1 /* 2 * Copyright (c) 2001, 2016, 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/heapMonitoring.hpp" 39 #include "runtime/java.hpp" 40 #include "runtime/jniHandles.hpp" 41 42 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL; 43 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL; 44 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0; 45 46 void referenceProcessor_init() { 47 ReferenceProcessor::init_statics(); 48 } 49 50 void ReferenceProcessor::init_statics() { 51 // We need a monotonically non-decreasing time in ms but 52 // os::javaTimeMillis() does not guarantee monotonicity. 53 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 54 55 // Initialize the soft ref timestamp clock. 56 _soft_ref_timestamp_clock = now; 57 // Also update the soft ref clock in j.l.r.SoftReference 58 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock); 59 60 _always_clear_soft_ref_policy = new AlwaysClearPolicy(); 61 if (is_server_compilation_mode_vm()) { 62 _default_soft_ref_policy = new LRUMaxHeapPolicy(); 63 } else { 64 _default_soft_ref_policy = new LRUCurrentHeapPolicy(); 65 } 66 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) { 67 vm_exit_during_initialization("Could not allocate reference policy object"); 68 } 69 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || 70 RefDiscoveryPolicy == ReferentBasedDiscovery, 71 "Unrecognized RefDiscoveryPolicy"); 72 } 73 74 void ReferenceProcessor::enable_discovery(bool check_no_refs) { 75 #ifdef ASSERT 76 // Verify that we're not currently discovering refs 77 assert(!_discovering_refs, "nested call?"); 78 79 if (check_no_refs) { 80 // Verify that the discovered lists are empty 81 verify_no_references_recorded(); 82 } 83 #endif // ASSERT 84 85 // Someone could have modified the value of the static 86 // field in the j.l.r.SoftReference class that holds the 87 // soft reference timestamp clock using reflection or 88 // Unsafe between GCs. Unconditionally update the static 89 // field in ReferenceProcessor here so that we use the new 90 // value during reference discovery. 91 92 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); 93 _discovering_refs = true; 94 } 95 96 ReferenceProcessor::ReferenceProcessor(MemRegion span, 97 bool mt_processing, 98 uint mt_processing_degree, 99 bool mt_discovery, 100 uint mt_discovery_degree, 101 bool atomic_discovery, 102 BoolObjectClosure* is_alive_non_header) : 103 _discovering_refs(false), 104 _enqueuing_is_done(false), 105 _is_alive_non_header(is_alive_non_header), 106 _processing_is_mt(mt_processing), 107 _next_id(0) 108 { 109 _span = span; 110 _discovery_is_atomic = atomic_discovery; 111 _discovery_is_mt = mt_discovery; 112 _num_q = MAX2(1U, mt_processing_degree); 113 _max_num_q = MAX2(_num_q, mt_discovery_degree); 114 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList, 115 _max_num_q * number_of_subclasses_of_ref(), mtGC); 116 117 if (_discovered_refs == NULL) { 118 vm_exit_during_initialization("Could not allocated RefProc Array"); 119 } 120 _discoveredSoftRefs = &_discovered_refs[0]; 121 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q]; 122 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q]; 123 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q]; 124 125 // Initialize all entries to NULL 126 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 127 _discovered_refs[i].set_head(NULL); 128 _discovered_refs[i].set_length(0); 129 } 130 131 setup_policy(false /* default soft ref policy */); 132 } 133 134 #ifndef PRODUCT 135 void ReferenceProcessor::verify_no_references_recorded() { 136 guarantee(!_discovering_refs, "Discovering refs?"); 137 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 138 guarantee(_discovered_refs[i].is_empty(), 139 "Found non-empty discovered list at %u", i); 140 } 141 } 142 #endif 143 144 void ReferenceProcessor::weak_oops_do(OopClosure* f) { 145 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 146 if (UseCompressedOops) { 147 f->do_oop((narrowOop*)_discovered_refs[i].adr_head()); 148 } else { 149 f->do_oop((oop*)_discovered_refs[i].adr_head()); 150 } 151 } 152 } 153 154 void ReferenceProcessor::update_soft_ref_master_clock() { 155 // Update (advance) the soft ref master clock field. This must be done 156 // after processing the soft ref list. 157 158 // We need a monotonically non-decreasing time in ms but 159 // os::javaTimeMillis() does not guarantee monotonicity. 160 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 161 jlong soft_ref_clock = java_lang_ref_SoftReference::clock(); 162 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync"); 163 164 NOT_PRODUCT( 165 if (now < _soft_ref_timestamp_clock) { 166 log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, 167 _soft_ref_timestamp_clock, now); 168 } 169 ) 170 // The values of now and _soft_ref_timestamp_clock are set using 171 // javaTimeNanos(), which is guaranteed to be monotonically 172 // non-decreasing provided the underlying platform provides such 173 // a time source (and it is bug free). 174 // In product mode, however, protect ourselves from non-monotonicity. 175 if (now > _soft_ref_timestamp_clock) { 176 _soft_ref_timestamp_clock = now; 177 java_lang_ref_SoftReference::set_clock(now); 178 } 179 // Else leave clock stalled at its old value until time progresses 180 // past clock value. 