1 /*
2 * Copyright (c) 2001, 2016, 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 "oops/oop.inline.hpp"
37 #include "runtime/java.hpp"
38 #include "runtime/jniHandles.hpp"
39
40 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
41 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
42 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0;
43
44 void referenceProcessor_init() {
45 ReferenceProcessor::init_statics();
46 }
47
48 void ReferenceProcessor::init_statics() {
49 // We need a monotonically non-decreasing time in ms but
50 // os::javaTimeMillis() does not guarantee monotonicity.
51 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
52
53 // Initialize the soft ref timestamp clock.
54 _soft_ref_timestamp_clock = now;
55 // Also update the soft ref clock in j.l.r.SoftReference
56 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock);
57
58 _always_clear_soft_ref_policy = new AlwaysClearPolicy();
59 #if defined(COMPILER2) || INCLUDE_JVMCI
60 _default_soft_ref_policy = new LRUMaxHeapPolicy();
61 #else
62 _default_soft_ref_policy = new LRUCurrentHeapPolicy();
63 #endif
64 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
65 vm_exit_during_initialization("Could not allocate reference policy object");
66 }
67 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
68 RefDiscoveryPolicy == ReferentBasedDiscovery,
69 "Unrecognized RefDiscoveryPolicy");
70 }
71
72 void ReferenceProcessor::enable_discovery(bool check_no_refs) {
73 #ifdef ASSERT
74 // Verify that we're not currently discovering refs
75 assert(!_discovering_refs, "nested call?");
76
77 if (check_no_refs) {
78 // Verify that the discovered lists are empty
79 verify_no_references_recorded();
80 }
81 #endif // ASSERT
82
83 // Someone could have modified the value of the static
84 // field in the j.l.r.SoftReference class that holds the
85 // soft reference timestamp clock using reflection or
86 // Unsafe between GCs. Unconditionally update the static
87 // field in ReferenceProcessor here so that we use the new
88 // value during reference discovery.
89
90 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
91 _discovering_refs = true;
92 }
93
94 ReferenceProcessor::ReferenceProcessor(MemRegion span,
95 bool mt_processing,
96 uint mt_processing_degree,
97 bool mt_discovery,
98 uint mt_discovery_degree,
99 bool atomic_discovery,
100 BoolObjectClosure* is_alive_non_header) :
101 _discovering_refs(false),
102 _enqueuing_is_done(false),
103 _is_alive_non_header(is_alive_non_header),
104 _processing_is_mt(mt_processing),
105 _next_id(0)
106 {
107 _span = span;
108 _discovery_is_atomic = atomic_discovery;
109 _discovery_is_mt = mt_discovery;
110 _num_q = MAX2(1U, mt_processing_degree);
111 _max_num_q = MAX2(_num_q, mt_discovery_degree);
112 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
113 _max_num_q * number_of_subclasses_of_ref(), mtGC);
114
115 if (_discovered_refs == NULL) {
116 vm_exit_during_initialization("Could not allocated RefProc Array");
117 }
118 _discoveredSoftRefs = &_discovered_refs[0];
119 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q];
120 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q];
121 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q];
122
123 // Initialize all entries to NULL
124 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
125 _discovered_refs[i].set_head(NULL);
126 _discovered_refs[i].set_length(0);
127 }
128
129 setup_policy(false /* default soft ref policy */);
130 }
131
132 #ifndef PRODUCT
133 void ReferenceProcessor::verify_no_references_recorded() {
134 guarantee(!_discovering_refs, "Discovering refs?");
135 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
136 guarantee(_discovered_refs[i].is_empty(),
137 "Found non-empty discovered list");
138 }
139 }
140 #endif
141
142 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
143 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
144 if (UseCompressedOops) {
145 f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
146 } else {
147 f->do_oop((oop*)_discovered_refs[i].adr_head());
148 }
149 }
150 }
151
152 void ReferenceProcessor::update_soft_ref_master_clock() {
153 // Update (advance) the soft ref master clock field. This must be done
154 // after processing the soft ref list.
155
156 // We need a monotonically non-decreasing time in ms but
157 // os::javaTimeMillis() does not guarantee monotonicity.
158 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
159 jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
160 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
161
162 NOT_PRODUCT(
163 if (now < _soft_ref_timestamp_clock) {
164 log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT,
165 _soft_ref_timestamp_clock, now);
166 }
167 )
168 // The values of now and _soft_ref_timestamp_clock are set using
169 // javaTimeNanos(), which is guaranteed to be monotonically
170 // non-decreasing provided the underlying platform provides such
171 // a time source (and it is bug free).
172 // In product mode, however, protect ourselves from non-monotonicity.
