1 /*
2 * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/javaClasses.inline.hpp"
27 #include "classfile/systemDictionary.hpp"
28 #include "gc/shared/collectedHeap.hpp"
29 #include "gc/shared/collectedHeap.inline.hpp"
30 #include "gc/shared/gcTimer.hpp"
31 #include "gc/shared/gcTraceTime.inline.hpp"
32 #include "gc/shared/referencePolicy.hpp"
33 #include "gc/shared/referenceProcessor.inline.hpp"
34 #include "logging/log.hpp"
35 #include "memory/allocation.inline.hpp"
36 #include "memory/resourceArea.hpp"
37 #include "oops/access.inline.hpp"
38 #include "oops/oop.inline.hpp"
39 #include "runtime/java.hpp"
40
41 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
42 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
43 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0;
44
45 void referenceProcessor_init() {
46 ReferenceProcessor::init_statics();
47 }
48
49 void ReferenceProcessor::init_statics() {
50 // We need a monotonically non-decreasing time in ms but
51 // os::javaTimeMillis() does not guarantee monotonicity.
52 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
53
54 // Initialize the soft ref timestamp clock.
55 _soft_ref_timestamp_clock = now;
56 // Also update the soft ref clock in j.l.r.SoftReference
57 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock);
58
59 _always_clear_soft_ref_policy = new AlwaysClearPolicy();
60 if (is_server_compilation_mode_vm()) {
61 _default_soft_ref_policy = new LRUMaxHeapPolicy();
62 } else {
63 _default_soft_ref_policy = new LRUCurrentHeapPolicy();
64 }
65 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
66 vm_exit_during_initialization("Could not allocate reference policy object");
67 }
68 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
69 RefDiscoveryPolicy == ReferentBasedDiscovery,
70 "Unrecognized RefDiscoveryPolicy");
71 }
72
73 void ReferenceProcessor::enable_discovery(bool check_no_refs) {
74 #ifdef ASSERT
75 // Verify that we're not currently discovering refs
76 assert(!_discovering_refs, "nested call?");
77
78 if (check_no_refs) {
79 // Verify that the discovered lists are empty
80 verify_no_references_recorded();
81 }
82 #endif // ASSERT
83
84 // Someone could have modified the value of the static
85 // field in the j.l.r.SoftReference class that holds the
86 // soft reference timestamp clock using reflection or
87 // Unsafe between GCs. Unconditionally update the static
88 // field in ReferenceProcessor here so that we use the new
89 // value during reference discovery.
90
91 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
92 _discovering_refs = true;
93 }
94
95 ReferenceProcessor::ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery,
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 _is_subject_to_discovery(is_subject_to_discovery),
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 assert(is_subject_to_discovery != NULL, "must be set");
110
111 _discovery_is_atomic = atomic_discovery;
112 _discovery_is_mt = mt_discovery;
113 _num_queues = MAX2(1U, mt_processing_degree);
114 _max_num_queues = MAX2(_num_queues, mt_discovery_degree);
115 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
116 _max_num_queues * number_of_subclasses_of_ref(), mtGC);
117
118 if (_discovered_refs == NULL) {
119 vm_exit_during_initialization("Could not allocated RefProc Array");
120 }
121 _discoveredSoftRefs = &_discovered_refs[0];
122 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_queues];
123 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_queues];
124 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_queues];
125
126 // Initialize all entries to NULL
127 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) {
128 _discovered_refs[i].set_head(NULL);
129 _discovered_refs[i].set_length(0);
130 }
131
132 setup_policy(false /* default soft ref policy */);
133 }
134
135 SpanReferenceProcessor::SpanReferenceProcessor(MemRegion span,
136 bool mt_processing,
137 uint mt_processing_degree,
138 bool mt_discovery,
139 uint mt_discovery_degree,
140 bool atomic_discovery,
141 BoolObjectClosure* is_alive_non_header) :
142 ReferenceProcessor(&_span_based_discoverer,
143 mt_processing,
144 mt_processing_degree,
145 mt_discovery,
146 mt_discovery_degree,
147 atomic_discovery,
148 is_alive_non_header),
149 _span_based_discoverer(span) {
150
151 }
152
153 #ifndef PRODUCT
154 void ReferenceProcessor::verify_no_references_recorded() {
155 guarantee(!_discovering_refs, "Discovering refs?");
156 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) {
157 guarantee(_discovered_refs[i].is_empty(),
158 "Found non-empty discovered list at %u", i);
159 }
160 }
161 #endif
162
163 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
164 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) {
165 if (UseCompressedOops) {
166 f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
167 } else {
168 f->do_oop((oop*)_discovered_refs[i].adr_head());
169 }
170 }
171 }
172
173 void ReferenceProcessor::update_soft_ref_master_clock() {
174 // Update (advance) the soft ref master clock field. This must be done
175 // after processing the soft ref list.
176
177 // We need a monotonically non-decreasing time in ms but
178 // os::javaTimeMillis() does not guarantee monotonicity.
179 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
180 jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
181 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
182
183 NOT_PRODUCT(
184 if (now < _soft_ref_timestamp_clock) {
185 log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT,
186 _soft_ref_timestamp_clock, now);
187 }
188 )
189 // The values of now and _soft_ref_timestamp_clock are set using
190 // javaTimeNanos(), which is guaranteed to be monotonically
191 // non-decreasing provided the underlying platform provides such
192 // a time source (and it is bug free).
