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 "logging/log.hpp" 35 #include "memory/allocation.inline.hpp" 36 #include "memory/resourceArea.hpp" 37 #include "oops/access.inline.hpp" 38 #include "oops/oop.inline.hpp" 39 #include "runtime/java.hpp" 40 41 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL; 42 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL; 43 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0; 44 45 void referenceProcessor_init() { 46 ReferenceProcessor::init_statics(); 47 } 48 49 void ReferenceProcessor::init_statics() { 50 // We need a monotonically non-decreasing time in ms but 51 // os::javaTimeMillis() does not guarantee monotonicity. 52 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 53 54 // Initialize the soft ref timestamp clock. 55 _soft_ref_timestamp_clock = now; 56 // Also update the soft ref clock in j.l.r.SoftReference 57 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock); 58 59 _always_clear_soft_ref_policy = new AlwaysClearPolicy(); 60 if (is_server_compilation_mode_vm()) { 61 _default_soft_ref_policy = new LRUMaxHeapPolicy(); 62 } else { 63 _default_soft_ref_policy = new LRUCurrentHeapPolicy(); 64 } 65 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) { 66 vm_exit_during_initialization("Could not allocate reference policy object"); 67 } 68 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || 69 RefDiscoveryPolicy == ReferentBasedDiscovery, 70 "Unrecognized RefDiscoveryPolicy"); 71 } 72 73 void ReferenceProcessor::enable_discovery(bool check_no_refs) { 74 #ifdef ASSERT 75 // Verify that we're not currently discovering refs 76 assert(!_discovering_refs, "nested call?"); 77 78 if (check_no_refs) { 79 // Verify that the discovered lists are empty 80 verify_no_references_recorded(); 81 } 82 #endif // ASSERT 83 84 // Someone could have modified the value of the static 85 // field in the j.l.r.SoftReference class that holds the 86 // soft reference timestamp clock using reflection or 87 // Unsafe between GCs. Unconditionally update the static 88 // field in ReferenceProcessor here so that we use the new 89 // value during reference discovery. 90 91 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); 92 _discovering_refs = true; 93 } 94 95 ReferenceProcessor::ReferenceProcessor(MemRegion span, 96 bool mt_processing, 97 uint mt_processing_degree, 98 bool mt_discovery, 99 uint mt_discovery_degree, 100 bool atomic_discovery, 101 BoolObjectClosure* is_alive_non_header) : 102 _discovering_refs(false), 103 _enqueuing_is_done(false), 104 _is_alive_non_header(is_alive_non_header), 105 _processing_is_mt(mt_processing), 106 _next_id(0) 107 { 108 _span = span; 109 _discovery_is_atomic = atomic_discovery; 110 _discovery_is_mt = mt_discovery; 111 _num_q = MAX2(1U, mt_processing_degree); 112 _max_num_q = MAX2(_num_q, mt_discovery_degree); 113 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList, 114 _max_num_q * number_of_subclasses_of_ref(), mtGC); 115 116 if (_discovered_refs == NULL) { 117 vm_exit_during_initialization("Could not allocated RefProc Array"); 118 } 119 _discoveredSoftRefs = &_discovered_refs[0]; 120 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q]; 121 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q]; 122 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q]; 123 124 // Initialize all entries to NULL 125 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 126 _discovered_refs[i].set_head(NULL); 127 _discovered_refs[i].set_length(0); 128 } 129 130 setup_policy(false /* default soft ref policy */); 131 } 132 133 #ifndef PRODUCT 134 void ReferenceProcessor::verify_no_references_recorded() { 135 guarantee(!_discovering_refs, "Discovering refs?"); 136 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 137 guarantee(_discovered_refs[i].is_empty(), 138 "Found non-empty discovered list at %u", i); 139 } 140 } 141 #endif 142 143 void ReferenceProcessor::weak_oops_do(OopClosure* f) { 144 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 145 if (UseCompressedOops) { 146 f->do_oop((narrowOop*)_discovered_refs[i].adr_head()); 147 } else { 148 f->do_oop((oop*)_discovered_refs[i].adr_head()); 149 } 150 } 151 } 152 153 void ReferenceProcessor::update_soft_ref_master_clock() { 154 // Update (advance) the soft ref master clock field. This must be done 155 // after processing the soft ref list. 156 157 // We need a monotonically non-decreasing time in ms but 158 // os::javaTimeMillis() does not guarantee monotonicity. 159 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 160 jlong soft_ref_clock = java_lang_ref_SoftReference::clock(); 161 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync"); 162 163 NOT_PRODUCT( 164 if (now < _soft_ref_timestamp_clock) { 165 log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, 166 _soft_ref_timestamp_clock, now); 167 } 168 ) 169 // The values of now and _soft_ref_timestamp_clock are set using 170 // javaTimeNanos(), which is guaranteed to be monotonically 171 // non-decreasing provided the underlying platform provides such 172 // a time source (and it is bug free). 173 // In product mode, however, protect ourselves from non-monotonicity. 174 if (now > _soft_ref_timestamp_clock) { 175 _soft_ref_timestamp_clock = now; 176 java_lang_ref_SoftReference::set_clock(now); 177 } 178 // Else leave clock stalled at its old value until time progresses 179 // past clock value. 