1 /*
2 * Copyright (c) 2001, 2019, 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 "gc/shared/referenceProcessorPhaseTimes.hpp"
35 #include "logging/log.hpp"
36 #include "memory/allocation.inline.hpp"
37 #include "memory/resourceArea.hpp"
38 #include "memory/universe.hpp"
39 #include "oops/access.inline.hpp"
40 #include "oops/oop.inline.hpp"
41 #include "runtime/java.hpp"
42
43 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
44 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
45 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0;
46
47 void referenceProcessor_init() {
48 ReferenceProcessor::init_statics();
49 }
50
51 void ReferenceProcessor::init_statics() {
52 // We need a monotonically non-decreasing time in ms but
53 // os::javaTimeMillis() does not guarantee monotonicity.
54 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
55
56 // Initialize the soft ref timestamp clock.
57 _soft_ref_timestamp_clock = now;
58 // Also update the soft ref clock in j.l.r.SoftReference
59 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock);
60
61 _always_clear_soft_ref_policy = new AlwaysClearPolicy();
62 if (is_server_compilation_mode_vm()) {
63 _default_soft_ref_policy = new LRUMaxHeapPolicy();
64 } else {
65 _default_soft_ref_policy = new LRUCurrentHeapPolicy();
66 }
67 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
68 vm_exit_during_initialization("Could not allocate reference policy object");
69 }
70 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
71 RefDiscoveryPolicy == ReferentBasedDiscovery,
72 "Unrecognized RefDiscoveryPolicy");
73 }
74
75 void ReferenceProcessor::enable_discovery(bool check_no_refs) {
76 #ifdef ASSERT
77 // Verify that we're not currently discovering refs
78 assert(!_discovering_refs, "nested call?");
79
80 if (check_no_refs) {
81 // Verify that the discovered lists are empty
82 verify_no_references_recorded();
83 }
84 #endif // ASSERT
85
86 // Someone could have modified the value of the static
87 // field in the j.l.r.SoftReference class that holds the
88 // soft reference timestamp clock using reflection or
89 // Unsafe between GCs. Unconditionally update the static
90 // field in ReferenceProcessor here so that we use the new
91 // value during reference discovery.
92
93 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
94 _discovering_refs = true;
95 }
96
97 ReferenceProcessor::ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery,
98 bool mt_processing,
99 uint mt_processing_degree,
100 bool mt_discovery,
101 uint mt_discovery_degree,
102 bool atomic_discovery,
103 BoolObjectClosure* is_alive_non_header,
104 bool adjust_no_of_processing_threads) :
105 _is_subject_to_discovery(is_subject_to_discovery),
106 _discovering_refs(false),
107 _enqueuing_is_done(false),
108 _processing_is_mt(mt_processing),
109 _next_id(0),
110 _adjust_no_of_processing_threads(adjust_no_of_processing_threads),
111 _is_alive_non_header(is_alive_non_header)
112 {
113 assert(is_subject_to_discovery != NULL, "must be set");
114
115 _discovery_is_atomic = atomic_discovery;
116 _discovery_is_mt = mt_discovery;
117 _num_queues = MAX2(1U, mt_processing_degree);
118 _max_num_queues = MAX2(_num_queues, mt_discovery_degree);
119 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
120 _max_num_queues * number_of_subclasses_of_ref(), mtGC);
121
122 _discoveredSoftRefs = &_discovered_refs[0];
123 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_queues];
124 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_queues];
125 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_queues];
126
127 // Initialize all entries to NULL
128 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) {
129 _discovered_refs[i].clear();
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 #ifdef ASSERT
193 void ReferenceProcessor::verify_total_count_zero(DiscoveredList lists[], const char* type) {
194 size_t count = total_count(lists);
195 assert(count == 0, "%ss must be empty but has " SIZE_FORMAT " elements", type, count);
196 }
197 #endif
198
199 ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
200 BoolObjectClosure* is_alive,
201 OopClosure* keep_alive,
202 VoidClosure* complete_gc,
203 AbstractRefProcTaskExecutor* task_executor,
204 ReferenceProcessorPhaseTimes* phase_times) {
205
206 double start_time = os::elapsedTime();
207
208 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
209 // Stop treating discovered references specially.
210 disable_discovery();
211
212 // If discovery was concurrent, someone could have modified
213 // the value of the static field in the j.l.r.SoftReference
214 // class that holds the soft reference timestamp clock using
215 // reflection or Unsafe between when discovery was enabled and
216 // now. Unconditionally update the static field in ReferenceProcessor
217 // here so that we use the new value during processing of the
218 // discovered soft refs.
219
220 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
221
222 ReferenceProcessorStats stats(total_count(_discoveredSoftRefs),
223 total_count(_discoveredWeakRefs),
224 total_count(_discoveredFinalRefs),
225 total_count(_discoveredPhantomRefs));
226
227 {
228 RefProcTotalPhaseTimesTracker tt(RefPhase1, phase_times, this);
229 process_soft_ref_reconsider(is_alive, keep_alive, complete_gc,
230 task_executor, phase_times);
231 }
232
233 update_soft_ref_master_clock();
234
235 {
236 RefProcTotalPhaseTimesTracker tt(RefPhase2, phase_times, this);
237 process_soft_weak_final_refs(is_alive, keep_alive, complete_gc, task_executor, phase_times);
238 }
239
240 {
241 RefProcTotalPhaseTimesTracker tt(RefPhase3, phase_times, this);
242 process_final_keep_alive(keep_alive, complete_gc, task_executor, phase_times);
243 }
244
245 {
246 RefProcTotalPhaseTimesTracker tt(RefPhase4, phase_times, this);
247 process_phantom_refs(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 DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
261 _current_discovered_addr = java_lang_ref_Reference::discovered_addr_raw(_current_discovered);
262 oop discovered = java_lang_ref_Reference::discovered(_current_discovered);
263 assert(_current_discovered_addr && oopDesc::is_oop_or_null(discovered),
264 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
265 _next_discovered = discovered;
266
267 _referent_addr = java_lang_ref_Reference::referent_addr_raw(_current_discovered);
268 _referent = java_lang_ref_Reference::referent(_current_discovered);
269 assert(Universe::heap()->is_in_reserved_or_null(_referent),
270 "Wrong oop found in java.lang.Reference object");
271 assert(allow_null_referent ?