193 // In product mode, however, protect ourselves from non-monotonicity.
194 if (now > _soft_ref_timestamp_clock) {
195 _soft_ref_timestamp_clock = now;
196 java_lang_ref_SoftReference::set_clock(now);
197 }
198 // Else leave clock stalled at its old value until time progresses
199 // past clock value.
200 }
201
202 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) const {
203 size_t total = 0;
204 for (uint i = 0; i < _max_num_queues; ++i) {
205 total += lists[i].length();
206 }
207 return total;
208 }
209
210 ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
211 BoolObjectClosure* is_alive,
212 OopClosure* keep_alive,
213 VoidClosure* complete_gc,
214 AbstractRefProcTaskExecutor* task_executor,
215 ReferenceProcessorPhaseTimes* phase_times) {
216
217 double start_time = os::elapsedTime();
218
219 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
220 // Stop treating discovered references specially.
221 disable_discovery();
222
223 // If discovery was concurrent, someone could have modified
224 // the value of the static field in the j.l.r.SoftReference
225 // class that holds the soft reference timestamp clock using
226 // reflection or Unsafe between when discovery was enabled and
227 // now. Unconditionally update the static field in ReferenceProcessor
228 // here so that we use the new value during processing of the
229 // discovered soft refs.
230
231 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
232
233 ReferenceProcessorStats stats(total_count(_discoveredSoftRefs),
234 total_count(_discoveredWeakRefs),
235 total_count(_discoveredFinalRefs),
236 total_count(_discoveredPhantomRefs));
237
238 // Soft references
239 {
240 RefProcPhaseTimesTracker tt(REF_SOFT, phase_times, this);
241 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
242 is_alive, keep_alive, complete_gc, task_executor, phase_times);
243 }
244
245 update_soft_ref_master_clock();
246
247 // Weak references
248 {
249 RefProcPhaseTimesTracker tt(REF_WEAK, phase_times, this);
250 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
251 is_alive, keep_alive, complete_gc, task_executor, phase_times);
252 }
253
254 // Final references
255 {
256 RefProcPhaseTimesTracker tt(REF_FINAL, phase_times, this);
257 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
258 is_alive, keep_alive, complete_gc, task_executor, phase_times);
259 }
260
261 // Phantom references
262 {
263 RefProcPhaseTimesTracker tt(REF_PHANTOM, phase_times, this);
264 process_discovered_reflist(_discoveredPhantomRefs, NULL, true,
265 is_alive, keep_alive, complete_gc, task_executor, phase_times);
266 }
267
268 if (task_executor != NULL) {
269 // Record the work done by the parallel workers.
270 task_executor->set_single_threaded_mode();
271 }
272
273 phase_times->set_total_time_ms((os::elapsedTime() - start_time) * 1000);
274
275 return stats;
276 }
277
278 void ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor,
279 ReferenceProcessorPhaseTimes* phase_times) {
280 // Enqueue references that are not made active again, and
281 // clear the decks for the next collection (cycle).
282 enqueue_discovered_reflists(task_executor, phase_times);
283
284 // Stop treating discovered references specially.
285 disable_discovery();
286 }
287
288 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list) {
289 // Given a list of refs linked through the "discovered" field
290 // (java.lang.ref.Reference.discovered), self-loop their "next" field
291 // thus distinguishing them from active References, then
292 // prepend them to the pending list.
293 //
294 // The Java threads will see the Reference objects linked together through
295 // the discovered field. Instead of trying to do the write barrier updates
296 // in all places in the reference processor where we manipulate the discovered
297 // field we make sure to do the barrier here where we anyway iterate through
298 // all linked Reference objects. Note that it is important to not dirty any
299 // cards during reference processing since this will cause card table
300 // verification to fail for G1.
301 log_develop_trace(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(&refs_list));
302
303 oop obj = NULL;
304 oop next_discovered = refs_list.head();
305 // Walk down the list, self-looping the next field
306 // so that the References are not considered active.
307 while (obj != next_discovered) {
308 obj = next_discovered;
309 assert(obj->is_instance(), "should be an instance object");
310 assert(InstanceKlass::cast(obj->klass())->is_reference_instance_klass(), "should be reference object");
311 next_discovered = java_lang_ref_Reference::discovered(obj);
312 log_develop_trace(gc, ref)(" obj " INTPTR_FORMAT "/next_discovered " INTPTR_FORMAT, p2i(obj), p2i(next_discovered));
313 assert(java_lang_ref_Reference::next(obj) == NULL,
314 "Reference not active; should not be discovered");
315 // Self-loop next, so as to make Ref not active.
316 java_lang_ref_Reference::set_next_raw(obj, obj);
317 if (next_discovered != obj) {
318 HeapAccess<AS_NO_KEEPALIVE>::oop_store_at(obj, java_lang_ref_Reference::discovered_offset, next_discovered);
319 } else {
320 // This is the last object.
321 // Swap refs_list into pending list and set obj's
322 // discovered to what we read from the pending list.
