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