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 "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 defined(COMPILER2) || INCLUDE_JVMCI
61 _default_soft_ref_policy = new LRUMaxHeapPolicy();
62 #else
63 _default_soft_ref_policy = new LRUCurrentHeapPolicy();
64 #endif
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 setup_policy(false /* default soft ref policy */);
131 }
132
133 #ifndef PRODUCT
134 void ReferenceProcessor::verify_no_references_recorded() {
135 guarantee(!_discovering_refs, "Discovering refs?");
136 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
137 guarantee(_discovered_refs[i].is_empty(),
138 "Found non-empty discovered list");
139 }
140 }
141 #endif
142
143 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
144 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
145 if (UseCompressedOops) {
146 f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
147 } else {
148 f->do_oop((oop*)_discovered_refs[i].adr_head());
149 }
150 }
151 }
152
153 void ReferenceProcessor::update_soft_ref_master_clock() {
154 // Update (advance) the soft ref master clock field. This must be done
155 // after processing the soft ref list.
156
157 // We need a monotonically non-decreasing time in ms but
158 // os::javaTimeMillis() does not guarantee monotonicity.
159 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
160 jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
161 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
162
163 NOT_PRODUCT(
164 if (now < _soft_ref_timestamp_clock) {
165 log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT,
166 _soft_ref_timestamp_clock, now);
167 }
168 )
169 // The values of now and _soft_ref_timestamp_clock are set using
170 // javaTimeNanos(), which is guaranteed to be monotonically
171 // non-decreasing provided the underlying platform provides such
172 // a time source (and it is bug free).
173 // In product mode, however, protect ourselves from non-monotonicity.
174 if (now > _soft_ref_timestamp_clock) {
175 _soft_ref_timestamp_clock = now;
176 java_lang_ref_SoftReference::set_clock(now);
177 }
178 // Else leave clock stalled at its old value until time progresses
179 // past clock value.
180 }
181
182 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) {
183 size_t total = 0;
184 for (uint i = 0; i < _max_num_q; ++i) {
185 total += lists[i].length();
186 }
187 return total;
188 }
189
190 ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
191 BoolObjectClosure* is_alive,
192 OopClosure* keep_alive,
193 VoidClosure* complete_gc,
194 AbstractRefProcTaskExecutor* task_executor,
195 GCTimer* gc_timer) {
196
197 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
198 // Stop treating discovered references specially.
199 disable_discovery();
200
201 // If discovery was concurrent, someone could have modified
202 // the value of the static field in the j.l.r.SoftReference
203 // class that holds the soft reference timestamp clock using
204 // reflection or Unsafe between when discovery was enabled and
205 // now. Unconditionally update the static field in ReferenceProcessor
206 // here so that we use the new value during processing of the
207 // discovered soft refs.
208
209 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
210
211 ReferenceProcessorStats stats(
212 total_count(_discoveredSoftRefs),
213 total_count(_discoveredWeakRefs),
214 total_count(_discoveredFinalRefs),
215 total_count(_discoveredPhantomRefs));
216
217 // Soft references
218 {
219 GCTraceTime(Debug, gc, ref) tt("SoftReference", gc_timer);
220 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
221 is_alive, keep_alive, complete_gc, task_executor);
222 }
223
224 update_soft_ref_master_clock();
225
226 // Weak references
227 {
228 GCTraceTime(Debug, gc, ref) tt("WeakReference", gc_timer);
229 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
230 is_alive, keep_alive, complete_gc, task_executor);
231 }
232
233 // Final references
234 {
235 GCTraceTime(Debug, gc, ref) tt("FinalReference", gc_timer);
236 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
237 is_alive, keep_alive, complete_gc, task_executor);
238 }
239
240 // Phantom references
241 {
242 GCTraceTime(Debug, gc, ref) tt("PhantomReference", gc_timer);
243 process_discovered_reflist(_discoveredPhantomRefs, NULL, true,
244 is_alive, keep_alive, complete_gc, task_executor);
245 }
246
247 // Weak global JNI references. It would make more sense (semantically) to
248 // traverse these simultaneously with the regular weak references above, but
249 // that is not how the JDK1.2 specification is. See #4126360. Native code can
250 // thus use JNI weak references to circumvent the phantom references and
251 // resurrect a "post-mortem" object.