323 oop old = Universe::swap_reference_pending_list(refs_list.head());
324 HeapAccess<AS_NO_KEEPALIVE>::oop_store_at(obj, java_lang_ref_Reference::discovered_offset, old);
325 }
326 }
327 }
328
329 // Parallel enqueue task
330 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
331 public:
332 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
333 DiscoveredList discovered_refs[],
334 int n_queues,
335 ReferenceProcessorPhaseTimes* phase_times)
336 : EnqueueTask(ref_processor, discovered_refs, n_queues, phase_times)
337 { }
338
339 virtual void work(unsigned int work_id) {
340 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefEnqueue, _phase_times, work_id);
341
342 assert(work_id < (unsigned int)_ref_processor.max_num_queues(), "Index out-of-bounds");
343 // Simplest first cut: static partitioning.
344 int index = work_id;
345 // The increment on "index" must correspond to the maximum number of queues
346 // (n_queues) with which that ReferenceProcessor was created. That
347 // is because of the "clever" way the discovered references lists were
348 // allocated and are indexed into.
349 assert(_n_queues == (int) _ref_processor.max_num_queues(), "Different number not expected");
350 for (int j = 0;
351 j < ReferenceProcessor::number_of_subclasses_of_ref();
352 j++, index += _n_queues) {
353 _ref_processor.enqueue_discovered_reflist(_refs_lists[index]);
354 _refs_lists[index].set_head(NULL);
355 _refs_lists[index].set_length(0);
356 }
357 }
358 };
359
360 // Enqueue references that are not made active again
361 void ReferenceProcessor::enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor,
362 ReferenceProcessorPhaseTimes* phase_times) {
363
364 ReferenceProcessorStats stats(total_count(_discoveredSoftRefs),
365 total_count(_discoveredWeakRefs),
366 total_count(_discoveredFinalRefs),
367 total_count(_discoveredPhantomRefs));
368
369 RefProcEnqueueTimeTracker tt(phase_times, stats);
370
371 if (_processing_is_mt && task_executor != NULL) {
372 // Parallel code
373 RefProcEnqueueTask tsk(*this, _discovered_refs, _max_num_queues, phase_times);
374 task_executor->execute(tsk);
375 } else {
376 // Serial code: call the parent class's implementation
377 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) {
378 enqueue_discovered_reflist(_discovered_refs[i]);
379 _discovered_refs[i].set_head(NULL);
380 _discovered_refs[i].set_length(0);
381 }
382 }
383 }
384
385 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
386 _current_discovered_addr = java_lang_ref_Reference::discovered_addr_raw(_current_discovered);
387 oop discovered = java_lang_ref_Reference::discovered(_current_discovered);
388 assert(_current_discovered_addr && oopDesc::is_oop_or_null(discovered),
389 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
390 _next_discovered = discovered;
391
392 _referent_addr = java_lang_ref_Reference::referent_addr_raw(_current_discovered);
393 _referent = java_lang_ref_Reference::referent(_current_discovered);
394 assert(Universe::heap()->is_in_reserved_or_null(_referent),
395 "Wrong oop found in java.lang.Reference object");
396 assert(allow_null_referent ?
397 oopDesc::is_oop_or_null(_referent)
398 : oopDesc::is_oop(_referent),
399 "Expected an oop%s for referent field at " PTR_FORMAT,
400 (allow_null_referent ? " or NULL" : ""),
401 p2i(_referent));
402 }
403
404 void DiscoveredListIterator::remove() {
405 assert(oopDesc::is_oop(_current_discovered), "Dropping a bad reference");
406 RawAccess<>::oop_store(_current_discovered_addr, oop(NULL));
407
408 // First _prev_next ref actually points into DiscoveredList (gross).
409 oop new_next;
410 if (_next_discovered == _current_discovered) {
411 // At the end of the list, we should make _prev point to itself.
412 // If _ref is the first ref, then _prev_next will be in the DiscoveredList,
413 // and _prev will be NULL.
414 new_next = _prev_discovered;
415 } else {
416 new_next = _next_discovered;
417 }
418 // Remove Reference object from discovered list. Note that G1 does not need a
419 // pre-barrier here because we know the Reference has already been found/marked,
420 // that's how it ended up in the discovered list in the first place.
421 RawAccess<>::oop_store(_prev_discovered_addr, new_next);
422 NOT_PRODUCT(_removed++);
423 _refs_list.dec_length(1);
424 }
425
426 void DiscoveredListIterator::clear_referent() {
427 RawAccess<>::oop_store(_referent_addr, oop(NULL));
428 }
429
430 // NOTE: process_phase*() are largely similar, and at a high level
431 // merely iterate over the extant list applying a predicate to
432 // each of its elements and possibly removing that element from the
433 // list and applying some further closures to that element.
434 // We should consider the possibility of replacing these
435 // process_phase*() methods by abstracting them into
436 // a single general iterator invocation that receives appropriate
437 // closures that accomplish this work.
438
439 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
440 // referents are not alive, but that should be kept alive for policy reasons.
441 // Keep alive the transitive closure of all such referents.
442 void
443 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
444 ReferencePolicy* policy,
445 BoolObjectClosure* is_alive,
446 OopClosure* keep_alive,
447 VoidClosure* complete_gc) {
448 assert(policy != NULL, "Must have a non-NULL policy");
449 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
450 // Decide which softly reachable refs should be kept alive.
