1 /*
2 * Copyright (c) 2001, 2015, 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.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.hpp"
32 #include "gc/shared/referencePolicy.hpp"
33 #include "gc/shared/referenceProcessor.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 _discoveredCleanerRefs = &_discoveredPhantomRefs[_max_num_q];
123
124 // Initialize all entries to NULL
125 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
126 _discovered_refs[i].set_head(NULL);
127 _discovered_refs[i].set_length(0);
128 }
129
130 setup_policy(false /* default soft ref policy */);
131 }
132
133 #ifndef PRODUCT
134 void ReferenceProcessor::verify_no_references_recorded() {
135 guarantee(!_discovering_refs, "Discovering refs?");
136 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
137 guarantee(_discovered_refs[i].is_empty(),
138 "Found non-empty discovered list");
139 }
140 }
141 #endif
142
143 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
144 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
145 if (UseCompressedOops) {
146 f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
147 } else {
148 f->do_oop((oop*)_discovered_refs[i].adr_head());
149 }
150 }
151 }
152
153 void ReferenceProcessor::update_soft_ref_master_clock() {
154 // Update (advance) the soft ref master clock field. This must be done
155 // after processing the soft ref list.
156
157 // We need a monotonically non-decreasing time in ms but
158 // os::javaTimeMillis() does not guarantee monotonicity.
159 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
160 jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
161 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
162
163 NOT_PRODUCT(
164 if (now < _soft_ref_timestamp_clock) {
165 warning("time warp: " JLONG_FORMAT " to " JLONG_FORMAT,
166 _soft_ref_timestamp_clock, now);
167 }
168 )
169 // The values of now and _soft_ref_timestamp_clock are set using
170 // javaTimeNanos(), which is guaranteed to be monotonically
171 // non-decreasing provided the underlying platform provides such
172 // a time source (and it is bug free).
173 // In product mode, however, protect ourselves from non-monotonicity.
174 if (now > _soft_ref_timestamp_clock) {
175 _soft_ref_timestamp_clock = now;
176 java_lang_ref_SoftReference::set_clock(now);
177 }
178 // Else leave clock stalled at its old value until time progresses
179 // past clock value.
180 }
181
182 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) {
183 size_t total = 0;
184 for (uint i = 0; i < _max_num_q; ++i) {
185 total += lists[i].length();
186 }
187 return total;
188 }
189
190 ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
191 BoolObjectClosure* is_alive,
192 OopClosure* keep_alive,
193 VoidClosure* complete_gc,
194 AbstractRefProcTaskExecutor* task_executor,
195 GCTimer* gc_timer) {
196
197 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
198 // Stop treating discovered references specially.
199 disable_discovery();
200
201 // If discovery was concurrent, someone could have modified
202 // the value of the static field in the j.l.r.SoftReference
203 // class that holds the soft reference timestamp clock using
204 // reflection or Unsafe between when discovery was enabled and
205 // now. Unconditionally update the static field in ReferenceProcessor
206 // here so that we use the new value during processing of the
207 // discovered soft refs.
208
209 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
210
211 // Include cleaners in phantom statistics. We expect Cleaner
212 // references to be temporary, and don't want to deal with
213 // possible incompatibilities arising from making it more visible.
214 ReferenceProcessorStats stats(
215 total_count(_discoveredSoftRefs),
216 total_count(_discoveredWeakRefs),
217 total_count(_discoveredFinalRefs),
218 total_count(_discoveredPhantomRefs) + total_count(_discoveredCleanerRefs));
219
220 // Soft references
221 {
222 GCTraceTime(Debug, gc, ref) tt("SoftReference", gc_timer);
223 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
224 is_alive, keep_alive, complete_gc, task_executor);
225 }
226
227 update_soft_ref_master_clock();
228
229 // Weak references
230 {
231 GCTraceTime(Debug, gc, ref) tt("WeakReference", gc_timer);
232 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
233 is_alive, keep_alive, complete_gc, task_executor);
234 }
235
236 // Final references
237 {
238 GCTraceTime(Debug, gc, ref) tt("FinalReference", gc_timer);
239 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
240 is_alive, keep_alive, complete_gc, task_executor);
241 }
242
243 // Phantom references
244 {
245 GCTraceTime(Debug, gc, ref) tt("PhantomReference", gc_timer);
246 process_discovered_reflist(_discoveredPhantomRefs, NULL, false,
247 is_alive, keep_alive, complete_gc, task_executor);
248
249 // Process cleaners, but include them in phantom timing. We expect
250 // Cleaner references to be temporary, and don't want to deal with
251 // possible incompatibilities arising from making it more visible.
