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