451 while (iter.has_next()) {
452 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
453 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
454 if (referent_is_dead &&
455 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
456 log_develop_trace(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
457 p2i(iter.obj()), iter.obj()->klass()->internal_name());
458 // Remove Reference object from list
459 iter.remove();
460 // keep the referent around
461 iter.make_referent_alive();
462 iter.move_to_next();
463 } else {
464 iter.next();
465 }
466 }
467 // Close the reachable set
468 complete_gc->do_void();
469 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT,
470 iter.removed(), iter.processed(), p2i(&refs_list));
471 }
472
473 void ReferenceProcessor::process_phase2(DiscoveredList& refs_list,
474 BoolObjectClosure* is_alive,
475 OopClosure* keep_alive,
476 VoidClosure* complete_gc) {
477 if (discovery_is_atomic()) {
478 // complete_gc is ignored in this case for this phase
479 pp2_work(refs_list, is_alive, keep_alive);
480 } else {
481 assert(complete_gc != NULL, "Error");
482 pp2_work_concurrent_discovery(refs_list, is_alive,
483 keep_alive, complete_gc);
484 }
485 }
486 // Traverse the list and remove any Refs that are not active, or
487 // whose referents are either alive or NULL.
488 void
489 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
490 BoolObjectClosure* is_alive,
491 OopClosure* keep_alive) {
492 assert(discovery_is_atomic(), "Error");
493 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
494 while (iter.has_next()) {
495 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
496 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
497 assert(next == NULL, "Should not discover inactive Reference");
498 if (iter.is_referent_alive()) {
499 log_develop_trace(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
500 p2i(iter.obj()), iter.obj()->klass()->internal_name());
501 // The referent is reachable after all.
502 // Remove Reference object from list.
503 iter.remove();
504 // Update the referent pointer as necessary: Note that this
505 // should not entail any recursive marking because the
506 // referent must already have been traversed.
507 iter.make_referent_alive();
508 iter.move_to_next();
509 } else {
510 iter.next();
511 }
512 }
513 NOT_PRODUCT(
514 if (iter.processed() > 0) {
515 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
516 " Refs in discovered list " INTPTR_FORMAT,
517 iter.removed(), iter.processed(), p2i(&refs_list));
518 }
519 )
520 }
521
522 void
523 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
524 BoolObjectClosure* is_alive,
525 OopClosure* keep_alive,
526 VoidClosure* complete_gc) {
527 assert(!discovery_is_atomic(), "Error");
528 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
529 while (iter.has_next()) {
530 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
531 HeapWord* next_addr = java_lang_ref_Reference::next_addr_raw(iter.obj());
532 oop next = java_lang_ref_Reference::next(iter.obj());
533 if ((iter.referent() == NULL || iter.is_referent_alive() ||
534 next != NULL)) {
535 assert(oopDesc::is_oop_or_null(next), "Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next));
536 // Remove Reference object from list
537 iter.remove();
538 // Trace the cohorts
539 iter.make_referent_alive();
540 if (UseCompressedOops) {
541 keep_alive->do_oop((narrowOop*)next_addr);
542 } else {
543 keep_alive->do_oop((oop*)next_addr);
544 }
545 iter.move_to_next();
546 } else {
547 iter.next();
548 }
549 }
550 // Now close the newly reachable set
551 complete_gc->do_void();
552 NOT_PRODUCT(
553 if (iter.processed() > 0) {
554 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
555 " Refs in discovered list " INTPTR_FORMAT,
556 iter.removed(), iter.processed(), p2i(&refs_list));
557 }
558 )
559 }
560
561 void ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
562 bool clear_referent,
563 BoolObjectClosure* is_alive,
564 OopClosure* keep_alive,
565 VoidClosure* complete_gc) {
566 ResourceMark rm;
567 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
568 while (iter.has_next()) {
569 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
570 if (clear_referent) {
571 // NULL out referent pointer
572 iter.clear_referent();
573 } else {
574 // keep the referent around
575 iter.make_referent_alive();
576 }
577 log_develop_trace(gc, ref)("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
578 clear_referent ? "cleared " : "", p2i(iter.obj()), iter.obj()->klass()->internal_name());
579 assert(oopDesc::is_oop(iter.obj(), UseConcMarkSweepGC), "Adding a bad reference");
580 iter.next();
581 }
582 // Close the reachable set
583 complete_gc->do_void();
584 }
585
586 void
587 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
588 oop obj = NULL;
589 oop next = refs_list.head();
590 while (next != obj) {
591 obj = next;
592 next = java_lang_ref_Reference::discovered(obj);
593 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
594 }
595 refs_list.set_head(NULL);
596 refs_list.set_length(0);
597 }
598
599 void ReferenceProcessor::abandon_partial_discovery() {
600 // loop over the lists
601 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) {
602 if ((i % _max_num_queues) == 0) {
603 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i));
604 }
605 clear_discovered_references(_discovered_refs[i]);
606 }
607 }
608
609 size_t ReferenceProcessor::total_reference_count(ReferenceType type) const {