252 process_discovered_reflist(_discoveredCleanerRefs, NULL, true,
253 is_alive, keep_alive, complete_gc, task_executor);
254 }
255
256 // Weak global JNI references. It would make more sense (semantically) to
257 // traverse these simultaneously with the regular weak references above, but
258 // that is not how the JDK1.2 specification is. See #4126360. Native code can
259 // thus use JNI weak references to circumvent the phantom references and
260 // resurrect a "post-mortem" object.
261 {
262 GCTraceTime(Debug, gc, ref) tt("JNI Weak Reference", gc_timer);
263 if (task_executor != NULL) {
264 task_executor->set_single_threaded_mode();
265 }
266 process_phaseJNI(is_alive, keep_alive, complete_gc);
267 }
268
269 log_debug(gc, ref)("Ref Counts: Soft: " SIZE_FORMAT " Weak: " SIZE_FORMAT " Final: " SIZE_FORMAT " Phantom: " SIZE_FORMAT,
270 stats.soft_count(), stats.weak_count(), stats.final_count(), stats.phantom_count());
271 log_develop(gc, ref)("JNI Weak Reference count: " SIZE_FORMAT, count_jni_refs());
272
273 return stats;
274 }
275
276 #ifndef PRODUCT
277 // Calculate the number of jni handles.
278 size_t ReferenceProcessor::count_jni_refs() {
279 class AlwaysAliveClosure: public BoolObjectClosure {
280 public:
281 virtual bool do_object_b(oop obj) { return true; }
282 };
283
284 class CountHandleClosure: public OopClosure {
285 private:
286 size_t _count;
287 public:
288 CountHandleClosure(): _count(0) {}
289 void do_oop(oop* unused) { _count++; }
290 void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
291 size_t count() { return _count; }
292 };
293 CountHandleClosure global_handle_count;
294 AlwaysAliveClosure always_alive;
295 JNIHandles::weak_oops_do(&always_alive, &global_handle_count);
296 return global_handle_count.count();
297 }
298 #endif
299
300 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
301 OopClosure* keep_alive,
302 VoidClosure* complete_gc) {
303 JNIHandles::weak_oops_do(is_alive, keep_alive);
304 complete_gc->do_void();
305 }
306
307
308 template <class T>
309 bool enqueue_discovered_ref_helper(ReferenceProcessor* ref,
310 AbstractRefProcTaskExecutor* task_executor) {
311
312 // Remember old value of pending references list
313 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr();
314 T old_pending_list_value = *pending_list_addr;
315
316 // Enqueue references that are not made active again, and
317 // clear the decks for the next collection (cycle).
318 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor);
319 // Do the post-barrier on pending_list_addr missed in
320 // enqueue_discovered_reflist.
321 oopDesc::bs()->write_ref_field(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr));
322
323 // Stop treating discovered references specially.
324 ref->disable_discovery();
325
326 // Return true if new pending references were added
327 return old_pending_list_value != *pending_list_addr;
328 }
329
330 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
331 if (UseCompressedOops) {
332 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
333 } else {
334 return enqueue_discovered_ref_helper<oop>(this, task_executor);
335 }
336 }
337
338 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
339 HeapWord* pending_list_addr) {
340 // Given a list of refs linked through the "discovered" field
341 // (java.lang.ref.Reference.discovered), self-loop their "next" field
342 // thus distinguishing them from active References, then
343 // prepend them to the pending list.
344 //
345 // The Java threads will see the Reference objects linked together through
346 // the discovered field. Instead of trying to do the write barrier updates
347 // in all places in the reference processor where we manipulate the discovered
348 // field we make sure to do the barrier here where we anyway iterate through
349 // all linked Reference objects. Note that it is important to not dirty any
350 // cards during reference processing since this will cause card table
351 // verification to fail for G1.
352 log_develop(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(refs_list.head()));
353
354 oop obj = NULL;
355 oop next_d = refs_list.head();
356 // Walk down the list, self-looping the next field
357 // so that the References are not considered active.
358 while (obj != next_d) {
359 obj = next_d;
360 assert(obj->is_instance(), "should be an instance object");
361 assert(InstanceKlass::cast(obj->klass())->is_reference_instance_klass(), "should be reference object");
362 next_d = java_lang_ref_Reference::discovered(obj);
363 log_develop(gc, ref)(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, p2i(obj), p2i(next_d));
364 assert(java_lang_ref_Reference::next(obj) == NULL,
365 "Reference not active; should not be discovered");
366 // Self-loop next, so as to make Ref not active.
367 java_lang_ref_Reference::set_next_raw(obj, obj);
368 if (next_d != obj) {
369 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
370 } else {
371 // This is the last object.
372 // Swap refs_list into pending_list_addr and
373 // set obj's discovered to what we read from pending_list_addr.