272 oopDesc::is_oop_or_null(_referent)
273 : oopDesc::is_oop(_referent),
274 "Expected an oop%s for referent field at " PTR_FORMAT,
275 (allow_null_referent ? " or NULL" : ""),
276 p2i(_referent));
277 }
278
279 void DiscoveredListIterator::remove() {
280 assert(oopDesc::is_oop(_current_discovered), "Dropping a bad reference");
281 RawAccess<>::oop_store(_current_discovered_addr, oop(NULL));
282
283 // First _prev_next ref actually points into DiscoveredList (gross).
284 oop new_next;
285 if (oopDesc::equals_raw(_next_discovered, _current_discovered)) {
286 // At the end of the list, we should make _prev point to itself.
287 // If _ref is the first ref, then _prev_next will be in the DiscoveredList,
288 // and _prev will be NULL.
289 new_next = _prev_discovered;
290 } else {
291 new_next = _next_discovered;
292 }
293 // Remove Reference object from discovered list. Note that G1 does not need a
294 // pre-barrier here because we know the Reference has already been found/marked,
295 // that's how it ended up in the discovered list in the first place.
296 RawAccess<>::oop_store(_prev_discovered_addr, new_next);
297 _removed++;
298 _refs_list.dec_length(1);
299 }
300
301 void DiscoveredListIterator::clear_referent() {
302 RawAccess<>::oop_store(_referent_addr, oop(NULL));
303 }
304
305 void DiscoveredListIterator::enqueue() {
306 HeapAccess<AS_NO_KEEPALIVE>::oop_store_at(_current_discovered,
307 java_lang_ref_Reference::discovered_offset,
308 _next_discovered);
309 }
310
311 void DiscoveredListIterator::complete_enqueue() {
312 if (_prev_discovered != NULL) {
313 // This is the last object.
314 // Swap refs_list into pending list and set obj's
315 // discovered to what we read from the pending list.
316 oop old = Universe::swap_reference_pending_list(_refs_list.head());
317 HeapAccess<AS_NO_KEEPALIVE>::oop_store_at(_prev_discovered, java_lang_ref_Reference::discovered_offset, old);
318 }
319 }
320
321 inline void log_dropped_ref(const DiscoveredListIterator& iter, const char* reason) {
322 if (log_develop_is_enabled(Trace, gc, ref)) {
323 ResourceMark rm;
324 log_develop_trace(gc, ref)("Dropping %s reference " PTR_FORMAT ": %s",
325 reason, p2i(iter.obj()),
326 iter.obj()->klass()->internal_name());
327 }
328 }
329
330 inline void log_enqueued_ref(const DiscoveredListIterator& iter, const char* reason) {
331 if (log_develop_is_enabled(Trace, gc, ref)) {
332 ResourceMark rm;
333 log_develop_trace(gc, ref)("Enqueue %s reference (" INTPTR_FORMAT ": %s)",
334 reason, p2i(iter.obj()), iter.obj()->klass()->internal_name());
335 }
336 assert(oopDesc::is_oop(iter.obj(), UseConcMarkSweepGC), "Adding a bad reference");
337 }
338
339 size_t ReferenceProcessor::process_soft_ref_reconsider_work(DiscoveredList& refs_list,
340 ReferencePolicy* policy,
341 BoolObjectClosure* is_alive,
342 OopClosure* keep_alive,
343 VoidClosure* complete_gc) {
344 assert(policy != NULL, "Must have a non-NULL policy");
345 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
346 // Decide which softly reachable refs should be kept alive.
347 while (iter.has_next()) {
348 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
349 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
350 if (referent_is_dead &&
351 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
352 log_dropped_ref(iter, "by policy");
353 // Remove Reference object from list
354 iter.remove();
355 // keep the referent around
356 iter.make_referent_alive();
357 iter.move_to_next();
358 } else {
359 iter.next();
360 }
361 }
362 // Close the reachable set
363 complete_gc->do_void();
364
365 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT,
366 iter.removed(), iter.processed(), p2i(&refs_list));
367 return iter.removed();
368 }
369
370 size_t ReferenceProcessor::process_soft_weak_final_refs_work(DiscoveredList& refs_list,
371 BoolObjectClosure* is_alive,
372 OopClosure* keep_alive,
373 bool do_enqueue_and_clear) {
374 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
375 while (iter.has_next()) {
376 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
377 if (iter.referent() == NULL) {
378 // Reference has been cleared since discovery; only possible if
379 // discovery is not atomic (checked by load_ptrs). Remove
380 // reference from list.
381 log_dropped_ref(iter, "cleared");
382 iter.remove();
383 iter.move_to_next();
384 } else if (iter.is_referent_alive()) {
385 // The referent is reachable after all.
386 // Remove reference from list.
387 log_dropped_ref(iter, "reachable");
388 iter.remove();
389 // Update the referent pointer as necessary. Note that this
390 // should not entail any recursive marking because the
391 // referent must already have been traversed.
392 iter.make_referent_alive();
393 iter.move_to_next();
394 } else {
395 if (do_enqueue_and_clear) {
396 iter.clear_referent();
397 iter.enqueue();
398 log_enqueued_ref(iter, "cleared");
399 }
400 // Keep in discovered list
401 iter.next();
402 }
403 }
404 if (do_enqueue_and_clear) {
405 iter.complete_enqueue();
406 refs_list.clear();
407 }
408
409 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
410 " Refs in discovered list " INTPTR_FORMAT,
411 iter.removed(), iter.processed(), p2i(&refs_list));
412 return iter.removed();
413 }
414
415 size_t ReferenceProcessor::process_final_keep_alive_work(DiscoveredList& refs_list,
416 OopClosure* keep_alive,
417 VoidClosure* complete_gc) {
418 DiscoveredListIterator iter(refs_list, keep_alive, NULL);
419 while (iter.has_next()) {
420 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
421 // keep the referent and followers around
422 iter.make_referent_alive();
423
424 // Self-loop next, to mark the FinalReference not active.