180 } 181 182 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) const { 183 size_t total = 0; 184 for (uint i = 0; i < _max_num_q; ++i) { 185 total += lists[i].length(); 186 } 187 return total; 188 } 189 190 ReferenceProcessorStats ReferenceProcessor::process_discovered_references( 191 BoolObjectClosure* is_alive, 192 OopClosure* keep_alive, 193 VoidClosure* complete_gc, 194 AbstractRefProcTaskExecutor* task_executor, 195 ReferenceProcessorPhaseTimes* phase_times) { 196 197 double start_time = os::elapsedTime(); 198 199 assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); 200 // Stop treating discovered references specially. 201 disable_discovery(); 202 203 // If discovery was concurrent, someone could have modified 204 // the value of the static field in the j.l.r.SoftReference 205 // class that holds the soft reference timestamp clock using 206 // reflection or Unsafe between when discovery was enabled and 207 // now. Unconditionally update the static field in ReferenceProcessor 208 // here so that we use the new value during processing of the 209 // discovered soft refs. 210 211 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); 212 213 ReferenceProcessorStats stats(total_count(_discoveredSoftRefs), 214 total_count(_discoveredWeakRefs), 215 total_count(_discoveredFinalRefs), 216 total_count(_discoveredPhantomRefs)); 217 218 // Soft references 219 { 220 RefProcPhaseTimesTracker tt(REF_SOFT, phase_times, this); 221 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true, 222 is_alive, keep_alive, complete_gc, task_executor, phase_times); 223 } 224 225 update_soft_ref_master_clock(); 226 227 // Weak references 228 { 229 RefProcPhaseTimesTracker tt(REF_WEAK, phase_times, this); 230 process_discovered_reflist(_discoveredWeakRefs, NULL, true, 231 is_alive, keep_alive, complete_gc, task_executor, phase_times); 232 } 233 234 // Final references 235 { 236 RefProcPhaseTimesTracker tt(REF_FINAL, phase_times, this); 237 process_discovered_reflist(_discoveredFinalRefs, NULL, false, 238 is_alive, keep_alive, complete_gc, task_executor, phase_times); 239 } 240 241 // Phantom references 242 { 243 RefProcPhaseTimesTracker tt(REF_PHANTOM, phase_times, this); 244 process_discovered_reflist(_discoveredPhantomRefs, NULL, true, 245 is_alive, keep_alive, complete_gc, task_executor, phase_times); 246 } 247 248 if (task_executor != NULL) { 249 // Record the work done by the parallel workers. 250 task_executor->set_single_threaded_mode(); 251 } 252 253 phase_times->set_total_time_ms((os::elapsedTime() - start_time) * 1000); 254 255 return stats; 256 } 257 258 void ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor, 259 ReferenceProcessorPhaseTimes* phase_times) { 260 // Enqueue references that are not made active again, and 261 // clear the decks for the next collection (cycle). 262 enqueue_discovered_reflists(task_executor, phase_times); 263 264 // Stop treating discovered references specially. 265 disable_discovery(); 266 } 267 268 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list) { 269 // Given a list of refs linked through the "discovered" field 270 // (java.lang.ref.Reference.discovered), self-loop their "next" field 271 // thus distinguishing them from active References, then 272 // prepend them to the pending list. 273 // 274 // The Java threads will see the Reference objects linked together through 275 // the discovered field. Instead of trying to do the write barrier updates 276 // in all places in the reference processor where we manipulate the discovered 277 // field we make sure to do the barrier here where we anyway iterate through 278 // all linked Reference objects. Note that it is important to not dirty any 279 // cards during reference processing since this will cause card table 280 // verification to fail for G1. 281 log_develop_trace(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(&refs_list)); 282 283 oop obj = NULL; 284 oop next_d = refs_list.head(); 285 // Walk down the list, self-looping the next field 286 // so that the References are not considered active. 287 while (obj != next_d) { 288 obj = next_d; 289 assert(obj->is_instance(), "should be an instance object"); 290 assert(InstanceKlass::cast(obj->klass())->is_reference_instance_klass(), "should be reference object"); 291 next_d = java_lang_ref_Reference::discovered(obj); 292 log_develop_trace(gc, ref)(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, p2i(obj), p2i(next_d)); 293 assert(java_lang_ref_Reference::next(obj) == NULL, 294 "Reference not active; should not be discovered"); 295 // Self-loop next, so as to make Ref not active. 296 java_lang_ref_Reference::set_next_raw(obj, obj); 297 if (next_d != obj) { 298 HeapAccess<AS_NO_KEEPALIVE>::oop_store_at(obj, java_lang_ref_Reference::discovered_offset, next_d); 299 } else { 300 // This is the last object. 301 // Swap refs_list into pending list and set obj's 302 // discovered to what we read from the pending list. 303 oop old = Universe::swap_reference_pending_list(refs_list.head()); 304 HeapAccess<AS_NO_KEEPALIVE>::oop_store_at(obj, java_lang_ref_Reference::discovered_offset, old); 305 } 306 } 307 } 308 309 // Parallel enqueue task 310 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { 311 public: 312 RefProcEnqueueTask(ReferenceProcessor& ref_processor, 313 DiscoveredList discovered_refs[], 314 int n_queues, 315 ReferenceProcessorPhaseTimes* phase_times) 316 : EnqueueTask(ref_processor, discovered_refs, n_queues, phase_times) 317 { } 318 319 virtual void work(unsigned int work_id) { 320 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefEnqueue, _phase_times, work_id); 321 322 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds"); 323 // Simplest first cut: static partitioning. 