252 {
253 GCTraceTime(Debug, gc, ref) tt("JNI Weak Reference", gc_timer);
254 if (task_executor != NULL) {
255 task_executor->set_single_threaded_mode();
256 }
257 process_phaseJNI(is_alive, keep_alive, complete_gc);
258 }
259
260 log_debug(gc, ref)("Ref Counts: Soft: " SIZE_FORMAT " Weak: " SIZE_FORMAT " Final: " SIZE_FORMAT " Phantom: " SIZE_FORMAT,
261 stats.soft_count(), stats.weak_count(), stats.final_count(), stats.phantom_count());
262 log_develop_trace(gc, ref)("JNI Weak Reference count: " SIZE_FORMAT, count_jni_refs());
263
264 return stats;
265 }
266
267 #ifndef PRODUCT
268 // Calculate the number of jni handles.
269 size_t ReferenceProcessor::count_jni_refs() {
270 class AlwaysAliveClosure: public BoolObjectClosure {
271 public:
272 virtual bool do_object_b(oop obj) { return true; }
273 };
274
275 class CountHandleClosure: public OopClosure {
276 private:
277 size_t _count;
278 public:
279 CountHandleClosure(): _count(0) {}
280 void do_oop(oop* unused) { _count++; }
281 void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
282 size_t count() { return _count; }
283 };
284 CountHandleClosure global_handle_count;
285 AlwaysAliveClosure always_alive;
286 JNIHandles::weak_oops_do(&always_alive, &global_handle_count);
287 return global_handle_count.count();
288 }
289 #endif
290
291 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
292 OopClosure* keep_alive,
293 VoidClosure* complete_gc) {
294 JNIHandles::weak_oops_do(is_alive, keep_alive);
295 complete_gc->do_void();
296 }
297
298
299 template <class T>
300 bool enqueue_discovered_ref_helper(ReferenceProcessor* ref,
301 AbstractRefProcTaskExecutor* task_executor) {
302
303 // Remember old value of pending references list
304 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr();
305 T old_pending_list_value = *pending_list_addr;
306
307 // Enqueue references that are not made active again, and
308 // clear the decks for the next collection (cycle).
309 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor);
310 // Do the post-barrier on pending_list_addr missed in
311 // enqueue_discovered_reflist.
312 oopDesc::bs()->write_ref_field(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr));
313
314 // Stop treating discovered references specially.
315 ref->disable_discovery();
316
317 // Return true if new pending references were added
318 return old_pending_list_value != *pending_list_addr;
319 }
320
321 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
322 if (UseCompressedOops) {
323 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
324 } else {
325 return enqueue_discovered_ref_helper<oop>(this, task_executor);
326 }
327 }
328
329 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
330 HeapWord* pending_list_addr) {
331 // Given a list of refs linked through the "discovered" field
332 // (java.lang.ref.Reference.discovered), self-loop their "next" field
333 // thus distinguishing them from active References, then
334 // prepend them to the pending list.
335 //
336 // The Java threads will see the Reference objects linked together through
337 // the discovered field. Instead of trying to do the write barrier updates
338 // in all places in the reference processor where we manipulate the discovered
339 // field we make sure to do the barrier here where we anyway iterate through
340 // all linked Reference objects. Note that it is important to not dirty any
341 // cards during reference processing since this will cause card table
342 // verification to fail for G1.
343 log_develop_trace(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(&refs_list));
344
345 oop obj = NULL;
346 oop next_d = refs_list.head();
347 // Walk down the list, self-looping the next field
348 // so that the References are not considered active.
349 while (obj != next_d) {
350 obj = next_d;
351 assert(obj->is_instance(), "should be an instance object");
352 assert(InstanceKlass::cast(obj->klass())->is_reference_instance_klass(), "should be reference object");
353 next_d = java_lang_ref_Reference::discovered(obj);
354 log_develop_trace(gc, ref)(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, p2i(obj), p2i(next_d));
355 assert(java_lang_ref_Reference::next(obj) == NULL,
356 "Reference not active; should not be discovered");
357 // Self-loop next, so as to make Ref not active.
358 java_lang_ref_Reference::set_next_raw(obj, obj);
359 if (next_d != obj) {
360 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
361 } else {
362 // This is the last object.
363 // Swap refs_list into pending_list_addr and
364 // set obj's discovered to what we read from pending_list_addr.
365 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
366 // Need post-barrier on pending_list_addr. See enqueue_discovered_ref_helper() above.
367 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
368 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
369 }
370 }
371 }
372
373 // Parallel enqueue task
374 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
375 public:
376 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
377 DiscoveredList discovered_refs[],
378 HeapWord* pending_list_addr,
379 int n_queues)
380 : EnqueueTask(ref_processor, discovered_refs,
381 pending_list_addr, n_queues)
382 { }
383
384 virtual void work(unsigned int work_id) {
385 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
386 // Simplest first cut: static partitioning.