181 } 182 183 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) { 184 size_t total = 0; 185 for (uint i = 0; i < _max_num_q; ++i) { 186 total += lists[i].length(); 187 } 188 return total; 189 } 190 191 ReferenceProcessorStats ReferenceProcessor::process_discovered_references( 192 BoolObjectClosure* is_alive, 193 OopClosure* keep_alive, 194 VoidClosure* complete_gc, 195 AbstractRefProcTaskExecutor* task_executor, 196 GCTimer* gc_timer) { 197 198 assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); 199 // Stop treating discovered references specially. 200 disable_discovery(); 201 202 // If discovery was concurrent, someone could have modified 203 // the value of the static field in the j.l.r.SoftReference 204 // class that holds the soft reference timestamp clock using 205 // reflection or Unsafe between when discovery was enabled and 206 // now. Unconditionally update the static field in ReferenceProcessor 207 // here so that we use the new value during processing of the 208 // discovered soft refs. 209 210 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); 211 212 ReferenceProcessorStats stats( 213 total_count(_discoveredSoftRefs), 214 total_count(_discoveredWeakRefs), 215 total_count(_discoveredFinalRefs), 216 total_count(_discoveredPhantomRefs)); 217 218 // Soft references 219 { 220 GCTraceTime(Debug, gc, ref) tt("SoftReference", gc_timer); 221 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true, 222 is_alive, keep_alive, complete_gc, task_executor); 223 } 224 225 update_soft_ref_master_clock(); 226 227 // Weak references 228 { 229 GCTraceTime(Debug, gc, ref) tt("WeakReference", gc_timer); 230 process_discovered_reflist(_discoveredWeakRefs, NULL, true, 231 is_alive, keep_alive, complete_gc, task_executor); 232 } 233 234 // Final references 235 { 236 GCTraceTime(Debug, gc, ref) tt("FinalReference", gc_timer); 237 process_discovered_reflist(_discoveredFinalRefs, NULL, false, 238 is_alive, keep_alive, complete_gc, task_executor); 239 } 240 241 // Phantom references 242 { 243 GCTraceTime(Debug, gc, ref) tt("PhantomReference", gc_timer); 244 process_discovered_reflist(_discoveredPhantomRefs, NULL, true, 245 is_alive, keep_alive, complete_gc, task_executor); 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", 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 size_t handled; 262 { 263 GCTraceTime(Debug, gc, ref) tt("Heap Monitoring Weak Reference", gc_timer); 264 handled = process_phaseHeapSampling(is_alive, keep_alive, complete_gc, task_executor); 265 } 266 267 log_debug(gc, ref)("Ref Counts: Soft: " SIZE_FORMAT " Weak: " SIZE_FORMAT " Final: " SIZE_FORMAT " Phantom: " SIZE_FORMAT, 268 stats.soft_count(), stats.weak_count(), stats.final_count(), stats.phantom_count()); 269 log_develop_trace(gc, ref)("JNI Weak Reference count: " SIZE_FORMAT, count_jni_refs()); 270 log_develop_trace(gc, ref)("Heap Sampler Weak Reference handled: " SIZE_FORMAT, handled); 271 272 return stats; 273 } 274 275 #ifndef PRODUCT 276 // Calculate the number of jni handles. 277 size_t ReferenceProcessor::count_jni_refs() { 278 class CountHandleClosure: public OopClosure { 279 private: 280 size_t _count; 281 public: 282 CountHandleClosure(): _count(0) {} 283 void do_oop(oop* unused) { _count++; } 284 void do_oop(narrowOop* unused) { ShouldNotReachHere(); } 285 size_t count() { return _count; } 286 }; 287 CountHandleClosure global_handle_count; 288 JNIHandles::weak_oops_do(&global_handle_count); 289 return global_handle_count.count(); 290 } 291 #endif 292 293 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive, 294 OopClosure* keep_alive, 295 VoidClosure* complete_gc) { 296 JNIHandles::weak_oops_do(is_alive, keep_alive); 297 complete_gc->do_void(); 298 } 299 300 size_t ReferenceProcessor::process_phaseHeapSampling( 301 BoolObjectClosure* is_alive, 302 OopClosure* keep_alive, 303 VoidClosure* complete_gc, 304 AbstractRefProcTaskExecutor* task_executor) { 305 size_t count = 0; 306 if (HeapMonitoring::enabled()) { 307 if (task_executor != NULL) { 308 task_executor->set_single_threaded_mode(); 309 } 310 count = HeapMonitoring::weak_oops_do(is_alive, keep_alive); 311 complete_gc->do_void(); 312 } 313 return count; 314 } 315 316 void ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) { 317 // Enqueue references that are not made active again, and 318 // clear the decks for the next collection (cycle). 319 enqueue_discovered_reflists(task_executor); 320 321 // Stop treating discovered references specially. 322 disable_discovery(); 323 } 324 325 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list) { 326 // Given a list of refs linked through the "discovered" field 327 // (java.lang.ref.Reference.discovered), self-loop their "next" field 328 // thus distinguishing them from active References, then 329 // prepend them to the pending list. 330 // 331 // The Java threads will see the Reference objects linked together through 332 // the discovered field. Instead of trying to do the write barrier updates 333 // in all places in the reference processor where we manipulate the discovered 334 // field we make sure to do the barrier here where we anyway iterate through 335 // all linked Reference objects. Note that it is important to not dirty any 336 // cards during reference processing since this will cause card table 337 // verification to fail for G1. 