374 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
375 // Need post-barrier on pending_list_addr. See enqueue_discovered_ref_helper() above.
376 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
377 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
378 }
379 }
380 }
381
382 // Parallel enqueue task
383 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
384 public:
385 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
386 DiscoveredList discovered_refs[],
387 HeapWord* pending_list_addr,
388 int n_queues)
389 : EnqueueTask(ref_processor, discovered_refs,
390 pending_list_addr, n_queues)
391 { }
392
393 virtual void work(unsigned int work_id) {
394 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
395 // Simplest first cut: static partitioning.
396 int index = work_id;
397 // The increment on "index" must correspond to the maximum number of queues
398 // (n_queues) with which that ReferenceProcessor was created. That
399 // is because of the "clever" way the discovered references lists were
400 // allocated and are indexed into.
401 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
402 for (int j = 0;
403 j < ReferenceProcessor::number_of_subclasses_of_ref();
404 j++, index += _n_queues) {
405 _ref_processor.enqueue_discovered_reflist(
406 _refs_lists[index], _pending_list_addr);
407 _refs_lists[index].set_head(NULL);
408 _refs_lists[index].set_length(0);
409 }
410 }
411 };
412
413 // Enqueue references that are not made active again
414 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr,
415 AbstractRefProcTaskExecutor* task_executor) {
416 if (_processing_is_mt && task_executor != NULL) {
417 // Parallel code
418 RefProcEnqueueTask tsk(*this, _discovered_refs,
419 pending_list_addr, _max_num_q);
420 task_executor->execute(tsk);
421 } else {
422 // Serial code: call the parent class's implementation
423 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
424 enqueue_discovered_reflist(_discovered_refs[i], pending_list_addr);
425 _discovered_refs[i].set_head(NULL);
426 _discovered_refs[i].set_length(0);
427 }
428 }
429 }
430
431 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
432 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
433 oop discovered = java_lang_ref_Reference::discovered(_ref);
434 assert(_discovered_addr && discovered->is_oop_or_null(),
435 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
436 _next = discovered;
437 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
438 _referent = java_lang_ref_Reference::referent(_ref);
439 assert(Universe::heap()->is_in_reserved_or_null(_referent),
440 "Wrong oop found in java.lang.Reference object");
441 assert(allow_null_referent ?
442 _referent->is_oop_or_null()
443 : _referent->is_oop(),
444 "Expected an oop%s for referent field at " PTR_FORMAT,
445 (allow_null_referent ? " or NULL" : ""),
446 p2i(_referent));
447 }
448
449 void DiscoveredListIterator::remove() {
450 assert(_ref->is_oop(), "Dropping a bad reference");
451 oop_store_raw(_discovered_addr, NULL);
452
453 // First _prev_next ref actually points into DiscoveredList (gross).
454 oop new_next;
455 if (_next == _ref) {
456 // At the end of the list, we should make _prev point to itself.
457 // If _ref is the first ref, then _prev_next will be in the DiscoveredList,
458 // and _prev will be NULL.
459 new_next = _prev;
460 } else {
461 new_next = _next;
462 }
463 // Remove Reference object from discovered list. Note that G1 does not need a
464 // pre-barrier here because we know the Reference has already been found/marked,
465 // that's how it ended up in the discovered list in the first place.
466 oop_store_raw(_prev_next, new_next);
467 NOT_PRODUCT(_removed++);
468 _refs_list.dec_length(1);
469 }
470
471 void DiscoveredListIterator::clear_referent() {
472 oop_store_raw(_referent_addr, NULL);
473 }
474
475 // NOTE: process_phase*() are largely similar, and at a high level
476 // merely iterate over the extant list applying a predicate to
477 // each of its elements and possibly removing that element from the
478 // list and applying some further closures to that element.
479 // We should consider the possibility of replacing these
480 // process_phase*() methods by abstracting them into
481 // a single general iterator invocation that receives appropriate
482 // closures that accomplish this work.
483
484 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
485 // referents are not alive, but that should be kept alive for policy reasons.
486 // Keep alive the transitive closure of all such referents.
487 void
488 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
489 ReferencePolicy* policy,
490 BoolObjectClosure* is_alive,
491 OopClosure* keep_alive,
492 VoidClosure* complete_gc) {
493 assert(policy != NULL, "Must have a non-NULL policy");
494 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
495 // Decide which softly reachable refs should be kept alive.
