1 /*
2 * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/javaClasses.inline.hpp"
27 #include "classfile/systemDictionary.hpp"
28 #include "gc/shared/collectedHeap.hpp"
29 #include "gc/shared/collectedHeap.inline.hpp"
30 #include "gc/shared/gcTimer.hpp"
31 #include "gc/shared/gcTraceTime.inline.hpp"
32 #include "gc/shared/referencePolicy.hpp"
33 #include "gc/shared/referenceProcessor.inline.hpp"
34 #include "logging/log.hpp"
35 #include "memory/allocation.hpp"
36 #include "memory/resourceArea.hpp"
37 #include "oops/oop.inline.hpp"
38 #include "runtime/heapMonitoring.hpp"
39 #include "runtime/java.hpp"
40 #include "runtime/jniHandles.hpp"
41
42 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
43 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
44 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0;
45
46 void referenceProcessor_init() {
47 ReferenceProcessor::init_statics();
48 }
49
50 void ReferenceProcessor::init_statics() {
51 // We need a monotonically non-decreasing time in ms but
52 // os::javaTimeMillis() does not guarantee monotonicity.
53 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
54
55 // Initialize the soft ref timestamp clock.
56 _soft_ref_timestamp_clock = now;
57 // Also update the soft ref clock in j.l.r.SoftReference
58 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock);
59
60 _always_clear_soft_ref_policy = new AlwaysClearPolicy();
61 if (is_server_compilation_mode_vm()) {
62 _default_soft_ref_policy = new LRUMaxHeapPolicy();
63 } else {
64 _default_soft_ref_policy = new LRUCurrentHeapPolicy();
65 }
66 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
67 vm_exit_during_initialization("Could not allocate reference policy object");
68 }
69 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
70 RefDiscoveryPolicy == ReferentBasedDiscovery,
71 "Unrecognized RefDiscoveryPolicy");
72 }
73
74 void ReferenceProcessor::enable_discovery(bool check_no_refs) {
75 #ifdef ASSERT
76 // Verify that we're not currently discovering refs
77 assert(!_discovering_refs, "nested call?");
78
79 if (check_no_refs) {
80 // Verify that the discovered lists are empty
81 verify_no_references_recorded();
82 }
83 #endif // ASSERT
84
85 // Someone could have modified the value of the static
86 // field in the j.l.r.SoftReference class that holds the
87 // soft reference timestamp clock using reflection or
88 // Unsafe between GCs. Unconditionally update the static
89 // field in ReferenceProcessor here so that we use the new
90 // value during reference discovery.
91
92 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
93 _discovering_refs = true;
94 }
95
96 ReferenceProcessor::ReferenceProcessor(MemRegion span,
97 bool mt_processing,
98 uint mt_processing_degree,
99 bool mt_discovery,
100 uint mt_discovery_degree,
101 bool atomic_discovery,
102 BoolObjectClosure* is_alive_non_header) :
103 _discovering_refs(false),
104 _enqueuing_is_done(false),
105 _is_alive_non_header(is_alive_non_header),
106 _processing_is_mt(mt_processing),
107 _next_id(0)
108 {
109 _span = span;
110 _discovery_is_atomic = atomic_discovery;
111 _discovery_is_mt = mt_discovery;
112 _num_q = MAX2(1U, mt_processing_degree);
113 _max_num_q = MAX2(_num_q, mt_discovery_degree);
114 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
115 _max_num_q * number_of_subclasses_of_ref(), mtGC);
116
117 if (_discovered_refs == NULL) {
118 vm_exit_during_initialization("Could not allocated RefProc Array");
119 }
120 _discoveredSoftRefs = &_discovered_refs[0];
121 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q];
122 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q];
123 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q];
124
125 // Initialize all entries to NULL
126 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
127 _discovered_refs[i].set_head(NULL);
128 _discovered_refs[i].set_length(0);
129 }
130
131 setup_policy(false /* default soft ref policy */);
132 }
133
134 #ifndef PRODUCT
135 void ReferenceProcessor::verify_no_references_recorded() {
136 guarantee(!_discovering_refs, "Discovering refs?");
137 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
138 guarantee(_discovered_refs[i].is_empty(),
139 "Found non-empty discovered list at %u", i);
140 }
141 }
142 #endif
143
144 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
145 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
146 if (UseCompressedOops) {
147 f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
148 } else {
149 f->do_oop((oop*)_discovered_refs[i].adr_head());
150 }
151 }
152 }
153
154 void ReferenceProcessor::update_soft_ref_master_clock() {
155 // Update (advance) the soft ref master clock field. This must be done
156 // after processing the soft ref list.
157
158 // We need a monotonically non-decreasing time in ms but
159 // os::javaTimeMillis() does not guarantee monotonicity.
160 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
161 jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
162 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
163
164 NOT_PRODUCT(
165 if (now < _soft_ref_timestamp_clock) {
166 log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT,
167 _soft_ref_timestamp_clock, now);
168 }
169 )
170 // The values of now and _soft_ref_timestamp_clock are set using
171 // javaTimeNanos(), which is guaranteed to be monotonically
172 // non-decreasing provided the underlying platform provides such
173 // a time source (and it is bug free).
174 // In product mode, however, protect ourselves from non-monotonicity.
