1 /* 2 * Copyright (c) 2001, 2017, 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.hpp" 36 #include "memory/resourceArea.hpp" 37 #include "oops/oop.inline.hpp" 38 #include "runtime/java.hpp" 39 #include "runtime/jniHandles.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 // Weak global JNI references. It would make more sense (semantically) to 249 // traverse these simultaneously with the regular weak references above, but 250 // that is not how the JDK1.2 specification is. See #4126360. Native code can 251 // thus use JNI weak references to circumvent the phantom references and 252 // resurrect a "post-mortem" object. 253 { 254 GCTraceTime(Debug, gc, ref) tt("JNI Weak Reference", phase_times->gc_timer()); 255 if (task_executor != NULL) { 256 task_executor->set_single_threaded_mode(); 257 } 258 process_phaseJNI(is_alive, keep_alive, complete_gc); 259 } 260 261 phase_times->set_total_time_ms((os::elapsedTime() - start_time) * 1000); 262 263 log_develop_trace(gc, ref)("JNI Weak Reference count: " SIZE_FORMAT, count_jni_refs()); 264 265 return stats; 266 } 267 268 #ifndef PRODUCT 269 // Calculate the number of jni handles. 270 size_t ReferenceProcessor::count_jni_refs() { 271 class CountHandleClosure: public OopClosure { 272 private: 273 size_t _count; 274 public: 275 CountHandleClosure(): _count(0) {} 276 void do_oop(oop* unused) { _count++; } 277 void do_oop(narrowOop* unused) { ShouldNotReachHere(); } 278 size_t count() { return _count; } 279 }; 280 CountHandleClosure global_handle_count; 281 JNIHandles::weak_oops_do(&global_handle_count); 282 return global_handle_count.count(); 283 } 284 #endif 285 286 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive, 287 OopClosure* keep_alive, 288 VoidClosure* complete_gc) { 289 JNIHandles::weak_oops_do(is_alive, keep_alive); 290 complete_gc->do_void(); 291 } 292 293 void ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor, 294 ReferenceProcessorPhaseTimes* phase_times) { 295 // Enqueue references that are not made active again, and 296 // clear the decks for the next collection (cycle). 297 enqueue_discovered_reflists(task_executor, phase_times); 298 299 // Stop treating discovered references specially. 300 disable_discovery(); 301 } 302 303 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list) { 304 // Given a list of refs linked through the "discovered" field 305 // (java.lang.ref.Reference.discovered), self-loop their "next" field 306 // thus distinguishing them from active References, then 307 // prepend them to the pending list. 308 // 309 // The Java threads will see the Reference objects linked together through 310 // the discovered field. Instead of trying to do the write barrier updates 311 // in all places in the reference processor where we manipulate the discovered 312 // field we make sure to do the barrier here where we anyway iterate through 313 // all linked Reference objects. Note that it is important to not dirty any 314 // cards during reference processing since this will cause card table 315 // verification to fail for G1. 316 log_develop_trace(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(&refs_list)); 317 318 oop obj = NULL; 319 oop next_d = refs_list.head(); 320 // Walk down the list, self-looping the next field 321 // so that the References are not considered active. 322 while (obj != next_d) { 323 obj = next_d; 324 assert(obj->is_instance(), "should be an instance object"); 325 assert(InstanceKlass::cast(obj->klass())->is_reference_instance_klass(), "should be reference object"); 326 next_d = java_lang_ref_Reference::discovered(obj); 327 log_develop_trace(gc, ref)(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, p2i(obj), p2i(next_d)); 328 assert(java_lang_ref_Reference::next(obj) == NULL, 329 "Reference not active; should not be discovered"); 330 // Self-loop next, so as to make Ref not active. 331 java_lang_ref_Reference::set_next_raw(obj, obj); 332 if (next_d != obj) { 333 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d); 334 } else { 335 // This is the last object. 336 // Swap refs_list into pending list and set obj's 337 // discovered to what we read from the pending list. 338 oop old = Universe::swap_reference_pending_list(refs_list.head()); 339 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL 340 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old); 341 } 342 } 343 } 344 345 // Parallel enqueue task 346 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { 347 public: 348 RefProcEnqueueTask(ReferenceProcessor& ref_processor, 349 DiscoveredList discovered_refs[], 350 int n_queues, 351 ReferenceProcessorPhaseTimes* phase_times) 352 : EnqueueTask(ref_processor, discovered_refs, n_queues, phase_times) 353 { } 354 355 virtual void work(unsigned int work_id) { 356 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefEnqueue, _phase_times, work_id); 357 358 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds"); 359 // Simplest first cut: static partitioning. 