496 while (iter.has_next()) {
497 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
498 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
499 if (referent_is_dead &&
500 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
501 log_develop(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
502 p2i(iter.obj()), iter.obj()->klass()->internal_name());
503 // Remove Reference object from list
504 iter.remove();
505 // keep the referent around
506 iter.make_referent_alive();
507 iter.move_to_next();
508 } else {
509 iter.next();
510 }
511 }
512 // Close the reachable set
513 complete_gc->do_void();
514 log_develop(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT,
515 iter.removed(), iter.processed(), p2i(refs_list.head()));
516 }
517
518 // Traverse the list and remove any Refs that are not active, or
519 // whose referents are either alive or NULL.
520 void
521 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
522 BoolObjectClosure* is_alive,
523 OopClosure* keep_alive) {
524 assert(discovery_is_atomic(), "Error");
525 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
526 while (iter.has_next()) {
527 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
528 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
529 assert(next == NULL, "Should not discover inactive Reference");
530 if (iter.is_referent_alive()) {
531 log_develop(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
532 p2i(iter.obj()), iter.obj()->klass()->internal_name());
533 // The referent is reachable after all.
534 // Remove Reference object from list.
535 iter.remove();
536 // Update the referent pointer as necessary: Note that this
537 // should not entail any recursive marking because the
538 // referent must already have been traversed.
539 iter.make_referent_alive();
540 iter.move_to_next();
541 } else {
542 iter.next();
543 }
544 }
545 NOT_PRODUCT(
546 if (iter.processed() > 0) {
547 log_develop(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
548 " Refs in discovered list " INTPTR_FORMAT,
549 iter.removed(), iter.processed(), p2i(refs_list.head()));
550 }
551 )
552 }
553
554 void
555 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
556 BoolObjectClosure* is_alive,
557 OopClosure* keep_alive,
558 VoidClosure* complete_gc) {
559 assert(!discovery_is_atomic(), "Error");
560 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
561 while (iter.has_next()) {
562 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
563 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
564 oop next = java_lang_ref_Reference::next(iter.obj());
565 if ((iter.referent() == NULL || iter.is_referent_alive() ||
566 next != NULL)) {
567 assert(next->is_oop_or_null(), "Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next));
568 // Remove Reference object from list
569 iter.remove();
570 // Trace the cohorts
571 iter.make_referent_alive();
572 if (UseCompressedOops) {
573 keep_alive->do_oop((narrowOop*)next_addr);
574 } else {
575 keep_alive->do_oop((oop*)next_addr);
576 }
577 iter.move_to_next();
578 } else {
579 iter.next();
580 }
581 }
582 // Now close the newly reachable set
583 complete_gc->do_void();
584 NOT_PRODUCT(
585 if (iter.processed() > 0) {
586 log_develop(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
587 " Refs in discovered list " INTPTR_FORMAT,
588 iter.removed(), iter.processed(), p2i(refs_list.head()));
589 }
590 )
591 }
592
593 // Traverse the list and process the referents, by either
594 // clearing them or keeping them (and their reachable
595 // closure) alive.
596 void
597 ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
598 bool clear_referent,
599 BoolObjectClosure* is_alive,
600 OopClosure* keep_alive,
601 VoidClosure* complete_gc) {
602 ResourceMark rm;
603 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
604 while (iter.has_next()) {
605 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
606 if (clear_referent) {
607 // NULL out referent pointer
608 iter.clear_referent();
609 } else {
610 // keep the referent around
611 iter.make_referent_alive();
612 }
613 log_develop(gc, ref)("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
614 clear_referent ? "cleared " : "", p2i(iter.obj()), iter.obj()->klass()->internal_name());
615 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
616 iter.next();
617 }
618 // Close the reachable set
619 complete_gc->do_void();
620 }
621
622 void
623 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
624 oop obj = NULL;
625 oop next = refs_list.head();
626 while (next != obj) {
627 obj = next;
628 next = java_lang_ref_Reference::discovered(obj);
629 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
630 }
631 refs_list.set_head(NULL);
632 refs_list.set_length(0);
633 }
634
635 void ReferenceProcessor::abandon_partial_discovery() {
636 // loop over the lists
637 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
638 if ((i % _max_num_q) == 0) {
639 log_develop(gc, ref)("\nAbandoning %s discovered list", list_name(i));
640 }
641 clear_discovered_references(_discovered_refs[i]);
642 }
643 }
644
645 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
646 public:
647 RefProcPhase1Task(ReferenceProcessor& ref_processor,
648 DiscoveredList refs_lists[],
649 ReferencePolicy* policy,
650 bool marks_oops_alive)
651 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
652 _policy(policy)
653 { }
654 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
655 OopClosure& keep_alive,
656 VoidClosure& complete_gc)
657 {
658 Thread* thr = Thread::current();
659 int refs_list_index = ((WorkerThread*)thr)->id();
660 _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy,
661 &is_alive, &keep_alive, &complete_gc);
662 }
663 private:
664 ReferencePolicy* _policy;
665 };
666
667 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
668 public:
669 RefProcPhase2Task(ReferenceProcessor& ref_processor,
670 DiscoveredList refs_lists[],
671 bool marks_oops_alive)
672 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
673 { }
674 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
675 OopClosure& keep_alive,
676 VoidClosure& complete_gc)
677 {
678 _ref_processor.process_phase2(_refs_lists[i],
679 &is_alive, &keep_alive, &complete_gc);
680 }
681 };
682
683 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
684 public:
685 RefProcPhase3Task(ReferenceProcessor& ref_processor,
686 DiscoveredList refs_lists[],
687 bool clear_referent,
688 bool marks_oops_alive)
689 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
690 _clear_referent(clear_referent)
691 { }
692 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
693 OopClosure& keep_alive,
694 VoidClosure& complete_gc)
695 {
696 // Don't use "refs_list_index" calculated in this way because
697 // balance_queues() has moved the Ref's into the first n queues.