425 assert(java_lang_ref_Reference::next(iter.obj()) == NULL, "enqueued FinalReference");
426 java_lang_ref_Reference::set_next_raw(iter.obj(), iter.obj());
427
428 iter.enqueue();
429 log_enqueued_ref(iter, "Final");
430 iter.next();
431 }
432 iter.complete_enqueue();
433 // Close the reachable set
434 complete_gc->do_void();
435 refs_list.clear();
436
437 assert(iter.removed() == 0, "This phase does not remove anything.");
438 return iter.removed();
439 }
440
441 size_t ReferenceProcessor::process_phantom_refs_work(DiscoveredList& refs_list,
442 BoolObjectClosure* is_alive,
443 OopClosure* keep_alive,
444 VoidClosure* complete_gc) {
445 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
446 while (iter.has_next()) {
447 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
448
449 oop const referent = iter.referent();
450
451 if (referent == NULL || iter.is_referent_alive()) {
452 iter.make_referent_alive();
453 iter.remove();
454 iter.move_to_next();
455 } else {
456 iter.clear_referent();
457 iter.enqueue();
458 log_enqueued_ref(iter, "cleared Phantom");
459 iter.next();
460 }
461 }
462 iter.complete_enqueue();
463 // Close the reachable set; needed for collectors which keep_alive_closure do
464 // not immediately complete their work.
465 complete_gc->do_void();
466 refs_list.clear();
467
468 return iter.removed();
469 }
470
471 void
472 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
473 oop obj = NULL;
474 oop next = refs_list.head();
475 while (!oopDesc::equals_raw(next, obj)) {
476 obj = next;
477 next = java_lang_ref_Reference::discovered(obj);
478 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
479 }
480 refs_list.clear();
481 }
482
483 void ReferenceProcessor::abandon_partial_discovery() {
484 // loop over the lists
485 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) {
486 if ((i % _max_num_queues) == 0) {
487 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i));
488 }
489 clear_discovered_references(_discovered_refs[i]);
490 }
491 }
492
493 size_t ReferenceProcessor::total_reference_count(ReferenceType type) const {
494 DiscoveredList* list = NULL;
495
496 switch (type) {
497 case REF_SOFT:
498 list = _discoveredSoftRefs;
499 break;
500 case REF_WEAK:
501 list = _discoveredWeakRefs;
502 break;
503 case REF_FINAL:
504 list = _discoveredFinalRefs;
505 break;
506 case REF_PHANTOM:
507 list = _discoveredPhantomRefs;
508 break;
509 case REF_OTHER:
510 case REF_NONE:
511 default:
512 ShouldNotReachHere();
513 }
514 return total_count(list);
515 }
516
517 class RefProcPhase1Task : public AbstractRefProcTaskExecutor::ProcessTask {
518 public:
519 RefProcPhase1Task(ReferenceProcessor& ref_processor,
520 ReferenceProcessorPhaseTimes* phase_times,
521 ReferencePolicy* policy)
522 : ProcessTask(ref_processor, true /* marks_oops_alive */, phase_times),
523 _policy(policy) { }
524
525 virtual void work(uint worker_id,
526 BoolObjectClosure& is_alive,
527 OopClosure& keep_alive,
528 VoidClosure& complete_gc)
529 {
530 RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::SoftRefSubPhase1, _phase_times, worker_id);
531 size_t const removed = _ref_processor.process_soft_ref_reconsider_work(_ref_processor._discoveredSoftRefs[worker_id],
532 _policy,
533 &is_alive,
534 &keep_alive,
535 &complete_gc);
536 _phase_times->add_ref_cleared(REF_SOFT, removed);
537 }
538 private:
539 ReferencePolicy* _policy;
540 };
541
542 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
543 void run_phase2(uint worker_id,
544 DiscoveredList list[],
545 BoolObjectClosure& is_alive,
546 OopClosure& keep_alive,
547 bool do_enqueue_and_clear,
548 ReferenceType ref_type) {
549 size_t const removed = _ref_processor.process_soft_weak_final_refs_work(list[worker_id],
550 &is_alive,
551 &keep_alive,
552 do_enqueue_and_clear);
553 _phase_times->add_ref_cleared(ref_type, removed);
554 }
555
556 public:
557 RefProcPhase2Task(ReferenceProcessor& ref_processor,
558 ReferenceProcessorPhaseTimes* phase_times)
559 : ProcessTask(ref_processor, false /* marks_oops_alive */, phase_times) { }
560
561 virtual void work(uint worker_id,
562 BoolObjectClosure& is_alive,
563 OopClosure& keep_alive,
564 VoidClosure& complete_gc) {
565 RefProcWorkerTimeTracker t(_phase_times->phase2_worker_time_sec(), worker_id);
566 {
567 RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::SoftRefSubPhase2, _phase_times, worker_id);
568 run_phase2(worker_id, _ref_processor._discoveredSoftRefs, is_alive, keep_alive, true /* do_enqueue_and_clear */, REF_SOFT);
569 }
570 {
571 RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::WeakRefSubPhase2, _phase_times, worker_id);
572 run_phase2(worker_id, _ref_processor._discoveredWeakRefs, is_alive, keep_alive, true /* do_enqueue_and_clear */, REF_WEAK);
573 }
574 {
575 RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::FinalRefSubPhase2, _phase_times, worker_id);
576 run_phase2(worker_id, _ref_processor._discoveredFinalRefs, is_alive, keep_alive, false /* do_enqueue_and_clear */, REF_FINAL);
577 }
578 // Close the reachable set; needed for collectors which keep_alive_closure do
579 // not immediately complete their work.