175 if (now > _soft_ref_timestamp_clock) {
176 _soft_ref_timestamp_clock = now;
177 java_lang_ref_SoftReference::set_clock(now);
178 }
179 // Else leave clock stalled at its old value until time progresses
180 // past clock value.
181 }
182
183 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) const {
184 size_t total = 0;
185 for (uint i = 0; i < _max_num_q; ++i) {
186 total += lists[i].length();
187 }
188 return total;
189 }
190
191 ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
192 BoolObjectClosure* is_alive,
193 OopClosure* keep_alive,
194 VoidClosure* complete_gc,
195 AbstractRefProcTaskExecutor* task_executor,
196 ReferenceProcessorPhaseTimes* phase_times) {
197
198 double start_time = os::elapsedTime();
199
200 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
201 // Stop treating discovered references specially.
202 disable_discovery();
203
204 // If discovery was concurrent, someone could have modified
205 // the value of the static field in the j.l.r.SoftReference
206 // class that holds the soft reference timestamp clock using
207 // reflection or Unsafe between when discovery was enabled and
208 // now. Unconditionally update the static field in ReferenceProcessor
209 // here so that we use the new value during processing of the
210 // discovered soft refs.
211
212 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
213
214 ReferenceProcessorStats stats(total_count(_discoveredSoftRefs),
215 total_count(_discoveredWeakRefs),
216 total_count(_discoveredFinalRefs),
217 total_count(_discoveredPhantomRefs));
218
219 // Soft references
220 {
221 RefProcPhaseTimesTracker tt(REF_SOFT, phase_times, this);
222 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
223 is_alive, keep_alive, complete_gc, task_executor, phase_times);
224 }
225
226 update_soft_ref_master_clock();
227
228 // Weak references
229 {
230 RefProcPhaseTimesTracker tt(REF_WEAK, phase_times, this);
231 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
232 is_alive, keep_alive, complete_gc, task_executor, phase_times);
233 }
234
235 // Final references
236 {
237 RefProcPhaseTimesTracker tt(REF_FINAL, phase_times, this);
238 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
239 is_alive, keep_alive, complete_gc, task_executor, phase_times);
240 }
241
242 // Phantom references
243 {
244 RefProcPhaseTimesTracker tt(REF_PHANTOM, phase_times, this);
245 process_discovered_reflist(_discoveredPhantomRefs, NULL, true,
246 is_alive, keep_alive, complete_gc, task_executor, phase_times);
247 }
248
249 // Weak global JNI references. It would make more sense (semantically) to
250 // traverse these simultaneously with the regular weak references above, but
251 // that is not how the JDK1.2 specification is. See #4126360. Native code can
252 // thus use JNI weak references to circumvent the phantom references and
253 // resurrect a "post-mortem" object.
254 {
255 GCTraceTime(Debug, gc, ref) tt("JNI Weak Reference", phase_times->gc_timer());
256 if (task_executor != NULL) {
257 task_executor->set_single_threaded_mode();
258 }
259 process_phaseJNI(is_alive, keep_alive, complete_gc);
260 }
261
262 // Heap Monitoring references
263 size_t handled;
264 {
265 GCTraceTime(Debug, gc, ref) tt("Heap Sampler Weak Reference", phase_times->gc_timer());
266 handled = process_phaseHeapSampling(is_alive, keep_alive, complete_gc);
267 }
268
269 phase_times->set_total_time_ms((os::elapsedTime() - start_time) * 1000);
270
271 log_develop_trace(gc, ref)("JNI Weak Reference count: " SIZE_FORMAT, count_jni_refs());
272 log_develop_trace(gc, ref)("Heap Sampler Weak Reference handled: " SIZE_FORMAT, handled);
273
274 return stats;
275 }
276
277 #ifndef PRODUCT
278 // Calculate the number of jni handles.
279 size_t ReferenceProcessor::count_jni_refs() {
280 class CountHandleClosure: public OopClosure {
281 private:
282 size_t _count;
283 public:
284 CountHandleClosure(): _count(0) {}
285 void do_oop(oop* unused) { _count++; }
286 void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
287 size_t count() { return _count; }
288 };
289 CountHandleClosure global_handle_count;
290 JNIHandles::weak_oops_do(&global_handle_count);
291 return global_handle_count.count();
292 }
293 #endif
294
295 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
296 OopClosure* keep_alive,
297 VoidClosure* complete_gc) {
298 JNIHandles::weak_oops_do(is_alive, keep_alive);
299 complete_gc->do_void();
300 }
301
302 size_t ReferenceProcessor::process_phaseHeapSampling(
303 BoolObjectClosure* is_alive,
304 OopClosure* keep_alive,
305 VoidClosure* complete_gc) {
306 size_t count = 0;
307 if (HeapMonitoring::enabled()) {
308 count = HeapMonitoring::weak_oops_do(is_alive, keep_alive);
309 complete_gc->do_void();
310 }
311 return count;
312 }
313
314 void ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor,
315 ReferenceProcessorPhaseTimes* phase_times) {
316 // Enqueue references that are not made active again, and
317 // clear the decks for the next collection (cycle).
318 enqueue_discovered_reflists(task_executor, phase_times);
319
320 // Stop treating discovered references specially.
321 disable_discovery();
322 }
323
324 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list) {
325 // Given a list of refs linked through the "discovered" field
326 // (java.lang.ref.Reference.discovered), self-loop their "next" field
327 // thus distinguishing them from active References, then
328 // prepend them to the pending list.