698 // Thread* thr = Thread::current();
699 // int refs_list_index = ((WorkerThread*)thr)->id();
700 // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent,
701 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
702 &is_alive, &keep_alive, &complete_gc);
703 }
704 private:
705 bool _clear_referent;
706 };
707
708 #ifndef PRODUCT
709 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], size_t total_refs) {
710 if (!Log<LogTag::gc, LogTag::ref>::is_level(LogLevel::Trace)) {
711 return;
712 }
713
714 stringStream st;
715 for (uint i = 0; i < _max_num_q; ++i) {
716 st.print(SIZE_FORMAT " ", ref_lists[i].length());
717 }
718 log_develop(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs);
719 }
720 #endif
721
722 // Balances reference queues.
723 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
724 // queues[0, 1, ..., _num_q-1] because only the first _num_q
725 // corresponding to the active workers will be processed.
726 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
727 {
728 // calculate total length
729 size_t total_refs = 0;
730 log_develop(gc, ref)("Balance ref_lists ");
731
732 for (uint i = 0; i < _max_num_q; ++i) {
733 total_refs += ref_lists[i].length();
734 }
735 log_reflist_counts(ref_lists, total_refs);
736 size_t avg_refs = total_refs / _num_q + 1;
737 uint to_idx = 0;
738 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) {
739 bool move_all = false;
740 if (from_idx >= _num_q) {
741 move_all = ref_lists[from_idx].length() > 0;
742 }
743 while ((ref_lists[from_idx].length() > avg_refs) ||
744 move_all) {
745 assert(to_idx < _num_q, "Sanity Check!");
746 if (ref_lists[to_idx].length() < avg_refs) {
747 // move superfluous refs
748 size_t refs_to_move;
749 // Move all the Ref's if the from queue will not be processed.
750 if (move_all) {
751 refs_to_move = MIN2(ref_lists[from_idx].length(),
752 avg_refs - ref_lists[to_idx].length());
753 } else {
754 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
755 avg_refs - ref_lists[to_idx].length());
756 }
757
758 assert(refs_to_move > 0, "otherwise the code below will fail");
759
760 oop move_head = ref_lists[from_idx].head();
761 oop move_tail = move_head;
762 oop new_head = move_head;
763 // find an element to split the list on
764 for (size_t j = 0; j < refs_to_move; ++j) {
765 move_tail = new_head;
766 new_head = java_lang_ref_Reference::discovered(new_head);
767 }
768
769 // Add the chain to the to list.
770 if (ref_lists[to_idx].head() == NULL) {
771 // to list is empty. Make a loop at the end.
772 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
773 } else {
774 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
775 }
776 ref_lists[to_idx].set_head(move_head);
777 ref_lists[to_idx].inc_length(refs_to_move);
778
779 // Remove the chain from the from list.
780 if (move_tail == new_head) {
781 // We found the end of the from list.