387 int index = work_id;
388 // The increment on "index" must correspond to the maximum number of queues
389 // (n_queues) with which that ReferenceProcessor was created. That
390 // is because of the "clever" way the discovered references lists were
391 // allocated and are indexed into.
392 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
393 for (int j = 0;
394 j < ReferenceProcessor::number_of_subclasses_of_ref();
395 j++, index += _n_queues) {
396 _ref_processor.enqueue_discovered_reflist(
397 _refs_lists[index], _pending_list_addr);
398 _refs_lists[index].set_head(NULL);
399 _refs_lists[index].set_length(0);
400 }
401 }
402 };
403
404 // Enqueue references that are not made active again
405 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr,
406 AbstractRefProcTaskExecutor* task_executor) {
407 if (_processing_is_mt && task_executor != NULL) {
408 // Parallel code
409 RefProcEnqueueTask tsk(*this, _discovered_refs,
410 pending_list_addr, _max_num_q);
411 task_executor->execute(tsk);
412 } else {
413 // Serial code: call the parent class's implementation
414 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
415 enqueue_discovered_reflist(_discovered_refs[i], pending_list_addr);
416 _discovered_refs[i].set_head(NULL);
417 _discovered_refs[i].set_length(0);
418 }
419 }
420 }
421
422 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
423 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
424 oop discovered = java_lang_ref_Reference::discovered(_ref);
425 assert(_discovered_addr && discovered->is_oop_or_null(),
426 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
427 _next = discovered;
428 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
429 _referent = java_lang_ref_Reference::referent(_ref);
430 assert(Universe::heap()->is_in_reserved_or_null(_referent),
431 "Wrong oop found in java.lang.Reference object");
432 assert(allow_null_referent ?
433 _referent->is_oop_or_null()
434 : _referent->is_oop(),
435 "Expected an oop%s for referent field at " PTR_FORMAT,
436 (allow_null_referent ? " or NULL" : ""),
437 p2i(_referent));
438 }
439
440 void DiscoveredListIterator::remove() {
441 assert(_ref->is_oop(), "Dropping a bad reference");
442 oop_store_raw(_discovered_addr, NULL);
443
444 // First _prev_next ref actually points into DiscoveredList (gross).
445 oop new_next;
446 if (_next == _ref) {
447 // At the end of the list, we should make _prev point to itself.
448 // If _ref is the first ref, then _prev_next will be in the DiscoveredList,
449 // and _prev will be NULL.
450 new_next = _prev;
451 } else {
452 new_next = _next;
453 }
454 // Remove Reference object from discovered list. Note that G1 does not need a
455 // pre-barrier here because we know the Reference has already been found/marked,
456 // that's how it ended up in the discovered list in the first place.
457 oop_store_raw(_prev_next, new_next);
458 NOT_PRODUCT(_removed++);
459 _refs_list.dec_length(1);
460 }
461
462 void DiscoveredListIterator::clear_referent() {
463 oop_store_raw(_referent_addr, NULL);
464 }
465
466 // NOTE: process_phase*() are largely similar, and at a high level
467 // merely iterate over the extant list applying a predicate to
468 // each of its elements and possibly removing that element from the
469 // list and applying some further closures to that element.
470 // We should consider the possibility of replacing these
471 // process_phase*() methods by abstracting them into
472 // a single general iterator invocation that receives appropriate
473 // closures that accomplish this work.
474
475 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
476 // referents are not alive, but that should be kept alive for policy reasons.
477 // Keep alive the transitive closure of all such referents.
478 void
479 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
480 ReferencePolicy* policy,
481 BoolObjectClosure* is_alive,
482 OopClosure* keep_alive,
483 VoidClosure* complete_gc) {
484 assert(policy != NULL, "Must have a non-NULL policy");
485 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
486 // Decide which softly reachable refs should be kept alive.
487 while (iter.has_next()) {
488 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
489 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
490 if (referent_is_dead &&
491 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
492 log_develop_trace(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
493 p2i(iter.obj()), iter.obj()->klass()->internal_name());
494 // Remove Reference object from list
495 iter.remove();
496 // keep the referent around
497 iter.make_referent_alive();
498 iter.move_to_next();
499 } else {
500 iter.next();
501 }
502 }
503 // Close the reachable set
504 complete_gc->do_void();
505 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT,
506 iter.removed(), iter.processed(), p2i(&refs_list));
507 }
508
509 // Traverse the list and remove any Refs that are not active, or
510 // whose referents are either alive or NULL.