338 log_develop_trace(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(&refs_list)); 339 340 oop obj = NULL; 341 oop next_d = refs_list.head(); 342 // Walk down the list, self-looping the next field 343 // so that the References are not considered active. 344 while (obj != next_d) { 345 obj = next_d; 346 assert(obj->is_instance(), "should be an instance object"); 347 assert(InstanceKlass::cast(obj->klass())->is_reference_instance_klass(), "should be reference object"); 348 next_d = java_lang_ref_Reference::discovered(obj); 349 log_develop_trace(gc, ref)(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, p2i(obj), p2i(next_d)); 350 assert(java_lang_ref_Reference::next(obj) == NULL, 351 "Reference not active; should not be discovered"); 352 // Self-loop next, so as to make Ref not active. 353 java_lang_ref_Reference::set_next_raw(obj, obj); 354 if (next_d != obj) { 355 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d); 356 } else { 357 // This is the last object. 358 // Swap refs_list into pending list and set obj's 359 // discovered to what we read from the pending list. 360 oop old = Universe::swap_reference_pending_list(refs_list.head()); 361 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL 362 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old); 363 } 364 } 365 } 366 367 // Parallel enqueue task 368 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { 369 public: 370 RefProcEnqueueTask(ReferenceProcessor& ref_processor, 371 DiscoveredList discovered_refs[], 372 int n_queues) 373 : EnqueueTask(ref_processor, discovered_refs, n_queues) 374 { } 375 376 virtual void work(unsigned int work_id) { 377 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds"); 378 // Simplest first cut: static partitioning. 379 int index = work_id; 380 // The increment on "index" must correspond to the maximum number of queues 381 // (n_queues) with which that ReferenceProcessor was created. That 382 // is because of the "clever" way the discovered references lists were 383 // allocated and are indexed into. 384 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected"); 385 for (int j = 0; 386 j < ReferenceProcessor::number_of_subclasses_of_ref(); 387 j++, index += _n_queues) { 388 _ref_processor.enqueue_discovered_reflist(_refs_lists[index]); 389 _refs_lists[index].set_head(NULL); 390 _refs_lists[index].set_length(0); 391 } 392 } 393 }; 394 395 // Enqueue references that are not made active again 396 void ReferenceProcessor::enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor) { 397 if (_processing_is_mt && task_executor != NULL) { 398 // Parallel code 399 RefProcEnqueueTask tsk(*this, _discovered_refs, _max_num_q); 400 task_executor->execute(tsk); 401 } else { 402 // Serial code: call the parent class's implementation 403 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 404 enqueue_discovered_reflist(_discovered_refs[i]); 405 _discovered_refs[i].set_head(NULL); 406 _discovered_refs[i].set_length(0); 407 } 408 } 409 } 410 411 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { 412 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref); 413 oop discovered = java_lang_ref_Reference::discovered(_ref); 414 assert(_discovered_addr && discovered->is_oop_or_null(), 415 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)); 416 _next = discovered; 417 _referent_addr = java_lang_ref_Reference::referent_addr(_ref); 418 _referent = java_lang_ref_Reference::referent(_ref); 419 assert(Universe::heap()->is_in_reserved_or_null(_referent), 420 "Wrong oop found in java.lang.Reference object"); 421 assert(allow_null_referent ? 422 _referent->is_oop_or_null() 423 : _referent->is_oop(), 424 "Expected an oop%s for referent field at " PTR_FORMAT, 425 (allow_null_referent ? " or NULL" : ""), 426 p2i(_referent)); 427 } 428 429 void DiscoveredListIterator::remove() { 430 assert(_ref->is_oop(), "Dropping a bad reference"); 431 oop_store_raw(_discovered_addr, NULL); 432 433 // First _prev_next ref actually points into DiscoveredList (gross). 434 oop new_next; 435 if (_next == _ref) { 436 // At the end of the list, we should make _prev point to itself. 437 // If _ref is the first ref, then _prev_next will be in the DiscoveredList, 438 // and _prev will be NULL. 439 new_next = _prev; 440 } else { 441 new_next = _next; 442 } 443 // Remove Reference object from discovered list. Note that G1 does not need a 444 // pre-barrier here because we know the Reference has already been found/marked, 445 // that's how it ended up in the discovered list in the first place. 446 oop_store_raw(_prev_next, new_next); 447 NOT_PRODUCT(_removed++); 448 _refs_list.dec_length(1); 449 } 450 451 void DiscoveredListIterator::clear_referent() { 452 oop_store_raw(_referent_addr, NULL); 453 } 454 455 // NOTE: process_phase*() are largely similar, and at a high level 456 // merely iterate over the extant list applying a predicate to 457 // each of its elements and possibly removing that element from the 458 // list and applying some further closures to that element. 459 // We should consider the possibility of replacing these 460 // process_phase*() methods by abstracting them into 461 // a single general iterator invocation that receives appropriate 462 // closures that accomplish this work. 463 464 // (SoftReferences only) Traverse the list and remove any SoftReferences whose 465 // referents are not alive, but that should be kept alive for policy reasons. 