782 ref_lists[from_idx].set_head(NULL);
783 } else {
784 ref_lists[from_idx].set_head(new_head);
785 }
786 ref_lists[from_idx].dec_length(refs_to_move);
787 if (ref_lists[from_idx].length() == 0) {
788 break;
789 }
790 } else {
791 to_idx = (to_idx + 1) % _num_q;
792 }
793 }
794 }
795 #ifdef ASSERT
796 size_t balanced_total_refs = 0;
797 for (uint i = 0; i < _max_num_q; ++i) {
798 balanced_total_refs += ref_lists[i].length();
799 }
800 log_reflist_counts(ref_lists, balanced_total_refs);
801 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
802 #endif
803 }
804
805 void ReferenceProcessor::balance_all_queues() {
806 balance_queues(_discoveredSoftRefs);
807 balance_queues(_discoveredWeakRefs);
808 balance_queues(_discoveredFinalRefs);
809 balance_queues(_discoveredPhantomRefs);
810 balance_queues(_discoveredCleanerRefs);
811 }
812
813 void ReferenceProcessor::process_discovered_reflist(
814 DiscoveredList refs_lists[],
815 ReferencePolicy* policy,
816 bool clear_referent,
817 BoolObjectClosure* is_alive,
818 OopClosure* keep_alive,
819 VoidClosure* complete_gc,
820 AbstractRefProcTaskExecutor* task_executor)
821 {
822 bool mt_processing = task_executor != NULL && _processing_is_mt;
823 // If discovery used MT and a dynamic number of GC threads, then
824 // the queues must be balanced for correctness if fewer than the
825 // maximum number of queues were used. The number of queue used
826 // during discovery may be different than the number to be used
827 // for processing so don't depend of _num_q < _max_num_q as part
828 // of the test.
829 bool must_balance = _discovery_is_mt;
830
831 if ((mt_processing && ParallelRefProcBalancingEnabled) ||
832 must_balance) {
833 balance_queues(refs_lists);
834 }
835
836 // Phase 1 (soft refs only):
837 // . Traverse the list and remove any SoftReferences whose
838 // referents are not alive, but that should be kept alive for
839 // policy reasons. Keep alive the transitive closure of all
840 // such referents.
841 if (policy != NULL) {
842 if (mt_processing) {
843 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
844 task_executor->execute(phase1);
845 } else {
846 for (uint i = 0; i < _max_num_q; i++) {
847 process_phase1(refs_lists[i], policy,
848 is_alive, keep_alive, complete_gc);
849 }
850 }
851 } else { // policy == NULL
852 assert(refs_lists != _discoveredSoftRefs,
853 "Policy must be specified for soft references.");
854 }
855
856 // Phase 2:
857 // . Traverse the list and remove any refs whose referents are alive.
858 if (mt_processing) {
859 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
860 task_executor->execute(phase2);
861 } else {
862 for (uint i = 0; i < _max_num_q; i++) {
863 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
864 }
865 }
866
867 // Phase 3:
868 // . Traverse the list and process referents as appropriate.
869 if (mt_processing) {
870 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
871 task_executor->execute(phase3);
872 } else {
873 for (uint i = 0; i < _max_num_q; i++) {
874 process_phase3(refs_lists[i], clear_referent,
875 is_alive, keep_alive, complete_gc);
876 }
877 }
878 }
879
880 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
881 uint id = 0;
882 // Determine the queue index to use for this object.
883 if (_discovery_is_mt) {
884 // During a multi-threaded discovery phase,
885 // each thread saves to its "own" list.
886 Thread* thr = Thread::current();
887 id = thr->as_Worker_thread()->id();
888 } else {
889 // single-threaded discovery, we save in round-robin
890 // fashion to each of the lists.
891 if (_processing_is_mt) {
892 id = next_id();
893 }
894 }
895 assert(id < _max_num_q, "Id is out-of-bounds (call Freud?)");
896
897 // Get the discovered queue to which we will add
898 DiscoveredList* list = NULL;
899 switch (rt) {
900 case REF_OTHER:
901 // Unknown reference type, no special treatment
902 break;
903 case REF_SOFT:
904 list = &_discoveredSoftRefs[id];
905 break;
906 case REF_WEAK:
907 list = &_discoveredWeakRefs[id];
908 break;
909 case REF_FINAL:
910 list = &_discoveredFinalRefs[id];
911 break;
912 case REF_PHANTOM:
913 list = &_discoveredPhantomRefs[id];
914 break;
915 case REF_CLEANER:
916 list = &_discoveredCleanerRefs[id];
917 break;
918 case REF_NONE:
919 // we should not reach here if we are an InstanceRefKlass
920 default:
921 ShouldNotReachHere();
922 }
923 log_develop(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list));
924 return list;
925 }
926
927 inline void
928 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
929 oop obj,
930 HeapWord* discovered_addr) {
931 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
932 // First we must make sure this object is only enqueued once. CAS in a non null
933 // discovered_addr.
934 oop current_head = refs_list.head();
935 // The last ref must have its discovered field pointing to itself.
936 oop next_discovered = (current_head != NULL) ? current_head : obj;
937
938 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr,
939 NULL);
940 if (retest == NULL) {
941 // This thread just won the right to enqueue the object.
942 // We have separate lists for enqueueing, so no synchronization
943 // is necessary.
