1, ..., _num_q-1] because only the first _num_q 694 // corresponding to the active workers will be processed. 695 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) 696 { 697 // calculate total length 698 size_t total_refs = 0; 699 log_develop_trace(gc, ref)("Balance ref_lists "); 700 701 log_reflist_counts(ref_lists, _max_num_queues); 702 703 for (uint i = 0; i < _max_num_queues; ++i) { 704 total_refs += ref_lists[i].length(); 705 } 706 size_t avg_refs = total_refs / _num_queues + 1; 707 uint to_idx = 0; 708 for (uint from_idx = 0; from_idx < _max_num_queues; from_idx++) { 709 bool move_all = false; 710 if (from_idx >= _num_queues) { 711 move_all = ref_lists[from_idx].length() > 0; 712 } 713 while ((ref_lists[from_idx].length() > avg_refs) || 714 move_all) { 715 assert(to_idx < _num_queues, "Sanity Check!"); 716 if (ref_lists[to_idx].length() < avg_refs) { 717 // move superfluous refs 718 size_t refs_to_move; 719 // Move all the Ref's if the from queue will not be processed. 720 if (move_all) { 721 refs_to_move = MIN2(ref_lists[from_idx].length(), 722 avg_refs - ref_lists[to_idx].length()); 723 } else { 724 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, 725 avg_refs - ref_lists[to_idx].length()); 726 } 727 728 assert(refs_to_move > 0, "otherwise the code below will fail"); 729 730 oop move_head = ref_lists[from_idx].head(); 731 oop move_tail = move_head; 732 oop new_head = move_head; 733 // find an element to split the list on 734 for (size_t j = 0; j < refs_to_move; ++j) { 735 move_tail = new_head; 736 new_head = java_lang_ref_Reference::discovered(new_head); 737 } 738 739 // Add the chain to the to list. 740 if (ref_lists[to_idx].head() == NULL) { 741 // to list is empty. Make a loop at the end. 742 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail); 743 } else { 744 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head()); 745 } 746 ref_lists[to_idx].set_head(move_head); 747 ref_lists[to_idx].inc_length(refs_to_move); 748 749 // Remove the chain from the from list. 750 if (oopDesc::equals_raw(move_tail, new_head)) { 751 // We found the end of the from list. 752 ref_lists[from_idx].set_head(NULL); 753 } else { 754 ref_lists[from_idx].set_head(new_head); 755 } 756 ref_lists[from_idx].dec_length(refs_to_move); 757 if (ref_lists[from_idx].length() == 0) { 758 break; 759 } 760 } else { 761 to_idx = (to_idx + 1) % _num_queues; 762 } 763 } 764 } 765 #ifdef ASSERT 766 log_reflist_counts(ref_lists, _num_queues); 767 size_t balanced_total_refs = 0; 768 for (uint i = 0; i < _num_queues; ++i) { 769 balanced_total_refs += ref_lists[i].length(); 770 } 771 assert(total_refs == balanced_total_refs, "Balancing was incomplete"); 772 #endif 773 } 774 775 bool ReferenceProcessor::is_mt_processing_set_up(AbstractRefProcTaskExecutor* task_executor) const { 776 return task_executor != NULL && _processing_is_mt; 777 } 778 779 void ReferenceProcessor::process_soft_ref_reconsider(BoolObjectClosure* is_alive, 780 OopClosure* keep_alive, 781 VoidClosure* complete_gc, 782 AbstractRefProcTaskExecutor* task_executor, 783 ReferenceProcessorPhaseTimes* phase_times) { 784 assert(!_processing_is_mt || task_executor != NULL, "Task executor must not be NULL when mt processing is set."); 785 786 size_t const num_soft_refs = total_count(_discoveredSoftRefs); 787 phase_times->set_ref_discovered(REF_SOFT, num_soft_refs); 788 789 phase_times->set_processing_is_mt(_processing_is_mt); 790 791 if (num_soft_refs == 0 || _current_soft_ref_policy == NULL) { 792 log_debug(gc, ref)("Skipped phase1 of Reference Processing due to unavailable references"); 793 return; 794 } 795 796 RefProcMTDegreeAdjuster a(this, RefPhase1, num_soft_refs); 797 798 if (_processing_is_mt) { 799 RefProcBalanceQueuesTimeTracker tt(RefPhase1, phase_times); 800 