610 DiscoveredList* list = NULL;
611
612 switch (type) {
613 case REF_SOFT:
614 list = _discoveredSoftRefs;
615 break;
616 case REF_WEAK:
617 list = _discoveredWeakRefs;
618 break;
619 case REF_FINAL:
620 list = _discoveredFinalRefs;
621 break;
622 case REF_PHANTOM:
623 list = _discoveredPhantomRefs;
624 break;
625 case REF_OTHER:
626 case REF_NONE:
627 default:
628 ShouldNotReachHere();
629 }
630 return total_count(list);
631 }
632
633 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
634 public:
635 RefProcPhase1Task(ReferenceProcessor& ref_processor,
636 DiscoveredList refs_lists[],
637 ReferencePolicy* policy,
638 bool marks_oops_alive,
639 ReferenceProcessorPhaseTimes* phase_times)
640 : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times),
641 _policy(policy)
642 { }
643 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
644 OopClosure& keep_alive,
645 VoidClosure& complete_gc)
646 {
647 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase1, _phase_times, i);
648
649 _ref_processor.process_phase1(_refs_lists[i], _policy,
650 &is_alive, &keep_alive, &complete_gc);
651 }
652 private:
653 ReferencePolicy* _policy;
654 };
655
656 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
657 public:
658 RefProcPhase2Task(ReferenceProcessor& ref_processor,
659 DiscoveredList refs_lists[],
660 bool marks_oops_alive,
661 ReferenceProcessorPhaseTimes* phase_times)
662 : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times)
663 { }
664 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
665 OopClosure& keep_alive,
666 VoidClosure& complete_gc)
667 {
668 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase2, _phase_times, i);
669
670 _ref_processor.process_phase2(_refs_lists[i],
671 &is_alive, &keep_alive, &complete_gc);
672 }
673 };
674
675 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
676 public:
677 RefProcPhase3Task(ReferenceProcessor& ref_processor,
678 DiscoveredList refs_lists[],
679 bool clear_referent,
680 bool marks_oops_alive,
681 ReferenceProcessorPhaseTimes* phase_times)
682 : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times),
683 _clear_referent(clear_referent)
684 { }
685 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
686 OopClosure& keep_alive,
687 VoidClosure& complete_gc)
688 {
689 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase3, _phase_times, i);
690
691 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
692 &is_alive, &keep_alive, &complete_gc);
693 }
694 private:
695 bool _clear_referent;
696 };
697
698 #ifndef PRODUCT
699 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_refs) {
700 if (!log_is_enabled(Trace, gc, ref)) {
701 return;
702 }
703
704 stringStream st;
705 for (uint i = 0; i < active_length; ++i) {
706 st.print(SIZE_FORMAT " ", ref_lists[i].length());
707 }
708 log_develop_trace(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs);
709 #ifdef ASSERT
710 for (uint i = active_length; i < _max_num_queues; i++) {
711 assert(ref_lists[i].length() == 0, SIZE_FORMAT " unexpected References in %u",
712 ref_lists[i].length(), i);
713 }
714 #endif
715 }
716 #endif
717
718 void ReferenceProcessor::set_active_mt_degree(uint v) {
719 _num_queues = v;
720 _next_id = 0;
721 }
722
723 // Balances reference queues.
724 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
725 // queues[0, 1, ..., _num_q-1] because only the first _num_q
726 // corresponding to the active workers will be processed.
727 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
728 {
729 // calculate total length
730 size_t total_refs = 0;
731 log_develop_trace(gc, ref)("Balance ref_lists ");
732
733 for (uint i = 0; i < _max_num_queues; ++i) {
734 total_refs += ref_lists[i].length();
735 }
736 log_reflist_counts(ref_lists, _max_num_queues, total_refs);
737 size_t avg_refs = total_refs / _num_queues + 1;
738 uint to_idx = 0;
739 for (uint from_idx = 0; from_idx < _max_num_queues; from_idx++) {
740 bool move_all = false;
741 if (from_idx >= _num_queues) {
742 move_all = ref_lists[from_idx].length() > 0;
743 }
744 while ((ref_lists[from_idx].length() > avg_refs) ||
745 move_all) {
746 assert(to_idx < _num_queues, "Sanity Check!");
747 if (ref_lists[to_idx].length() < avg_refs) {
748 // move superfluous refs
749 size_t refs_to_move;
750 // Move all the Ref's if the from queue will not be processed.
751 if (move_all) {
752 refs_to_move = MIN2(ref_lists[from_idx].length(),
753 avg_refs - ref_lists[to_idx].length());
754 } else {
755 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
756 avg_refs - ref_lists[to_idx].length());
757 }
758
759 assert(refs_to_move > 0, "otherwise the code below will fail");
760
761 oop move_head = ref_lists[from_idx].head();
762 oop move_tail = move_head;
763 oop new_head = move_head;
764 // find an element to split the list on
765 for (size_t j = 0; j < refs_to_move; ++j) {
766 move_tail = new_head;
767 new_head = java_lang_ref_Reference::discovered(new_head);
768 }
769
770 // Add the chain to the to list.
771 if (ref_lists[to_idx].head() == NULL) {
772 // to list is empty. Make a loop at the end.
773 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
774 } else {
775 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
776 }
777 ref_lists[to_idx].set_head(move_head);
778 ref_lists[to_idx].inc_length(refs_to_move);
779
780 // Remove the chain from the from list.
781 if (move_tail == new_head) {
782 // We found the end of the from list.