173 if (now > _soft_ref_timestamp_clock) {
174 _soft_ref_timestamp_clock = now;
175 java_lang_ref_SoftReference::set_clock(now);
176 }
177 // Else leave clock stalled at its old value until time progresses
178 // past clock value.
179 }
180
181 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) {
182 size_t total = 0;
183 for (uint i = 0; i < _max_num_q; ++i) {
184 total += lists[i].length();
185 }
186 return total;
187 }
188
189 ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
190 BoolObjectClosure* is_alive,
191 OopClosure* keep_alive,
192 VoidClosure* complete_gc,
193 AbstractRefProcTaskExecutor* task_executor,
194 GCTimer* gc_timer) {
195
196 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
197 // Stop treating discovered references specially.
198 disable_discovery();
199
200 // If discovery was concurrent, someone could have modified
201 // the value of the static field in the j.l.r.SoftReference
202 // class that holds the soft reference timestamp clock using
203 // reflection or Unsafe between when discovery was enabled and
204 // now. Unconditionally update the static field in ReferenceProcessor
205 // here so that we use the new value during processing of the
206 // discovered soft refs.
207
208 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
209
210 ReferenceProcessorStats stats(
211 total_count(_discoveredSoftRefs),
212 total_count(_discoveredWeakRefs),
213 total_count(_discoveredFinalRefs),
214 total_count(_discoveredPhantomRefs));
215
216 // Soft references
217 {
218 GCTraceTime(Debug, gc, ref) tt("SoftReference", gc_timer);
219 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
220 is_alive, keep_alive, complete_gc, task_executor);
221 }
222
223 update_soft_ref_master_clock();
224
225 // Weak references
226 {
227 GCTraceTime(Debug, gc, ref) tt("WeakReference", gc_timer);
228 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
229 is_alive, keep_alive, complete_gc, task_executor);
230 }
231
232 // Final references
233 {
234 GCTraceTime(Debug, gc, ref) tt("FinalReference", gc_timer);
235 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
236 is_alive, keep_alive, complete_gc, task_executor);
237 }
238
239 // Phantom references
240 {
241 GCTraceTime(Debug, gc, ref) tt("PhantomReference", gc_timer);
242 process_discovered_reflist(_discoveredPhantomRefs, NULL, true,
243 is_alive, keep_alive, complete_gc, task_executor);
244 }
245
246 // Weak global JNI references. It would make more sense (semantically) to
247 // traverse these simultaneously with the regular weak references above, but
248 // that is not how the JDK1.2 specification is. See #4126360. Native code can
249 // thus use JNI weak references to circumvent the phantom references and
250 // resurrect a "post-mortem" object.
251 {
252 GCTraceTime(Debug, gc, ref) tt("JNI Weak Reference", gc_timer);
253 if (task_executor != NULL) {
254 task_executor->set_single_threaded_mode();
255 }
256 process_phaseJNI(is_alive, keep_alive, complete_gc);
257 }
258
259 log_debug(gc, ref)("Ref Counts: Soft: " SIZE_FORMAT " Weak: " SIZE_FORMAT " Final: " SIZE_FORMAT " Phantom: " SIZE_FORMAT,
260 stats.soft_count(), stats.weak_count(), stats.final_count(), stats.phantom_count());
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
292 template <class T>
293 bool enqueue_discovered_ref_helper(ReferenceProcessor* ref,
294 AbstractRefProcTaskExecutor* task_executor) {
295
296 // Remember old value of pending references list
297 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr();
298 T old_pending_list_value = *pending_list_addr;
299
300 // Enqueue references that are not made active again, and
301 // clear the decks for the next collection (cycle).
302 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor);
303 // Do the post-barrier on pending_list_addr missed in
304 // enqueue_discovered_reflist.
305 oopDesc::bs()->write_ref_field(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr));
306
307 // Stop treating discovered references specially.
308 ref->disable_discovery();
309
310 // Return true if new pending references were added
311 return old_pending_list_value != *pending_list_addr;
312 }
313
314 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
315 if (UseCompressedOops) {
316 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
317 } else {
318 return enqueue_discovered_ref_helper<oop>(this, task_executor);
319 }
320 }
321
322 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
323 HeapWord* pending_list_addr) {
324 // Given a list of refs linked through the "discovered" field
325 // (java.lang.ref.Reference.discovered), self-loop their "next" field
326 // thus distinguishing them from active References, then
327 // prepend them to the pending list.
328 //
329 // The Java threads will see the Reference objects linked together through
330 // the discovered field. Instead of trying to do the write barrier updates
331 // in all places in the reference processor where we manipulate the discovered
332 // field we make sure to do the barrier here where we anyway iterate through
333 // all linked Reference objects. Note that it is important to not dirty any
334 // cards during reference processing since this will cause card table
335 // verification to fail for G1.