580 complete_gc.do_void();
581 }
582 };
583
584 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
585 public:
586 RefProcPhase3Task(ReferenceProcessor& ref_processor,
587 ReferenceProcessorPhaseTimes* phase_times)
588 : ProcessTask(ref_processor, true /* marks_oops_alive */, phase_times) { }
589
590 virtual void work(uint worker_id,
591 BoolObjectClosure& is_alive,
592 OopClosure& keep_alive,
593 VoidClosure& complete_gc)
594 {
595 RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::FinalRefSubPhase3, _phase_times, worker_id);
596 _ref_processor.process_final_keep_alive_work(_ref_processor._discoveredFinalRefs[worker_id], &keep_alive, &complete_gc);
597 }
598 };
599
600 class RefProcPhase4Task: public AbstractRefProcTaskExecutor::ProcessTask {
601 public:
602 RefProcPhase4Task(ReferenceProcessor& ref_processor,
603 ReferenceProcessorPhaseTimes* phase_times)
604 : ProcessTask(ref_processor, false /* marks_oops_alive */, phase_times) { }
605
606 virtual void work(uint worker_id,
607 BoolObjectClosure& is_alive,
608 OopClosure& keep_alive,
609 VoidClosure& complete_gc)
610 {
611 RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::PhantomRefSubPhase4, _phase_times, worker_id);
612 size_t const removed = _ref_processor.process_phantom_refs_work(_ref_processor._discoveredPhantomRefs[worker_id],
613 &is_alive,
614 &keep_alive,
615 &complete_gc);
616 _phase_times->add_ref_cleared(REF_PHANTOM, removed);
617 }
618 };
619
620 void ReferenceProcessor::log_reflist(const char* prefix, DiscoveredList list[], uint num_active_queues) {
621 LogTarget(Trace, gc, ref) lt;
622
623 if (!lt.is_enabled()) {
624 return;
625 }
626
627 size_t total = 0;
628
629 LogStream ls(lt);
630 ls.print("%s", prefix);
631 for (uint i = 0; i < num_active_queues; i++) {
632 ls.print(SIZE_FORMAT " ", list[i].length());
633 total += list[i].length();
634 }
635 ls.print_cr("(" SIZE_FORMAT ")", total);
636 }
637
638 #ifndef PRODUCT
639 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint num_active_queues) {
640 if (!log_is_enabled(Trace, gc, ref)) {
641 return;
642 }
643
644 log_reflist("", ref_lists, num_active_queues);
645 #ifdef ASSERT
646 for (uint i = num_active_queues; i < _max_num_queues; i++) {
647 assert(ref_lists[i].length() == 0, SIZE_FORMAT " unexpected References in %u",
648 ref_lists[i].length(), i);
649 }
650 #endif
651 }
652 #endif
653
654 void ReferenceProcessor::set_active_mt_degree(uint v) {
655 _num_queues = v;
656 _next_id = 0;
657 }
658
659 bool ReferenceProcessor::need_balance_queues(DiscoveredList refs_lists[]) {
660 assert(_processing_is_mt, "why balance non-mt processing?");
661 // _num_queues is the processing degree. Only list entries up to
662 // _num_queues will be processed, so any non-empty lists beyond
663 // that must be redistributed to lists in that range. Even if not
664 // needed for that, balancing may be desirable to eliminate poor
665 // distribution of references among the lists.
666 if (ParallelRefProcBalancingEnabled) {
667 return true; // Configuration says do it.
668 } else {
669 // Configuration says don't balance, but if there are non-empty
670 // lists beyond the processing degree, then must ignore the
671 // configuration and balance anyway.
672 for (uint i = _num_queues; i < _max_num_queues; ++i) {
673 if (!refs_lists[i].is_empty()) {
674 return true; // Must balance despite configuration.
675 }
676 }
677 return false; // Safe to obey configuration and not balance.
678 }
679 }
680
681 void ReferenceProcessor::maybe_balance_queues(DiscoveredList refs_lists[]) {
682 assert(_processing_is_mt, "Should not call this otherwise");
683 if (need_balance_queues(refs_lists)) {
684 balance_queues(refs_lists);
685 }
686 }
687
688 // Balances reference queues.
689 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
690 // queues[0, 1, ..., _num_q-1] because only the first _num_q
691 // corresponding to the active workers will be processed.
692 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
693 {
694 // calculate total length
695 size_t total_refs = 0;
696 log_develop_trace(gc, ref)("Balance ref_lists ");
697
698 log_reflist_counts(ref_lists, _max_num_queues);
699
700 for (uint i = 0; i < _max_num_queues; ++i) {
701 total_refs += ref_lists[i].length();
702 }
703 size_t avg_refs = total_refs / _num_queues + 1;
704 uint to_idx = 0;
705 for (uint from_idx = 0; from_idx < _max_num_queues; from_idx++) {
706 bool move_all = false;
707 if (from_idx >= _num_queues) {
708 move_all = ref_lists[from_idx].length() > 0;
709 }
710 while ((ref_lists[from_idx].length() > avg_refs) ||
711 move_all) {
712 assert(to_idx < _num_queues, "Sanity Check!");
713 if (ref_lists[to_idx].length() < avg_refs) {
714 // move superfluous refs
715 size_t refs_to_move;
716 // Move all the Ref's if the from queue will not be processed.
717 if (move_all) {
718 refs_to_move = MIN2(ref_lists[from_idx].length(),
719 avg_refs - ref_lists[to_idx].length());
720 } else {
721 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
722 avg_refs - ref_lists[to_idx].length());
723 }
724
725 assert(refs_to_move > 0, "otherwise the code below will fail");
726
727 oop move_head = ref_lists[from_idx].head();
728 oop move_tail = move_head;
729 oop new_head = move_head;
730 // find an element to split the list on
731 for (size_t j = 0; j < refs_to_move; ++j) {
732 move_tail = new_head;
733 new_head = java_lang_ref_Reference::discovered(new_head);
734 }
735
736 // Add the chain to the to list.
737 if (ref_lists[to_idx].head() == NULL) {
738 // to list is empty. Make a loop at the end.
739 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
740 } else {
741 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
742 }
743 ref_lists[to_idx].set_head(move_head);
744 ref_lists[to_idx].inc_length(refs_to_move);
745
746 // Remove the chain from the from list.
747 if (oopDesc::equals_raw(move_tail, new_head)) {
748 // We found the end of the from list.