329 //
330 // The Java threads will see the Reference objects linked together through
331 // the discovered field. Instead of trying to do the write barrier updates
332 // in all places in the reference processor where we manipulate the discovered
333 // field we make sure to do the barrier here where we anyway iterate through
334 // all linked Reference objects. Note that it is important to not dirty any
335 // cards during reference processing since this will cause card table
336 // verification to fail for G1.
337 log_develop_trace(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(&refs_list));
338
339 oop obj = NULL;
340 oop next_d = refs_list.head();
341 // Walk down the list, self-looping the next field
342 // so that the References are not considered active.
343 while (obj != next_d) {
344 obj = next_d;
345 assert(obj->is_instance(), "should be an instance object");
346 assert(InstanceKlass::cast(obj->klass())->is_reference_instance_klass(), "should be reference object");
347 next_d = java_lang_ref_Reference::discovered(obj);
348 log_develop_trace(gc, ref)(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, p2i(obj), p2i(next_d));
349 assert(java_lang_ref_Reference::next(obj) == NULL,
350 "Reference not active; should not be discovered");
351 // Self-loop next, so as to make Ref not active.
352 java_lang_ref_Reference::set_next_raw(obj, obj);
353 if (next_d != obj) {
354 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
355 } else {
356 // This is the last object.
357 // Swap refs_list into pending list and set obj's
358 // discovered to what we read from the pending list.
359 oop old = Universe::swap_reference_pending_list(refs_list.head());
360 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
361 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
362 }
363 }
364 }
365
366 // Parallel enqueue task
367 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
368 public:
369 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
370 DiscoveredList discovered_refs[],
371 int n_queues,
372 ReferenceProcessorPhaseTimes* phase_times)
373 : EnqueueTask(ref_processor, discovered_refs, n_queues, phase_times)
374 { }
375
376 virtual void work(unsigned int work_id) {
377 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefEnqueue, _phase_times, work_id);
378
379 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
380 // Simplest first cut: static partitioning.
381 int index = work_id;
382 // The increment on "index" must correspond to the maximum number of queues
383 // (n_queues) with which that ReferenceProcessor was created. That
384 // is because of the "clever" way the discovered references lists were
385 // allocated and are indexed into.
386 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
387 for (int j = 0;
388 j < ReferenceProcessor::number_of_subclasses_of_ref();
389 j++, index += _n_queues) {
390 _ref_processor.enqueue_discovered_reflist(_refs_lists[index]);
391 _refs_lists[index].set_head(NULL);
392 _refs_lists[index].set_length(0);
393 }
394 }
395 };
396
397 // Enqueue references that are not made active again
398 void ReferenceProcessor::enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor,
399 ReferenceProcessorPhaseTimes* phase_times) {
400
401 ReferenceProcessorStats stats(total_count(_discoveredSoftRefs),
402 total_count(_discoveredWeakRefs),
403 total_count(_discoveredFinalRefs),
404 total_count(_discoveredPhantomRefs));
405
406 RefProcEnqueueTimeTracker tt(phase_times, stats);
407
408 if (_processing_is_mt && task_executor != NULL) {
409 // Parallel code
410 RefProcEnqueueTask tsk(*this, _discovered_refs, _max_num_q, phase_times);
411 task_executor->execute(tsk);
412 } else {
413 // Serial code: call the parent class's implementation
414 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
415 enqueue_discovered_reflist(_discovered_refs[i]);
416 _discovered_refs[i].set_head(NULL);
417 _discovered_refs[i].set_length(0);
418 }
419 }
420 }
421
422 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
423 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
424 oop discovered = java_lang_ref_Reference::discovered(_ref);
425 assert(_discovered_addr && oopDesc::is_oop_or_null(discovered),
426 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
427 _next = discovered;
428 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
429 _referent = java_lang_ref_Reference::referent(_ref);
430 assert(Universe::heap()->is_in_reserved_or_null(_referent),
431 "Wrong oop found in java.lang.Reference object");
432 assert(allow_null_referent ?
433 oopDesc::is_oop_or_null(_referent)
434 : oopDesc::is_oop(_referent),
435 "Expected an oop%s for referent field at " PTR_FORMAT,
436 (allow_null_referent ? " or NULL" : ""),
437 p2i(_referent));
438 }
439
440 void DiscoveredListIterator::remove() {
441 assert(oopDesc::is_oop(_ref), "Dropping a bad reference");
442 oop_store_raw(_discovered_addr, NULL);
443
444 // First _prev_next ref actually points into DiscoveredList (gross).
445 oop new_next;
446 if (_next == _ref) {
447 // At the end of the list, we should make _prev point to itself.
448 // If _ref is the first ref, then _prev_next will be in the DiscoveredList,
449 // and _prev will be NULL.
450 new_next = _prev;
451 } else {
452 new_next = _next;
453 }
454 // Remove Reference object from discovered list. Note that G1 does not need a
455 // pre-barrier here because we know the Reference has already been found/marked,
456 // that's how it ended up in the discovered list in the first place.
457 oop_store_raw(_prev_next, new_next);
458 NOT_PRODUCT(_removed++);
459 _refs_list.dec_length(1);
460 }
461
462 void DiscoveredListIterator::clear_referent() {
463 oop_store_raw(_referent_addr, NULL);
464 }
465
466 // NOTE: process_phase*() are largely similar, and at a high level
467 // merely iterate over the extant list applying a predicate to
468 // each of its elements and possibly removing that element from the
469 // list and applying some further closures to that element.