336 log_develop_trace(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(&refs_list));
337
338 oop obj = NULL;
339 oop next_d = refs_list.head();
340 // Walk down the list, self-looping the next field
341 // so that the References are not considered active.
342 while (obj != next_d) {
343 obj = next_d;
344 assert(obj->is_instance(), "should be an instance object");
345 assert(InstanceKlass::cast(obj->klass())->is_reference_instance_klass(), "should be reference object");
346 next_d = java_lang_ref_Reference::discovered(obj);
347 log_develop_trace(gc, ref)(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, p2i(obj), p2i(next_d));
348 assert(java_lang_ref_Reference::next(obj) == NULL,
349 "Reference not active; should not be discovered");
350 // Self-loop next, so as to make Ref not active.
351 java_lang_ref_Reference::set_next_raw(obj, obj);
352 if (next_d != obj) {
353 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
354 } else {
355 // This is the last object.
356 // Swap refs_list into pending_list_addr and
357 // set obj's discovered to what we read from pending_list_addr.
358 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
359 // Need post-barrier on pending_list_addr. See enqueue_discovered_ref_helper() above.
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 HeapWord* pending_list_addr,
372 int n_queues)
373 : EnqueueTask(ref_processor, discovered_refs,
374 pending_list_addr, n_queues)
375 { }
376
377 virtual void work(unsigned int work_id) {
378 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
379 // Simplest first cut: static partitioning.
380 int index = work_id;
381 // The increment on "index" must correspond to the maximum number of queues
382 // (n_queues) with which that ReferenceProcessor was created. That
383 // is because of the "clever" way the discovered references lists were
384 // allocated and are indexed into.
385 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
386 for (int j = 0;
387 j < ReferenceProcessor::number_of_subclasses_of_ref();
388 j++, index += _n_queues) {
389 _ref_processor.enqueue_discovered_reflist(
390 _refs_lists[index], _pending_list_addr);
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(HeapWord* pending_list_addr,
399 AbstractRefProcTaskExecutor* task_executor) {
400 if (_processing_is_mt && task_executor != NULL) {
401 // Parallel code
402 RefProcEnqueueTask tsk(*this, _discovered_refs,
403 pending_list_addr, _max_num_q);
404 task_executor->execute(tsk);
405 } else {
406 // Serial code: call the parent class's implementation
407 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
408 enqueue_discovered_reflist(_discovered_refs[i], pending_list_addr);
409 _discovered_refs[i].set_head(NULL);
410 _discovered_refs[i].set_length(0);
411 }
412 }
413 }
414
415 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
416 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
417 oop discovered = java_lang_ref_Reference::discovered(_ref);
418 assert(_discovered_addr && discovered->is_oop_or_null(),
419 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
420 _next = discovered;
421 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
422 _referent = java_lang_ref_Reference::referent(_ref);
423 assert(Universe::heap()->is_in_reserved_or_null(_referent),
424 "Wrong oop found in java.lang.Reference object");
425 assert(allow_null_referent ?
426 _referent->is_oop_or_null()
427 : _referent->is_oop(),
428 "Expected an oop%s for referent field at " PTR_FORMAT,
429 (allow_null_referent ? " or NULL" : ""),
430 p2i(_referent));
431 }
432
433 void DiscoveredListIterator::remove() {
434 assert(_ref->is_oop(), "Dropping a bad reference");
435 oop_store_raw(_discovered_addr, NULL);
436
437 // First _prev_next ref actually points into DiscoveredList (gross).
438 oop new_next;
439 if (_next == _ref) {
440 // At the end of the list, we should make _prev point to itself.
441 // If _ref is the first ref, then _prev_next will be in the DiscoveredList,
442 // and _prev will be NULL.
443 new_next = _prev;
444 } else {
445 new_next = _next;
446 }
447 // Remove Reference object from discovered list. Note that G1 does not need a
448 // pre-barrier here because we know the Reference has already been found/marked,
449 // that's how it ended up in the discovered list in the first place.
450 oop_store_raw(_prev_next, new_next);
451 NOT_PRODUCT(_removed++);
452 _refs_list.dec_length(1);
453 }
454
455 void DiscoveredListIterator::clear_referent() {
456 oop_store_raw(_referent_addr, NULL);
457 }
458
459 // NOTE: process_phase*() are largely similar, and at a high level
460 // merely iterate over the extant list applying a predicate to
461 // each of its elements and possibly removing that element from the
462 // list and applying some further closures to that element.
463 // We should consider the possibility of replacing these
464 // process_phase*() methods by abstracting them into
465 // a single general iterator invocation that receives appropriate
466 // closures that accomplish this work.
467
468 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
469 // referents are not alive, but that should be kept alive for policy reasons.
470 // Keep alive the transitive closure of all such referents.