749 ref_lists[from_idx].set_head(NULL);
750 } else {
751 ref_lists[from_idx].set_head(new_head);
752 }
753 ref_lists[from_idx].dec_length(refs_to_move);
754 if (ref_lists[from_idx].length() == 0) {
755 break;
756 }
757 } else {
758 to_idx = (to_idx + 1) % _num_queues;
759 }
760 }
761 }
762 #ifdef ASSERT
763 log_reflist_counts(ref_lists, _num_queues);
764 size_t balanced_total_refs = 0;
765 for (uint i = 0; i < _num_queues; ++i) {
766 balanced_total_refs += ref_lists[i].length();
767 }
768 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
769 #endif
770 }
771
772 bool ReferenceProcessor::is_mt_processing_set_up(AbstractRefProcTaskExecutor* task_executor) const {
773 return task_executor != NULL && _processing_is_mt;
774 }
775
776 void ReferenceProcessor::process_soft_ref_reconsider(BoolObjectClosure* is_alive,
777 OopClosure* keep_alive,
778 VoidClosure* complete_gc,
779 AbstractRefProcTaskExecutor* task_executor,
780 ReferenceProcessorPhaseTimes* phase_times) {
781 assert(!_processing_is_mt || task_executor != NULL, "Task executor must not be NULL when mt processing is set.");
782
783 size_t const num_soft_refs = total_count(_discoveredSoftRefs);
784 phase_times->set_ref_discovered(REF_SOFT, num_soft_refs);
785
786 phase_times->set_processing_is_mt(_processing_is_mt);
787
788 if (num_soft_refs == 0 || _current_soft_ref_policy == NULL) {
789 log_debug(gc, ref)("Skipped phase1 of Reference Processing due to unavailable references");
790 return;
791 }
792
793 RefProcMTDegreeAdjuster a(this, RefPhase1, num_soft_refs);
794
795 if (_processing_is_mt) {
796 RefProcBalanceQueuesTimeTracker tt(RefPhase1, phase_times);
797 maybe_balance_queues(_discoveredSoftRefs);
798 }
799
800 RefProcPhaseTimeTracker tt(RefPhase1, phase_times);
801
802 log_reflist("Phase1 Soft before", _discoveredSoftRefs, _max_num_queues);
803 if (_processing_is_mt) {
804 RefProcPhase1Task phase1(*this, phase_times, _current_soft_ref_policy);
805 task_executor->execute(phase1, num_queues());
806 } else {
807 size_t removed = 0;
808
809 RefProcSubPhasesWorkerTimeTracker tt2(SoftRefSubPhase1, phase_times, 0);
810 for (uint i = 0; i < _max_num_queues; i++) {
811 removed += process_soft_ref_reconsider_work(_discoveredSoftRefs[i], _current_soft_ref_policy,
812 is_alive, keep_alive, complete_gc);
813 }
814
815 phase_times->add_ref_cleared(REF_SOFT, removed);
816 }
817 log_reflist("Phase1 Soft after", _discoveredSoftRefs, _max_num_queues);
818 }
819
820 void ReferenceProcessor::process_soft_weak_final_refs(BoolObjectClosure* is_alive,
821 OopClosure* keep_alive,
822 VoidClosure* complete_gc,
823 AbstractRefProcTaskExecutor* task_executor,
824 ReferenceProcessorPhaseTimes* phase_times) {
825 assert(!_processing_is_mt || task_executor != NULL, "Task executor must not be NULL when mt processing is set.");
826
827 size_t const num_soft_refs = total_count(_discoveredSoftRefs);
828 size_t const num_weak_refs = total_count(_discoveredWeakRefs);
829 size_t const num_final_refs = total_count(_discoveredFinalRefs);
830 size_t const num_total_refs = num_soft_refs + num_weak_refs + num_final_refs;
831 phase_times->set_ref_discovered(REF_WEAK, num_weak_refs);
832 phase_times->set_ref_discovered(REF_FINAL, num_final_refs);
833
834 phase_times->set_processing_is_mt(_processing_is_mt);
835
836 if (num_total_refs == 0) {
837 log_debug(gc, ref)("Skipped phase2 of Reference Processing due to unavailable references");
838 return;
839 }
840
841 RefProcMTDegreeAdjuster a(this, RefPhase2, num_total_refs);
842
843 if (_processing_is_mt) {
844 RefProcBalanceQueuesTimeTracker tt(RefPhase2, phase_times);
845 maybe_balance_queues(_discoveredSoftRefs);
846 maybe_balance_queues(_discoveredWeakRefs);
847 maybe_balance_queues(_discoveredFinalRefs);
848 }
849
850 RefProcPhaseTimeTracker tt(RefPhase2, phase_times);
851
852 log_reflist("Phase2 Soft before", _discoveredSoftRefs, _max_num_queues);
853 log_reflist("Phase2 Weak before", _discoveredWeakRefs, _max_num_queues);
854 log_reflist("Phase2 Final before", _discoveredFinalRefs, _max_num_queues);
855 if (_processing_is_mt) {
856 RefProcPhase2Task phase2(*this, phase_times);
857 task_executor->execute(phase2, num_queues());
858 } else {
859 RefProcWorkerTimeTracker t(phase_times->phase2_worker_time_sec(), 0);
860 {
861 size_t removed = 0;
862
863 RefProcSubPhasesWorkerTimeTracker tt2(SoftRefSubPhase2, phase_times, 0);
864 for (uint i = 0; i < _max_num_queues; i++) {
865 removed += process_soft_weak_final_refs_work(_discoveredSoftRefs[i], is_alive, keep_alive, true /* do_enqueue */);
866 }
867
868 phase_times->add_ref_cleared(REF_SOFT, removed);
869 }
870 {
871 size_t removed = 0;
872
873 RefProcSubPhasesWorkerTimeTracker tt2(WeakRefSubPhase2, phase_times, 0);
874 for (uint i = 0; i < _max_num_queues; i++) {
875 removed += process_soft_weak_final_refs_work(_discoveredWeakRefs[i], is_alive, keep_alive, true /* do_enqueue */);
876 }
877
878 phase_times->add_ref_cleared(REF_WEAK, removed);
879 }
880 {
881 size_t removed = 0;
882
883 RefProcSubPhasesWorkerTimeTracker tt2(FinalRefSubPhase2, phase_times, 0);
884 for (uint i = 0; i < _max_num_queues; i++) {
885 removed += process_soft_weak_final_refs_work(_discoveredFinalRefs[i], is_alive, keep_alive, false /* do_enqueue */);
886 }
887
888 phase_times->add_ref_cleared(REF_FINAL, removed);
889 }
890 complete_gc->do_void();
891 }
892 verify_total_count_zero(_discoveredSoftRefs, "SoftReference");
893 verify_total_count_zero(_discoveredWeakRefs, "WeakReference");
894 log_reflist("Phase2 Final after", _discoveredFinalRefs, _max_num_queues);
895 }
896
897 void ReferenceProcessor::process_final_keep_alive(OopClosure* keep_alive,
898 VoidClosure* complete_gc,
899 AbstractRefProcTaskExecutor* task_executor,
900 ReferenceProcessorPhaseTimes* phase_times) {
901 assert(!_processing_is_mt || task_executor != NULL, "Task executor must not be NULL when mt processing is set.");
902
903 size_t const num_final_refs = total_count(_discoveredFinalRefs);
904
905 phase_times->set_processing_is_mt(_processing_is_mt);
906
907 if (num_final_refs == 0) {
908 log_debug(gc, ref)("Skipped phase3 of Reference Processing due to unavailable references");
909 return;
910 }
911
912 RefProcMTDegreeAdjuster a(this, RefPhase3, num_final_refs);
913
914 if (_processing_is_mt) {
915 RefProcBalanceQueuesTimeTracker tt(RefPhase3, phase_times);
916 maybe_balance_queues(_discoveredFinalRefs);
917 }
918
919 // Phase 3:
920 // . Traverse referents of final references and keep them and followers alive.