324 int index = work_id; 325 // The increment on "index" must correspond to the maximum number of queues 326 // (n_queues) with which that ReferenceProcessor was created. That 327 // is because of the "clever" way the discovered references lists were 328 // allocated and are indexed into. 329 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected"); 330 for (int j = 0; 331 j < ReferenceProcessor::number_of_subclasses_of_ref(); 332 j++, index += _n_queues) { 333 _ref_processor.enqueue_discovered_reflist(_refs_lists[index]); 334 _refs_lists[index].set_head(NULL); 335 _refs_lists[index].set_length(0); 336 } 337 } 338 }; 339 340 // Enqueue references that are not made active again 341 void ReferenceProcessor::enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor, 342 ReferenceProcessorPhaseTimes* phase_times) { 343 344 ReferenceProcessorStats stats(total_count(_discoveredSoftRefs), 345 total_count(_discoveredWeakRefs), 346 total_count(_discoveredFinalRefs), 347 total_count(_discoveredPhantomRefs)); 348 349 RefProcEnqueueTimeTracker tt(phase_times, stats); 350 351 if (_processing_is_mt && task_executor != NULL) { 352 // Parallel code 353 RefProcEnqueueTask tsk(*this, _discovered_refs, _max_num_q, phase_times); 354 task_executor->execute(tsk); 355 } else { 356 // Serial code: call the parent class's implementation 357 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 358 enqueue_discovered_reflist(_discovered_refs[i]); 359 _discovered_refs[i].set_head(NULL); 360 _discovered_refs[i].set_length(0); 361 } 362 } 363 } 364 365 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { 366 _discovered_addr = java_lang_ref_Reference::discovered_addr_raw(_ref); 367 oop discovered = java_lang_ref_Reference::discovered(_ref); 368 assert(_discovered_addr && oopDesc::is_oop_or_null(discovered), 369 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)); 370 _next = discovered; 371 _referent_addr = java_lang_ref_Reference::referent_addr_raw(_ref); 372 _referent = java_lang_ref_Reference::referent(_ref); 373 assert(Universe::heap()->is_in_reserved_or_null(_referent), 374 "Wrong oop found in java.lang.Reference object"); 375 assert(allow_null_referent ? 376 oopDesc::is_oop_or_null(_referent) 377 : oopDesc::is_oop(_referent), 378 "Expected an oop%s for referent field at " PTR_FORMAT, 379 (allow_null_referent ? " or NULL" : ""), 380 p2i(_referent)); 381 } 382 383 void DiscoveredListIterator::remove() { 384 assert(oopDesc::is_oop(_ref), "Dropping a bad reference"); 385 RawAccess<>::oop_store(_discovered_addr, oop(NULL)); 386 387 // First _prev_next ref actually points into DiscoveredList (gross). 388 oop new_next; 389 if (_next == _ref) { 390 // At the end of the list, we should make _prev point to itself. 391 // If _ref is the first ref, then _prev_next will be in the DiscoveredList, 392 // and _prev will be NULL. 393 new_next = _prev; 394 } else { 395 new_next = _next; 396 } 397 // Remove Reference object from discovered list. Note that G1 does not need a 398 // pre-barrier here because we know the Reference has already been found/marked, 399 // that's how it ended up in the discovered list in the first place. 400 RawAccess<>::oop_store(_prev_next, new_next); 401 NOT_PRODUCT(_removed++); 402 _refs_list.dec_length(1); 403 } 404 405 void DiscoveredListIterator::clear_referent() { 406 RawAccess<>::oop_store(_referent_addr, oop(NULL)); 407 } 408 409 // NOTE: process_phase*() are largely similar, and at a high level 410 // merely iterate over the extant list applying a predicate to 411 // each of its elements and possibly removing that element from the 412 // list and applying some further closures to that element. 413 // We should consider the possibility of replacing these 414 // process_phase*() methods by abstracting them into 415 // a single general iterator invocation that receives appropriate 416 // closures that accomplish this work. 417 418 // (SoftReferences only) Traverse the list and remove any SoftReferences whose 419 // referents are not alive, but that should be kept alive for policy reasons. 420 // Keep alive the transitive closure of all such referents. 421 void 422 ReferenceProcessor::process_phase1(DiscoveredList& refs_list, 423 ReferencePolicy* policy, 424 BoolObjectClosure* is_alive, 425 OopClosure* keep_alive, 426 VoidClosure* complete_gc) { 427 assert(policy != NULL, "Must have a non-NULL policy"); 428 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 429 // Decide which softly reachable refs should be kept alive. 