360 int index = work_id; 361 // The increment on "index" must correspond to the maximum number of queues 362 // (n_queues) with which that ReferenceProcessor was created. That 363 // is because of the "clever" way the discovered references lists were 364 // allocated and are indexed into. 365 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected"); 366 for (int j = 0; 367 j < ReferenceProcessor::number_of_subclasses_of_ref(); 368 j++, index += _n_queues) { 369 _ref_processor.enqueue_discovered_reflist(_refs_lists[index]); 370 _refs_lists[index].set_head(NULL); 371 _refs_lists[index].set_length(0); 372 } 373 } 374 }; 375 376 // Enqueue references that are not made active again 377 void ReferenceProcessor::enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor, 378 ReferenceProcessorPhaseTimes* phase_times) { 379 380 ReferenceProcessorStats stats(total_count(_discoveredSoftRefs), 381 total_count(_discoveredWeakRefs), 382 total_count(_discoveredFinalRefs), 383 total_count(_discoveredPhantomRefs)); 384 385 RefProcEnqueueTimeTracker tt(phase_times, stats); 386 387 if (_processing_is_mt && task_executor != NULL) { 388 // Parallel code 389 RefProcEnqueueTask tsk(*this, _discovered_refs, _max_num_q, phase_times); 390 task_executor->execute(tsk); 391 } else { 392 // Serial code: call the parent class's implementation 393 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 394 enqueue_discovered_reflist(_discovered_refs[i]); 395 _discovered_refs[i].set_head(NULL); 396 _discovered_refs[i].set_length(0); 397 } 398 } 399 } 400 401 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { 402 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref); 403 oop discovered = java_lang_ref_Reference::discovered(_ref); 404 assert(_discovered_addr && oopDesc::is_oop_or_null(discovered), 405 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)); 406 _next = discovered; 407 _referent_addr = java_lang_ref_Reference::referent_addr(_ref); 408 _referent = java_lang_ref_Reference::referent(_ref); 409 assert(Universe::heap()->is_in_reserved_or_null(_referent), 410 "Wrong oop found in java.lang.Reference object"); 411 assert(allow_null_referent ? 412 oopDesc::is_oop_or_null(_referent) 413 : oopDesc::is_oop(_referent), 414 "Expected an oop%s for referent field at " PTR_FORMAT, 415 (allow_null_referent ? " or NULL" : ""), 416 p2i(_referent)); 417 } 418 419 void DiscoveredListIterator::remove() { 420 assert(oopDesc::is_oop(_ref), "Dropping a bad reference"); 421 oop_store_raw(_discovered_addr, NULL); 422 423 // First _prev_next ref actually points into DiscoveredList (gross). 424 oop new_next; 425 if (_next == _ref) { 426 // At the end of the list, we should make _prev point to itself. 427 // If _ref is the first ref, then _prev_next will be in the DiscoveredList, 428 // and _prev will be NULL. 429 new_next = _prev; 430 } else { 431 new_next = _next; 432 } 433 // Remove Reference object from discovered list. Note that G1 does not need a 434 // pre-barrier here because we know the Reference has already been found/marked, 435 // that's how it ended up in the discovered list in the first place. 436 oop_store_raw(_prev_next, new_next); 437 NOT_PRODUCT(_removed++); 438 _refs_list.dec_length(1); 439 } 440 441 void DiscoveredListIterator::clear_referent() { 442 oop_store_raw(_referent_addr, NULL); 443 } 444 445 // NOTE: process_phase*() are largely similar, and at a high level 446 // merely iterate over the extant list applying a predicate to 447 // each of its elements and possibly removing that element from the 448 // list and applying some further closures to that element. 449 // We should consider the possibility of replacing these 450 // process_phase*() methods by abstracting them into 451 // a single general iterator invocation that receives appropriate 452 // closures that accomplish this work. 453 454 // (SoftReferences only) Traverse the list and remove any SoftReferences whose 455 // referents are not alive, but that should be kept alive for policy reasons. 456 // Keep alive the transitive closure of all such referents. 