maybe_balance_queues(_discoveredSoftRefs); 801 } 802 803 RefProcPhaseTimeTracker tt(RefPhase1, phase_times); 804 805 log_reflist("Phase1 Soft before", _discoveredSoftRefs, _max_num_queues); 806 if (_processing_is_mt) { 807 RefProcPhase1Task phase1(*this, phase_times, _current_soft_ref_policy); 808 task_executor->execute(phase1, num_queues()); 809 } else { 810 size_t removed = 0; 811 812 RefProcSubPhasesWorkerTimeTracker tt2(SoftRefSubPhase1, phase_times, 0); 813 for (uint i = 0; i < _max_num_queues; i++) { 814 removed += process_soft_ref_reconsider_work(_discoveredSoftRefs[i], _current_soft_ref_policy, 815 is_alive, keep_alive, complete_gc); 816 } 817 818 phase_times->add_ref_cleared(REF_SOFT, removed); 819 } 820 log_reflist("Phase1 Soft after", _discoveredSoftRefs, _max_num_queues); 821 } 822 823 void ReferenceProcessor::process_soft_weak_final_refs(BoolObjectClosure* is_alive, 824 OopClosure* keep_alive, 825 VoidClosure* complete_gc, 826 AbstractRefProcTaskExecutor* task_executor, 827 ReferenceProcessorPhaseTimes* phase_times) { 828 assert(!_processing_is_mt || task_executor != NULL, "Task executor must not be NULL when mt processing is set."); 829 830 size_t const num_soft_refs = total_count(_discoveredSoftRefs); 831 size_t const num_weak_refs = total_count(_discoveredWeakRefs); 832 size_t const num_final_refs = total_count(_discoveredFinalRefs); 833 size_t const num_total_refs = num_soft_refs + num_weak_refs + num_final_refs; 834 phase_times->set_ref_discovered(REF_WEAK, num_weak_refs); 835 phase_times->set_ref_discovered(REF_FINAL, num_final_refs); 836 837 phase_times->set_processing_is_mt(_processing_is_mt); 838 839 if (num_total_refs == 0) { 840 log_debug(gc, ref)("Skipped phase2 of Reference Processing due to unavailable references"); 841 return; 842 } 843 844 RefProcMTDegreeAdjuster a(this, RefPhase2, num_total_refs); 845 846 if (_processing_is_mt) { 847 RefProcBalanceQueuesTimeTracker tt(RefPhase2, phase_times); 848 maybe_balance_queues(_discoveredSoftRefs); 849 maybe_balance_queues(_discoveredWeakRefs); 850 maybe_balance_queues(_discoveredFinalRefs); 851 } 852 853 RefProcPhaseTimeTracker tt(RefPhase2, phase_times); 854 855 log_reflist("Phase2 Soft before", _discoveredSoftRefs, _max_num_queues); 856 log_reflist("Phase2 Weak before", _discoveredWeakRefs, _max_num_queues); 857 log_reflist("Phase2 Final before", _discoveredFinalRefs, _max_num_queues); 858 if (_processing_is_mt) { 859 RefProcPhase2Task phase2(*this, phase_times); 860 task_executor->execute(phase2, num_queues()); 861 } else { 862 RefProcWorkerTimeTracker t(phase_times->phase2_worker_time_sec(), 0); 863 { 864 size_t removed = 0; 865 866 RefProcSubPhasesWorkerTimeTracker tt2(SoftRefSubPhase2, phase_times, 0); 867 for (uint i = 0; i < _max_num_queues; i++) { 868 removed += process_soft_weak_final_refs_work(_discoveredSoftRefs[i], is_alive, keep_alive, true /* do_enqueue */); 869 } 870 871 phase_times->add_ref_cleared(REF_SOFT, removed); 872 } 873 { 874 size_t removed = 0; 875 876 RefProcSubPhasesWorkerTimeTracker tt2(WeakRefSubPhase2, phase_times, 0); 877 for (uint i = 0; i < _max_num_queues; i++) { 878 removed += process_soft_weak_final_refs_work(_discoveredWeakRefs[i], is_alive, keep_alive, true /* do_enqueue */); 879 } 880 881 phase_times->add_ref_cleared(REF_WEAK, removed); 882 } 883 { 884 size_t removed = 0; 885 886 RefProcSubPhasesWorkerTimeTracker tt2(FinalRefSubPhase2, phase_times, 0); 887 for (uint i = 0; i < _max_num_queues; i++) { 888 removed += process_soft_weak_final_refs_work(_discoveredFinalRefs[i], is_alive, keep_alive, false /* do_enqueue */); 889 } 890 891 phase_times->add_ref_cleared(REF_FINAL, removed); 892 } 893 complete_gc->do_void(); 894 } 895 verify_total_count_zero(_discoveredSoftRefs, "SoftReference"); 896 verify_total_count_zero(_discoveredWeakRefs, "WeakReference"); 897 log_reflist("Phase2 Final after", _discoveredFinalRefs, _max_num_queues); 898 } 899 900 void ReferenceProcessor::process_final_keep_alive(OopClosure* keep_alive, 901 VoidClosure* complete_gc, 902 AbstractRefProcTaskExecutor* task_executor, 903 ReferenceProcessorPhaseTimes* phase_times) { 904 assert(!