511 void
512 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
513 BoolObjectClosure* is_alive,
514 OopClosure* keep_alive) {
515 assert(discovery_is_atomic(), "Error");
516 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
517 while (iter.has_next()) {
518 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
519 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
520 assert(next == NULL, "Should not discover inactive Reference");
521 if (iter.is_referent_alive()) {
522 log_develop_trace(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
523 p2i(iter.obj()), iter.obj()->klass()->internal_name());
524 // The referent is reachable after all.
525 // Remove Reference object from list.
526 iter.remove();
527 // Update the referent pointer as necessary: Note that this
528 // should not entail any recursive marking because the
529 // referent must already have been traversed.
530 iter.make_referent_alive();
531 iter.move_to_next();
532 } else {
533 iter.next();
534 }
535 }
536 NOT_PRODUCT(
537 if (iter.processed() > 0) {
538 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
539 " Refs in discovered list " INTPTR_FORMAT,
540 iter.removed(), iter.processed(), p2i(&refs_list));
541 }
542 )
543 }
544
545 void
546 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
547 BoolObjectClosure* is_alive,
548 OopClosure* keep_alive,
549 VoidClosure* complete_gc) {
550 assert(!discovery_is_atomic(), "Error");
551 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
552 while (iter.has_next()) {
553 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
554 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
555 oop next = java_lang_ref_Reference::next(iter.obj());
556 if ((iter.referent() == NULL || iter.is_referent_alive() ||
557 next != NULL)) {
558 assert(next->is_oop_or_null(), "Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next));
559 // Remove Reference object from list
560 iter.remove();
561 // Trace the cohorts
562 iter.make_referent_alive();
563 if (UseCompressedOops) {
564 keep_alive->do_oop((narrowOop*)next_addr);
565 } else {
566 keep_alive->do_oop((oop*)next_addr);
567 }
568 iter.move_to_next();
569 } else {
570 iter.next();
571 }
572 }
573 // Now close the newly reachable set
574 complete_gc->do_void();
575 NOT_PRODUCT(
576 if (iter.processed() > 0) {
577 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
578 " Refs in discovered list " INTPTR_FORMAT,
579 iter.removed(), iter.processed(), p2i(&refs_list));
580 }
581 )
582 }
583
584 // Traverse the list and process the referents, by either
585 // clearing them or keeping them (and their reachable
586 // closure) alive.
587 void
588 ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
589 bool clear_referent,
590 BoolObjectClosure* is_alive,
591 OopClosure* keep_alive,
592 VoidClosure* complete_gc) {
593 ResourceMark rm;
594 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
595 while (iter.has_next()) {
596 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
597 if (clear_referent) {
598 // NULL out referent pointer
599 iter.clear_referent();
600 } else {
601 // keep the referent around
602 iter.make_referent_alive();
603 }
604 log_develop_trace(gc, ref)("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
605 clear_referent ? "cleared " : "", p2i(iter.obj()), iter.obj()->klass()->internal_name());
606 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
607 iter.next();
608 }
609 // Close the reachable set
610 complete_gc->do_void();
611 }
612
613 void
614 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
615 oop obj = NULL;
616 oop next = refs_list.head();
617 while (next != obj) {
618 obj = next;
619 next = java_lang_ref_Reference::discovered(obj);
620 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
621 }
622 refs_list.set_head(NULL);
623 refs_list.set_length(0);
624 }
625
626 void ReferenceProcessor::abandon_partial_discovery() {
627 // loop over the lists
628 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
629 if ((i % _max_num_q) == 0) {
630 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i));
631 }
632 clear_discovered_references(_discovered_refs[i]);
633 }
634 }
635
636 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
637 public:
638 RefProcPhase1Task(ReferenceProcessor& ref_processor,
639 DiscoveredList refs_lists[],
640 ReferencePolicy* policy,
641 bool marks_oops_alive)
642 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
643 _policy(policy)
644 { }
645 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
646 OopClosure& keep_alive,
647 VoidClosure& complete_gc)
648 {
649 _ref_processor.process_phase1(_refs_lists[i], _policy,
650 &is_alive, &keep_alive, &complete_gc);
651 }
652 private:
653 ReferencePolicy* _policy;
654 };
655
656 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
657 public:
658 RefProcPhase2Task(ReferenceProcessor& ref_processor,
659 DiscoveredList refs_lists[],
660 bool marks_oops_alive)
661 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
662 { }
663 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
664 OopClosure& keep_alive,
665 VoidClosure& complete_gc)
666 {
667 _ref_processor.process_phase2(_refs_lists[i],
668 &is_alive, &keep_alive, &complete_gc);
669 }
670 };
671
672 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
673 public:
674 RefProcPhase3Task(ReferenceProcessor& ref_processor,
675 DiscoveredList refs_lists[],
676 bool clear_referent,
677 bool marks_oops_alive)
678 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
679 _clear_referent(clear_referent)
680 { }
681 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
682 OopClosure& keep_alive,
683 VoidClosure& complete_gc)
684 {
685 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
686 &is_alive, &keep_alive, &complete_gc);
687 }
688 private:
689 bool _clear_referent;
690 };
691
692 #ifndef PRODUCT
693 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], size_t total_refs) {
694 if (!log_is_enabled(Trace, gc, ref)) {
695 return;
696 }
697
698 stringStream st;
699 for (uint i = 0; i < _max_num_q; ++i) {
700 st.print(SIZE_FORMAT " ", ref_lists[i].length());
701 }
702 log_develop_trace(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs);
703 }
704 #endif
705
706 // Balances reference queues.