430 while (iter.has_next()) { 431 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); 432 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); 433 if (referent_is_dead && 434 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) { 435 log_develop_trace(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", 436 p2i(iter.obj()), iter.obj()->klass()->internal_name()); 437 // Remove Reference object from list 438 iter.remove(); 439 // keep the referent around 440 iter.make_referent_alive(); 441 iter.move_to_next(); 442 } else { 443 iter.next(); 444 } 445 } 446 // Close the reachable set 447 complete_gc->do_void(); 448 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT, 449 iter.removed(), iter.processed(), p2i(&refs_list)); 450 } 451 452 // Traverse the list and remove any Refs that are not active, or 453 // whose referents are either alive or NULL. 454 void 455 ReferenceProcessor::pp2_work(DiscoveredList& refs_list, 456 BoolObjectClosure* is_alive, 457 OopClosure* keep_alive) { 458 assert(discovery_is_atomic(), "Error"); 459 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 460 while (iter.has_next()) { 461 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); 462 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());) 463 assert(next == NULL, "Should not discover inactive Reference"); 464 if (iter.is_referent_alive()) { 465 log_develop_trace(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", 466 p2i(iter.obj()), iter.obj()->klass()->internal_name()); 467 // The referent is reachable after all. 468 // Remove Reference object from list. 469 iter.remove(); 470 // Update the referent pointer as necessary: Note that this 471 // should not entail any recursive marking because the 472 // referent must already have been traversed. 473 iter.make_referent_alive(); 474 iter.move_to_next(); 475 } else { 476 iter.next(); 477 } 478 } 479 NOT_PRODUCT( 480 if (iter.processed() > 0) { 481 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT 482 " Refs in discovered list " INTPTR_FORMAT, 483 iter.removed(), iter.processed(), p2i(&refs_list)); 484 } 485 ) 486 } 487 488 void 489 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list, 490 BoolObjectClosure* is_alive, 491 OopClosure* keep_alive, 492 VoidClosure* complete_gc) { 493 assert(!discovery_is_atomic(), "Error"); 494 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 495 while (iter.has_next()) { 496 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); 497 HeapWord* next_addr = java_lang_ref_Reference::next_addr_raw(iter.obj()); 498 oop next = java_lang_ref_Reference::next(iter.obj()); 499 if ((iter.referent() == NULL || iter.is_referent_alive() || 500 next != NULL)) { 501 assert(oopDesc::is_oop_or_null(next), "Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next)); 502 // Remove Reference object from list 503 iter.remove(); 504 // Trace the cohorts 505 iter.make_referent_alive(); 506 if (UseCompressedOops) { 507 keep_alive->do_oop((narrowOop*)next_addr); 508 } else { 509 keep_alive->do_oop((oop*)next_addr); 510 } 511 iter.move_to_next(); 512 } else { 513 iter.next(); 514 } 515 } 516 // Now close the newly reachable set 517 complete_gc->do_void(); 518 NOT_PRODUCT( 519 if (iter.processed() > 0) { 520 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT 521 " Refs in discovered list " INTPTR_FORMAT, 522 iter.removed(), iter.processed(), p2i(&refs_list)); 523 } 524 ) 525 } 526 527 // Traverse the list and process the referents, by either 528 // clearing them or keeping them (and their reachable 529 // closure) alive. 530 void 531 ReferenceProcessor::process_phase3(DiscoveredList& refs_list, 532 bool clear_referent, 533 BoolObjectClosure* is_alive, 534 OopClosure* keep_alive, 535 VoidClosure* complete_gc) { 536 ResourceMark rm; 537 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 538 while (iter.has_next()) { 539 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); 540 if (clear_referent) { 541 // NULL out referent pointer 542 iter.clear_referent(); 543 } else { 544 // keep the referent around 545 iter.make_referent_alive(); 546 } 547 log_develop_trace(gc, ref)("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", 548 clear_referent ? "cleared " : "", p2i(iter.obj()), iter.obj()->klass()->internal_name()); 549 assert(oopDesc::is_oop(iter.obj(), UseConcMarkSweepGC), "Adding a bad reference"); 550 iter.next(); 551 } 552 // Close the reachable set 553 complete_gc->do_void(); 554 } 555 556 void 557 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) { 558 oop obj = NULL; 559 oop next = refs_list.head(); 560 while (next != obj) { 561 obj = next; 562 next = java_lang_ref_Reference::discovered(obj); 563 java_lang_ref_Reference::set_discovered_raw(obj, NULL); 564 } 565 refs_list.set_head(NULL); 566 refs_list.set_length(0); 567 } 568 569 void ReferenceProcessor::abandon_partial_discovery() { 570 // loop over the lists 571 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 572 if ((i % _max_num_q) == 0) { 573 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i)); 574 } 575 clear_discovered_references(_discovered_refs[i]); 576 } 577 } 578 579 size_t ReferenceProcessor::total_reference_count(ReferenceType type) const { 580 DiscoveredList* list = NULL; 581 582 switch (type) { 583 case REF_SOFT: 584 list = _discoveredSoftRefs; 585 break; 586 case REF_WEAK: 587 list = _discoveredWeakRefs; 588 break; 589 case REF_FINAL: 590 list = _discoveredFinalRefs; 591 break; 592 case REF_PHANTOM: 593 list = _discoveredPhantomRefs; 594 break; 595 case REF_OTHER: 596 case REF_NONE: 597 default: 598 ShouldNotReachHere(); 599 } 600 return total_count(list); 601 } 602 603 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { 604 public: 605 RefProcPhase1Task(ReferenceProcessor& ref_processor, 606 DiscoveredList refs_lists[], 607 ReferencePolicy* policy, 608 bool marks_oops_alive, 609 ReferenceProcessorPhaseTimes* phase_times) 610 : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times), 