_processing_is_mt || task_executor != NULL, "Task executor must not be NULL when mt processing is set."); 905 906 size_t const num_final_refs = total_count(_discoveredFinalRefs); 907 908 phase_times->set_processing_is_mt(_processing_is_mt); 909 910 if (num_final_refs == 0) { 911 log_debug(gc, ref)("Skipped phase3 of Reference Processing due to unavailable references"); 912 return; 913 } 914 915 RefProcMTDegreeAdjuster a(this, RefPhase3, num_final_refs); 916 917 if (_processing_is_mt) { 918 RefProcBalanceQueuesTimeTracker tt(RefPhase3, phase_times); 919 maybe_balance_queues(_discoveredFinalRefs); 920 } 921 922 // Phase 3: 923 // . Traverse referents of final references and keep them and followers alive. 924 RefProcPhaseTimeTracker tt(RefPhase3, phase_times); 925 926 if (_processing_is_mt) { 927 RefProcPhase3Task phase3(*this, phase_times); 928 task_executor->execute(phase3, num_queues()); 929 } else { 930 RefProcSubPhasesWorkerTimeTracker tt2(FinalRefSubPhase3, phase_times, 0); 931 for (uint i = 0; i < _max_num_queues; i++) { 932 process_final_keep_alive_work(_discoveredFinalRefs[i], keep_alive, complete_gc); 933 } 934 } 935 verify_total_count_zero(_discoveredFinalRefs, "FinalReference"); 936 } 937 938 void ReferenceProcessor::process_phantom_refs(BoolObjectClosure* is_alive, 939 OopClosure* keep_alive, 940 VoidClosure* complete_gc, 941 AbstractRefProcTaskExecutor* task_executor, 942 ReferenceProcessorPhaseTimes* phase_times) { 943 assert(!_processing_is_mt || task_executor != NULL, "Task executor must not be NULL when mt processing is set."); 944 945 size_t const num_phantom_refs = total_count(_discoveredPhantomRefs); 946 phase_times->set_ref_discovered(REF_PHANTOM, num_phantom_refs); 947 948 phase_times->set_processing_is_mt(_processing_is_mt); 949 950 if (num_phantom_refs == 0) { 951 log_debug(gc, ref)("Skipped phase4 of Reference Processing due to unavailable references"); 952 return; 953 } 954 955 RefProcMTDegreeAdjuster a(this, RefPhase4, num_phantom_refs); 956 957 if (_processing_is_mt) { 958 RefProcBalanceQueuesTimeTracker tt(RefPhase4, phase_times); 959 maybe_balance_queues(_discoveredPhantomRefs); 960 } 961 962 // Phase 4: Walk phantom references appropriately. 963 RefProcPhaseTimeTracker tt(RefPhase4, phase_times); 964 965 log_reflist("Phase4 Phantom before", _discoveredPhantomRefs, _max_num_queues); 966 if (_processing_is_mt) { 967 RefProcPhase4Task phase4(*this, phase_times); 968 task_executor->execute(phase4, num_queues()); 969 } else { 970 size_t removed = 0; 971 972 RefProcSubPhasesWorkerTimeTracker tt(PhantomRefSubPhase4, phase_times, 0); 973 for (uint i = 0; i < _max_num_queues; i++) { 974 removed += process_phantom_refs_work(_discoveredPhantomRefs[i], is_alive, keep_alive, complete_gc); 975 } 976 977 phase_times->add_ref_cleared(REF_PHANTOM, removed); 978 } 979 verify_total_count_zero(_discoveredPhantomRefs, "PhantomReference"); 980 } 981 982 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { 983 uint id = 0; 984 // Determine the queue index to use for this object. 985 if (_discovery_is_mt) { 986 // During a multi-threaded discovery phase, 987 // each thread saves to its "own" list. 988 Thread* thr = Thread::current(); 989 id = thr->as_Worker_thread()->id(); 990 } else { 991 // single-threaded discovery, we save in round-robin 992 // fashion to each of the lists. 