921 RefProcPhaseTimeTracker tt(RefPhase3, phase_times);
922
923 if (_processing_is_mt) {
924 RefProcPhase3Task phase3(*this, phase_times);
925 task_executor->execute(phase3, num_queues());
926 } else {
927 RefProcSubPhasesWorkerTimeTracker tt2(FinalRefSubPhase3, phase_times, 0);
928 for (uint i = 0; i < _max_num_queues; i++) {
929 process_final_keep_alive_work(_discoveredFinalRefs[i], keep_alive, complete_gc);
930 }
931 }
932 verify_total_count_zero(_discoveredFinalRefs, "FinalReference");
933 }
934
935 void ReferenceProcessor::process_phantom_refs(BoolObjectClosure* is_alive,
936 OopClosure* keep_alive,
937 VoidClosure* complete_gc,
938 AbstractRefProcTaskExecutor* task_executor,
939 ReferenceProcessorPhaseTimes* phase_times) {
940 assert(!_processing_is_mt || task_executor != NULL, "Task executor must not be NULL when mt processing is set.");
941
942 size_t const num_phantom_refs = total_count(_discoveredPhantomRefs);
943 phase_times->set_ref_discovered(REF_PHANTOM, num_phantom_refs);
944
945 phase_times->set_processing_is_mt(_processing_is_mt);
946
947 if (num_phantom_refs == 0) {
948 log_debug(gc, ref)("Skipped phase4 of Reference Processing due to unavailable references");
949 return;
950 }
951
952 RefProcMTDegreeAdjuster a(this, RefPhase4, num_phantom_refs);
953
954 if (_processing_is_mt) {
955 RefProcBalanceQueuesTimeTracker tt(RefPhase4, phase_times);
956 maybe_balance_queues(_discoveredPhantomRefs);
957 }
958
959 // Phase 4: Walk phantom references appropriately.
960 RefProcPhaseTimeTracker tt(RefPhase4, phase_times);
961
962 log_reflist("Phase4 Phantom before", _discoveredPhantomRefs, _max_num_queues);
963 if (_processing_is_mt) {
964 RefProcPhase4Task phase4(*this, phase_times);
965 task_executor->execute(phase4, num_queues());
966 } else {
967 size_t removed = 0;
968
969 RefProcSubPhasesWorkerTimeTracker tt(PhantomRefSubPhase4, phase_times, 0);
970 for (uint i = 0; i < _max_num_queues; i++) {
971 removed += process_phantom_refs_work(_discoveredPhantomRefs[i], is_alive, keep_alive, complete_gc);
972 }
973
974 phase_times->add_ref_cleared(REF_PHANTOM, removed);
975 }
976 verify_total_count_zero(_discoveredPhantomRefs, "PhantomReference");
977 }
978
979 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
980 uint id = 0;
981 // Determine the queue index to use for this object.
982 if (_discovery_is_mt) {
983 // During a multi-threaded discovery phase,
984 // each thread saves to its "own" list.
985 Thread* thr = Thread::current();
986 id = thr->as_Worker_thread()->id();
987 } else {
988 // single-threaded discovery, we save in round-robin
989 // fashion to each of the lists.
990 if (_processing_is_mt) {
991 id = next_id();
992 }
993 }
994 assert(id < _max_num_queues, "Id is out of bounds id %u and max id %u)", id, _max_num_queues);
995
996 // Get the discovered queue to which we will add
997 DiscoveredList* list = NULL;
998 switch (rt) {
999 case REF_OTHER:
1000 // Unknown reference type, no special treatment
1001 break;
1002 case REF_SOFT:
1003 list = &_discoveredSoftRefs[id];
1004 break;
1005 case REF_WEAK:
1006 list = &_discoveredWeakRefs[id];
1007 break;
1008 case REF_FINAL:
1009 list = &_discoveredFinalRefs[id];
1010 break;
1011 case REF_PHANTOM:
1012 list = &_discoveredPhantomRefs[id];
1013 break;
1014 case REF_NONE:
1015 // we should not reach here if we are an InstanceRefKlass
1016 default:
1017 ShouldNotReachHere();
1018 }
1019 log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list));
1020 return list;
1021 }
1022
1023 inline void
1024 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
1025 oop obj,
1026 HeapWord* discovered_addr) {
1027 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
1028 // First we must make sure this object is only enqueued once. CAS in a non null
1029 // discovered_addr.
1030 oop current_head = refs_list.head();
1031 // The last ref must have its discovered field pointing to itself.
1032 oop next_discovered = (current_head != NULL) ? current_head : obj;
1033
1034 oop retest = HeapAccess<AS_NO_KEEPALIVE>::oop_atomic_cmpxchg(next_discovered, discovered_addr, oop(NULL));
1035
1036 if (retest == NULL) {
1037 // This thread just won the right to enqueue the object.
1038 // We have separate lists for enqueueing, so no synchronization
1039 // is necessary.
1040 refs_list.set_head(obj);
1041 refs_list.inc_length(1);
1042
1043 log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
1044 p2i(obj), obj->klass()->internal_name());
1045 } else {
1046 // If retest was non NULL, another thread beat us to it:
1047 // The reference has already been discovered...
1048 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
1049 p2i(obj), obj->klass()->internal_name());
1050 }
1051 }
1052
1053 #ifndef PRODUCT
1054 // Non-atomic (i.e. concurrent) discovery might allow us
1055 // to observe j.l.References with NULL referents, being those
1056 // cleared concurrently by mutators during (or after) discovery.