783 ref_lists[from_idx].set_head(NULL);
784 } else {
785 ref_lists[from_idx].set_head(new_head);
786 }
787 ref_lists[from_idx].dec_length(refs_to_move);
788 if (ref_lists[from_idx].length() == 0) {
789 break;
790 }
791 } else {
792 to_idx = (to_idx + 1) % _num_queues;
793 }
794 }
795 }
796 #ifdef ASSERT
797 size_t balanced_total_refs = 0;
798 for (uint i = 0; i < _num_queues; ++i) {
799 balanced_total_refs += ref_lists[i].length();
800 }
801 log_reflist_counts(ref_lists, _num_queues, balanced_total_refs);
802 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
803 #endif
804 }
805
806 void ReferenceProcessor::balance_all_queues() {
807 balance_queues(_discoveredSoftRefs);
808 balance_queues(_discoveredWeakRefs);
809 balance_queues(_discoveredFinalRefs);
810 balance_queues(_discoveredPhantomRefs);
811 }
812
813 void ReferenceProcessor::process_discovered_reflist(
814 DiscoveredList refs_lists[],
815 ReferencePolicy* policy,
816 bool clear_referent,
817 BoolObjectClosure* is_alive,
818 OopClosure* keep_alive,
819 VoidClosure* complete_gc,
820 AbstractRefProcTaskExecutor* task_executor,
821 ReferenceProcessorPhaseTimes* phase_times)
822 {
823 bool mt_processing = task_executor != NULL && _processing_is_mt;
824
825 phase_times->set_processing_is_mt(mt_processing);
826
827 if (mt_processing && ParallelRefProcBalancingEnabled) {
828 RefProcBalanceQueuesTimeTracker tt(phase_times);
829 balance_queues(refs_lists);
830 }
831
832 // Phase 1 (soft refs only):
833 // . Traverse the list and remove any SoftReferences whose
834 // referents are not alive, but that should be kept alive for
835 // policy reasons. Keep alive the transitive closure of all
836 // such referents.
837 if (policy != NULL) {
838 RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase1, phase_times);
839
840 if (mt_processing) {
841 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/, phase_times);
842 task_executor->execute(phase1);
843 } else {
844 for (uint i = 0; i < _max_num_queues; i++) {
845 process_phase1(refs_lists[i], policy,
846 is_alive, keep_alive, complete_gc);
847 }
848 }
849 } else { // policy == NULL
850 assert(refs_lists != _discoveredSoftRefs,
851 "Policy must be specified for soft references.");
852 }
853
854 // Phase 2:
855 // . Traverse the list and remove any refs whose referents are alive.
856 {
857 RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase2, phase_times);
858
859 if (mt_processing) {
860 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/, phase_times);
861 task_executor->execute(phase2);
862 } else {
863 for (uint i = 0; i < _max_num_queues; i++) {
864 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
865 }
866 }
867 }
868
869 // Phase 3:
870 // . Traverse the list and process referents as appropriate.
871 {
872 RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase3, phase_times);
873
874 if (mt_processing) {
875 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/, phase_times);
876 task_executor->execute(phase3);
877 } else {
878 for (uint i = 0; i < _max_num_queues; i++) {
879 process_phase3(refs_lists[i], clear_referent,
880 is_alive, keep_alive, complete_gc);
881 }
882 }
883 }
884 }
885
886 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
887 uint id = 0;
888 // Determine the queue index to use for this object.
889 if (_discovery_is_mt) {
890 // During a multi-threaded discovery phase,
891 // each thread saves to its "own" list.
892 Thread* thr = Thread::current();
893 id = thr->as_Worker_thread()->id();
894 } else {
895 // single-threaded discovery, we save in round-robin
896 // fashion to each of the lists.
897 if (_processing_is_mt) {
898 id = next_id();
899 }
900 }
901 assert(id < _max_num_queues, "Id is out-of-bounds id %u and max id %u)", id, _max_num_queues);
902
903 // Get the discovered queue to which we will add
904 DiscoveredList* list = NULL;
905 switch (rt) {
906 case REF_OTHER:
907 // Unknown reference type, no special treatment
908 break;
909 case REF_SOFT:
910 list = &_discoveredSoftRefs[id];
911 break;
912 case REF_WEAK:
913 list = &_discoveredWeakRefs[id];
914 break;
915 case REF_FINAL:
916 list = &_discoveredFinalRefs[id];
917 break;
918 case REF_PHANTOM:
919 list = &_discoveredPhantomRefs[id];
920 break;
921 case REF_NONE:
922 // we should not reach here if we are an InstanceRefKlass
923 default:
924 ShouldNotReachHere();
925 }
926 log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list));
927 return list;
928 }
929
930 inline void
931 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
932 oop obj,
933 HeapWord* discovered_addr) {
934 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
935 // First we must make sure this object is only enqueued once. CAS in a non null
936 // discovered_addr.
937 oop current_head = refs_list.head();
938 // The last ref must have its discovered field pointing to itself.
939 oop next_discovered = (current_head != NULL) ? current_head : obj;
940
941 oop retest = RawAccess<>::oop_atomic_cmpxchg(next_discovered, discovered_addr, oop(NULL));
942
943 if (retest == NULL) {
944 // This thread just won the right to enqueue the object.