993 if (_processing_is_mt) { 994 id = next_id(); 995 } 996 } 997 assert(id < _max_num_queues, "Id is out of bounds id %u and max id %u)", id, _max_num_queues); 998 999 // Get the discovered queue to which we will add 1000 DiscoveredList* list = NULL; 1001 switch (rt) { 1002 case REF_OTHER: 1003 // Unknown reference type, no special treatment 1004 break; 1005 case REF_SOFT: 1006 list = &_discoveredSoftRefs[id]; 1007 break; 1008 case REF_WEAK: 1009 list = &_discoveredWeakRefs[id]; 1010 break; 1011 case REF_FINAL: 1012 list = &_discoveredFinalRefs[id]; 1013 break; 1014 case REF_PHANTOM: 1015 list = &_discoveredPhantomRefs[id]; 1016 break; 1017 case REF_NONE: 1018 // we should not reach here if we are an InstanceRefKlass 1019 default: 1020 ShouldNotReachHere(); 1021 } 1022 log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list)); 1023 return list; 1024 } 1025 1026 inline void 1027 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, 1028 oop obj, 1029 HeapWord* discovered_addr) { 1030 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); 1031 // First we must make sure this object is only enqueued once. CAS in a non null 1032 // discovered_addr. 1033 oop current_head = refs_list.head(); 1034 // The last ref must have its discovered field pointing to itself. 1035 oop next_discovered = (current_head != NULL) ? current_head : obj; 1036 1037 oop retest = HeapAccess<AS_NO_KEEPALIVE>::oop_atomic_cmpxchg(next_discovered, discovered_addr, oop(NULL)); 1038 1039 if (retest == NULL) { 1040 // This thread just won the right to enqueue the object. 1041 // We have separate lists for enqueueing, so no synchronization 1042 // is necessary. 1043 refs_list.set_head(obj); 1044 refs_list.inc_length(1); 1045 1046 log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)", 1047 p2i(obj), obj->klass()->internal_name()); 1048 } else { 1049 // If retest was non NULL, another thread beat us to it: 1050 // The reference has already been discovered... 1051 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)", 1052 p2i(obj), obj->klass()->internal_name()); 1053 } 1054 } 1055 1056 #ifndef PRODUCT 1057 // Non-atomic (i.e. concurrent) discovery might allow us 1058 // to observe j.l.References with NULL referents, being those 1059 // cleared concurrently by mutators during (or after) discovery. 1060 void ReferenceProcessor::verify_referent(oop obj) { 1061 bool da = discovery_is_atomic(); 1062 oop referent = java_lang_ref_Reference::referent(obj); 1063 assert(da ? oopDesc::is_oop(referent) : oopDesc::is_oop_or_null(referent), 1064 "Bad referent " INTPTR_FORMAT " found in Reference " 1065 INTPTR_FORMAT " during %satomic discovery ", 1066 p2i(referent), p2i(obj), da ? "" : "non-"); 1067 } 1068 #endif 1069 1070 bool ReferenceProcessor::is_subject_to_discovery(oop const obj) const { 1071 return _is_subject_to_discovery->do_object_b(obj); 1072 } 1073 1074 // We mention two of several possible choices here: 1075 // #0: if the reference object is not in the "originating generation" 1076 // (or part of the heap being collected, indicated by our "span" 1077 // we don't treat it specially (i.e. we scan it as we would 1078 // a normal oop, treating its references as strong references). 1079 // This means that references can't be discovered unless their 1080 // referent is also in the same span. This is the simplest, 1081 // most "local" and most conservative approach, albeit one 1082 // that may cause weak references to be enqueued least promptly. 1083 // We call this choice the "ReferenceBasedDiscovery" policy. 1084 // #1: the reference object may be in any generation (span), but if 1085 // the referent is in the generation (span) being currently collected 1086 // then we can discover the reference object, provided 1087 // the object has not already been discovered by 1088 // a different concurrently running collector (as may be the 1089 // case, for instance, if the reference object is in CMS and 1090 // the referent in DefNewGeneration), and provided the processing 1091 // of this reference object by the current collector will 1092 // appear atomic to every other collector in the system. 