466 // Keep alive the transitive closure of all such referents. 467 void 468 ReferenceProcessor::process_phase1(DiscoveredList& refs_list, 469 ReferencePolicy* policy, 470 BoolObjectClosure* is_alive, 471 OopClosure* keep_alive, 472 VoidClosure* complete_gc) { 473 assert(policy != NULL, "Must have a non-NULL policy"); 474 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 475 // Decide which softly reachable refs should be kept alive. 476 while (iter.has_next()) { 477 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); 478 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); 479 if (referent_is_dead && 480 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) { 481 log_develop_trace(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", 482 p2i(iter.obj()), iter.obj()->klass()->internal_name()); 483 // Remove Reference object from list 484 iter.remove(); 485 // keep the referent around 486 iter.make_referent_alive(); 487 iter.move_to_next(); 488 } else { 489 iter.next(); 490 } 491 } 492 // Close the reachable set 493 complete_gc->do_void(); 494 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT, 495 iter.removed(), iter.processed(), p2i(&refs_list)); 496 } 497 498 // Traverse the list and remove any Refs that are not active, or 499 // whose referents are either alive or NULL. 500 void 501 ReferenceProcessor::pp2_work(DiscoveredList& refs_list, 502 BoolObjectClosure* is_alive, 503 OopClosure* keep_alive) { 504 assert(discovery_is_atomic(), "Error"); 505 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 506 while (iter.has_next()) { 507 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); 508 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());) 509 assert(next == NULL, "Should not discover inactive Reference"); 510 if (iter.is_referent_alive()) { 511 log_develop_trace(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", 512 p2i(iter.obj()), iter.obj()->klass()->internal_name()); 513 // The referent is reachable after all. 514 // Remove Reference object from list. 515 iter.remove(); 516 // Update the referent pointer as necessary: Note that this 517 // should not entail any recursive marking because the 518 // referent must already have been traversed. 519 iter.make_referent_alive(); 520 iter.move_to_next(); 521 } else { 522 iter.next(); 523 } 524 } 525 NOT_PRODUCT( 526 if (iter.processed() > 0) { 527 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT 528 " Refs in discovered list " INTPTR_FORMAT, 529 iter.removed(), iter.processed(), p2i(&refs_list)); 530 } 531 ) 532 } 533 534 void 535 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list, 536 BoolObjectClosure* is_alive, 537 OopClosure* keep_alive, 538 VoidClosure* complete_gc) { 539 assert(!discovery_is_atomic(), "Error"); 540 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 541 while (iter.has_next()) { 542 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); 543 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); 544 oop next = java_lang_ref_Reference::next(iter.obj()); 545 if ((iter.referent() == NULL || iter.is_referent_alive() || 546 next != NULL)) { 547 assert(next->is_oop_or_null(), "Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next)); 548 // Remove Reference object from list 549 iter.remove(); 550 // Trace the cohorts 551 iter.make_referent_alive(); 552 if (UseCompressedOops) { 553 keep_alive->do_oop((narrowOop*)next_addr); 554 } else { 555 keep_alive->do_oop((oop*)next_addr); 556 } 557 iter.move_to_next(); 558 } else { 559 iter.next(); 560 } 561 } 562 // Now close the newly reachable set 563 complete_gc->do_void(); 564 NOT_PRODUCT( 565 if (iter.processed() > 0) { 566 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT 567 " Refs in discovered list " INTPTR_FORMAT, 568 iter.removed(), iter.processed(), p2i(&refs_list)); 569 } 570 ) 571 } 572 573 // Traverse the list and process the referents, by either 574 // clearing them or keeping them (and their reachable 575 // closure) alive. 576 void 577 ReferenceProcessor::process_phase3(DiscoveredList& refs_list, 578 bool clear_referent, 579 BoolObjectClosure* is_alive, 580 OopClosure* keep_alive, 581 VoidClosure* complete_gc) { 582 ResourceMark rm; 583 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 584 while (iter.has_next()) { 585 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); 586 if (clear_referent) { 587 // NULL out referent pointer 588 iter.clear_referent(); 589 } else { 590 // keep the referent around 591 iter.make_referent_alive(); 592 } 593 log_develop_trace(gc, ref)("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", 594 clear_referent ? "cleared " : "", p2i(iter.obj()), iter.obj()->klass()->internal_name()); 595 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference"); 596 iter.next(); 597 } 598 // Close the reachable set 599 complete_gc->do_void(); 600 } 601 602 void 603 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) { 604 oop obj = NULL; 605 oop next = refs_list.head(); 606 while (next != obj) { 607 obj = next; 608 next = java_lang_ref_Reference::discovered(obj); 609 java_lang_ref_Reference::set_discovered_raw(obj, NULL); 610 } 611 refs_list.set_head(NULL); 612 refs_list.set_length(0); 