944 refs_list.set_head(obj);
945 refs_list.inc_length(1);
946
947 log_develop(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
948 p2i(obj), obj->klass()->internal_name());
949 } else {
950 // If retest was non NULL, another thread beat us to it:
951 // The reference has already been discovered...
952 log_develop(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
953 p2i(obj), obj->klass()->internal_name());
954 }
955 }
956
957 #ifndef PRODUCT
958 // Non-atomic (i.e. concurrent) discovery might allow us
959 // to observe j.l.References with NULL referents, being those
960 // cleared concurrently by mutators during (or after) discovery.
961 void ReferenceProcessor::verify_referent(oop obj) {
962 bool da = discovery_is_atomic();
963 oop referent = java_lang_ref_Reference::referent(obj);
964 assert(da ? referent->is_oop() : referent->is_oop_or_null(),
965 "Bad referent " INTPTR_FORMAT " found in Reference "
966 INTPTR_FORMAT " during %satomic discovery ",
967 p2i(referent), p2i(obj), da ? "" : "non-");
968 }
969 #endif
970
971 // We mention two of several possible choices here:
972 // #0: if the reference object is not in the "originating generation"
973 // (or part of the heap being collected, indicated by our "span"
974 // we don't treat it specially (i.e. we scan it as we would
975 // a normal oop, treating its references as strong references).
976 // This means that references can't be discovered unless their
977 // referent is also in the same span. This is the simplest,
978 // most "local" and most conservative approach, albeit one
979 // that may cause weak references to be enqueued least promptly.
980 // We call this choice the "ReferenceBasedDiscovery" policy.
981 // #1: the reference object may be in any generation (span), but if
982 // the referent is in the generation (span) being currently collected
983 // then we can discover the reference object, provided
984 // the object has not already been discovered by
985 // a different concurrently running collector (as may be the
986 // case, for instance, if the reference object is in CMS and
987 // the referent in DefNewGeneration), and provided the processing
988 // of this reference object by the current collector will
989 // appear atomic to every other collector in the system.
990 // (Thus, for instance, a concurrent collector may not
991 // discover references in other generations even if the
992 // referent is in its own generation). This policy may,
993 // in certain cases, enqueue references somewhat sooner than
994 // might Policy #0 above, but at marginally increased cost
995 // and complexity in processing these references.
996 // We call this choice the "RefeferentBasedDiscovery" policy.
997 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
998 // Make sure we are discovering refs (rather than processing discovered refs).
999 if (!_discovering_refs || !RegisterReferences) {
1000 return false;
1001 }
1002 // We only discover active references.
1003 oop next = java_lang_ref_Reference::next(obj);
1004 if (next != NULL) { // Ref is no longer active
1005 return false;
1006 }
1007
1008 HeapWord* obj_addr = (HeapWord*)obj;
1009 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1010 !_span.contains(obj_addr)) {
1011 // Reference is not in the originating generation;
1012 // don't treat it specially (i.e. we want to scan it as a normal
1013 // object with strong references).
1014 return false;
1015 }
1016
1017 // We only discover references whose referents are not (yet)
1018 // known to be strongly reachable.
1019 if (is_alive_non_header() != NULL) {
1020 verify_referent(obj);
1021 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
1022 return false; // referent is reachable
1023 }
1024 }
1025 if (rt == REF_SOFT) {
1026 // For soft refs we can decide now if these are not
1027 // current candidates for clearing, in which case we
1028 // can mark through them now, rather than delaying that
1029 // to the reference-processing phase. Since all current
1030 // time-stamp policies advance the soft-ref clock only
1031 // at a full collection cycle, this is always currently
1032 // accurate.
1033 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
1034 return false;
1035 }
1036 }
1037
1038 ResourceMark rm; // Needed for tracing.
1039
1040 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
1041 const oop discovered = java_lang_ref_Reference::discovered(obj);
1042 assert(discovered->is_oop_or_null(), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
1043 if (discovered != NULL) {
1044 // The reference has already been discovered...
1045 log_develop(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
1046 p2i(obj), obj->klass()->internal_name());
1047 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1048 // assumes that an object is not processed twice;
1049 // if it's been already discovered it must be on another
1050 // generation's discovered list; so we won't discover it.
1051 return false;
1052 } else {
1053 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1054 "Unrecognized policy");
1055 // Check assumption that an object is not potentially
1056 // discovered twice except by concurrent collectors that potentially
1057 // trace the same Reference object twice.