1057 void ReferenceProcessor::verify_referent(oop obj) {
1058 bool da = discovery_is_atomic();
1059 oop referent = java_lang_ref_Reference::referent(obj);
1060 assert(da ? oopDesc::is_oop(referent) : oopDesc::is_oop_or_null(referent),
1061 "Bad referent " INTPTR_FORMAT " found in Reference "
1062 INTPTR_FORMAT " during %satomic discovery ",
1063 p2i(referent), p2i(obj), da ? "" : "non-");
1064 }
1065 #endif
1066
1067 bool ReferenceProcessor::is_subject_to_discovery(oop const obj) const {
1068 return _is_subject_to_discovery->do_object_b(obj);
1069 }
1070
1071 // We mention two of several possible choices here:
1072 // #0: if the reference object is not in the "originating generation"
1073 // (or part of the heap being collected, indicated by our "span"
1074 // we don't treat it specially (i.e. we scan it as we would
1075 // a normal oop, treating its references as strong references).
1076 // This means that references can't be discovered unless their
1077 // referent is also in the same span. This is the simplest,
1078 // most "local" and most conservative approach, albeit one
1079 // that may cause weak references to be enqueued least promptly.
1080 // We call this choice the "ReferenceBasedDiscovery" policy.
1081 // #1: the reference object may be in any generation (span), but if
1082 // the referent is in the generation (span) being currently collected
1083 // then we can discover the reference object, provided
1084 // the object has not already been discovered by
1085 // a different concurrently running collector (as may be the
1086 // case, for instance, if the reference object is in CMS and
1087 // the referent in DefNewGeneration), and provided the processing
1088 // of this reference object by the current collector will
1089 // appear atomic to every other collector in the system.
1090 // (Thus, for instance, a concurrent collector may not
1091 // discover references in other generations even if the
1092 // referent is in its own generation). This policy may,
1093 // in certain cases, enqueue references somewhat sooner than
1094 // might Policy #0 above, but at marginally increased cost
1095 // and complexity in processing these references.
1096 // We call this choice the "RefeferentBasedDiscovery" policy.
1097 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
1098 // Make sure we are discovering refs (rather than processing discovered refs).
1099 if (!_discovering_refs || !RegisterReferences) {
1100 return false;
1101 }
1102
1103 if ((rt == REF_FINAL) && (java_lang_ref_Reference::next(obj) != NULL)) {
1104 // Don't rediscover non-active FinalReferences.
1105 return false;
1106 }
1107
1108 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1109 !is_subject_to_discovery(obj)) {
1110 // Reference is not in the originating generation;
1111 // don't treat it specially (i.e. we want to scan it as a normal
1112 // object with strong references).
1113 return false;
1114 }
1115
1116 // We only discover references whose referents are not (yet)
1117 // known to be strongly reachable.
1118 if (is_alive_non_header() != NULL) {
1119 verify_referent(obj);
1120 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
1121 return false; // referent is reachable
1122 }
1123 }
1124 if (rt == REF_SOFT) {
1125 // For soft refs we can decide now if these are not
1126 // current candidates for clearing, in which case we
1127 // can mark through them now, rather than delaying that
1128 // to the reference-processing phase. Since all current
1129 // time-stamp policies advance the soft-ref clock only
1130 // at a full collection cycle, this is always currently
1131 // accurate.
1132 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
1133 return false;
1134 }
1135 }
1136
1137 ResourceMark rm; // Needed for tracing.
1138
1139 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr_raw(obj);
1140 const oop discovered = java_lang_ref_Reference::discovered(obj);
1141 assert(oopDesc::is_oop_or_null(discovered), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
1142 if (discovered != NULL) {
1143 // The reference has already been discovered...
1144 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
1145 p2i(obj), obj->klass()->internal_name());
1146 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1147 // assumes that an object is not processed twice;
1148 // if it's been already discovered it must be on another
1149 // generation's discovered list; so we won't discover it.
1150 return false;
1151 } else {
1152 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1153 "Unrecognized policy");
1154 // Check assumption that an object is not potentially
1155 // discovered twice except by concurrent collectors that potentially
1156 // trace the same Reference object twice.
1157 assert(UseConcMarkSweepGC || UseG1GC || UseShenandoahGC,
1158 "Only possible with a concurrent marking collector");
1159 return true;
1160 }
1161 }
1162
1163 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1164 verify_referent(obj);
1165 // Discover if and only if EITHER:
1166 // .. reference is in our span, OR
1167 // .. we are an atomic collector and referent is in our span
1168 if (is_subject_to_discovery(obj) ||
1169 (discovery_is_atomic() &&
1170 is_subject_to_discovery(java_lang_ref_Reference::referent(obj)))) {
1171 } else {
1172 return false;
1173 }
1174 } else {
1175 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1176 is_subject_to_discovery(obj), "code inconsistency");
1177 }
1178
1179 // Get the right type of discovered queue head.
1180 DiscoveredList* list = get_discovered_list(rt);
1181 if (list == NULL) {
1182 return false; // nothing special needs to be done
1183 }
1184
1185 if (_discovery_is_mt) {
1186 add_to_discovered_list_mt(*list, obj, discovered_addr);
1187 } else {
1188 // We do a raw store here: the field will be visited later when processing
1189 // the discovered references.
1190 oop current_head = list->head();
1191 // The last ref must have its discovered field pointing to itself.
1192 oop next_discovered = (current_head != NULL) ? current_head : obj;
1193
1194 assert(discovered == NULL, "control point invariant");
1195 RawAccess<>::oop_store(discovered_addr, next_discovered);
1196 list->set_head(obj);
1197 list->inc_length(1);
1198
1199 log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name());
1200 }
1201 assert(oopDesc::is_oop(obj), "Discovered a bad reference");
1202 verify_referent(obj);
1203 return true;
1204 }
1205
1206 bool ReferenceProcessor::has_discovered_references() {
1207 for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) {
1208 if (!_discovered_refs[i].is_empty()) {
1209 return true;
1210 }
1211 }
1212 return false;
1213 }
1214
1215 void ReferenceProcessor::preclean_discovered_references(BoolObjectClosure* is_alive,
1216 OopClosure* keep_alive,
1217 VoidClosure* complete_gc,
1218 YieldClosure* yield,
1219 GCTimer* gc_timer) {
1220 // These lists can be handled here in any order and, indeed, concurrently.