613 } 614 615 void ReferenceProcessor::abandon_partial_discovery() { 616 // loop over the lists 617 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 618 if ((i % _max_num_q) == 0) { 619 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i)); 620 } 621 clear_discovered_references(_discovered_refs[i]); 622 } 623 } 624 625 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { 626 public: 627 RefProcPhase1Task(ReferenceProcessor& ref_processor, 628 DiscoveredList refs_lists[], 629 ReferencePolicy* policy, 630 bool marks_oops_alive) 631 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), 632 _policy(policy) 633 { } 634 virtual void work(unsigned int i, BoolObjectClosure& is_alive, 635 OopClosure& keep_alive, 636 VoidClosure& complete_gc) 637 { 638 _ref_processor.process_phase1(_refs_lists[i], _policy, 639 &is_alive, &keep_alive, &complete_gc); 640 } 641 private: 642 ReferencePolicy* _policy; 643 }; 644 645 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { 646 public: 647 RefProcPhase2Task(ReferenceProcessor& ref_processor, 648 DiscoveredList refs_lists[], 649 bool marks_oops_alive) 650 : ProcessTask(ref_processor, refs_lists, marks_oops_alive) 651 { } 652 virtual void work(unsigned int i, BoolObjectClosure& is_alive, 653 OopClosure& keep_alive, 654 VoidClosure& complete_gc) 655 { 656 _ref_processor.process_phase2(_refs_lists[i], 657 &is_alive, &keep_alive, &complete_gc); 658 } 659 }; 660 661 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { 662 public: 663 RefProcPhase3Task(ReferenceProcessor& ref_processor, 664 DiscoveredList refs_lists[], 665 bool clear_referent, 666 bool marks_oops_alive) 667 : ProcessTask(ref_processor, refs_lists, marks_oops_alive), 668 _clear_referent(clear_referent) 669 { } 670 virtual void work(unsigned int i, BoolObjectClosure& is_alive, 671 OopClosure& keep_alive, 672 VoidClosure& complete_gc) 673 { 674 _ref_processor.process_phase3(_refs_lists[i], _clear_referent, 675 &is_alive, &keep_alive, &complete_gc); 676 } 677 private: 678 bool _clear_referent; 679 }; 680 681 #ifndef PRODUCT 682 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_refs) { 683 if (!log_is_enabled(Trace, gc, ref)) { 684 return; 685 } 686 687 stringStream st; 688 for (uint i = 0; i < active_length; ++i) { 689 st.print(SIZE_FORMAT " ", ref_lists[i].length()); 690 } 691 log_develop_trace(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs); 692 #ifdef ASSERT 693 for (uint i = active_length; i < _max_num_q; i++) { 694 assert(ref_lists[i].length() == 0, SIZE_FORMAT " unexpected References in %u", 695 ref_lists[i].length(), i); 696 } 697 #endif 698 } 699 #endif 700 701 void ReferenceProcessor::set_active_mt_degree(uint v) { 702 _num_q = v; 703 _next_id = 0; 704 } 705 706 // Balances reference queues. 707 // Move entries from all queues[0, 1, ..., _max_num_q-1] to 708 // queues[0, 1, ..., _num_q-1] because only the first _num_q 709 // corresponding to the active workers will be processed. 710 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) 711 { 712 // calculate total length 713 size_t total_refs = 0; 714 log_develop_trace(gc, ref)("Balance ref_lists "); 715 716 for (uint i = 0; i < _max_num_q; ++i) { 717 total_refs += ref_lists[i].length(); 718 } 719 log_reflist_counts(ref_lists, _max_num_q, total_refs); 720 size_t avg_refs = total_refs / _num_q + 1; 721 uint to_idx = 0; 722 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) { 723 bool move_all = false; 724 if (from_idx >= _num_q) { 725 move_all = ref_lists[from_idx].length() > 0; 726 } 727 while ((ref_lists[from_idx].length() > avg_refs) || 728 move_all) { 729 assert(to_idx < _num_q, "Sanity Check!"); 730 if (ref_lists[to_idx].length() < avg_refs) { 731 // move superfluous refs 732 size_t refs_to_move; 733 // Move all the Ref's if the from queue will not be processed. 734 if (move_all) { 735 refs_to_move = MIN2(ref_lists[from_idx].length(), 736 avg_refs - ref_lists[to_idx].length()); 737 } else { 738 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, 739 avg_refs - ref_lists[to_idx].length()); 740 } 741 742 assert(refs_to_move > 0, "otherwise the code below will fail"); 743 744 oop move_head = ref_lists[from_idx].head(); 745 oop move_tail = move_head; 746 oop new_head = move_head; 747 // find an element to split the list on 748 for (size_t j = 0; j < refs_to_move; ++j) { 749 move_tail = new_head; 750 new_head = java_lang_ref_Reference::discovered(new_head); 751 } 752 753 // Add the chain to the to list. 754 if (ref_lists[to_idx].head() == NULL) { 755 // to list is empty. Make a loop at the end. 756 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail); 757 } else { 758 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head()); 759 } 760 ref_lists[to_idx].set_head(move_head); 761 ref_lists[to_idx].inc_length(refs_to_move); 762 763 // Remove the chain from the from list. 764 if (move_tail == new_head) { 765 // We found the end of the from list. 766 ref_lists[from_idx].set_head(NULL); 767 } else { 768 ref_lists[from_idx].set_head(new_head); 769 } 770 ref_lists[from_idx].dec_length(refs_to_move); 771 if (ref_lists[from_idx].length() == 0) { 772 break; 773 } 774 } else { 775 to_idx = (to_idx + 1) % _num_q; 776 } 777 } 778 } 779 #ifdef ASSERT 780 size_t balanced_total_refs = 0; 781 for (uint i = 0; i < _num_q; ++i) { 782 balanced_total_refs += ref_lists[i].length(); 783 } 784 log_reflist_counts(ref_lists, _num_q, balanced_total_refs); 785 assert(total_refs == balanced_total_refs, "Balancing was incomplete"); 786 #endif 787 } 788 789 void ReferenceProcessor::balance_all_queues() { 790 balance_queues(_discoveredSoftRefs); 791 balance_queues(_discoveredWeakRefs); 792 balance_queues(_discoveredFinalRefs); 793 balance_queues(_discoveredPhantomRefs); 794 } 795 796 void ReferenceProcessor::process_discovered_reflist( 797 DiscoveredList refs_lists[], 798 ReferencePolicy* policy, 799 bool clear_referent, 800 BoolObjectClosure* is_alive, 801 OopClosure* keep_alive, 802 VoidClosure* complete_gc, 803 AbstractRefProcTaskExecutor* task_executor) 804 { 805 bool mt_processing = task_executor != NULL && _processing_is_mt; 806 // If discovery used MT and a dynamic number of GC threads, then 807 // the queues must be balanced for correctness if fewer than the 808 // maximum number of queues were used. The number of queue used 809 // during discovery may be different than the number to be used 810 // for processing so don't depend of _num_q < _max_num_q as part 811 // of the test. 812 bool must_balance = _discovery_is_mt; 813 814 if ((mt_processing && ParallelRefProcBalancingEnabled) || 815 must_balance) { 816 balance_queues(refs_lists); 817 } 818 819 // Phase 1 (soft refs only): 820 // . Traverse the list and remove any SoftReferences whose 821 // referents are not alive, but that should be kept alive for 822 // policy reasons. Keep alive the transitive closure of all 823 // such referents. 824 if (policy != NULL) { 825 if (mt_processing) { 826 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/); 827 task_executor->execute(phase1); 828 } else { 829 for (uint i = 0; i < _max_num_q; i++) { 830 process_phase1(refs_lists[i], policy, 831 is_alive, keep_alive, complete_gc); 832 } 833 } 834 } else { // policy == NULL 835 assert(refs_lists != _discoveredSoftRefs, 836 "Policy must be specified for soft references."); 837 } 838 839 // Phase 2: 840 // . Traverse the list and remove any refs whose referents are alive. 841 if (mt_processing) { 842 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/); 843 task_executor->execute(phase2); 844 } else { 845 for (uint i = 0; i < _max_num_q; i++) { 846 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); 847 } 848 } 849 850 // Phase 3: 851 // . Traverse the list and process referents as appropriate. 852 if (mt_processing) { 853 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/); 854 task_executor->execute(phase3); 855 } else { 856 for (uint i = 0; i < _max_num_q; i++) { 857 process_phase3(refs_lists[i], clear_referent, 858 is_alive, keep_alive, complete_gc); 859 } 860 } 861 } 862 863 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { 864 uint id = 0; 865 // Determine the queue index to use for this object. 866 if (_discovery_is_mt) { 867 // During a multi-threaded discovery phase, 868 // each thread saves to its "own" list. 869 Thread* thr = Thread::current(); 870 id = thr->as_Worker_thread()->id(); 871 } else { 872 // single-threaded discovery, we save in round-robin 873 // fashion to each of the lists. 874 if (_processing_is_mt) { 875 id = next_id(); 876 } 877 } 878 assert(id < _max_num_q, "Id is out-of-bounds id %u and max id %u)", id, _max_num_q); 879 880 // Get the discovered queue to which we will add 881 DiscoveredList* list = NULL; 882 switch (rt) { 883 case REF_OTHER: 884 // Unknown reference type, no special treatment 885 break; 886 case REF_SOFT: 887 list = &_discoveredSoftRefs[id]; 888 break; 889 case REF_WEAK: 890 list = &_discoveredWeakRefs[id]; 891 break; 892 case REF_FINAL: 893 list = &_discoveredFinalRefs[id]; 894 break; 895 case REF_PHANTOM: 896 list = &_discoveredPhantomRefs[id]; 897 break; 898 case REF_NONE: 899 // we should not reach here if we are an InstanceRefKlass 900 default: 901 ShouldNotReachHere(); 902 } 903 log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list)); 904 return list; 905 } 906 907 inline void 908 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, 909 oop obj, 910 HeapWord* discovered_addr) { 911 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); 912 // First we must make sure this object is only enqueued once. CAS in a non null 913 // discovered_addr. 914 oop current_head = refs_list.head(); 915 // The last ref must have its discovered field pointing to itself. 916 oop next_discovered = (current_head != NULL) ? current_head : obj; 917 918 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr, 919 NULL); 920 if (retest == NULL) { 921 // This thread just won the right to enqueue the object. 922 // We have separate lists for enqueueing, so no synchronization 923 // is necessary. 924 refs_list.set_head(obj); 925 refs_list.inc_length(1); 926 927 log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)", 928 p2i(obj), obj->klass()->internal_name()); 929 } else { 930 // If retest was non NULL, another thread beat us to it: 931 // The reference has already been discovered... 932 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)", 933 p2i(obj), obj->klass()->internal_name()); 934 } 935 } 936 937 #ifndef PRODUCT 938 // Non-atomic (i.e. concurrent) discovery might allow us 939 // to observe j.l.References with NULL referents, being those 940 // cleared concurrently by mutators during (or after) discovery. 