1093 // (Thus, for instance, a concurrent collector may not 1094 // discover references in other generations even if the 1095 // referent is in its own generation). This policy may, 1096 // in certain cases, enqueue references somewhat sooner than 1097 // might Policy #0 above, but at marginally increased cost 1098 // and complexity in processing these references. 1099 // We call this choice the "RefeferentBasedDiscovery" policy. 1100 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { 1101 // Make sure we are discovering refs (rather than processing discovered refs). 1102 if (!_discovering_refs || !RegisterReferences) { 1103 return false; 1104 } 1105 1106 if ((rt == REF_FINAL) && (java_lang_ref_Reference::next(obj) != NULL)) { 1107 // Don't rediscover non-active FinalReferences. 1108 return false; 1109 } 1110 1111 if (RefDiscoveryPolicy == ReferenceBasedDiscovery && 1112 !is_subject_to_discovery(obj)) { 1113 // Reference is not in the originating generation; 1114 // don't treat it specially (i.e. we want to scan it as a normal 1115 // object with strong references). 1116 return false; 1117 } 1118 1119 // We only discover references whose referents are not (yet) 1120 // known to be strongly reachable. 1121 if (is_alive_non_header() != NULL) { 1122 verify_referent(obj); 1123 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) { 1124 return false; // referent is reachable 1125 } 1126 } 1127 if (rt == REF_SOFT) { 1128 // For soft refs we can decide now if these are not 1129 // current candidates for clearing, in which case we 1130 // can mark through them now, rather than delaying that 1131 // to the reference-processing phase. Since all current 1132 // time-stamp policies advance the soft-ref clock only 1133 // at a full collection cycle, this is always currently 1134 // accurate. 1135 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) { 1136 return false; 1137 } 1138 } 1139 1140 ResourceMark rm; // Needed for tracing. 1141 1142 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr_raw(obj); 1143 const oop discovered = java_lang_ref_Reference::discovered(obj); 1144 assert(oopDesc::is_oop_or_null(discovered), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)); 1145 if (discovered != NULL) { 1146 // The reference has already been discovered... 1147 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)", 1148 p2i(obj), obj->klass()->internal_name()); 1149 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { 1150 // assumes that an object is not processed twice; 1151 // if it's been already discovered it must be on another 1152 // generation's discovered list; so we won't discover it. 1153 return false; 1154 } else { 1155 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, 1156 "Unrecognized policy"); 1157 // Check assumption that an object is not potentially 1158 // discovered twice except by concurrent collectors that potentially 1159 // trace the same Reference object twice. 1160 assert(UseConcMarkSweepGC || UseG1GC || UseShenandoahGC, 1161 "Only possible with a concurrent marking collector"); 1162 return true; 1163 } 1164 } 1165 1166 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { 1167 verify_referent(obj); 1168 // Discover if and only if EITHER: 1169 // .. reference is in our span, OR 1170 // .. we are an atomic collector and referent is in our span 1171 if (is_subject_to_discovery(obj) || 1172 (discovery_is_atomic() && 1173 is_subject_to_discovery(java_lang_ref_Reference::referent(obj)))) { 1174 } else { 1175 return false; 1176 } 1177 } else { 1178 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && 1179 is_subject_to_discovery(obj), "code inconsistency"); 1180 } 1181 1182 // Get the right type of discovered queue head. 1183 DiscoveredList* list = get_discovered_list(rt); 1184 if (list == NULL) { 1185 return false; // nothing special needs to be done 1186 } 1187 1188 if (_discovery_is_mt) { 1189 add_to_discovered_list_mt(*list, obj, discovered_addr); 1190 } else { 1191 // We do a raw store here: the field will be visited later when processing 1192 // the discovered references. 