470 // We should consider the possibility of replacing these
471 // process_phase*() methods by abstracting them into
472 // a single general iterator invocation that receives appropriate
473 // closures that accomplish this work.
474
475 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
476 // referents are not alive, but that should be kept alive for policy reasons.
477 // Keep alive the transitive closure of all such referents.
478 void
479 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
480 ReferencePolicy* policy,
481 BoolObjectClosure* is_alive,
482 OopClosure* keep_alive,
483 VoidClosure* complete_gc) {
484 assert(policy != NULL, "Must have a non-NULL policy");
485 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
486 // Decide which softly reachable refs should be kept alive.
487 while (iter.has_next()) {
488 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
489 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
490 if (referent_is_dead &&
491 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
492 log_develop_trace(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
493 p2i(iter.obj()), iter.obj()->klass()->internal_name());
494 // Remove Reference object from list
495 iter.remove();
496 // keep the referent around
497 iter.make_referent_alive();
498 iter.move_to_next();
499 } else {
500 iter.next();
501 }
502 }
503 // Close the reachable set
504 complete_gc->do_void();
505 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT,
506 iter.removed(), iter.processed(), p2i(&refs_list));
507 }
508
509 // Traverse the list and remove any Refs that are not active, or
510 // whose referents are either alive or NULL.
511 void
512 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
513 BoolObjectClosure* is_alive,
514 OopClosure* keep_alive) {
515 assert(discovery_is_atomic(), "Error");
516 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
517 while (iter.has_next()) {
518 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
519 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
520 assert(next == NULL, "Should not discover inactive Reference");
521 if (iter.is_referent_alive()) {
522 log_develop_trace(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
523 p2i(iter.obj()), iter.obj()->klass()->internal_name());
524 // The referent is reachable after all.
525 // Remove Reference object from list.
526 iter.remove();
527 // Update the referent pointer as necessary: Note that this
528 // should not entail any recursive marking because the
529 // referent must already have been traversed.
530 iter.make_referent_alive();
531 iter.move_to_next();
532 } else {
533 iter.next();
534 }
535 }
536 NOT_PRODUCT(
537 if (iter.processed() > 0) {
538 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
539 " Refs in discovered list " INTPTR_FORMAT,
540 iter.removed(), iter.processed(), p2i(&refs_list));
541 }
542 )
543 }
544
545 void
546 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
547 BoolObjectClosure* is_alive,
548 OopClosure* keep_alive,
549 VoidClosure* complete_gc) {
550 assert(!discovery_is_atomic(), "Error");
551 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
552 while (iter.has_next()) {
553 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
554 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
555 oop next = java_lang_ref_Reference::next(iter.obj());
556 if ((iter.referent() == NULL || iter.is_referent_alive() ||
557 next != NULL)) {
558 assert(oopDesc::is_oop_or_null(next), "Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next));
559 // Remove Reference object from list
560 iter.remove();
561 // Trace the cohorts
562 iter.make_referent_alive();
563 if (UseCompressedOops) {
564 keep_alive->do_oop((narrowOop*)next_addr);
565 } else {
566 keep_alive->do_oop((oop*)next_addr);
567 }
568 iter.move_to_next();
569 } else {
570 iter.next();
571 }
572 }
573 // Now close the newly reachable set
574 complete_gc->do_void();
575 NOT_PRODUCT(
576 if (iter.processed() > 0) {
577 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
578 " Refs in discovered list " INTPTR_FORMAT,
579 iter.removed(), iter.processed(), p2i(&refs_list));
580 }
581 )
582 }
583
584 // Traverse the list and process the referents, by either
585 // clearing them or keeping them (and their reachable
586 // closure) alive.