941 void ReferenceProcessor::verify_referent(oop obj) { 942 bool da = discovery_is_atomic(); 943 oop referent = java_lang_ref_Reference::referent(obj); 944 assert(da ? referent->is_oop() : referent->is_oop_or_null(), 945 "Bad referent " INTPTR_FORMAT " found in Reference " 946 INTPTR_FORMAT " during %satomic discovery ", 947 p2i(referent), p2i(obj), da ? "" : "non-"); 948 } 949 #endif 950 951 // We mention two of several possible choices here: 952 // #0: if the reference object is not in the "originating generation" 953 // (or part of the heap being collected, indicated by our "span" 954 // we don't treat it specially (i.e. we scan it as we would 955 // a normal oop, treating its references as strong references). 956 // This means that references can't be discovered unless their 957 // referent is also in the same span. This is the simplest, 958 // most "local" and most conservative approach, albeit one 959 // that may cause weak references to be enqueued least promptly. 960 // We call this choice the "ReferenceBasedDiscovery" policy. 961 // #1: the reference object may be in any generation (span), but if 962 // the referent is in the generation (span) being currently collected 963 // then we can discover the reference object, provided 964 // the object has not already been discovered by 965 // a different concurrently running collector (as may be the 966 // case, for instance, if the reference object is in CMS and 967 // the referent in DefNewGeneration), and provided the processing 968 // of this reference object by the current collector will 969 // appear atomic to every other collector in the system. 970 // (Thus, for instance, a concurrent collector may not 971 // discover references in other generations even if the 972 // referent is in its own generation). This policy may, 973 // in certain cases, enqueue references somewhat sooner than 974 // might Policy #0 above, but at marginally increased cost 975 // and complexity in processing these references. 976 // We call this choice the "RefeferentBasedDiscovery" policy. 977 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { 978 // Make sure we are discovering refs (rather than processing discovered refs). 979 if (!_discovering_refs || !RegisterReferences) { 980 return false; 981 } 982 // We only discover active references. 983 oop next = java_lang_ref_Reference::next(obj); 984 if (next != NULL) { // Ref is no longer active 985 return false; 986 } 987 988 HeapWord* obj_addr = (HeapWord*)obj; 989 if (RefDiscoveryPolicy == ReferenceBasedDiscovery && 990 !_span.contains(obj_addr)) { 991 // Reference is not in the originating generation; 992 // don't treat it specially (i.e. we want to scan it as a normal 993 // object with strong references). 994 return false; 995 } 996 997 // We only discover references whose referents are not (yet) 998 // known to be strongly reachable. 999 if (is_alive_non_header() != NULL) { 1000 verify_referent(obj); 1001 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) { 1002 return false; // referent is reachable 1003 } 1004 } 1005 if (rt == REF_SOFT) { 1006 // For soft refs we can decide now if these are not 1007 // current candidates for clearing, in which case we 1008 // can mark through them now, rather than delaying that 1009 // to the reference-processing phase. Since all current 1010 // time-stamp policies advance the soft-ref clock only 1011 // at a full collection cycle, this is always currently 1012 // accurate. 1013 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) { 1014 return false; 1015 } 1016 } 1017 1018 ResourceMark rm; // Needed for tracing. 1019 1020 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj); 1021 const oop discovered = java_lang_ref_Reference::discovered(obj); 1022 assert(discovered->is_oop_or_null(), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)); 1023 if (discovered != NULL) { 1024 // The reference has already been discovered... 1025 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)", 1026 p2i(obj), obj->klass()->internal_name()); 1027 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { 1028 // assumes that an object is not processed twice; 1029 // if it's been already discovered it must be on another 1030 // generation's discovered list; so we won't discover it. 1031 return false; 1032 } else { 1033 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, 1034 "Unrecognized policy"); 1035 // Check assumption that an object is not potentially 1036 // discovered twice except by concurrent collectors that potentially 1037 // trace the same Reference object twice. 1038 assert(UseConcMarkSweepGC || UseG1GC, 1039 "Only possible with a concurrent marking collector"); 1040 return true; 1041 } 1042 } 1043 1044 if (RefDiscoveryPolicy == ReferentBasedDiscovery) { 1045 verify_referent(obj); 1046 // Discover if and only if EITHER: 1047 // .. reference is in our span, OR 1048 // .. we are an atomic collector and referent is in our span 1049 if (_span.contains(obj_addr) || 1050 (discovery_is_atomic() && 1051 _span.contains(java_lang_ref_Reference::referent(obj)))) { 1052 // should_enqueue = true; 1053 } else { 1054 return false; 1055 } 1056 } else { 1057 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && 1058 _span.contains(obj_addr), "code inconsistency"); 1059 } 1060 1061 // Get the right type of discovered queue head. 1062 DiscoveredList* list = get_discovered_list(rt); 1063 if (list == NULL) { 1064 return false; // nothing special needs to be done 1065 } 1066 1067 if (_discovery_is_mt) { 1068 add_to_discovered_list_mt(*list, obj, discovered_addr); 1069 } else { 1070 // We do a raw store here: the field will be visited later when processing 1071 // the discovered references. 