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