707 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
708 // queues[0, 1, ..., _num_q-1] because only the first _num_q
709 // corresponding to the active workers will be processed.
710 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
711 {
712 // calculate total length
713 size_t total_refs = 0;
714 log_develop_trace(gc, ref)("Balance ref_lists ");
715
716 for (uint i = 0; i < _max_num_q; ++i) {
717 total_refs += ref_lists[i].length();
718 }
719 log_reflist_counts(ref_lists, total_refs);
720 size_t avg_refs = total_refs / _num_q + 1;
721 uint to_idx = 0;
722 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) {
723 bool move_all = false;
724 if (from_idx >= _num_q) {
725 move_all = ref_lists[from_idx].length() > 0;
726 }
727 while ((ref_lists[from_idx].length() > avg_refs) ||
728 move_all) {
729 assert(to_idx < _num_q, "Sanity Check!");
730 if (ref_lists[to_idx].length() < avg_refs) {
731 // move superfluous refs
732 size_t refs_to_move;
733 // Move all the Ref's if the from queue will not be processed.
734 if (move_all) {
735 refs_to_move = MIN2(ref_lists[from_idx].length(),
736 avg_refs - ref_lists[to_idx].length());
737 } else {
738 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
739 avg_refs - ref_lists[to_idx].length());
740 }
741
742 assert(refs_to_move > 0, "otherwise the code below will fail");
743
744 oop move_head = ref_lists[from_idx].head();
745 oop move_tail = move_head;
746 oop new_head = move_head;
747 // find an element to split the list on
748 for (size_t j = 0; j < refs_to_move; ++j) {
749 move_tail = new_head;
750 new_head = java_lang_ref_Reference::discovered(new_head);
751 }
752
753 // Add the chain to the to list.
754 if (ref_lists[to_idx].head() == NULL) {
755 // to list is empty. Make a loop at the end.
756 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
757 } else {
758 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
759 }
760 ref_lists[to_idx].set_head(move_head);
761 ref_lists[to_idx].inc_length(refs_to_move);
762
763 // Remove the chain from the from list.
764 if (move_tail == new_head) {
765 // We found the end of the from list.
766 ref_lists[from_idx].set_head(NULL);
767 } else {
768 ref_lists[from_idx].set_head(new_head);
769 }
770 ref_lists[from_idx].dec_length(refs_to_move);
771 if (ref_lists[from_idx].length() == 0) {
772 break;
773 }
774 } else {
775 to_idx = (to_idx + 1) % _num_q;
776 }
777 }
778 }
779 #ifdef ASSERT
780 size_t balanced_total_refs = 0;
781 for (uint i = 0; i < _max_num_q; ++i) {
782 balanced_total_refs += ref_lists[i].length();
783 }
784 log_reflist_counts(ref_lists, balanced_total_refs);
785 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
786 #endif
787 }
788
789 void ReferenceProcessor::balance_all_queues() {
790 balance_queues(_discoveredSoftRefs);
791 balance_queues(_discoveredWeakRefs);
792 balance_queues(_discoveredFinalRefs);
793 balance_queues(_discoveredPhantomRefs);
794 }
795
796 void ReferenceProcessor::process_discovered_reflist(
797 DiscoveredList refs_lists[],
798 ReferencePolicy* policy,
799 bool clear_referent,
800 BoolObjectClosure* is_alive,
801 OopClosure* keep_alive,
802 VoidClosure* complete_gc,
803 AbstractRefProcTaskExecutor* task_executor)
804 {
805 bool mt_processing = task_executor != NULL && _processing_is_mt;
806 // If discovery used MT and a dynamic number of GC threads, then
807 // the queues must be balanced for correctness if fewer than the
808 // maximum number of queues were used. The number of queue used
809 // during discovery may be different than the number to be used
810 // for processing so don't depend of _num_q < _max_num_q as part
811 // of the test.