611 _policy(policy) 612 { } 613 virtual void work(unsigned int i, BoolObjectClosure& is_alive, 614 OopClosure& keep_alive, 615 VoidClosure& complete_gc) 616 { 617 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase1, _phase_times, i); 618 619 _ref_processor.process_phase1(_refs_lists[i], _policy, 620 &is_alive, &keep_alive, &complete_gc); 621 } 622 private: 623 ReferencePolicy* _policy; 624 }; 625 626 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { 627 public: 628 RefProcPhase2Task(ReferenceProcessor& ref_processor, 629 DiscoveredList refs_lists[], 630 bool marks_oops_alive, 631 ReferenceProcessorPhaseTimes* phase_times) 632 : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times) 633 { } 634 virtual void work(unsigned int i, BoolObjectClosure& is_alive, 635 OopClosure& keep_alive, 636 VoidClosure& complete_gc) 637 { 638 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase2, _phase_times, i); 639 640 _ref_processor.process_phase2(_refs_lists[i], 641 &is_alive, &keep_alive, &complete_gc); 642 } 643 }; 644 645 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { 646 public: 647 RefProcPhase3Task(ReferenceProcessor& ref_processor, 648 DiscoveredList refs_lists[], 649 bool clear_referent, 650 bool marks_oops_alive, 651 ReferenceProcessorPhaseTimes* phase_times) 652 : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times), 653 _clear_referent(clear_referent) 654 { } 655 virtual void work(unsigned int i, BoolObjectClosure& is_alive, 656 OopClosure& keep_alive, 657 VoidClosure& complete_gc) 658 { 659 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase3, _phase_times, i); 660 661 _ref_processor.process_phase3(_refs_lists[i], _clear_referent, 662 &is_alive, &keep_alive, &complete_gc); 663 } 664 private: 665 bool _clear_referent; 666 }; 667 668 #ifndef PRODUCT 669 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_refs) { 670 if (!log_is_enabled(Trace, gc, ref)) { 671 return; 672 } 673 674 stringStream st; 675 for (uint i = 0; i < active_length; ++i) { 676 st.print(SIZE_FORMAT " ", ref_lists[i].length()); 677 } 678 log_develop_trace(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs); 679 #ifdef ASSERT 680 for (uint i = active_length; i < _max_num_q; i++) { 681 assert(ref_lists[i].length() == 0, SIZE_FORMAT " unexpected References in %u", 682 ref_lists[i].length(), i); 683 } 684 #endif 685 } 686 #endif 687 688 void ReferenceProcessor::set_active_mt_degree(uint v) { 689 _num_q = v; 690 _next_id = 0; 691 } 692 693 // Balances reference queues. 694 // Move entries from all queues[0, 1, ..., _max_num_q-1] to 695 // queues[0, 1, ..., _num_q-1] because only the first _num_q 696 // corresponding to the active workers will be processed. 697 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) 698 { 699 // calculate total length 700 size_t total_refs = 0; 701 log_develop_trace(gc, ref)("Balance ref_lists "); 702 703 for (uint i = 0; i < _max_num_q; ++i) { 704 total_refs += ref_lists[i].length(); 705 } 706 log_reflist_counts(ref_lists, _max_num_q, total_refs); 707 size_t avg_refs = total_refs / _num_q + 1; 708 uint to_idx = 0; 709 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) { 710 bool move_all = false; 711 if (from_idx >= _num_q) { 712 move_all = ref_lists[from_idx].length() > 0; 713 } 714 while ((ref_lists[from_idx].length() > avg_refs) || 715 move_all) { 716 assert(to_idx < _num_q, "Sanity Check!"); 717 if (ref_lists[to_idx].length() < avg_refs) { 718 // move superfluous refs 719 size_t refs_to_move; 720 // Move all the Ref's if the from queue will not be processed. 721 if (move_all) { 722 refs_to_move = MIN2(ref_lists[from_idx].length(), 723 avg_refs - ref_lists[to_idx].length()); 724 } else { 725 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, 726 avg_refs - ref_lists[to_idx].length()); 727 } 728 729 assert(refs_to_move > 0, "otherwise the code below will fail"); 730 731 oop move_head = ref_lists[from_idx].head(); 732 oop move_tail = move_head; 733 oop new_head = move_head; 734 // find an element to split the list on 735 for (size_t j = 0; j < refs_to_move; ++j) { 736 move_tail = new_head; 737 new_head = java_lang_ref_Reference::discovered(new_head); 738 } 739 740 // Add the chain to the to list. 741 if (ref_lists[to_idx].head() == NULL) { 742 // to list is empty. Make a loop at the end. 743 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail); 744 } else { 745 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head()); 746 } 747 ref_lists[to_idx].set_head(move_head); 748 ref_lists[to_idx].inc_length(refs_to_move); 749 750 // Remove the chain from the from list. 751 if (move_tail == new_head) { 752 // We found the end of the from list. 753 ref_lists[from_idx].set_head(NULL); 754 } else { 755 ref_lists[from_idx].set_head(new_head); 756 } 757 ref_lists[from_idx].dec_length(refs_to_move); 758 if (ref_lists[from_idx].length() == 0) { 759 break; 760 } 761 } else { 762 to_idx = (to_idx + 1) % _num_q; 763 } 764 } 765 } 766 #ifdef ASSERT 767 size_t balanced_total_refs = 0; 768 for (uint i = 0; i < _num_q; ++i) { 769 balanced_total_refs += ref_lists[i].length(); 770 } 771 log_reflist_counts(ref_lists, _num_q, balanced_total_refs); 772 assert(total_refs == balanced_total_refs, "Balancing was incomplete"); 773 #endif 774 } 775 776 void ReferenceProcessor::balance_all_queues() { 777 balance_queues(_discoveredSoftRefs); 778 balance_queues(_discoveredWeakRefs); 