587 void
588 ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
589 bool clear_referent,
590 BoolObjectClosure* is_alive,
591 OopClosure* keep_alive,
592 VoidClosure* complete_gc) {
593 ResourceMark rm;
594 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
595 while (iter.has_next()) {
596 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
597 if (clear_referent) {
598 // NULL out referent pointer
599 iter.clear_referent();
600 } else {
601 // keep the referent around
602 iter.make_referent_alive();
603 }
604 log_develop_trace(gc, ref)("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
605 clear_referent ? "cleared " : "", p2i(iter.obj()), iter.obj()->klass()->internal_name());
606 assert(oopDesc::is_oop(iter.obj(), UseConcMarkSweepGC), "Adding a bad reference");
607 iter.next();
608 }
609 // Close the reachable set
610 complete_gc->do_void();
611 }
612
613 void
614 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
615 oop obj = NULL;
616 oop next = refs_list.head();
617 while (next != obj) {
618 obj = next;
619 next = java_lang_ref_Reference::discovered(obj);
620 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
621 }
622 refs_list.set_head(NULL);
623 refs_list.set_length(0);
624 }
625
626 void ReferenceProcessor::abandon_partial_discovery() {
627 // loop over the lists
628 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
629 if ((i % _max_num_q) == 0) {
630 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i));
631 }
632 clear_discovered_references(_discovered_refs[i]);
633 }
634 }
635
636 size_t ReferenceProcessor::total_reference_count(ReferenceType type) const {
637 DiscoveredList* list = NULL;
638
639 switch (type) {
640 case REF_SOFT:
641 list = _discoveredSoftRefs;
642 break;
643 case REF_WEAK:
644 list = _discoveredWeakRefs;
645 break;
646 case REF_FINAL:
647 list = _discoveredFinalRefs;
648 break;
649 case REF_PHANTOM:
650 list = _discoveredPhantomRefs;
651 break;
652 case REF_OTHER:
653 case REF_NONE:
654 default:
655 ShouldNotReachHere();
656 }
657 return total_count(list);
658 }
659
660 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
661 public:
662 RefProcPhase1Task(ReferenceProcessor& ref_processor,
663 DiscoveredList refs_lists[],
664 ReferencePolicy* policy,
665 bool marks_oops_alive,
666 ReferenceProcessorPhaseTimes* phase_times)
667 : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times),
668 _policy(policy)
669 { }
670 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
671 OopClosure& keep_alive,
672 VoidClosure& complete_gc)
673 {
674 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase1, _phase_times, i);
675
676 _ref_processor.process_phase1(_refs_lists[i], _policy,
677 &is_alive, &keep_alive, &complete_gc);
678 }
679 private:
680 ReferencePolicy* _policy;
681 };
682
683 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
684 public:
685 RefProcPhase2Task(ReferenceProcessor& ref_processor,
686 DiscoveredList refs_lists[],
687 bool marks_oops_alive,
688 ReferenceProcessorPhaseTimes* phase_times)
689 : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times)
690 { }
691 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
692 OopClosure& keep_alive,
693 VoidClosure& complete_gc)
694 {
695 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase2, _phase_times, i);
696
697 _ref_processor.process_phase2(_refs_lists[i],
698 &is_alive, &keep_alive, &complete_gc);
699 }
700 };
701
702 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
703 public:
704 RefProcPhase3Task(ReferenceProcessor& ref_processor,
705 DiscoveredList refs_lists[],
706 bool clear_referent,
707 bool marks_oops_alive,
708 ReferenceProcessorPhaseTimes* phase_times)
709 : ProcessTask(ref_processor, refs_lists, marks_oops_alive, phase_times),
710 _clear_referent(clear_referent)
711 { }
712 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
713 OopClosure& keep_alive,
714 VoidClosure& complete_gc)
715 {
716 RefProcWorkerTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase3, _phase_times, i);
717
718 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
719 &is_alive, &keep_alive, &complete_gc);
720 }
721 private:
722 bool _clear_referent;
723 };
724
725 #ifndef PRODUCT
726 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_refs) {
727 if (!log_is_enabled(Trace, gc, ref)) {
728 return;
729 }
730
731 stringStream st;
732 for (uint i = 0; i < active_length; ++i) {
733 st.print(SIZE_FORMAT " ", ref_lists[i].length());
734 }
735 log_develop_trace(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs);
736 #ifdef ASSERT
737 for (uint i = active_length; i < _max_num_q; i++) {
738 assert(ref_lists[i].length() == 0, SIZE_FORMAT " unexpected References in %u",
739 ref_lists[i].length(), i);
740 }
741 #endif
742 }
743 #endif
744
745 void ReferenceProcessor::set_active_mt_degree(uint v) {
746 _num_q = v;
747 _next_id = 0;
748 }
749
750 // Balances reference queues.
751 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
752 // queues[0, 1, ..., _num_q-1] because only the first _num_q
753 // corresponding to the active workers will be processed.
754 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
755 {
756 // calculate total length
757 size_t total_refs = 0;
758 log_develop_trace(gc, ref)("Balance ref_lists ");
759
760 for (uint i = 0; i < _max_num_q; ++i) {
761 total_refs += ref_lists[i].length();
762 }
763 log_reflist_counts(ref_lists, _max_num_q, total_refs);
764 size_t avg_refs = total_refs / _num_q + 1;
765 uint to_idx = 0;
766 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) {
767 bool move_all = false;
768 if (from_idx >= _num_q) {
769 move_all = ref_lists[from_idx].length() > 0;
770 }
771 while ((ref_lists[from_idx].length() > avg_refs) ||
772 move_all) {
773 assert(to_idx < _num_q, "Sanity Check!");
774 if (ref_lists[to_idx].length() < avg_refs) {
775 // move superfluous refs
776 size_t refs_to_move;
777 // Move all the Ref's if the from queue will not be processed.
778 if (move_all) {
779 refs_to_move = MIN2(ref_lists[from_idx].length(),
780 avg_refs - ref_lists[to_idx].length());
781 } else {
782 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
783 avg_refs - ref_lists[to_idx].length());
784 }
785
786 assert(refs_to_move > 0, "otherwise the code below will fail");
787
788 oop move_head = ref_lists[from_idx].head();
789 oop move_tail = move_head;
790 oop new_head = move_head;
791 // find an element to split the list on
792 for (size_t j = 0; j < refs_to_move; ++j) {
793 move_tail = new_head;
794 new_head = java_lang_ref_Reference::discovered(new_head);
795 }
796
797 // Add the chain to the to list.
798 if (ref_lists[to_idx].head() == NULL) {
799 // to list is empty. Make a loop at the end.
800 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
801 } else {
802 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
803 }
804 ref_lists[to_idx].set_head(move_head);
805 ref_lists[to_idx].inc_length(refs_to_move);
806
807 // Remove the chain from the from list.
808 if (move_tail == new_head) {
809 // We found the end of the from list.