812 bool must_balance = _discovery_is_mt;
813
814 if ((mt_processing && ParallelRefProcBalancingEnabled) ||
815 must_balance) {
816 balance_queues(refs_lists);
817 }
818
819 // Phase 1 (soft refs only):
820 // . Traverse the list and remove any SoftReferences whose
821 // referents are not alive, but that should be kept alive for
822 // policy reasons. Keep alive the transitive closure of all
823 // such referents.
824 if (policy != NULL) {
825 if (mt_processing) {
826 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
827 task_executor->execute(phase1);
828 } else {
829 for (uint i = 0; i < _max_num_q; i++) {
830 process_phase1(refs_lists[i], policy,
831 is_alive, keep_alive, complete_gc);
832 }
833 }
834 } else { // policy == NULL
835 assert(refs_lists != _discoveredSoftRefs,
836 "Policy must be specified for soft references.");
837 }
838
839 // Phase 2:
840 // . Traverse the list and remove any refs whose referents are alive.
841 if (mt_processing) {
842 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
843 task_executor->execute(phase2);
844 } else {
845 for (uint i = 0; i < _max_num_q; i++) {
846 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
847 }
848 }
849
850 // Phase 3:
851 // . Traverse the list and process referents as appropriate.
852 if (mt_processing) {
853 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
854 task_executor->execute(phase3);
855 } else {
856 for (uint i = 0; i < _max_num_q; i++) {
857 process_phase3(refs_lists[i], clear_referent,
858 is_alive, keep_alive, complete_gc);
859 }
860 }
861 }
862
863 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
864 uint id = 0;
865 // Determine the queue index to use for this object.
866 if (_discovery_is_mt) {
867 // During a multi-threaded discovery phase,
868 // each thread saves to its "own" list.
869 Thread* thr = Thread::current();
870 id = thr->as_Worker_thread()->id();
871 } else {
872 // single-threaded discovery, we save in round-robin
873 // fashion to each of the lists.
874 if (_processing_is_mt) {
875 id = next_id();
876 }
877 }
878 assert(id < _max_num_q, "Id is out-of-bounds (call Freud?)");
879
880 // Get the discovered queue to which we will add
881 DiscoveredList* list = NULL;
882 switch (rt) {
883 case REF_OTHER:
884 // Unknown reference type, no special treatment
885 break;
886 case REF_SOFT:
887 list = &_discoveredSoftRefs[id];
888 break;
889 case REF_WEAK:
890 list = &_discoveredWeakRefs[id];
891 break;
892 case REF_FINAL:
893 list = &_discoveredFinalRefs[id];
894 break;
895 case REF_PHANTOM:
896 list = &_discoveredPhantomRefs[id];
897 break;
898 case REF_NONE:
899 // we should not reach here if we are an InstanceRefKlass
900 default:
901 ShouldNotReachHere();
902 }
903 log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list));
904 return list;
905 }
906
907 inline void
908 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
909 oop obj,
910 HeapWord* discovered_addr) {
911 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
912 // First we must make sure this object is only enqueued once. CAS in a non null
913 // discovered_addr.
914 oop current_head = refs_list.head();
915 // The last ref must have its discovered field pointing to itself.
916 oop next_discovered = (current_head != NULL) ? current_head : obj;
917
918 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr,
919 NULL);
920 if (retest == NULL) {
921 // This thread just won the right to enqueue the object.
922 // We have separate lists for enqueueing, so no synchronization
923 // is necessary.
924 refs_list.set_head(obj);
925 refs_list.inc_length(1);
926
927 log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
928 p2i(obj), obj->klass()->internal_name());
929 } else {
930 // If retest was non NULL, another thread beat us to it:
931 // The reference has already been discovered...
932 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
933 p2i(obj), obj->klass()->internal_name());
934 }
935 }
936
937 #ifndef PRODUCT
938 // Non-atomic (i.e. concurrent) discovery might allow us
939 // to observe j.l.References with NULL referents, being those
940 // cleared concurrently by mutators during (or after) discovery.