471 void
472 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
473 ReferencePolicy* policy,
474 BoolObjectClosure* is_alive,
475 OopClosure* keep_alive,
476 VoidClosure* complete_gc) {
477 assert(policy != NULL, "Must have a non-NULL policy");
478 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
479 // Decide which softly reachable refs should be kept alive.
480 while (iter.has_next()) {
481 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
482 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
483 if (referent_is_dead &&
484 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
485 log_develop_trace(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
486 p2i(iter.obj()), iter.obj()->klass()->internal_name());
487 // Remove Reference object from list
488 iter.remove();
489 // keep the referent around
490 iter.make_referent_alive();
491 iter.move_to_next();
492 } else {
493 iter.next();
494 }
495 }
496 // Close the reachable set
497 complete_gc->do_void();
498 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT,
499 iter.removed(), iter.processed(), p2i(&refs_list));
500 }
501
502 // Traverse the list and remove any Refs that are not active, or
503 // whose referents are either alive or NULL.
504 void
505 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
506 BoolObjectClosure* is_alive,
507 OopClosure* keep_alive) {
508 assert(discovery_is_atomic(), "Error");
509 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
510 while (iter.has_next()) {
511 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
512 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
513 assert(next == NULL, "Should not discover inactive Reference");
514 if (iter.is_referent_alive()) {
515 log_develop_trace(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
516 p2i(iter.obj()), iter.obj()->klass()->internal_name());
517 // The referent is reachable after all.
518 // Remove Reference object from list.
519 iter.remove();
520 // Update the referent pointer as necessary: Note that this
521 // should not entail any recursive marking because the
522 // referent must already have been traversed.
523 iter.make_referent_alive();
524 iter.move_to_next();
525 } else {
526 iter.next();
527 }
528 }
529 NOT_PRODUCT(
530 if (iter.processed() > 0) {
531 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
532 " Refs in discovered list " INTPTR_FORMAT,
533 iter.removed(), iter.processed(), p2i(&refs_list));
534 }
535 )
536 }
537
538 void
539 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
540 BoolObjectClosure* is_alive,
541 OopClosure* keep_alive,
542 VoidClosure* complete_gc) {
543 assert(!discovery_is_atomic(), "Error");
544 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
545 while (iter.has_next()) {
546 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
547 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
548 oop next = java_lang_ref_Reference::next(iter.obj());
549 if ((iter.referent() == NULL || iter.is_referent_alive() ||
550 next != NULL)) {
551 assert(next->is_oop_or_null(), "Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next));
552 // Remove Reference object from list
553 iter.remove();
554 // Trace the cohorts
555 iter.make_referent_alive();
556 if (UseCompressedOops) {
557 keep_alive->do_oop((narrowOop*)next_addr);
558 } else {
559 keep_alive->do_oop((oop*)next_addr);
560 }
561 iter.move_to_next();
562 } else {
563 iter.next();
564 }
565 }
566 // Now close the newly reachable set
567 complete_gc->do_void();
568 NOT_PRODUCT(
569 if (iter.processed() > 0) {
570 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
571 " Refs in discovered list " INTPTR_FORMAT,
572 iter.removed(), iter.processed(), p2i(&refs_list));
573 }
574 )
575 }
576
577 // Traverse the list and process the referents, by either
578 // clearing them or keeping them (and their reachable
579 // closure) alive.
580 void
581 ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
582 bool clear_referent,
583 BoolObjectClosure* is_alive,
584 OopClosure* keep_alive,
585 VoidClosure* complete_gc) {
586 ResourceMark rm;
587 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
588 while (iter.has_next()) {
589 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
590 if (clear_referent) {
591 // NULL out referent pointer
592 iter.clear_referent();
593 } else {
594 // keep the referent around
595 iter.make_referent_alive();
596 }
597 log_develop_trace(gc, ref)("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
598 clear_referent ? "cleared " : "", p2i(iter.obj()), iter.obj()->klass()->internal_name());
599 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
600 iter.next();
601 }
602 // Close the reachable set
603 complete_gc->do_void();
604 }
605
606 void
607 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