945 // We have separate lists for enqueueing, so no synchronization
946 // is necessary.
947 refs_list.set_head(obj);
948 refs_list.inc_length(1);
949
950 log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
951 p2i(obj), obj->klass()->internal_name());
952 } else {
953 // If retest was non NULL, another thread beat us to it:
954 // The reference has already been discovered...
955 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
956 p2i(obj), obj->klass()->internal_name());
957 }
958 }
959
960 #ifndef PRODUCT
961 // Non-atomic (i.e. concurrent) discovery might allow us
962 // to observe j.l.References with NULL referents, being those
963 // cleared concurrently by mutators during (or after) discovery.
964 void ReferenceProcessor::verify_referent(oop obj) {
965 bool da = discovery_is_atomic();
966 oop referent = java_lang_ref_Reference::referent(obj);
967 assert(da ? oopDesc::is_oop(referent) : oopDesc::is_oop_or_null(referent),
968 "Bad referent " INTPTR_FORMAT " found in Reference "
969 INTPTR_FORMAT " during %satomic discovery ",
970 p2i(referent), p2i(obj), da ? "" : "non-");
971 }
972 #endif
973
974 template <class T>
975 bool ReferenceProcessor::is_subject_to_discovery(T const obj) const {
976 return _is_subject_to_discovery->do_object_b(obj);
977 }
978
979 // We mention two of several possible choices here:
980 // #0: if the reference object is not in the "originating generation"
981 // (or part of the heap being collected, indicated by our "span"
982 // we don't treat it specially (i.e. we scan it as we would
983 // a normal oop, treating its references as strong references).
984 // This means that references can't be discovered unless their
985 // referent is also in the same span. This is the simplest,
986 // most "local" and most conservative approach, albeit one
987 // that may cause weak references to be enqueued least promptly.
988 // We call this choice the "ReferenceBasedDiscovery" policy.
989 // #1: the reference object may be in any generation (span), but if
990 // the referent is in the generation (span) being currently collected
991 // then we can discover the reference object, provided
992 // the object has not already been discovered by
993 // a different concurrently running collector (as may be the
994 // case, for instance, if the reference object is in CMS and
995 // the referent in DefNewGeneration), and provided the processing
996 // of this reference object by the current collector will
997 // appear atomic to every other collector in the system.
998 // (Thus, for instance, a concurrent collector may not
999 // discover references in other generations even if the
1000 // referent is in its own generation). This policy may,
1001 // in certain cases, enqueue references somewhat sooner than
1002 // might Policy #0 above, but at marginally increased cost
1003 // and complexity in processing these references.
1004 // We call this choice the "RefeferentBasedDiscovery" policy.
1005 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
1006 // Make sure we are discovering refs (rather than processing discovered refs).
1007 if (!_discovering_refs || !RegisterReferences) {
1008 return false;
1009 }
1010 // We only discover active references.
1011 oop next = java_lang_ref_Reference::next(obj);
1012 if (next != NULL) { // Ref is no longer active
1013 return false;
1014 }
1015
1016 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1017 !is_subject_to_discovery(obj)) {
1018 // Reference is not in the originating generation;
1019 // don't treat it specially (i.e. we want to scan it as a normal
1020 // object with strong references).
1021 return false;
1022 }
1023
1024 // We only discover references whose referents are not (yet)
1025 // known to be strongly reachable.
1026 if (is_alive_non_header() != NULL) {
1027 verify_referent(obj);
1028 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
1029 return false; // referent is reachable
1030 }
1031 }
1032 if (rt == REF_SOFT) {
1033 // For soft refs we can decide now if these are not
1034 // current candidates for clearing, in which case we
1035 // can mark through them now, rather than delaying that
1036 // to the reference-processing phase. Since all current
1037 // time-stamp policies advance the soft-ref clock only
1038 // at a full collection cycle, this is always currently
1039 // accurate.
1040 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
1041 return false;
1042 }
1043 }
1044
1045 ResourceMark rm; // Needed for tracing.
1046
1047 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr_raw(obj);
1048 const oop discovered = java_lang_ref_Reference::discovered(obj);
1049 assert(oopDesc::is_oop_or_null(discovered), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
1050 if (discovered != NULL) {
1051 // The reference has already been discovered...
1052 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
1053 p2i(obj), obj->klass()->internal_name());
1054 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1055 // assumes that an object is not processed twice;
1056 // if it's been already discovered it must be on another
1057 // generation's discovered list; so we won't discover it.
1058 return false;
1059 } else {
1060 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1061 "Unrecognized policy");
1062 // Check assumption that an object is not potentially
1063 // discovered twice except by concurrent collectors that potentially
1064 // trace the same Reference object twice.
1065 assert(UseConcMarkSweepGC || UseG1GC,
1066 "Only possible with a concurrent marking collector");
1067 return true;
1068 }
1069 }
1070
1071 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1072 verify_referent(obj);
1073 // Discover if and only if EITHER:
1074 // .. reference is in our span, OR
1075 // .. we are an atomic collector and referent is in our span
1076 if (is_subject_to_discovery(obj) ||
1077 (discovery_is_atomic() &&
1078 is_subject_to_discovery(java_lang_ref_Reference::referent(obj)))) {
1079 } else {
1080 return false;
1081 }
1082 } else {
1083 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1084 is_subject_to_discovery(obj), "code inconsistency");
1085 }
1086
1087 // Get the right type of discovered queue head.