457 void 458 ReferenceProcessor::process_phase1(DiscoveredList& refs_list, 459 ReferencePolicy* policy, 460 BoolObjectClosure* is_alive, 461 OopClosure* keep_alive, 462 VoidClosure* complete_gc) { 463 assert(policy != NULL, "Must have a non-NULL policy"); 464 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 465 // Decide which softly reachable refs should be kept alive. 466 while (iter.has_next()) { 467 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); 468 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); 469 if (referent_is_dead && 470 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) { 471 log_develop_trace(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", 472 p2i(iter.obj()), iter.obj()->klass()->internal_name()); 473 // Remove Reference object from list 474 iter.remove(); 475 // keep the referent around 476 iter.make_referent_alive(); 477 iter.move_to_next(); 478 } else { 479 iter.next(); 480 } 481 } 482 // Close the reachable set 483 complete_gc->do_void(); 484 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT, 485 iter.removed(), iter.processed(), p2i(&refs_list)); 486 } 487 488 // Traverse the list and remove any Refs that are not active, or 489 // whose referents are either alive or NULL. 490 void 491 ReferenceProcessor::pp2_work(DiscoveredList& refs_list, 492 BoolObjectClosure* is_alive, 493 OopClosure* keep_alive) { 494 assert(discovery_is_atomic(), "Error"); 495 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 496 while (iter.has_next()) { 497 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); 498 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());) 499 assert(next == NULL, "Should not discover inactive Reference"); 500 if (iter.is_referent_alive()) { 501 log_develop_trace(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", 502 p2i(iter.obj()), iter.obj()->klass()->internal_name()); 503 // The referent is reachable after all. 504 // Remove Reference object from list. 505 iter.remove(); 506 // Update the referent pointer as necessary: Note that this 507 // should not entail any recursive marking because the 508 // referent must already have been traversed. 509 iter.make_referent_alive(); 510 iter.move_to_next(); 511 } else { 512 iter.next(); 513 } 514 } 515 NOT_PRODUCT( 516 if (iter.processed() > 0) { 517 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT 518 " Refs in discovered list " INTPTR_FORMAT, 519 iter.removed(), iter.processed(), p2i(&refs_list)); 520 } 521 ) 522 } 523 524 void 525 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list, 526 BoolObjectClosure* is_alive, 527 OopClosure* keep_alive, 528 VoidClosure* complete_gc) { 529 assert(!discovery_is_atomic(), "Error"); 530 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 531 while (iter.has_next()) { 532 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); 533 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); 534 oop next = java_lang_ref_Reference::next(iter.obj()); 535 if ((iter.referent() == NULL || iter.is_referent_alive() || 536 next != NULL)) { 537 assert(oopDesc::is_oop_or_null(next), "Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next)); 538 // Remove Reference object from list 539 iter.remove(); 540 // Trace the cohorts 541 iter.make_referent_alive(); 542 if (UseCompressedOops) { 543 keep_alive->do_oop((narrowOop*)next_addr); 544 } else { 545 keep_alive->do_oop((oop*)next_addr); 546 } 547 iter.move_to_next(); 548 } else { 549 iter.next(); 550 } 551 } 552 // Now close the newly reachable set 553 complete_gc->do_void(); 554 NOT_PRODUCT( 555 if (iter.processed() > 0) { 556 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT 557 " Refs in discovered list " INTPTR_FORMAT, 558 iter.removed(), iter.processed(), p2i(&refs_list)); 559 } 560 ) 561 } 562 563 // Traverse the list and process the referents, by either 564 // clearing them or keeping them (and their reachable 565 // closure) alive. 566 void 567 ReferenceProcessor::process_phase3(DiscoveredList& refs_list, 568 bool clear_referent, 569 BoolObjectClosure* is_alive, 570 OopClosure* keep_alive, 571 VoidClosure* complete_gc) { 572 ResourceMark rm; 573 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 574 while (iter.has_next()) { 575 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); 576 if (clear_referent) { 577 // NULL out referent pointer 578 iter.clear_referent(); 579 } else { 580 // keep the referent around 581 iter.make_referent_alive(); 582 } 583 log_develop_trace(gc, ref)("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", 584 clear_referent ? "cleared " : "", p2i(iter.obj()), iter.obj()->klass()->internal_name()); 585 assert(oopDesc::is_oop(iter.obj(), UseConcMarkSweepGC), "Adding a bad reference"); 586 iter.next(); 587 } 588 // Close the reachable set 589 complete_gc->do_void(); 