1193 oop current_head = list->head(); 1194 // The last ref must have its discovered field pointing to itself. 1195 oop next_discovered = (current_head != NULL) ? current_head : obj; 1196 1197 assert(discovered == NULL, "control point invariant"); 1198 RawAccess<>::oop_store(discovered_addr, next_discovered); 1199 list->set_head(obj); 1200 list->inc_length(1); 1201 1202 log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name()); 1203 } 1204 assert(oopDesc::is_oop(obj), "Discovered a bad reference"); 1205 verify_referent(obj); 1206 return true; 1207 } 1208 1209 bool ReferenceProcessor::has_discovered_references() { 1210 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) { 1211 if (!_discovered_refs[i].is_empty()) { 1212 return true; 1213 } 1214 } 1215 return false; 1216 } 1217 1218 void ReferenceProcessor::preclean_discovered_references(BoolObjectClosure* is_alive, 1219 OopClosure* keep_alive, 1220 VoidClosure* complete_gc, 1221 YieldClosure* yield, 1222 GCTimer* gc_timer) { 1223 // These lists can be handled here in any order and, indeed, concurrently. 1224 1225 // Soft references 1226 { 1227 GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer); 1228 log_reflist("SoftRef before: ", _discoveredSoftRefs, _max_num_queues); 1229 for (uint i = 0; i < _max_num_queues; i++) { 1230 if (yield->should_return()) { 1231 return; 1232 } 1233 if (preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, 1234 keep_alive, complete_gc, yield)) { 1235 log_reflist("SoftRef abort: ", _discoveredSoftRefs, _max_num_queues); 1236 return; 1237 } 1238 } 1239 log_reflist("SoftRef after: ", _discoveredSoftRefs, _max_num_queues); 1240 } 1241 1242 // Weak references 1243 { 1244 GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer); 1245 log_reflist("WeakRef before: ", _discoveredWeakRefs, _max_num_queues); 1246 for (uint i = 0; i < _max_num_queues; i++) { 1247 if (yield->should_return()) { 1248 return; 1249 } 1250 if (preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, 1251 keep_alive, complete_gc, yield)) { 1252 log_reflist("WeakRef abort: ", _discoveredWeakRefs, _max_num_queues); 1253 return; 1254 } 1255 } 1256 log_reflist("WeakRef after: ", _discoveredWeakRefs, _max_num_queues); 1257 } 1258 1259 // Final references 1260 { 1261 GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer); 1262 log_reflist("FinalRef before: ", _discoveredFinalRefs, _max_num_queues); 1263 for (uint i = 0; i < _max_num_queues; i++) { 1264 if (yield->should_return()) { 1265 return; 1266 } 1267 if (preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, 1268 keep_alive, complete_gc, yield)) { 1269 log_reflist("FinalRef abort: ", _discoveredFinalRefs, _max_num_queues); 1270 return; 1271 } 1272 } 1273 log_reflist("FinalRef after: ", _discoveredFinalRefs, _max_num_queues); 1274 } 1275 1276 // Phantom references 1277 { 1278 GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer); 1279 log_reflist("PhantomRef before: ", _discoveredPhantomRefs, _max_num_queues); 1280 for (uint i = 0; i < _max_num_queues; i++) { 1281 if (yield->should_return()) { 1282 return; 1283 } 1284 if (preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, 1285 keep_alive, complete_gc, yield)) { 1286 log_reflist("PhantomRef abort: ", _discoveredPhantomRefs, _max_num_queues); 