1221
1222 // Soft references
1223 {
1224 GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer);
1225 log_reflist("SoftRef before: ", _discoveredSoftRefs, _max_num_queues);
1226 for (uint i = 0; i < _max_num_queues; i++) {
1227 if (yield->should_return()) {
1228 return;
1229 }
1230 if (preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1231 keep_alive, complete_gc, yield)) {
1232 log_reflist("SoftRef abort: ", _discoveredSoftRefs, _max_num_queues);
1233 return;
1234 }
1235 }
1236 log_reflist("SoftRef after: ", _discoveredSoftRefs, _max_num_queues);
1237 }
1238
1239 // Weak references
1240 {
1241 GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer);
1242 log_reflist("WeakRef before: ", _discoveredWeakRefs, _max_num_queues);
1243 for (uint i = 0; i < _max_num_queues; i++) {
1244 if (yield->should_return()) {
1245 return;
1246 }
1247 if (preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1248 keep_alive, complete_gc, yield)) {
1249 log_reflist("WeakRef abort: ", _discoveredWeakRefs, _max_num_queues);
1250 return;
1251 }
1252 }
1253 log_reflist("WeakRef after: ", _discoveredWeakRefs, _max_num_queues);
1254 }
1255
1256 // Final references
1257 {
1258 GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer);
1259 log_reflist("FinalRef before: ", _discoveredFinalRefs, _max_num_queues);
1260 for (uint i = 0; i < _max_num_queues; i++) {
1261 if (yield->should_return()) {
1262 return;
1263 }
1264 if (preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1265 keep_alive, complete_gc, yield)) {
1266 log_reflist("FinalRef abort: ", _discoveredFinalRefs, _max_num_queues);
1267 return;
1268 }
1269 }
1270 log_reflist("FinalRef after: ", _discoveredFinalRefs, _max_num_queues);
1271 }
1272
1273 // Phantom references
1274 {
1275 GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer);
1276 log_reflist("PhantomRef before: ", _discoveredPhantomRefs, _max_num_queues);
1277 for (uint i = 0; i < _max_num_queues; i++) {
1278 if (yield->should_return()) {
1279 return;
1280 }
1281 if (preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1282 keep_alive, complete_gc, yield)) {
1283 log_reflist("PhantomRef abort: ", _discoveredPhantomRefs, _max_num_queues);
1284 return;
1285 }
1286 }
1287 log_reflist("PhantomRef after: ", _discoveredPhantomRefs, _max_num_queues);
1288 }
1289 }
1290
1291 // Walk the given discovered ref list, and remove all reference objects
1292 // whose referents are still alive, whose referents are NULL or which
1293 // are not active (have a non-NULL next field). NOTE: When we are
1294 // thus precleaning the ref lists (which happens single-threaded today),
1295 // we do not disable refs discovery to honor the correct semantics of
1296 // java.lang.Reference. As a result, we need to be careful below
1297 // that ref removal steps interleave safely with ref discovery steps
1298 // (in this thread).
1299 bool ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1300 BoolObjectClosure* is_alive,
1301 OopClosure* keep_alive,
1302 VoidClosure* complete_gc,
1303 YieldClosure* yield) {
1304 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1305 while (iter.has_next()) {
1306 if (yield->should_return_fine_grain()) {
1307 return true;
1308 }
1309 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1310 if (iter.referent() == NULL || iter.is_referent_alive()) {
1311 // The referent has been cleared, or is alive; we need to trace
1312 // and mark its cohort.
1313 log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1314 p2i(iter.obj()), iter.obj()->klass()->internal_name());
1315 // Remove Reference object from list
1316 iter.remove();
1317 // Keep alive its cohort.
1318 iter.make_referent_alive();
1319 iter.move_to_next();
1320 } else {
1321 iter.next();
1322 }
1323 }
1324 // Close the reachable set
1325 complete_gc->do_void();
1326
1327 if (iter.processed() > 0) {
1328 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT,
1329 iter.removed(), iter.processed(), p2i(&refs_list));
1330 }
1331 return false;
1332 }
1333
1334 const char* ReferenceProcessor::list_name(uint i) {
1335 assert(i <= _max_num_queues * number_of_subclasses_of_ref(),
1336 "Out of bounds index");
1337
1338 int j = i / _max_num_queues;
1339 switch (j) {
1340 case 0: return "SoftRef";
1341 case 1: return "WeakRef";
1342 case 2: return "FinalRef";
1343 case 3: return "PhantomRef";
1344 }
1345 ShouldNotReachHere();
1346 return NULL;
1347 }
1348
1349 uint RefProcMTDegreeAdjuster::ergo_proc_thread_count(size_t ref_count,
1350 uint max_threads,
1351 RefProcPhases phase) const {
1352 assert(0 < max_threads, "must allow at least one thread");
1353
1354 if (use_max_threads(phase) || (ReferencesPerThread == 0)) {
1355 return max_threads;
1356 }
1357
1358 size_t thread_count = 1 + (ref_count / ReferencesPerThread);
1359 return (uint)MIN3(thread_count,
1360 static_cast<size_t>(max_threads),
1361 (size_t)os::active_processor_count());
1362 }
1363
1364 bool RefProcMTDegreeAdjuster::use_max_threads(RefProcPhases phase) const {
1365 // Even a small number of references in either of those cases could produce large amounts of work.
1366 return (phase == ReferenceProcessor::RefPhase1 || phase == ReferenceProcessor::RefPhase3);
1367 }
1368
1369 RefProcMTDegreeAdjuster::RefProcMTDegreeAdjuster(ReferenceProcessor* rp,
1370 RefProcPhases phase,
1371 size_t ref_count):
1372 _rp(rp),
1373 _saved_mt_processing(_rp->processing_is_mt()),
1374 _saved_num_queues(_rp->num_queues()) {
1375 if (!_rp->processing_is_mt() || !_rp->adjust_no_of_processing_threads() || (ReferencesPerThread == 0)) {
1376 return;
1377 }
1378
1379 uint workers = ergo_proc_thread_count(ref_count, _rp->num_queues(), phase);
1380
1381 _rp->set_mt_processing(workers > 1);
1382 _rp->set_active_mt_degree(workers);
1383 }
1384
1385 RefProcMTDegreeAdjuster::~RefProcMTDegreeAdjuster() {
1386 // Revert to previous status.
1387 _rp->set_mt_processing(_saved_mt_processing);
1388 _rp->set_active_mt_degree(_saved_num_queues);
1389 }