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