1072 oop current_head = list->head(); 1073 // The last ref must have its discovered field pointing to itself. 1074 oop next_discovered = (current_head != NULL) ? current_head : obj; 1075 1076 assert(discovered == NULL, "control point invariant"); 1077 oop_store_raw(discovered_addr, next_discovered); 1078 list->set_head(obj); 1079 list->inc_length(1); 1080 1081 log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name()); 1082 } 1083 assert(obj->is_oop(), "Discovered a bad reference"); 1084 verify_referent(obj); 1085 return true; 1086 } 1087 1088 bool ReferenceProcessor::has_discovered_references() { 1089 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) { 1090 if (!_discovered_refs[i].is_empty()) { 1091 return true; 1092 } 1093 } 1094 return false; 1095 } 1096 1097 // Preclean the discovered references by removing those 1098 // whose referents are alive, and by marking from those that 1099 // are not active. These lists can be handled here 1100 // in any order and, indeed, concurrently. 1101 void ReferenceProcessor::preclean_discovered_references( 1102 BoolObjectClosure* is_alive, 1103 OopClosure* keep_alive, 1104 VoidClosure* complete_gc, 1105 YieldClosure* yield, 1106 GCTimer* gc_timer) { 1107 1108 // Soft references 1109 { 1110 GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer); 1111 for (uint i = 0; i < _max_num_q; i++) { 1112 if (yield->should_return()) { 1113 return; 1114 } 1115 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, 1116 keep_alive, complete_gc, yield); 1117 } 1118 } 1119 1120 // Weak references 1121 { 1122 GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer); 1123 for (uint i = 0; i < _max_num_q; i++) { 1124 if (yield->should_return()) { 1125 return; 1126 } 1127 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, 1128 keep_alive, complete_gc, yield); 1129 } 1130 } 1131 1132 // Final references 1133 { 1134 GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer); 1135 for (uint i = 0; i < _max_num_q; i++) { 1136 if (yield->should_return()) { 1137 return; 1138 } 1139 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, 1140 keep_alive, complete_gc, yield); 1141 } 1142 } 1143 1144 // Phantom references 1145 { 1146 GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer); 1147 for (uint i = 0; i < _max_num_q; i++) { 1148 if (yield->should_return()) { 1149 return; 1150 } 1151 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, 1152 keep_alive, complete_gc, yield); 1153 } 1154 } 1155 } 1156 1157 // Walk the given discovered ref list, and remove all reference objects 1158 // whose referents are still alive, whose referents are NULL or which 1159 // are not active (have a non-NULL next field). NOTE: When we are 1160 // thus precleaning the ref lists (which happens single-threaded today), 1161 // we do not disable refs discovery to honor the correct semantics of 1162 // java.lang.Reference. As a result, we need to be careful below 1163 // that ref removal steps interleave safely with ref discovery steps 1164 // (in this thread). 1165 void 1166 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, 1167 BoolObjectClosure* is_alive, 1168 OopClosure* keep_alive, 1169 VoidClosure* complete_gc, 1170 YieldClosure* yield) { 1171 DiscoveredListIterator iter(refs_list, keep_alive, is_alive); 1172 while (iter.has_next()) { 1173 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); 1174 oop obj = iter.obj(); 1175 oop next = java_lang_ref_Reference::next(obj); 1176 if (iter.referent() == NULL || iter.is_referent_alive() || 1177 next != NULL) { 1178 // The referent has been cleared, or is alive, or the Reference is not 1179 // active; we need to trace and mark its cohort. 1180 log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)", 1181 p2i(iter.obj()), iter.obj()->klass()->internal_name()); 1182 // Remove Reference object from list 1183 iter.remove(); 1184 // Keep alive its cohort. 1185 iter.make_referent_alive(); 1186 if (UseCompressedOops) { 1187 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj); 1188 keep_alive->do_oop(next_addr); 1189 } else { 1190 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj); 1191 keep_alive->do_oop(next_addr); 1192 } 1193 iter.move_to_next(); 1194 } else { 1195 iter.next(); 1196 } 1197 } 1198 // Close the reachable set 1199 complete_gc->do_void(); 1200 1201 NOT_PRODUCT( 1202 if (iter.processed() > 0) { 1203 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT, 1204 iter.removed(), iter.processed(), p2i(&refs_list)); 1205 } 1206 ) 1207 } 1208 1209 const char* ReferenceProcessor::list_name(uint i) { 1210 assert(i <= _max_num_q * number_of_subclasses_of_ref(), 1211 "Out of bounds index"); 1212 1213 int j = i / _max_num_q; 1214 switch (j) { 1215 case 0: return "SoftRef"; 1216 case 1: return "WeakRef"; 1217 case 2: return "FinalRef"; 1218 case 3: return "PhantomRef"; 1219 } 1220 ShouldNotReachHere(); 1221 return NULL; 1222 } 1223