779 balance_queues(_discoveredFinalRefs); 780 balance_queues(_discoveredPhantomRefs); 781 } 782 783 void ReferenceProcessor::process_discovered_reflist( 784 DiscoveredList refs_lists[], 785 ReferencePolicy* policy, 786 bool clear_referent, 787 BoolObjectClosure* is_alive, 788 OopClosure* keep_alive, 789 VoidClosure* complete_gc, 790 AbstractRefProcTaskExecutor* task_executor, 791 ReferenceProcessorPhaseTimes* phase_times) 792 { 793 bool mt_processing = task_executor != NULL && _processing_is_mt; 794 795 phase_times->set_processing_is_mt(mt_processing); 796 797 // If discovery used MT and a dynamic number of GC threads, then 798 // the queues must be balanced for correctness if fewer than the 799 // maximum number of queues were used. The number of queue used 800 // during discovery may be different than the number to be used 801 // for processing so don't depend of _num_q < _max_num_q as part 802 // of the test. 803 bool must_balance = _discovery_is_mt; 804 805 if ((mt_processing && ParallelRefProcBalancingEnabled) || 806 must_balance) { 807 RefProcBalanceQueuesTimeTracker tt(phase_times); 808 balance_queues(refs_lists); 809 } 810 811 // Phase 1 (soft refs only): 812 // . Traverse the list and remove any SoftReferences whose 813 // referents are not alive, but that should be kept alive for 814 // policy reasons. Keep alive the transitive closure of all 815 // such referents. 816 if (policy != NULL) { 817 RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase1, phase_times); 818 819 if (mt_processing) { 820 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/, phase_times); 821 task_executor->execute(phase1); 822 } else { 823 for (uint i = 0; i < _max_num_q; i++) { 824 process_phase1(refs_lists[i], policy, 825 is_alive, keep_alive, complete_gc); 826 } 827 } 828 } else { // policy == NULL 829 assert(refs_lists != _discoveredSoftRefs, 830 "Policy must be specified for soft references."); 831 } 832 833 // Phase 2: 834 // . Traverse the list and remove any refs whose referents are alive. 835 { 836 RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase2, phase_times); 837 838 if (mt_processing) { 839 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/, phase_times); 840 task_executor->execute(phase2); 841 } else { 842 for (uint i = 0; i < _max_num_q; i++) { 843 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); 844 } 845 } 846 } 847 848 // Phase 3: 849 // . Traverse the list and process referents as appropriate. 850 { 851 RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase3, phase_times); 852 853 if (mt_processing) { 854 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/, phase_times); 855 task_executor->execute(phase3); 856 } else { 857 for (uint i = 0; i < _max_num_q; i++) { 858 process_phase3(refs_lists[i], clear_referent, 859 is_alive, keep_alive, complete_gc); 860 } 861 } 862 } 863 } 864 865 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { 866 uint id = 0; 867 // Determine the queue index to use for this object. 868 if (_discovery_is_mt) { 869 // During a multi-threaded discovery phase, 870 // each thread saves to its "own" list. 871 Thread* thr = Thread::current(); 872 id = thr->as_Worker_thread()->id(); 873 } else { 874 // single-threaded discovery, we save in round-robin 875 // fashion to each of the lists. 876 if (_processing_is_mt) { 877 id = next_id(); 878 } 879 } 880 assert(id < _max_num_q, "Id is out-of-bounds id %u and max id %u)", id, _max_num_q); 881 882 // Get the discovered queue to which we will add 883 DiscoveredList* list = NULL; 884 switch (rt) { 885 case REF_OTHER: 886 // Unknown reference type, no special treatment 887 break; 888 case REF_SOFT: 889 list = &_discoveredSoftRefs[id]; 890 break; 891 case REF_WEAK: 892 list = &_discoveredWeakRefs[id]; 893 break; 894 case REF_FINAL: 895 list = &_discoveredFinalRefs[id]; 896 break; 897 case REF_PHANTOM: 898 list = &_discoveredPhantomRefs[id]; 899 break; 900 case REF_NONE: 901 // we should not reach here if we are an InstanceRefKlass 902 default: 903 ShouldNotReachHere(); 904 } 905 log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list)); 906 return list; 907 } 908 909 inline void 910 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, 911 oop obj, 912 HeapWord* discovered_addr) { 913 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); 914 // First we must make sure this object is only enqueued once. CAS in a non null 915 // discovered_addr. 916 oop current_head = refs_list.head(); 917 // The last ref must have its discovered field pointing to itself. 918 oop next_discovered = (current_head != NULL) ? current_head : obj; 919 920 oop retest = RawAccess<>::oop_atomic_cmpxchg(next_discovered, discovered_addr, oop(NULL)); 921 922 if (retest == NULL) { 923 // This thread just won the right to enqueue the object. 924 // We have separate lists for enqueueing, so no synchronization 925 // is necessary. 926 refs_list.set_head(obj); 927 refs_list.inc_length(1); 928 929 log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)", 930 p2i(obj), obj->klass()->internal_name()); 931 } else { 932 // If retest was non NULL, another thread beat us to it: 933 // The reference has already been discovered... 934 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)", 935 p2i(obj), obj->klass()->internal_name()); 936 } 937 } 938 939 #ifndef PRODUCT 940 // Non-atomic (i.e. concurrent) discovery might allow us 941 // to observe j.l.References with NULL referents, being those 942 // cleared concurrently by mutators during (or after) discovery. 