941 void ReferenceProcessor::verify_referent(oop obj) {
942 bool da = discovery_is_atomic();
943 oop referent = java_lang_ref_Reference::referent(obj);
944 assert(da ? referent->is_oop() : referent->is_oop_or_null(),
945 "Bad referent " INTPTR_FORMAT " found in Reference "
946 INTPTR_FORMAT " during %satomic discovery ",
947 p2i(referent), p2i(obj), da ? "" : "non-");
948 }
949 #endif
950
951 // We mention two of several possible choices here:
952 // #0: if the reference object is not in the "originating generation"
953 // (or part of the heap being collected, indicated by our "span"
954 // we don't treat it specially (i.e. we scan it as we would
955 // a normal oop, treating its references as strong references).
956 // This means that references can't be discovered unless their
957 // referent is also in the same span. This is the simplest,
958 // most "local" and most conservative approach, albeit one
959 // that may cause weak references to be enqueued least promptly.
960 // We call this choice the "ReferenceBasedDiscovery" policy.
961 // #1: the reference object may be in any generation (span), but if
962 // the referent is in the generation (span) being currently collected
963 // then we can discover the reference object, provided
964 // the object has not already been discovered by
965 // a different concurrently running collector (as may be the
966 // case, for instance, if the reference object is in CMS and
967 // the referent in DefNewGeneration), and provided the processing
968 // of this reference object by the current collector will
969 // appear atomic to every other collector in the system.
970 // (Thus, for instance, a concurrent collector may not
971 // discover references in other generations even if the
972 // referent is in its own generation). This policy may,
973 // in certain cases, enqueue references somewhat sooner than
974 // might Policy #0 above, but at marginally increased cost
975 // and complexity in processing these references.
976 // We call this choice the "RefeferentBasedDiscovery" policy.
977 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
978 // Make sure we are discovering refs (rather than processing discovered refs).
979 if (!_discovering_refs || !RegisterReferences) {
980 return false;
981 }
982 // We only discover active references.
983 oop next = java_lang_ref_Reference::next(obj);
984 if (next != NULL) { // Ref is no longer active
985 return false;
986 }
987
988 HeapWord* obj_addr = (HeapWord*)obj;
989 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
990 !_span.contains(obj_addr)) {
991 // Reference is not in the originating generation;
992 // don't treat it specially (i.e. we want to scan it as a normal
993 // object with strong references).
994 return false;
995 }
996
997 // We only discover references whose referents are not (yet)
998 // known to be strongly reachable.
999 if (is_alive_non_header() != NULL) {
1000 verify_referent(obj);
1001 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
1002 return false; // referent is reachable
1003 }
1004 }
1005 if (rt == REF_SOFT) {
1006 // For soft refs we can decide now if these are not
1007 // current candidates for clearing, in which case we
1008 // can mark through them now, rather than delaying that
1009 // to the reference-processing phase. Since all current
1010 // time-stamp policies advance the soft-ref clock only
1011 // at a full collection cycle, this is always currently
1012 // accurate.
1013 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
1014 return false;
1015 }
1016 }
1017
1018 ResourceMark rm; // Needed for tracing.
1019
1020 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
1021 const oop discovered = java_lang_ref_Reference::discovered(obj);
1022 assert(discovered->is_oop_or_null(), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
1023 if (discovered != NULL) {
1024 // The reference has already been discovered...
1025 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
1026 p2i(obj), obj->klass()->internal_name());
1027 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1028 // assumes that an object is not processed twice;
1029 // if it's been already discovered it must be on another
1030 // generation's discovered list; so we won't discover it.
1031 return false;
1032 } else {
1033 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1034 "Unrecognized policy");
1035 // Check assumption that an object is not potentially
1036 // discovered twice except by concurrent collectors that potentially
1037 // trace the same Reference object twice.
1038 assert(UseConcMarkSweepGC || UseG1GC,
1039 "Only possible with a concurrent marking collector");
1040 return true;
1041 }
1042 }
1043
1044 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1045 verify_referent(obj);
1046 // Discover if and only if EITHER:
1047 // .. reference is in our span, OR
1048 // .. we are an atomic collector and referent is in our span
1049 if (_span.contains(obj_addr) ||
1050 (discovery_is_atomic() &&
1051 _span.contains(java_lang_ref_Reference::referent(obj)))) {
1052 // should_enqueue = true;
1053 } else {
1054 return false;
1055 }
1056 } else {
1057 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1058 _span.contains(obj_addr), "code inconsistency");
1059 }
1060
1061 // Get the right type of discovered queue head.
1062 DiscoveredList* list = get_discovered_list(rt);
1063 if (list == NULL) {
1064 return false; // nothing special needs to be done
1065 }
1066
1067 if (_discovery_is_mt) {
1068 add_to_discovered_list_mt(*list, obj, discovered_addr);
1069 } else {
1070 // We do a raw store here: the field will be visited later when processing
1071 // the discovered references.