1287 return; 1288 } 1289 } 1290 log_reflist("PhantomRef after: ", _discoveredPhantomRefs, _max_num_queues); 1291 } 1292 } 1293 1294 // Walk the given discovered ref list, and remove all reference objects 1295 // whose referents are still alive, whose referents are NULL or which 1296 // are not active (have a non-NULL next field). NOTE: When we are 1297 // thus precleaning the ref lists (which happens single-threaded today), 1298 // we do not disable refs discovery to honor the correct semantics of 1299 // java.lang.Reference. As a result, we need to be careful below 1300 // that ref removal steps interleave safely with ref discovery steps 1301 // (in this thread). 1302 bool ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, 1303 BoolObjectClosure* is_alive, 1304 OopClosure* keep_alive, 1305 VoidClosure* complete_gc, 1306 YieldClosure* yield) { 1307 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 1308 while (iter.has_next()) { 1309 if (yield->should_return_fine_grain()) { 1310 return true; 1311 } 1312 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); 1313 if (iter.referent() == NULL || iter.is_referent_alive()) { 1314 // The referent has been cleared, or is alive; we need to trace 1315 // and mark its cohort. 1316 log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)", 1317 p2i(iter.obj()), iter.obj()->klass()->internal_name()); 1318 // Remove Reference object from list 1319 iter.remove(); 1320 // Keep alive its cohort. 1321 iter.make_referent_alive(); 1322 iter.move_to_next(); 1323 } else { 1324 iter.next(); 1325 } 1326 } 1327 // Close the reachable set 1328 complete_gc->do_void(); 1329 1330 if (iter.processed() > 0) { 1331 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT, 1332 iter.removed(), iter.processed(), p2i(&refs_list)); 1333 } 1334 return false; 1335 } 1336 1337 const char* ReferenceProcessor::list_name(uint i) { 1338 assert(i <= _max_num_queues * number_of_subclasses_of_ref(), 1339 "Out of bounds index"); 1340 1341 int j = i / _max_num_queues; 1342 switch (j) { 1343 case 0: return "SoftRef"; 1344 case 1: return "WeakRef"; 1345 case 2: return "FinalRef"; 1346 case 3: return "PhantomRef"; 1347 } 1348 ShouldNotReachHere(); 1349 return NULL; 1350 } 1351 1352 uint RefProcMTDegreeAdjuster::ergo_proc_thread_count(size_t ref_count, 1353 uint max_threads, 1354 RefProcPhases phase) const { 1355 assert(0 < max_threads, "must allow at least one thread"); 1356 1357 if (use_max_threads(phase) || (ReferencesPerThread == 0)) { 1358 return max_threads; 1359 } 1360 1361 size_t thread_count = 1 + (ref_count / ReferencesPerThread); 1362 return (uint)MIN3(thread_count, 1363 static_cast<size_t>(max_threads), 1364 (size_t)os::active_processor_count()); 1365 } 1366 1367 bool RefProcMTDegreeAdjuster::use_max_threads(RefProcPhases phase) const { 1368 // Even a small number of references in either of those cases could produce large amounts of work. 1369 return (phase == ReferenceProcessor::RefPhase1 || phase == ReferenceProcessor::RefPhase3); 1370 } 1371 1372 RefProcMTDegreeAdjuster::RefProcMTDegreeAdjuster(ReferenceProcessor* rp, 1373 RefProcPhases phase, 1374 size_t ref_count): 1375 _rp(rp), 1376 _saved_mt_processing(_rp->processing_is_mt()), 1377 _saved_num_queues(_rp->num_queues()) { 1378 if (!_rp->processing_is_mt() || !_rp->adjust_no_of_processing_threads() || (ReferencesPerThread == 0)) { 1379 return; 1380 } 1381 1382 uint workers = ergo_proc_thread_count(ref_count, _rp->num_queues(), phase); 1383 1384 _rp->set_mt_processing(workers > 1); 1385 _rp->set_active_mt_degree(workers); 1386 } 1387 1388 RefProcMTDegreeAdjuster::~RefProcMTDegreeAdjuster() { 1389 // Revert to previous status. 1390 _rp->set_mt_processing(_saved_mt_processing); 1391 _rp->set_active_mt_degree(_saved_num_queues); 1392 }