590 } 591 592 void 593 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) { 594 oop obj = NULL; 595 oop next = refs_list.head(); 596 while (next != obj) { 597 obj = next; 598 next = java_lang_ref_Reference::discovered(obj); 599 java_lang_ref_Reference::set_discovered_raw(obj, NULL); 600 } 601 refs_list.set_head(NULL); 602 refs_list.set_length(0); 603 } 604 605 void ReferenceProcessor::abandon_partial_discovery() { 606 // loop over the lists 607 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 608 if ((i % _max_num_q) == 0) { 609 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i)); 610 } 611 clear_discovered_references(_discovered_refs[i]); 612 } 613 } 614 615 size_t ReferenceProcessor::total_reference_count(ReferenceType type) const { 616 DiscoveredList* list = NULL; 617 618 switch (type) { 619 case REF_SOFT: 620 list = _discoveredSoftRefs; 621 break; 622 case REF_WEAK: 623 list = _discoveredWeakRefs; 624 break; 625 case REF_FINAL: 626 list = _discoveredFinalRefs; 627 break; 628 case REF_PHANTOM: 629 list = _discoveredPhantomRefs; 630 break; 631 case REF_OTHER: 632 case REF_NONE: 633 default: 634 ShouldNotReachHere(); 635 } 636 return total_count(list); 637 } 638 639 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { 640 public: 641 RefProcPhase1Task(ReferenceProcessor& ref_processor, 642 DiscoveredList refs_lists[], 643 ReferencePolicy* policy, 644 bool marks_oops_alive, 645 ReferenceProcessorPhaseTimes* phase_times) 646 : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times), 647 _policy(policy) 648 { } 649 virtual void work(unsigned int i, BoolObjectClosure& is_alive, 650 OopClosure& keep_alive, 651 VoidClosure& complete_gc) 652 { 653 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase1, _phase_times, i); 654 655 _ref_processor.process_phase1(_refs_lists[i], _policy, 656 &is_alive, &keep_alive, &complete_gc); 657 } 658 private: 659 ReferencePolicy* _policy; 660 }; 661 662 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { 663 public: 664 RefProcPhase2Task(ReferenceProcessor& ref_processor, 665 DiscoveredList refs_lists[], 666 bool marks_oops_alive, 667 ReferenceProcessorPhaseTimes* phase_times) 668 : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times) 669 { } 670 virtual void work(unsigned int i, BoolObjectClosure& is_alive, 671 OopClosure& keep_alive, 672 VoidClosure& complete_gc) 673 { 674 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase2, _phase_times, i); 675 676 _ref_processor.process_phase2(_refs_lists[i], 677 &is_alive, &keep_alive, &complete_gc); 678 } 679 }; 680 681 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { 682 public: 683 RefProcPhase3Task(ReferenceProcessor& ref_processor, 684 DiscoveredList refs_lists[], 685 bool clear_referent, 686 bool marks_oops_alive, 687 ReferenceProcessorPhaseTimes* phase_times) 688 : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times), 689 _clear_referent(clear_referent) 690 { } 691 virtual void work(unsigned int i, BoolObjectClosure& is_alive, 692 OopClosure& keep_alive, 693 VoidClosure& complete_gc) 694 { 695 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase3, _phase_times, i); 696 697 _ref_processor.process_phase3(_refs_lists[i], _clear_referent, 698 &is_alive, &keep_alive, &complete_gc); 699 } 700 private: 701 bool _clear_referent; 702 }; 703 704 #ifndef PRODUCT 705 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_refs) { 706 if (!log_is_enabled(Trace, gc, ref)) { 707 return; 708 } 709 710 stringStream st; 711 for (uint i = 0; i < active_length; ++i) { 712 st.print(SIZE_FORMAT " ", ref_lists[i].length()); 713 } 714 log_develop_trace(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs); 715 #ifdef ASSERT 716 for (uint i = active_length; i < _max_num_q; i++) { 717 assert(ref_lists[i].length() == 0, SIZE_FORMAT " unexpected References in %u", 718 ref_lists[i].length(), i); 719 } 720 #endif 721 } 722 #endif 723 724 void ReferenceProcessor::set_active_mt_degree(uint v) { 725 _num_q = v; 726 _next_id = 0; 727 } 728 729 // Balances reference queues. 730 // Move entries from all queues[0, 1, ..., _max_num_q-1] to 731 // queues[0, 1, ..., _num_q-1] because only the first _num_q 732 // corresponding to the active workers will be processed. 