608 oop obj = NULL;
609 oop next = refs_list.head();
610 while (next != obj) {
611 obj = next;
612 next = java_lang_ref_Reference::discovered(obj);
613 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
614 }
615 refs_list.set_head(NULL);
616 refs_list.set_length(0);
617 }
618
619 void ReferenceProcessor::abandon_partial_discovery() {
620 // loop over the lists
621 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
622 if ((i % _max_num_q) == 0) {
623 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i));
624 }
625 clear_discovered_references(_discovered_refs[i]);
626 }
627 }
628
629 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
630 public:
631 RefProcPhase1Task(ReferenceProcessor& ref_processor,
632 DiscoveredList refs_lists[],
633 ReferencePolicy* policy,
634 bool marks_oops_alive)
635 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
636 _policy(policy)
637 { }
638 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
639 OopClosure& keep_alive,
640 VoidClosure& complete_gc)
641 {
642 _ref_processor.process_phase1(_refs_lists[i], _policy,
643 &is_alive, &keep_alive, &complete_gc);
644 }
645 private:
646 ReferencePolicy* _policy;
647 };
648
649 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
650 public:
651 RefProcPhase2Task(ReferenceProcessor& ref_processor,
652 DiscoveredList refs_lists[],
653 bool marks_oops_alive)
654 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
655 { }
656 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
657 OopClosure& keep_alive,
658 VoidClosure& complete_gc)
659 {
660 _ref_processor.process_phase2(_refs_lists[i],
661 &is_alive, &keep_alive, &complete_gc);
662 }
663 };
664
665 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
666 public:
667 RefProcPhase3Task(ReferenceProcessor& ref_processor,
668 DiscoveredList refs_lists[],
669 bool clear_referent,
670 bool marks_oops_alive)
671 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
672 _clear_referent(clear_referent)
673 { }
674 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
675 OopClosure& keep_alive,
676 VoidClosure& complete_gc)
677 {
678 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
679 &is_alive, &keep_alive, &complete_gc);
680 }
681 private:
682 bool _clear_referent;
683 };
684
685 #ifndef PRODUCT
686 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], size_t total_refs) {
687 if (!log_is_enabled(Trace, gc, ref)) {
688 return;
689 }
690
691 stringStream st;
692 for (uint i = 0; i < _max_num_q; ++i) {
693 st.print(SIZE_FORMAT " ", ref_lists[i].length());
694 }
695 log_develop_trace(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs);
696 }
697 #endif
698
699 // Balances reference queues.
700 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
701 // queues[0, 1, ..., _num_q-1] because only the first _num_q
702 // corresponding to the active workers will be processed.
703 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
704 {
705 // calculate total length
706 size_t total_refs = 0;
707 log_develop_trace(gc, ref)("Balance ref_lists ");
708
709 for (uint i = 0; i < _max_num_q; ++i) {
710 total_refs += ref_lists[i].length();
711 }
712 log_reflist_counts(ref_lists, total_refs);
713 size_t avg_refs = total_refs / _num_q + 1;
714 uint to_idx = 0;
715 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) {
716 bool move_all = false;
717 if (from_idx >= _num_q) {
718 move_all = ref_lists[from_idx].length() > 0;
719 }
720 while ((ref_lists[from_idx].length() > avg_refs) ||
721 move_all) {
722 assert(to_idx < _num_q, "Sanity Check!");
723 if (ref_lists[to_idx].length() < avg_refs) {
724 // move superfluous refs
725 size_t refs_to_move;
726 // Move all the Ref's if the from queue will not be processed.
727 if (move_all) {
728 refs_to_move = MIN2(ref_lists[from_idx].length(),
729 avg_refs - ref_lists[to_idx].length());
730 } else {
731 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
732 avg_refs - ref_lists[to_idx].length());
733 }
734
735 assert(refs_to_move > 0, "otherwise the code below will fail");
736
737 oop move_head = ref_lists[from_idx].head();
738 oop move_tail = move_head;
739 oop new_head = move_head;
740 // find an element to split the list on
741 for (size_t j = 0; j < refs_to_move; ++j) {
742 move_tail = new_head;
743 new_head = java_lang_ref_Reference::discovered(new_head);
744 }
745
746 // Add the chain to the to list.
747 if (ref_lists[to_idx].head() == NULL) {
748 // to list is empty. Make a loop at the end.
749 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
750 } else {
751 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
752 }
753 ref_lists[to_idx].set_head(move_head);
754 ref_lists[to_idx].inc_length(refs_to_move);
755
756 // Remove the chain from the from list.
757 if (move_tail == new_head) {
758 // We found the end of the from list.