810 ref_lists[from_idx].set_head(NULL);
811 } else {
812 ref_lists[from_idx].set_head(new_head);
813 }
814 ref_lists[from_idx].dec_length(refs_to_move);
815 if (ref_lists[from_idx].length() == 0) {
816 break;
817 }
818 } else {
819 to_idx = (to_idx + 1) % _num_q;
820 }
821 }
822 }
823 #ifdef ASSERT
824 size_t balanced_total_refs = 0;
825 for (uint i = 0; i < _num_q; ++i) {
826 balanced_total_refs += ref_lists[i].length();
827 }
828 log_reflist_counts(ref_lists, _num_q, balanced_total_refs);
829 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
830 #endif
831 }
832
833 void ReferenceProcessor::balance_all_queues() {
834 balance_queues(_discoveredSoftRefs);
835 balance_queues(_discoveredWeakRefs);
836 balance_queues(_discoveredFinalRefs);
837 balance_queues(_discoveredPhantomRefs);
838 }
839
840 void ReferenceProcessor::process_discovered_reflist(
841 DiscoveredList refs_lists[],
842 ReferencePolicy* policy,
843 bool clear_referent,
844 BoolObjectClosure* is_alive,
845 OopClosure* keep_alive,
846 VoidClosure* complete_gc,
847 AbstractRefProcTaskExecutor* task_executor,
848 ReferenceProcessorPhaseTimes* phase_times)
849 {
850 bool mt_processing = task_executor != NULL && _processing_is_mt;
851
852 phase_times->set_processing_is_mt(mt_processing);
853
854 // If discovery used MT and a dynamic number of GC threads, then
855 // the queues must be balanced for correctness if fewer than the
856 // maximum number of queues were used. The number of queue used
857 // during discovery may be different than the number to be used
858 // for processing so don't depend of _num_q < _max_num_q as part
859 // of the test.
860 bool must_balance = _discovery_is_mt;
861
862 if ((mt_processing && ParallelRefProcBalancingEnabled) ||
863 must_balance) {
864 RefProcBalanceQueuesTimeTracker tt(phase_times);
865 balance_queues(refs_lists);
866 }
867
868 // Phase 1 (soft refs only):
869 // . Traverse the list and remove any SoftReferences whose
870 // referents are not alive, but that should be kept alive for
871 // policy reasons. Keep alive the transitive closure of all
872 // such referents.
873 if (policy != NULL) {
874 RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase1, phase_times);
875
876 if (mt_processing) {
877 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/, phase_times);
878 task_executor->execute(phase1);
879 } else {
880 for (uint i = 0; i < _max_num_q; i++) {
881 process_phase1(refs_lists[i], policy,
882 is_alive, keep_alive, complete_gc);
883 }
884 }
885 } else { // policy == NULL
886 assert(refs_lists != _discoveredSoftRefs,
887 "Policy must be specified for soft references.");
888 }
889
890 // Phase 2:
891 // . Traverse the list and remove any refs whose referents are alive.
892 {
893 RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase2, phase_times);
894
895 if (mt_processing) {
896 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/, phase_times);
897 task_executor->execute(phase2);
898 } else {
899 for (uint i = 0; i < _max_num_q; i++) {
900 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
901 }
902 }
903 }
904
905 // Phase 3:
906 // . Traverse the list and process referents as appropriate.
907 {
908 RefProcParPhaseTimeTracker tt(ReferenceProcessorPhaseTimes::RefPhase3, phase_times);
909
910 if (mt_processing) {
911 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/, phase_times);
912 task_executor->execute(phase3);
913 } else {
914 for (uint i = 0; i < _max_num_q; i++) {
915 process_phase3(refs_lists[i], clear_referent,
916 is_alive, keep_alive, complete_gc);
917 }
918 }
919 }
920 }
921
922 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
923 uint id = 0;
924 // Determine the queue index to use for this object.
925 if (_discovery_is_mt) {
926 // During a multi-threaded discovery phase,
927 // each thread saves to its "own" list.
928 Thread* thr = Thread::current();
929 id = thr->as_Worker_thread()->id();
930 } else {
931 // single-threaded discovery, we save in round-robin
932 // fashion to each of the lists.
933 if (_processing_is_mt) {
934 id = next_id();
935 }
936 }
937 assert(id < _max_num_q, "Id is out-of-bounds id %u and max id %u)", id, _max_num_q);
938
939 // Get the discovered queue to which we will add
940 DiscoveredList* list = NULL;
941 switch (rt) {
942 case REF_OTHER:
943 // Unknown reference type, no special treatment
944 break;
945 case REF_SOFT:
946 list = &_discoveredSoftRefs[id];
947 break;
948 case REF_WEAK:
949 list = &_discoveredWeakRefs[id];
950 break;
951 case REF_FINAL:
952 list = &_discoveredFinalRefs[id];
953 break;
954 case REF_PHANTOM:
955 list = &_discoveredPhantomRefs[id];
956 break;
957 case REF_NONE:
958 // we should not reach here if we are an InstanceRefKlass
959 default:
960 ShouldNotReachHere();
961 }
962 log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list));
963 return list;
964 }
965
966 inline void
967 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
968 oop obj,
969 HeapWord* discovered_addr) {
970 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
971 // First we must make sure this object is only enqueued once. CAS in a non null
972 // discovered_addr.