733 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) 734 { 735 // calculate total length 736 size_t total_refs = 0; 737 log_develop_trace(gc, ref)("Balance ref_lists "); 738 739 for (uint i = 0; i < _max_num_q; ++i) { 740 total_refs += ref_lists[i].length(); 741 } 742 log_reflist_counts(ref_lists, _max_num_q, total_refs); 743 size_t avg_refs = total_refs / _num_q + 1; 744 uint to_idx = 0; 745 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) { 746 bool move_all = false; 747 if (from_idx >= _num_q) { 748 move_all = ref_lists[from_idx].length() > 0; 749 } 750 while ((ref_lists[from_idx].length() > avg_refs) || 751 move_all) { 752 assert(to_idx < _num_q, "Sanity Check!"); 753 if (ref_lists[to_idx].length() < avg_refs) { 754 // move superfluous refs 755 size_t refs_to_move; 756 // Move all the Ref's if the from queue will not be processed. 757 if (move_all) { 758 refs_to_move = MIN2(ref_lists[from_idx].length(), 759 avg_refs - ref_lists[to_idx].length()); 760 } else { 761 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, 762 avg_refs - ref_lists[to_idx].length()); 763 } 764 765 assert(refs_to_move > 0, "otherwise the code below will fail"); 766 767 oop move_head = ref_lists[from_idx].head(); 768 oop move_tail = move_head; 769 oop new_head = move_head; 770 // find an element to split the list on 771 for (size_t j = 0; j < refs_to_move; ++j) { 772 move_tail = new_head; 773 new_head = java_lang_ref_Reference::discovered(new_head); 774 } 775 776 // Add the chain to the to list. 777 if (ref_lists[to_idx].head() == NULL) { 778 // to list is empty. Make a loop at the end. 779 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail); 780 } else { 781 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head()); 782 } 783 ref_lists[to_idx].set_head(move_head); 784 ref_lists[to_idx].inc_length(refs_to_move); 785 786 // Remove the chain from the from list. 787 if (move_tail == new_head) { 788 // We found the end of the from list. 789 ref_lists[from_idx].set_head(NULL); 790 } else { 791 ref_lists[from_idx].set_head(new_head); 792 } 793 ref_lists[from_idx].dec_length(refs_to_move); 794 if (ref_lists[from_idx].length() == 0) { 795 break; 796 } 797 } else { 798 to_idx = (to_idx + 1) % _num_q; 799 } 800 } 801 } 802 #ifdef ASSERT 803 size_t balanced_total_refs = 0; 804 for (uint i = 0; i < _num_q; ++i) { 805 balanced_total_refs += ref_lists[i].length(); 806 } 807 log_reflist_counts(ref_lists, _num_q, balanced_total_refs); 808 assert(total_refs == balanced_total_refs, "Balancing was incomplete"); 809 #endif 810 } 811 812 void ReferenceProcessor::balance_all_queues() { 813 balance_queues(_discoveredSoftRefs); 814 balance_queues(_discoveredWeakRefs); 815 balance_queues(_discoveredFinalRefs); 816 balance_queues(_discoveredPhantomRefs); 817 } 818 819 void ReferenceProcessor::process_discovered_reflist( 820 DiscoveredList refs_lists[], 821 ReferencePolicy* policy, 822 bool clear_referent, 823 BoolObjectClosure* is_alive, 824 OopClosure* keep_alive, 825 VoidClosure* complete_gc, 826 AbstractRefProcTaskExecutor* task_executor, 827 ReferenceProcessorPhaseTimes* phase_times) 828 { 829 bool mt_processing = task_executor != NULL && _processing_is_mt; 830 831 phase_times->set_processing_is_mt(mt_processing); 832 833 // If discovery used MT and a dynamic number of GC threads, then 834 // the queues must be balanced for correctness if fewer than the 835 // maximum number of queues were used. The number of queue used 836 // during discovery may be different than the number to be used 837 // for processing so don't depend of _num_q < _max_num_q as part 838 // of the test. 839 bool must_balance = _discovery_is_mt; 840 841 if ((mt_processing && ParallelRefProcBalancingEnabled) || 842 must_balance) { 843 RefProcBalanceQueuesTimeTracker tt(phase_times); 844 balance_queues(refs_lists); 845 } 846 847 // Phase 1 (soft refs only): 848 // . Traverse the list and remove any SoftReferences whose 849 // referents are not alive, but that should be kept alive for 850 // policy reasons. Keep alive the transitive closure of all 851 // such referents. 852 if (policy != NULL) { 853 RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase1, phase_times); 854 855 if (mt_processing) { 856 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/, phase_times); 857 task_executor->execute(phase1); 858 } else { 859 for (uint i = 0; i < _max_num_q; i++) { 860 process_phase1(refs_lists[i], policy, 861 is_alive, keep_alive, complete_gc); 862 } 863 } 864 } else { // policy == NULL 865 assert(refs_lists != _discoveredSoftRefs, 866 "Policy must be specified for soft references."); 867 } 868 869 // Phase 2: 870 // . Traverse the list and remove any refs whose referents are alive. 871 { 872 RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase2, phase_times); 873 874 if (mt_processing) { 875 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/, phase_times); 876 task_executor->execute(phase2); 877 } else { 878 for (uint i = 0; i < _max_num_q; i++) { 879 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); 880 } 881 } 882 } 883 884 // Phase 3: 885 // . Traverse the list and process referents as appropriate. 