759 ref_lists[from_idx].set_head(NULL);
760 } else {
761 ref_lists[from_idx].set_head(new_head);
762 }
763 ref_lists[from_idx].dec_length(refs_to_move);
764 if (ref_lists[from_idx].length() == 0) {
765 break;
766 }
767 } else {
768 to_idx = (to_idx + 1) % _num_q;
769 }
770 }
771 }
772 #ifdef ASSERT
773 size_t balanced_total_refs = 0;
774 for (uint i = 0; i < _max_num_q; ++i) {
775 balanced_total_refs += ref_lists[i].length();
776 }
777 log_reflist_counts(ref_lists, balanced_total_refs);
778 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
779 #endif
780 }
781
782 void ReferenceProcessor::balance_all_queues() {
783 balance_queues(_discoveredSoftRefs);
784 balance_queues(_discoveredWeakRefs);
785 balance_queues(_discoveredFinalRefs);
786 balance_queues(_discoveredPhantomRefs);
787 }
788
789 void ReferenceProcessor::process_discovered_reflist(
790 DiscoveredList refs_lists[],
791 ReferencePolicy* policy,
792 bool clear_referent,
793 BoolObjectClosure* is_alive,
794 OopClosure* keep_alive,
795 VoidClosure* complete_gc,
796 AbstractRefProcTaskExecutor* task_executor)
797 {
798 bool mt_processing = task_executor != NULL && _processing_is_mt;
799 // If discovery used MT and a dynamic number of GC threads, then
800 // the queues must be balanced for correctness if fewer than the
801 // maximum number of queues were used. The number of queue used
802 // during discovery may be different than the number to be used
803 // for processing so don't depend of _num_q < _max_num_q as part
804 // of the test.
805 bool must_balance = _discovery_is_mt;
806
807 if ((mt_processing && ParallelRefProcBalancingEnabled) ||
808 must_balance) {
809 balance_queues(refs_lists);
810 }
811
812 // Phase 1 (soft refs only):
813 // . Traverse the list and remove any SoftReferences whose
814 // referents are not alive, but that should be kept alive for
815 // policy reasons. Keep alive the transitive closure of all
816 // such referents.
817 if (policy != NULL) {
818 if (mt_processing) {
819 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
820 task_executor->execute(phase1);
821 } else {
822 for (uint i = 0; i < _max_num_q; i++) {
823 process_phase1(refs_lists[i], policy,
824 is_alive, keep_alive, complete_gc);
825 }
826 }
827 } else { // policy == NULL
828 assert(refs_lists != _discoveredSoftRefs,
829 "Policy must be specified for soft references.");
830 }
831
832 // Phase 2:
833 // . Traverse the list and remove any refs whose referents are alive.
834 if (mt_processing) {
835 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
836 task_executor->execute(phase2);
837 } else {
838 for (uint i = 0; i < _max_num_q; i++) {
839 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
840 }
841 }
842
843 // Phase 3:
844 // . Traverse the list and process referents as appropriate.
845 if (mt_processing) {
846 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
847 task_executor->execute(phase3);
848 } else {
849 for (uint i = 0; i < _max_num_q; i++) {
850 process_phase3(refs_lists[i], clear_referent,
851 is_alive, keep_alive, complete_gc);
852 }
853 }
854 }
855
856 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
857 uint id = 0;
858 // Determine the queue index to use for this object.
859 if (_discovery_is_mt) {
860 // During a multi-threaded discovery phase,
861 // each thread saves to its "own" list.
862 Thread* thr = Thread::current();
863 id = thr->as_Worker_thread()->id();
864 } else {
865 // single-threaded discovery, we save in round-robin
866 // fashion to each of the lists.
867 if (_processing_is_mt) {
868 id = next_id();
869 }
870 }
871 assert(id < _max_num_q, "Id is out-of-bounds (call Freud?)");
872
873 // Get the discovered queue to which we will add
874 DiscoveredList* list = NULL;
875 switch (rt) {
876 case REF_OTHER:
877 // Unknown reference type, no special treatment
878 break;
879 case REF_SOFT:
880 list = &_discoveredSoftRefs[id];
881 break;
882 case REF_WEAK:
883 list = &_discoveredWeakRefs[id];
884 break;
885 case REF_FINAL:
886 list = &_discoveredFinalRefs[id];
887 break;
888 case REF_PHANTOM:
889 list = &_discoveredPhantomRefs[id];
890 break;
891 case REF_NONE:
892 // we should not reach here if we are an InstanceRefKlass
893 default:
894 ShouldNotReachHere();
895 }
896 log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list));
897 return list;
898 }
899
900 inline void
901 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
902 oop obj,
903 HeapWord* discovered_addr) {
904 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
905 // First we must make sure this object is only enqueued once. CAS in a non null
906 // discovered_addr.
907 oop current_head = refs_list.head();
908 // The last ref must have its discovered field pointing to itself.
909 oop next_discovered = (current_head != NULL) ? current_head : obj;
910
911 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr,
912 NULL);
913 if (retest == NULL) {
914 // This thread just won the right to enqueue the object.
915 // We have separate lists for enqueueing, so no synchronization
916 // is necessary.
917 refs_list.set_head(obj);
918 refs_list.inc_length(1);
919
920 log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
921 p2i(obj), obj->klass()->internal_name());
922 } else {
923 // If retest was non NULL, another thread beat us to it:
924 // The reference has already been discovered...
925 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
926 p2i(obj), obj->klass()->internal_name());
927 }
928 }
929
930 #ifndef PRODUCT
931 // Non-atomic (i.e. concurrent) discovery might allow us
932 // to observe j.l.References with NULL referents, being those
933 // cleared concurrently by mutators during (or after) discovery.