1072 oop current_head = list->head();
1073 // The last ref must have its discovered field pointing to itself.
1074 oop next_discovered = (current_head != NULL) ? current_head : obj;
1075
1076 assert(discovered == NULL, "control point invariant");
1077 oop_store_raw(discovered_addr, next_discovered);
1078 list->set_head(obj);
1079 list->inc_length(1);
1080
1081 log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name());
1082 }
1083 assert(obj->is_oop(), "Discovered a bad reference");
1084 verify_referent(obj);
1085 return true;
1086 }
1087
1088 // Preclean the discovered references by removing those
1089 // whose referents are alive, and by marking from those that
1090 // are not active. These lists can be handled here
1091 // in any order and, indeed, concurrently.
1092 void ReferenceProcessor::preclean_discovered_references(
1093 BoolObjectClosure* is_alive,
1094 OopClosure* keep_alive,
1095 VoidClosure* complete_gc,
1096 YieldClosure* yield,
1097 GCTimer* gc_timer) {
1098
1099 // Soft references
1100 {
1101 GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer);
1102 for (uint i = 0; i < _max_num_q; i++) {
1103 if (yield->should_return()) {
1104 return;
1105 }
1106 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1107 keep_alive, complete_gc, yield);
1108 }
1109 }
1110
1111 // Weak references
1112 {
1113 GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer);
1114 for (uint i = 0; i < _max_num_q; i++) {
1115 if (yield->should_return()) {
1116 return;
1117 }
1118 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1119 keep_alive, complete_gc, yield);
1120 }
1121 }
1122
1123 // Final references
1124 {
1125 GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer);
1126 for (uint i = 0; i < _max_num_q; i++) {
1127 if (yield->should_return()) {
1128 return;
1129 }
1130 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1131 keep_alive, complete_gc, yield);
1132 }
1133 }
1134
1135 // Phantom references
1136 {
1137 GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer);
1138 for (uint i = 0; i < _max_num_q; i++) {
1139 if (yield->should_return()) {
1140 return;
1141 }
1142 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1143 keep_alive, complete_gc, yield);
1144 }
1145 }
1146 }
1147
1148 // Walk the given discovered ref list, and remove all reference objects
1149 // whose referents are still alive, whose referents are NULL or which
1150 // are not active (have a non-NULL next field). NOTE: When we are
1151 // thus precleaning the ref lists (which happens single-threaded today),
1152 // we do not disable refs discovery to honor the correct semantics of
1153 // java.lang.Reference. As a result, we need to be careful below
1154 // that ref removal steps interleave safely with ref discovery steps
1155 // (in this thread).
1156 void
1157 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1158 BoolObjectClosure* is_alive,
1159 OopClosure* keep_alive,
1160 VoidClosure* complete_gc,
1161 YieldClosure* yield) {
1162 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1163 while (iter.has_next()) {
1164 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1165 oop obj = iter.obj();
1166 oop next = java_lang_ref_Reference::next(obj);
1167 if (iter.referent() == NULL || iter.is_referent_alive() ||
1168 next != NULL) {
1169 // The referent has been cleared, or is alive, or the Reference is not
1170 // active; we need to trace and mark its cohort.
1171 log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1172 p2i(iter.obj()), iter.obj()->klass()->internal_name());
1173 // Remove Reference object from list
1174 iter.remove();
1175 // Keep alive its cohort.
1176 iter.make_referent_alive();
1177 if (UseCompressedOops) {
1178 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
1179 keep_alive->do_oop(next_addr);
1180 } else {
1181 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
1182 keep_alive->do_oop(next_addr);
1183 }
1184 iter.move_to_next();
1185 } else {
1186 iter.next();
1187 }
1188 }
1189 // Close the reachable set
1190 complete_gc->do_void();
1191
1192 NOT_PRODUCT(
1193 if (iter.processed() > 0) {
1194 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT,
1195 iter.removed(), iter.processed(), p2i(&refs_list));
1196 }
1197 )
1198 }
1199
1200 const char* ReferenceProcessor::list_name(uint i) {
1201 assert(i <= _max_num_q * number_of_subclasses_of_ref(),
1202 "Out of bounds index");
1203
1204 int j = i / _max_num_q;
1205 switch (j) {
1206 case 0: return "SoftRef";
1207 case 1: return "WeakRef";
1208 case 2: return "FinalRef";
1209 case 3: return "PhantomRef";
1210 }
1211 ShouldNotReachHere();
1212 return NULL;
1213 }
1214