943 void ReferenceProcessor::verify_referent(oop obj) { 944 bool da = discovery_is_atomic(); 945 oop referent = java_lang_ref_Reference::referent(obj); 946 assert(da ? oopDesc::is_oop(referent) : oopDesc::is_oop_or_null(referent), 947 "Bad referent " INTPTR_FORMAT " found in Reference " 948 INTPTR_FORMAT " during %satomic discovery ", 949 p2i(referent), p2i(obj), da ? "" : "non-"); 950 } 951 #endif 952 953 // We mention two of several possible choices here: 954 // #0: if the reference object is not in the "originating generation" 955 // (or part of the heap being collected, indicated by our "span" 956 // we don't treat it specially (i.e. we scan it as we would 957 // a normal oop, treating its references as strong references). 958 // This means that references can't be discovered unless their 959 // referent is also in the same span. This is the simplest, 960 // most "local" and most conservative approach, albeit one 961 // that may cause weak references to be enqueued least promptly. 962 // We call this choice the "ReferenceBasedDiscovery" policy. 963 // #1: the reference object may be in any generation (span), but if 964 // the referent is in the generation (span) being currently collected 965 // then we can discover the reference object, provided 966 // the object has not already been discovered by 967 // a different concurrently running collector (as may be the 968 // case, for instance, if the reference object is in CMS and 969 // the referent in DefNewGeneration), and provided the processing 970 // of this reference object by the current collector will 971 // appear atomic to every other collector in the system. 972 // (Thus, for instance, a concurrent collector may not 973 // discover references in other generations even if the 974 // referent is in its own generation). This policy may, 975 // in certain cases, enqueue references somewhat sooner than 976 // might Policy #0 above, but at marginally increased cost 977 // and complexity in processing these references. 978 // We call this choice the "RefeferentBasedDiscovery" policy. 979 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { 980 // Make sure we are discovering refs (rather than processing discovered refs). 981 if (!_discovering_refs || !RegisterReferences) { 982 return false; 983 } 984 // We only discover active references. 985 oop next = java_lang_ref_Reference::next(obj); 986 if (next != NULL) { // Ref is no longer active 987 return false; 988 } 989 990 HeapWord* obj_addr = (HeapWord*)obj; 991 if (RefDiscoveryPolicy == ReferenceBasedDiscovery && 992 !_span.contains(obj_addr)) { 993 // Reference is not in the originating generation; 994 // don't treat it specially (i.e. we want to scan it as a normal 995 // object with strong references). 996 return false; 997 } 998 999 // We only discover references whose referents are not (yet) 1000 // known to be strongly reachable. 1001 if (is_alive_non_header() != NULL) { 1002 verify_referent(obj); 1003 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) { 1004 return false; // referent is reachable 1005 } 1006 } 1007 if (rt == REF_SOFT) { 1008 // For soft refs we can decide now if these are not 1009 // current candidates for clearing, in which case we 1010 // can mark through them now, rather than delaying that 1011 // to the reference-processing phase. Since all current 1012 // time-stamp policies advance the soft-ref clock only 1013 // at a full collection cycle, this is always currently 1014 // accurate. 1015 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) { 1016 return false; 1017 } 1018 } 1019 1020 ResourceMark rm; // Needed for tracing. 1021 1022 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr_raw(obj); 1023 const oop discovered = java_lang_ref_Reference::discovered(obj); 1024 assert(oopDesc::is_oop_or_null(discovered), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)); 1025 if (discovered != NULL) { 1026 // The reference has already been discovered... 1027 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)", 1028 p2i(obj), obj->klass()->internal_name()); 1029 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { 1030 // assumes that an object is not processed twice; 1031 // if it's been already discovered it must be on another 1032 // generation's discovered list; so we won't discover it. 1033 return false; 1034 } else { 1035 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, 1036 "Unrecognized policy"); 1037 // Check assumption that an object is not potentially 1038 // discovered twice except by concurrent collectors that potentially 1039 // trace the same Reference object twice. 1040 assert(UseConcMarkSweepGC || UseG1GC, 1041 "Only possible with a concurrent marking collector"); 1042 return true; 1043 } 1044 } 1045 1046 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { 1047 verify_referent(obj); 1048 // Discover if and only if EITHER: 1049 // .. reference is in our span, OR 1050 // .. we are an atomic collector and referent is in our span 1051 if (_span.contains(obj_addr) || 1052 (discovery_is_atomic() && 1053 _span.contains(java_lang_ref_Reference::referent(obj)))) { 1054 // should_enqueue = true; 1055 } else { 1056 return false; 1057 } 1058 } else { 1059 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && 1060 _span.contains(obj_addr), "code inconsistency"); 1061 } 1062 1063 // Get the right type of discovered queue head. 1064 DiscoveredList* list = get_discovered_list(rt); 1065 if (list == NULL) { 1066 return false; // nothing special needs to be done 1067 } 1068 1069 if (_discovery_is_mt) { 1070 add_to_discovered_list_mt(*list, obj, discovered_addr); 1071 } else { 1072 // We do a raw store here: the field will be visited later when processing 1073 // the discovered references. 