934 void ReferenceProcessor::verify_referent(oop obj) {
935 bool da = discovery_is_atomic();
936 oop referent = java_lang_ref_Reference::referent(obj);
937 assert(da ? referent->is_oop() : referent->is_oop_or_null(),
938 "Bad referent " INTPTR_FORMAT " found in Reference "
939 INTPTR_FORMAT " during %satomic discovery ",
940 p2i(referent), p2i(obj), da ? "" : "non-");
941 }
942 #endif
943
944 // We mention two of several possible choices here:
945 // #0: if the reference object is not in the "originating generation"
946 // (or part of the heap being collected, indicated by our "span"
947 // we don't treat it specially (i.e. we scan it as we would
948 // a normal oop, treating its references as strong references).
949 // This means that references can't be discovered unless their
950 // referent is also in the same span. This is the simplest,
951 // most "local" and most conservative approach, albeit one
952 // that may cause weak references to be enqueued least promptly.
953 // We call this choice the "ReferenceBasedDiscovery" policy.
954 // #1: the reference object may be in any generation (span), but if
955 // the referent is in the generation (span) being currently collected
956 // then we can discover the reference object, provided
957 // the object has not already been discovered by
958 // a different concurrently running collector (as may be the
959 // case, for instance, if the reference object is in CMS and
960 // the referent in DefNewGeneration), and provided the processing
961 // of this reference object by the current collector will
962 // appear atomic to every other collector in the system.
963 // (Thus, for instance, a concurrent collector may not
964 // discover references in other generations even if the
965 // referent is in its own generation). This policy may,
966 // in certain cases, enqueue references somewhat sooner than
967 // might Policy #0 above, but at marginally increased cost
968 // and complexity in processing these references.
969 // We call this choice the "RefeferentBasedDiscovery" policy.
970 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
971 // Make sure we are discovering refs (rather than processing discovered refs).
972 if (!_discovering_refs || !RegisterReferences) {
973 return false;
974 }
975 // We only discover active references.
976 oop next = java_lang_ref_Reference::next(obj);
977 if (next != NULL) { // Ref is no longer active
978 return false;
979 }
980
981 HeapWord* obj_addr = (HeapWord*)obj;
982 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
983 !_span.contains(obj_addr)) {
984 // Reference is not in the originating generation;
985 // don't treat it specially (i.e. we want to scan it as a normal
986 // object with strong references).
987 return false;
988 }
989
990 // We only discover references whose referents are not (yet)
991 // known to be strongly reachable.
992 if (is_alive_non_header() != NULL) {
993 verify_referent(obj);
994 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
995 return false; // referent is reachable
996 }
997 }
998 if (rt == REF_SOFT) {
999 // For soft refs we can decide now if these are not
1000 // current candidates for clearing, in which case we
1001 // can mark through them now, rather than delaying that
1002 // to the reference-processing phase. Since all current
1003 // time-stamp policies advance the soft-ref clock only
1004 // at a full collection cycle, this is always currently
1005 // accurate.
1006 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
1007 return false;
1008 }
1009 }
1010
1011 ResourceMark rm; // Needed for tracing.
1012
1013 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
1014 const oop discovered = java_lang_ref_Reference::discovered(obj);
1015 assert(discovered->is_oop_or_null(), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
1016 if (discovered != NULL) {
1017 // The reference has already been discovered...
1018 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
1019 p2i(obj), obj->klass()->internal_name());
1020 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1021 // assumes that an object is not processed twice;
1022 // if it's been already discovered it must be on another
1023 // generation's discovered list; so we won't discover it.
1024 return false;
1025 } else {
1026 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1027 "Unrecognized policy");
1028 // Check assumption that an object is not potentially
1029 // discovered twice except by concurrent collectors that potentially
1030 // trace the same Reference object twice.
1031 assert(UseConcMarkSweepGC || UseG1GC,
1032 "Only possible with a concurrent marking collector");
1033 return true;
1034 }
1035 }
1036
1037 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1038 verify_referent(obj);
1039 // Discover if and only if EITHER:
1040 // .. reference is in our span, OR
1041 // .. we are an atomic collector and referent is in our span
1042 if (_span.contains(obj_addr) ||
1043 (discovery_is_atomic() &&
1044 _span.contains(java_lang_ref_Reference::referent(obj)))) {
1045 // should_enqueue = true;
1046 } else {
1047 return false;
1048 }
1049 } else {
1050 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1051 _span.contains(obj_addr), "code inconsistency");
1052 }
1053
1054 // Get the right type of discovered queue head.