886 { 887 RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase3, phase_times); 888 889 if (mt_processing) { 890 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/, phase_times); 891 task_executor->execute(phase3); 892 } else { 893 for (uint i = 0; i < _max_num_q; i++) { 894 process_phase3(refs_lists[i], clear_referent, 895 is_alive, keep_alive, complete_gc); 896 } 897 } 898 } 899 } 900 901 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { 902 uint id = 0; 903 // Determine the queue index to use for this object. 904 if (_discovery_is_mt) { 905 // During a multi-threaded discovery phase, 906 // each thread saves to its "own" list. 907 Thread* thr = Thread::current(); 908 id = thr->as_Worker_thread()->id(); 909 } else { 910 // single-threaded discovery, we save in round-robin 911 // fashion to each of the lists. 912 if (_processing_is_mt) { 913 id = next_id(); 914 } 915 } 916 assert(id < _max_num_q, "Id is out-of-bounds id %u and max id %u)", id, _max_num_q); 917 918 // Get the discovered queue to which we will add 919 DiscoveredList* list = NULL; 920 switch (rt) { 921 case REF_OTHER: 922 // Unknown reference type, no special treatment 923 break; 924 case REF_SOFT: 925 list = &_discoveredSoftRefs[id]; 926 break; 927 case REF_WEAK: 928 list = &_discoveredWeakRefs[id]; 929 break; 930 case REF_FINAL: 931 list = &_discoveredFinalRefs[id]; 932 break; 933 case REF_PHANTOM: 934 list = &_discoveredPhantomRefs[id]; 935 break; 936 case REF_NONE: 937 // we should not reach here if we are an InstanceRefKlass 938 default: 939 ShouldNotReachHere(); 940 } 941 log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list)); 942 return list; 943 } 944 945 inline void 946 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, 947 oop obj, 948 HeapWord* discovered_addr) { 949 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); 950 // First we must make sure this object is only enqueued once. CAS in a non null 951 // discovered_addr. 952 oop current_head = refs_list.head(); 953 // The last ref must have its discovered field pointing to itself. 954 oop next_discovered = (current_head != NULL) ? current_head : obj; 955 956 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr, 957 NULL); 958 if (retest == NULL) { 959 // This thread just won the right to enqueue the object. 960 // We have separate lists for enqueueing, so no synchronization 961 // is necessary. 962 refs_list.set_head(obj); 963 refs_list.inc_length(1); 964 965 log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)", 966 p2i(obj), obj->klass()->internal_name()); 967 } else { 968 // If retest was non NULL, another thread beat us to it: 969 // The reference has already been discovered... 970 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)", 971 p2i(obj), obj->klass()->internal_name()); 972 } 973 } 974 975 #ifndef PRODUCT 976 // Non-atomic (i.e. concurrent) discovery might allow us 977 // to observe j.l.References with NULL referents, being those 978 // cleared concurrently by mutators during (or after) discovery. 979 void ReferenceProcessor::verify_referent(oop obj) { 980 bool da = discovery_is_atomic(); 981 oop referent = java_lang_ref_Reference::referent(obj); 982 assert(da ? oopDesc::is_oop(referent) : oopDesc::is_oop_or_null(referent), 983 "Bad referent " INTPTR_FORMAT " found in Reference " 984 INTPTR_FORMAT " during %satomic discovery ", 985 p2i(referent), p2i(obj), da ? "" : "non-"); 986 } 987 #endif 988 989 // We mention two of several possible choices here: 990 // #0: if the reference object is not in the "originating generation" 991 // (or part of the heap being collected, indicated by our "span" 992 // we don't treat it specially (i.e. we scan it as we would 993 // a normal oop, treating its references as strong references). 994 // This means that references can't be discovered unless their 995 // referent is also in the same span. This is the simplest, 996 // most "local" and most conservative approach, albeit one 997 // that may cause weak references to be enqueued least promptly. 998 // We call this choice the "ReferenceBasedDiscovery" policy. 999 // #1: the reference object may be in any generation (span), but if 1000 // the referent is in the generation (span) being currently collected 1001 // then we can discover the reference object, provided 1002 // the object has not already been discovered by 1003 // a different concurrently running collector (as may be the 1004 // case, for instance, if the reference object is in CMS and 1005 // the referent in DefNewGeneration), and provided the processing 1006 // of this reference object by the current collector will 1007 // appear atomic to every other collector in the system. 