973 oop current_head = refs_list.head();
974 // The last ref must have its discovered field pointing to itself.
975 oop next_discovered = (current_head != NULL) ? current_head : obj;
976
977 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr,
978 NULL);
979 if (retest == NULL) {
980 // This thread just won the right to enqueue the object.
981 // We have separate lists for enqueueing, so no synchronization
982 // is necessary.
983 refs_list.set_head(obj);
984 refs_list.inc_length(1);
985
986 log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
987 p2i(obj), obj->klass()->internal_name());
988 } else {
989 // If retest was non NULL, another thread beat us to it:
990 // The reference has already been discovered...
991 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
992 p2i(obj), obj->klass()->internal_name());
993 }
994 }
995
996 #ifndef PRODUCT
997 // Non-atomic (i.e. concurrent) discovery might allow us
998 // to observe j.l.References with NULL referents, being those
999 // cleared concurrently by mutators during (or after) discovery.
1000 void ReferenceProcessor::verify_referent(oop obj) {
1001 bool da = discovery_is_atomic();
1002 oop referent = java_lang_ref_Reference::referent(obj);
1003 assert(da ? oopDesc::is_oop(referent) : oopDesc::is_oop_or_null(referent),
1004 "Bad referent " INTPTR_FORMAT " found in Reference "
1005 INTPTR_FORMAT " during %satomic discovery ",
1006 p2i(referent), p2i(obj), da ? "" : "non-");
1007 }
1008 #endif
1009
1010 // We mention two of several possible choices here:
1011 // #0: if the reference object is not in the "originating generation"
1012 // (or part of the heap being collected, indicated by our "span"
1013 // we don't treat it specially (i.e. we scan it as we would
1014 // a normal oop, treating its references as strong references).
1015 // This means that references can't be discovered unless their
1016 // referent is also in the same span. This is the simplest,
1017 // most "local" and most conservative approach, albeit one
1018 // that may cause weak references to be enqueued least promptly.
1019 // We call this choice the "ReferenceBasedDiscovery" policy.
1020 // #1: the reference object may be in any generation (span), but if
1021 // the referent is in the generation (span) being currently collected
1022 // then we can discover the reference object, provided
1023 // the object has not already been discovered by
1024 // a different concurrently running collector (as may be the
1025 // case, for instance, if the reference object is in CMS and
1026 // the referent in DefNewGeneration), and provided the processing
1027 // of this reference object by the current collector will
1028 // appear atomic to every other collector in the system.
1029 // (Thus, for instance, a concurrent collector may not
1030 // discover references in other generations even if the
1031 // referent is in its own generation). This policy may,
1032 // in certain cases, enqueue references somewhat sooner than
1033 // might Policy #0 above, but at marginally increased cost
1034 // and complexity in processing these references.
1035 // We call this choice the "RefeferentBasedDiscovery" policy.
1036 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
1037 // Make sure we are discovering refs (rather than processing discovered refs).
1038 if (!_discovering_refs || !RegisterReferences) {
1039 return false;
1040 }
1041 // We only discover active references.
1042 oop next = java_lang_ref_Reference::next(obj);
1043 if (next != NULL) { // Ref is no longer active
1044 return false;
1045 }
1046
1047 HeapWord* obj_addr = (HeapWord*)obj;
1048 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1049 !_span.contains(obj_addr)) {
1050 // Reference is not in the originating generation;
1051 // don't treat it specially (i.e. we want to scan it as a normal
1052 // object with strong references).
1053 return false;
1054 }
1055
1056 // We only discover references whose referents are not (yet)
1057 // known to be strongly reachable.
1058 if (is_alive_non_header() != NULL) {
1059 verify_referent(obj);
1060 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
1061 return false; // referent is reachable
1062 }
1063 }
1064 if (rt == REF_SOFT) {
1065 // For soft refs we can decide now if these are not
1066 // current candidates for clearing, in which case we
1067 // can mark through them now, rather than delaying that
1068 // to the reference-processing phase. Since all current
1069 // time-stamp policies advance the soft-ref clock only
1070 // at a full collection cycle, this is always currently
1071 // accurate.
1072 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
1073 return false;
1074 }
1075 }
1076
1077 ResourceMark rm; // Needed for tracing.
1078
1079 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
1080 const oop discovered = java_lang_ref_Reference::discovered(obj);
1081 assert(oopDesc::is_oop_or_null(discovered), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
1082 if (discovered != NULL) {
1083 // The reference has already been discovered...
1084 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
1085 p2i(obj), obj->klass()->internal_name());
1086 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1087 // assumes that an object is not processed twice;
1088 // if it's been already discovered it must be on another
1089 // generation's discovered list; so we won't discover it.
1090 return false;
1091 } else {
1092 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1093 "Unrecognized policy");
1094 // Check assumption that an object is not potentially
1095 // discovered twice except by concurrent collectors that potentially
1096 // trace the same Reference object twice.
1097 assert(UseConcMarkSweepGC || UseG1GC,
1098 "Only possible with a concurrent marking collector");
1099 return true;
1100 }
1101 }
1102
1103 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1104 verify_referent(obj);
1105 // Discover if and only if EITHER:
1106 // .. reference is in our span, OR
1107 // .. we are an atomic collector and referent is in our span
1108 if (_span.contains(obj_addr) ||
1109 (discovery_is_atomic() &&
1110 _span.contains(java_lang_ref_Reference::referent(obj)))) {
1111 // should_enqueue = true;
1112 } else {
1113 return false;
1114 }
1115 } else {
1116 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1117 _span.contains(obj_addr), "code inconsistency");
1118 }
1119
1120 // Get the right type of discovered queue head.