1055 DiscoveredList* list = get_discovered_list(rt);
1056 if (list == NULL) {
1057 return false; // nothing special needs to be done
1058 }
1059
1060 if (_discovery_is_mt) {
1061 add_to_discovered_list_mt(*list, obj, discovered_addr);
1062 } else {
1063 // We do a raw store here: the field will be visited later when processing
1064 // the discovered references.
1065 oop current_head = list->head();
1066 // The last ref must have its discovered field pointing to itself.
1067 oop next_discovered = (current_head != NULL) ? current_head : obj;
1068
1069 assert(discovered == NULL, "control point invariant");
1070 oop_store_raw(discovered_addr, next_discovered);
1071 list->set_head(obj);
1072 list->inc_length(1);
1073
1074 log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name());
1075 }
1076 assert(obj->is_oop(), "Discovered a bad reference");
1077 verify_referent(obj);
1078 return true;
1079 }
1080
1081 // Preclean the discovered references by removing those
1082 // whose referents are alive, and by marking from those that
1083 // are not active. These lists can be handled here
1084 // in any order and, indeed, concurrently.
1085 void ReferenceProcessor::preclean_discovered_references(
1086 BoolObjectClosure* is_alive,
1087 OopClosure* keep_alive,
1088 VoidClosure* complete_gc,
1089 YieldClosure* yield,
1090 GCTimer* gc_timer) {
1091
1092 // Soft references
1093 {
1094 GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer);
1095 for (uint i = 0; i < _max_num_q; i++) {
1096 if (yield->should_return()) {
1097 return;
1098 }
1099 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1100 keep_alive, complete_gc, yield);
1101 }
1102 }
1103
1104 // Weak references
1105 {
1106 GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer);
1107 for (uint i = 0; i < _max_num_q; i++) {
1108 if (yield->should_return()) {
1109 return;
1110 }
1111 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1112 keep_alive, complete_gc, yield);
1113 }
1114 }
1115
1116 // Final references
1117 {
1118 GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer);
1119 for (uint i = 0; i < _max_num_q; i++) {
1120 if (yield->should_return()) {
1121 return;
1122 }
1123 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1124 keep_alive, complete_gc, yield);
1125 }
1126 }
1127
1128 // Phantom references
1129 {
1130 GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer);
1131 for (uint i = 0; i < _max_num_q; i++) {
1132 if (yield->should_return()) {
1133 return;
1134 }
1135 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1136 keep_alive, complete_gc, yield);
1137 }
1138 }
1139 }
1140
1141 // Walk the given discovered ref list, and remove all reference objects
1142 // whose referents are still alive, whose referents are NULL or which
1143 // are not active (have a non-NULL next field). NOTE: When we are
1144 // thus precleaning the ref lists (which happens single-threaded today),
1145 // we do not disable refs discovery to honor the correct semantics of
1146 // java.lang.Reference. As a result, we need to be careful below
1147 // that ref removal steps interleave safely with ref discovery steps
1148 // (in this thread).
1149 void
1150 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1151 BoolObjectClosure* is_alive,
1152 OopClosure* keep_alive,
1153 VoidClosure* complete_gc,
1154 YieldClosure* yield) {
1155 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1156 while (iter.has_next()) {
1157 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1158 oop obj = iter.obj();
1159 oop next = java_lang_ref_Reference::next(obj);
1160 if (iter.referent() == NULL || iter.is_referent_alive() ||
1161 next != NULL) {
1162 // The referent has been cleared, or is alive, or the Reference is not
1163 // active; we need to trace and mark its cohort.
1164 log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1165 p2i(iter.obj()), iter.obj()->klass()->internal_name());
1166 // Remove Reference object from list
1167 iter.remove();
1168 // Keep alive its cohort.
1169 iter.make_referent_alive();
1170 if (UseCompressedOops) {
1171 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
1172 keep_alive->do_oop(next_addr);
1173 } else {
1174 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
1175 keep_alive->do_oop(next_addr);
1176 }
1177 iter.move_to_next();
1178 } else {
1179 iter.next();
1180 }
1181 }
1182 // Close the reachable set
1183 complete_gc->do_void();
1184
1185 NOT_PRODUCT(
1186 if (iter.processed() > 0) {
1187 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT,
1188 iter.removed(), iter.processed(), p2i(&refs_list));
1189 }
1190 )
1191 }
1192
1193 const char* ReferenceProcessor::list_name(uint i) {
1194 assert(i <= _max_num_q * number_of_subclasses_of_ref(),
1195 "Out of bounds index");
1196
1197 int j = i / _max_num_q;
1198 switch (j) {
1199 case 0: return "SoftRef";
1200 case 1: return "WeakRef";
1201 case 2: return "FinalRef";
1202 case 3: return "PhantomRef";
1203 }
1204 ShouldNotReachHere();
1205 return NULL;
1206 }
1207