1008 // (Thus, for instance, a concurrent collector may not 1009 // discover references in other generations even if the 1010 // referent is in its own generation). This policy may, 1011 // in certain cases, enqueue references somewhat sooner than 1012 // might Policy #0 above, but at marginally increased cost 1013 // and complexity in processing these references. 1014 // We call this choice the "RefeferentBasedDiscovery" policy. 1015 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { 1016 // Make sure we are discovering refs (rather than processing discovered refs). 1017 if (!_discovering_refs || !RegisterReferences) { 1018 return false; 1019 } 1020 // We only discover active references. 1021 oop next = java_lang_ref_Reference::next(obj); 1022 if (next != NULL) { // Ref is no longer active 1023 return false; 1024 } 1025 1026 HeapWord* obj_addr = (HeapWord*)obj; 1027 if (RefDiscoveryPolicy == ReferenceBasedDiscovery && 1028 !_span.contains(obj_addr)) { 1029 // Reference is not in the originating generation; 1030 // don't treat it specially (i.e. we want to scan it as a normal 1031 // object with strong references). 1032 return false; 1033 } 1034 1035 // We only discover references whose referents are not (yet) 1036 // known to be strongly reachable. 1037 if (is_alive_non_header() != NULL) { 1038 verify_referent(obj); 1039 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) { 1040 return false; // referent is reachable 1041 } 1042 } 1043 if (rt == REF_SOFT) { 1044 // For soft refs we can decide now if these are not 1045 // current candidates for clearing, in which case we 1046 // can mark through them now, rather than delaying that 1047 // to the reference-processing phase. Since all current 1048 // time-stamp policies advance the soft-ref clock only 1049 // at a full collection cycle, this is always currently 1050 // accurate. 1051 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) { 1052 return false; 1053 } 1054 } 1055 1056 ResourceMark rm; // Needed for tracing. 1057 1058 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj); 1059 const oop discovered = java_lang_ref_Reference::discovered(obj); 1060 assert(oopDesc::is_oop_or_null(discovered), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)); 1061 if (discovered != NULL) { 1062 // The reference has already been discovered... 1063 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)", 1064 p2i(obj), obj->klass()->internal_name()); 1065 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { 1066 // assumes that an object is not processed twice; 1067 // if it's been already discovered it must be on another 1068 // generation's discovered list; so we won't discover it. 1069 return false; 1070 } else { 1071 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, 1072 "Unrecognized policy"); 1073 // Check assumption that an object is not potentially 1074 // discovered twice except by concurrent collectors that potentially 1075 // trace the same Reference object twice. 1076 assert(UseConcMarkSweepGC || UseG1GC, 1077 "Only possible with a concurrent marking collector"); 1078 return true; 1079 } 1080 } 1081 1082 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { 1083 verify_referent(obj); 1084 // Discover if and only if EITHER: 1085 // .. reference is in our span, OR 1086 // .. we are an atomic collector and referent is in our span 1087 if (_span.contains(obj_addr) || 1088 (discovery_is_atomic() && 1089 _span.contains(java_lang_ref_Reference::referent(obj)))) { 1090 // should_enqueue = true; 1091 } else { 1092 return false; 1093 } 1094 } else { 1095 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && 1096 _span.contains(obj_addr), "code inconsistency"); 1097 } 1098 1099 // Get the right type of discovered queue head. 1100 DiscoveredList* list = get_discovered_list(rt); 1101 if (list == NULL) { 1102 return false; // nothing special needs to be done 1103 } 1104 1105 if (_discovery_is_mt) { 1106 add_to_discovered_list_mt(*list, obj, discovered_addr); 1107 } else { 1108 // We do a raw store here: the field will be visited later when processing 1109 // the discovered references. 1110 oop current_head = list->head(); 1111 // The last ref must have its discovered field pointing to itself. 