1121 DiscoveredList* list = get_discovered_list(rt);
1122 if (list == NULL) {
1123 return false; // nothing special needs to be done
1124 }
1125
1126 if (_discovery_is_mt) {
1127 add_to_discovered_list_mt(*list, obj, discovered_addr);
1128 } else {
1129 // We do a raw store here: the field will be visited later when processing
1130 // the discovered references.
1131 oop current_head = list->head();
1132 // The last ref must have its discovered field pointing to itself.
1133 oop next_discovered = (current_head != NULL) ? current_head : obj;
1134
1135 assert(discovered == NULL, "control point invariant");
1136 oop_store_raw(discovered_addr, next_discovered);
1137 list->set_head(obj);
1138 list->inc_length(1);
1139
1140 log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name());
1141 }
1142 assert(oopDesc::is_oop(obj), "Discovered a bad reference");
1143 verify_referent(obj);
1144 return true;
1145 }
1146
1147 bool ReferenceProcessor::has_discovered_references() {
1148 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
1149 if (!_discovered_refs[i].is_empty()) {
1150 return true;
1151 }
1152 }
1153 return false;
1154 }
1155
1156 // Preclean the discovered references by removing those
1157 // whose referents are alive, and by marking from those that
1158 // are not active. These lists can be handled here
1159 // in any order and, indeed, concurrently.
1160 void ReferenceProcessor::preclean_discovered_references(
1161 BoolObjectClosure* is_alive,
1162 OopClosure* keep_alive,
1163 VoidClosure* complete_gc,
1164 YieldClosure* yield,
1165 GCTimer* gc_timer) {
1166
1167 // Soft references
1168 {
1169 GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer);
1170 for (uint i = 0; i < _max_num_q; i++) {
1171 if (yield->should_return()) {
1172 return;
1173 }
1174 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1175 keep_alive, complete_gc, yield);
1176 }
1177 }
1178
1179 // Weak references
1180 {
1181 GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer);
1182 for (uint i = 0; i < _max_num_q; i++) {
1183 if (yield->should_return()) {
1184 return;
1185 }
1186 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1187 keep_alive, complete_gc, yield);
1188 }
1189 }
1190
1191 // Final references
1192 {
1193 GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer);
1194 for (uint i = 0; i < _max_num_q; i++) {
1195 if (yield->should_return()) {
1196 return;
1197 }
1198 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1199 keep_alive, complete_gc, yield);
1200 }
1201 }
1202
1203 // Phantom references
1204 {
1205 GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer);
1206 for (uint i = 0; i < _max_num_q; i++) {
1207 if (yield->should_return()) {
1208 return;
1209 }
1210 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1211 keep_alive, complete_gc, yield);
1212 }
1213 }
1214 }
1215
1216 // Walk the given discovered ref list, and remove all reference objects
1217 // whose referents are still alive, whose referents are NULL or which
1218 // are not active (have a non-NULL next field). NOTE: When we are
1219 // thus precleaning the ref lists (which happens single-threaded today),
1220 // we do not disable refs discovery to honor the correct semantics of
1221 // java.lang.Reference. As a result, we need to be careful below
1222 // that ref removal steps interleave safely with ref discovery steps
1223 // (in this thread).
1224 void
1225 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1226 BoolObjectClosure* is_alive,
1227 OopClosure* keep_alive,
1228 VoidClosure* complete_gc,
1229 YieldClosure* yield) {
1230 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1231 while (iter.has_next()) {
1232 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1233 oop obj = iter.obj();
1234 oop next = java_lang_ref_Reference::next(obj);
1235 if (iter.referent() == NULL || iter.is_referent_alive() ||
1236 next != NULL) {
1237 // The referent has been cleared, or is alive, or the Reference is not
1238 // active; we need to trace and mark its cohort.
1239 log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1240 p2i(iter.obj()), iter.obj()->klass()->internal_name());
1241 // Remove Reference object from list
1242 iter.remove();
1243 // Keep alive its cohort.
1244 iter.make_referent_alive();
1245 if (UseCompressedOops) {
1246 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
1247 keep_alive->do_oop(next_addr);
1248 } else {
1249 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
1250 keep_alive->do_oop(next_addr);
1251 }
1252 iter.move_to_next();
1253 } else {
1254 iter.next();
1255 }
1256 }
1257 // Close the reachable set
1258 complete_gc->do_void();
1259
1260 NOT_PRODUCT(
1261 if (iter.processed() > 0) {
1262 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT,
1263 iter.removed(), iter.processed(), p2i(&refs_list));
1264 }
1265 )
1266 }
1267
1268 const char* ReferenceProcessor::list_name(uint i) {
1269 assert(i <= _max_num_q * number_of_subclasses_of_ref(),
1270 "Out of bounds index");
1271
1272 int j = i / _max_num_q;
1273 switch (j) {
1274 case 0: return "SoftRef";
1275 case 1: return "WeakRef";
1276 case 2: return "FinalRef";
1277 case 3: return "PhantomRef";
1278 }
1279 ShouldNotReachHere();
1280 return NULL;
1281 }