1074 oop current_head = list->head(); 1075 // The last ref must have its discovered field pointing to itself. 1076 oop next_discovered = (current_head != NULL) ? current_head : obj; 1077 1078 assert(discovered == NULL, "control point invariant"); 1079 RawAccess<>::oop_store(discovered_addr, next_discovered); 1080 list->set_head(obj); 1081 list->inc_length(1); 1082 1083 log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name()); 1084 } 1085 assert(oopDesc::is_oop(obj), "Discovered a bad reference"); 1086 verify_referent(obj); 1087 return true; 1088 } 1089 1090 bool ReferenceProcessor::has_discovered_references() { 1091 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 1092 if (!_discovered_refs[i].is_empty()) { 1093 return true; 1094 } 1095 } 1096 return false; 1097 } 1098 1099 // Preclean the discovered references by removing those 1100 // whose referents are alive, and by marking from those that 1101 // are not active. These lists can be handled here 1102 // in any order and, indeed, concurrently. 1103 void ReferenceProcessor::preclean_discovered_references( 1104 BoolObjectClosure* is_alive, 1105 OopClosure* keep_alive, 1106 VoidClosure* complete_gc, 1107 YieldClosure* yield, 1108 GCTimer* gc_timer) { 1109 1110 // Soft references 1111 { 1112 GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer); 1113 for (uint i = 0; i < _max_num_q; i++) { 1114 if (yield->should_return()) { 1115 return; 1116 } 1117 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, 1118 keep_alive, complete_gc, yield); 1119 } 1120 } 1121 1122 // Weak references 1123 { 1124 GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer); 1125 for (uint i = 0; i < _max_num_q; i++) { 1126 if (yield->should_return()) { 1127 return; 1128 } 1129 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, 1130 keep_alive, complete_gc, yield); 1131 } 1132 } 1133 1134 // Final references 1135 { 1136 GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer); 1137 for (uint i = 0; i < _max_num_q; i++) { 1138 if (yield->should_return()) { 1139 return; 1140 } 1141 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, 1142 keep_alive, complete_gc, yield); 1143 } 1144 } 1145 1146 // Phantom references 1147 { 1148 GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer); 1149 for (uint i = 0; i < _max_num_q; i++) { 1150 if (yield->should_return()) { 1151 return; 1152 } 1153 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, 1154 keep_alive, complete_gc, yield); 1155 } 1156 } 1157 } 1158 1159 // Walk the given discovered ref list, and remove all reference objects 1160 // whose referents are still alive, whose referents are NULL or which 1161 // are not active (have a non-NULL next field). NOTE: When we are 1162 // thus precleaning the ref lists (which happens single-threaded today), 1163 // we do not disable refs discovery to honor the correct semantics of 1164 // java.lang.Reference. As a result, we need to be careful below 1165 // that ref removal steps interleave safely with ref discovery steps 1166 // (in this thread). 1167 void 1168 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, 1169 BoolObjectClosure* is_alive, 1170 OopClosure* keep_alive, 1171 VoidClosure* complete_gc, 1172 YieldClosure* yield) { 1173 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 1174 while (iter.has_next()) { 1175 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); 1176 oop obj = iter.obj(); 1177 oop next = java_lang_ref_Reference::next(obj); 1178 if (iter.referent() == NULL || iter.is_referent_alive() || 1179 next != NULL) { 1180 // The referent has been cleared, or is alive, or the Reference is not 1181 // active; we need to trace and mark its cohort. 1182 log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)", 1183 p2i(iter.obj()), iter.obj()->klass()->internal_name()); 1184 // Remove Reference object from list 1185 iter.remove(); 1186 // Keep alive its cohort. 1187 iter.make_referent_alive(); 1188 if (UseCompressedOops) { 1189 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr_raw(obj); 1190 keep_alive->do_oop(next_addr); 1191 } else { 1192 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr_raw(obj); 1193 keep_alive->do_oop(next_addr); 1194 } 1195 iter.move_to_next(); 1196 } else { 1197 iter.next(); 1198 } 1199 } 1200 // Close the reachable set 1201 complete_gc->do_void(); 1202 1203 NOT_PRODUCT( 1204 if (iter.processed() > 0) { 1205 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT, 1206 iter.removed(), iter.processed(), p2i(&refs_list)); 1207 } 1208 ) 1209 } 1210 1211 const char* ReferenceProcessor::list_name(uint i) { 1212 assert(i <= _max_num_q * number_of_subclasses_of_ref(), 1213 "Out of bounds index"); 1214 1215 int j = i / _max_num_q; 1216 switch (j) { 1217 case 0: return "SoftRef"; 1218 case 1: return "WeakRef"; 1219 case 2: return "FinalRef"; 1220 case 3: return "PhantomRef"; 1221 } 1222 ShouldNotReachHere(); 1223 return NULL; 1224 }