1088 DiscoveredList* list = get_discovered_list(rt);
1089 if (list == NULL) {
1090 return false; // nothing special needs to be done
1091 }
1092
1093 if (_discovery_is_mt) {
1094 add_to_discovered_list_mt(*list, obj, discovered_addr);
1095 } else {
1096 // We do a raw store here: the field will be visited later when processing
1097 // the discovered references.
1098 oop current_head = list->head();
1099 // The last ref must have its discovered field pointing to itself.
1100 oop next_discovered = (current_head != NULL) ? current_head : obj;
1101
1102 assert(discovered == NULL, "control point invariant");
1103 RawAccess<>::oop_store(discovered_addr, next_discovered);
1104 list->set_head(obj);
1105 list->inc_length(1);
1106
1107 log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name());
1108 }
1109 assert(oopDesc::is_oop(obj), "Discovered a bad reference");
1110 verify_referent(obj);
1111 return true;
1112 }
1113
1114 bool ReferenceProcessor::has_discovered_references() {
1115 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) {
1116 if (!_discovered_refs[i].is_empty()) {
1117 return true;
1118 }
1119 }
1120 return false;
1121 }
1122
1123 // Preclean the discovered references by removing those
1124 // whose referents are alive, and by marking from those that
1125 // are not active. These lists can be handled here
1126 // in any order and, indeed, concurrently.
1127 void ReferenceProcessor::preclean_discovered_references(
1128 BoolObjectClosure* is_alive,
1129 OopClosure* keep_alive,
1130 VoidClosure* complete_gc,
1131 YieldClosure* yield,
1132 GCTimer* gc_timer) {
1133
1134 // Soft references
1135 {
1136 GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer);
1137 for (uint i = 0; i < _max_num_queues; i++) {
1138 if (yield->should_return()) {
1139 return;
1140 }
1141 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1142 keep_alive, complete_gc, yield);
1143 }
1144 }
1145
1146 // Weak references
1147 {
1148 GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer);
1149 for (uint i = 0; i < _max_num_queues; i++) {
1150 if (yield->should_return()) {
1151 return;
1152 }
1153 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1154 keep_alive, complete_gc, yield);
1155 }
1156 }
1157
1158 // Final references
1159 {
1160 GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer);
1161 for (uint i = 0; i < _max_num_queues; i++) {
1162 if (yield->should_return()) {
1163 return;
1164 }
1165 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1166 keep_alive, complete_gc, yield);
1167 }
1168 }
1169
1170 // Phantom references
1171 {
1172 GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer);
1173 for (uint i = 0; i < _max_num_queues; i++) {
1174 if (yield->should_return()) {
1175 return;
1176 }
1177 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1178 keep_alive, complete_gc, yield);
1179 }
1180 }
1181 }
1182
1183 // Walk the given discovered ref list, and remove all reference objects
1184 // whose referents are still alive, whose referents are NULL or which
1185 // are not active (have a non-NULL next field). NOTE: When we are
1186 // thus precleaning the ref lists (which happens single-threaded today),
1187 // we do not disable refs discovery to honor the correct semantics of
1188 // java.lang.Reference. As a result, we need to be careful below
1189 // that ref removal steps interleave safely with ref discovery steps
1190 // (in this thread).
1191 void
1192 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1193 BoolObjectClosure* is_alive,
1194 OopClosure* keep_alive,
1195 VoidClosure* complete_gc,
1196 YieldClosure* yield) {
1197 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1198 while (iter.has_next()) {
1199 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1200 oop obj = iter.obj();
1201 oop next = java_lang_ref_Reference::next(obj);
1202 if (iter.referent() == NULL || iter.is_referent_alive() ||
1203 next != NULL) {
1204 // The referent has been cleared, or is alive, or the Reference is not
1205 // active; we need to trace and mark its cohort.
1206 log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1207 p2i(iter.obj()), iter.obj()->klass()->internal_name());
1208 // Remove Reference object from list
1209 iter.remove();
1210 // Keep alive its cohort.
1211 iter.make_referent_alive();
1212 if (UseCompressedOops) {
1213 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr_raw(obj);
1214 keep_alive->do_oop(next_addr);
1215 } else {
1216 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr_raw(obj);
1217 keep_alive->do_oop(next_addr);
1218 }
1219 iter.move_to_next();
1220 } else {
1221 iter.next();
1222 }
1223 }
1224 // Close the reachable set
1225 complete_gc->do_void();
1226
1227 NOT_PRODUCT(
1228 if (iter.processed() > 0) {
1229 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT,
1230 iter.removed(), iter.processed(), p2i(&refs_list));
1231 }
1232 )
1233 }
1234
1235 const char* ReferenceProcessor::list_name(uint i) {
1236 assert(i <= _max_num_queues * number_of_subclasses_of_ref(),
1237 "Out of bounds index");
1238
1239 int j = i / _max_num_queues;
1240 switch (j) {
1241 case 0: return "SoftRef";
1242 case 1: return "WeakRef";
1243 case 2: return "FinalRef";
1244 case 3: return "PhantomRef";
1245 }
1246 ShouldNotReachHere();
1247 return NULL;
1248 }