1112 oop next_discovered = (current_head != NULL) ? current_head : obj; 1113 1114 assert(discovered == NULL, "control point invariant"); 1115 oop_store_raw(discovered_addr, next_discovered); 1116 list->set_head(obj); 1117 list->inc_length(1); 1118 1119 log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name()); 1120 } 1121 assert(oopDesc::is_oop(obj), "Discovered a bad reference"); 1122 verify_referent(obj); 1123 return true; 1124 } 1125 1126 bool ReferenceProcessor::has_discovered_references() { 1127 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 1128 if (!_discovered_refs[i].is_empty()) { 1129 return true; 1130 } 1131 } 1132 return false; 1133 } 1134 1135 // Preclean the discovered references by removing those 1136 // whose referents are alive, and by marking from those that 1137 // are not active. These lists can be handled here 1138 // in any order and, indeed, concurrently. 1139 void ReferenceProcessor::preclean_discovered_references( 1140 BoolObjectClosure* is_alive, 1141 OopClosure* keep_alive, 1142 VoidClosure* complete_gc, 1143 YieldClosure* yield, 1144 GCTimer* gc_timer) { 1145 1146 // Soft references 1147 { 1148 GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer); 1149 for (uint i = 0; i < _max_num_q; i++) { 1150 if (yield->should_return()) { 1151 return; 1152 } 1153 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, 1154 keep_alive, complete_gc, yield); 1155 } 1156 } 1157 1158 // Weak references 1159 { 1160 GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer); 1161 for (uint i = 0; i < _max_num_q; i++) { 1162 if (yield->should_return()) { 1163 return; 1164 } 1165 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, 1166 keep_alive, complete_gc, yield); 1167 } 1168 } 1169 1170 // Final references 1171 { 1172 GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer); 1173 for (uint i = 0; i < _max_num_q; i++) { 1174 if (yield->should_return()) { 1175 return; 1176 } 1177 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, 1178 keep_alive, complete_gc, yield); 1179 } 1180 } 1181 1182 // Phantom references 1183 { 1184 GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer); 1185 for (uint i = 0; i < _max_num_q; i++) { 1186 if (yield->should_return()) { 1187 return; 1188 } 1189 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, 1190 keep_alive, complete_gc, yield); 1191 } 1192 } 1193 } 1194 1195 // Walk the given discovered ref list, and remove all reference objects 1196 // whose referents are still alive, whose referents are NULL or which 1197 // are not active (have a non-NULL next field). NOTE: When we are 1198 // thus precleaning the ref lists (which happens single-threaded today), 1199 // we do not disable refs discovery to honor the correct semantics of 1200 // java.lang.Reference. As a result, we need to be careful below 1201 // that ref removal steps interleave safely with ref discovery steps 1202 // (in this thread). 1203 void 1204 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, 1205 BoolObjectClosure* is_alive, 1206 OopClosure* keep_alive, 1207 VoidClosure* complete_gc, 1208 YieldClosure* yield) { 1209 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 1210 while (iter.has_next()) { 1211 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); 1212 oop obj = iter.obj(); 1213 oop next = java_lang_ref_Reference::next(obj); 1214 if (iter.referent() == NULL || iter.is_referent_alive() || 1215 next != NULL) { 1216 // The referent has been cleared, or is alive, or the Reference is not 1217 // active; we need to trace and mark its cohort. 1218 log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)", 1219 p2i(iter.obj()), iter.obj()->klass()->internal_name()); 1220 // Remove Reference object from list 1221 iter.remove(); 1222 // Keep alive its cohort. 1223 iter.make_referent_alive(); 1224 if (UseCompressedOops) { 1225 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj); 1226 keep_alive->do_oop(next_addr); 1227 } else { 1228 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj); 1229 keep_alive->do_oop(next_addr); 1230 } 1231 iter.move_to_next(); 1232 } else { 1233 iter.next(); 1234 } 1235 } 1236 // Close the reachable set 1237 complete_gc->do_void(); 1238 1239 NOT_PRODUCT( 1240 if (iter.processed() > 0) { 1241 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT, 1242 iter.removed(), iter.processed(), p2i(&refs_list)); 1243 } 1244 ) 1245 } 1246 1247 const char* ReferenceProcessor::list_name(uint i) { 1248 assert(i <= _max_num_q * number_of_subclasses_of_ref(), 1249 "Out of bounds index"); 1250 1251 int j = i / _max_num_q; 1252 switch (j) { 1253 case 0: return "SoftRef"; 1254 case 1: return "WeakRef"; 1255 case 2: return "FinalRef"; 1256 case 3: return "PhantomRef"; 1257 } 1258 ShouldNotReachHere(); 1259 return NULL; 1260 }