1058 assert(UseConcMarkSweepGC || UseG1GC,
1059 "Only possible with a concurrent marking collector");
1060 return true;
1061 }
1062 }
1063
1064 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1065 verify_referent(obj);
1066 // Discover if and only if EITHER:
1067 // .. reference is in our span, OR
1068 // .. we are an atomic collector and referent is in our span
1069 if (_span.contains(obj_addr) ||
1070 (discovery_is_atomic() &&
1071 _span.contains(java_lang_ref_Reference::referent(obj)))) {
1072 // should_enqueue = true;
1073 } else {
1074 return false;
1075 }
1076 } else {
1077 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1078 _span.contains(obj_addr), "code inconsistency");
1079 }
1080
1081 // Get the right type of discovered queue head.
1082 DiscoveredList* list = get_discovered_list(rt);
1083 if (list == NULL) {
1084 return false; // nothing special needs to be done
1085 }
1086
1087 if (_discovery_is_mt) {
1088 add_to_discovered_list_mt(*list, obj, discovered_addr);
1089 } else {
1090 // We do a raw store here: the field will be visited later when processing
1091 // the discovered references.
1092 oop current_head = list->head();
1093 // The last ref must have its discovered field pointing to itself.
1094 oop next_discovered = (current_head != NULL) ? current_head : obj;
1095
1096 assert(discovered == NULL, "control point invariant");
1097 oop_store_raw(discovered_addr, next_discovered);
1098 list->set_head(obj);
1099 list->inc_length(1);
1100
1101 log_develop(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name());
1102 }
1103 assert(obj->is_oop(), "Discovered a bad reference");
1104 verify_referent(obj);
1105 return true;
1106 }
1107
1108 // Preclean the discovered references by removing those
1109 // whose referents are alive, and by marking from those that
1110 // are not active. These lists can be handled here
1111 // in any order and, indeed, concurrently.
1112 void ReferenceProcessor::preclean_discovered_references(
1113 BoolObjectClosure* is_alive,
1114 OopClosure* keep_alive,
1115 VoidClosure* complete_gc,
1116 YieldClosure* yield,
1117 GCTimer* gc_timer) {
1118
1119 // Soft references
1120 {
1121 GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer);
1122 for (uint i = 0; i < _max_num_q; i++) {
1123 if (yield->should_return()) {
1124 return;
1125 }
1126 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1127 keep_alive, complete_gc, yield);
1128 }
1129 }
1130
1131 // Weak references
1132 {
1133 GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer);
1134 for (uint i = 0; i < _max_num_q; i++) {
1135 if (yield->should_return()) {
1136 return;
1137 }
1138 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1139 keep_alive, complete_gc, yield);
1140 }
1141 }
1142
1143 // Final references
1144 {
1145 GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer);
1146 for (uint i = 0; i < _max_num_q; i++) {
1147 if (yield->should_return()) {
1148 return;
1149 }
1150 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1151 keep_alive, complete_gc, yield);
1152 }
1153 }
1154
1155 // Phantom references
1156 {
1157 GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer);
1158 for (uint i = 0; i < _max_num_q; i++) {
1159 if (yield->should_return()) {
1160 return;
1161 }
1162 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1163 keep_alive, complete_gc, yield);
1164 }
1165
1166 // Cleaner references. Included in timing for phantom references. We
1167 // expect Cleaner references to be temporary, and don't want to deal with
1168 // possible incompatibilities arising from making it more visible.
1169 for (uint i = 0; i < _max_num_q; i++) {
1170 if (yield->should_return()) {
1171 return;
1172 }
1173 preclean_discovered_reflist(_discoveredCleanerRefs[i], is_alive,
1174 keep_alive, complete_gc, yield);
1175 }
1176 }
1177 }
1178
1179 // Walk the given discovered ref list, and remove all reference objects
1180 // whose referents are still alive, whose referents are NULL or which
1181 // are not active (have a non-NULL next field). NOTE: When we are
1182 // thus precleaning the ref lists (which happens single-threaded today),
1183 // we do not disable refs discovery to honor the correct semantics of
1184 // java.lang.Reference. As a result, we need to be careful below
1185 // that ref removal steps interleave safely with ref discovery steps
1186 // (in this thread).
1187 void
1188 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1189 BoolObjectClosure* is_alive,
1190 OopClosure* keep_alive,
1191 VoidClosure* complete_gc,
1192 YieldClosure* yield) {
1193 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1194 while (iter.has_next()) {
1195 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1196 oop obj = iter.obj();
1197 oop next = java_lang_ref_Reference::next(obj);
1198 if (iter.referent() == NULL || iter.is_referent_alive() ||
1199 next != NULL) {
1200 // The referent has been cleared, or is alive, or the Reference is not
1201 // active; we need to trace and mark its cohort.
1202 log_develop(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1203 p2i(iter.obj()), iter.obj()->klass()->internal_name());
1204 // Remove Reference object from list
1205 iter.remove();
1206 // Keep alive its cohort.
1207 iter.make_referent_alive();
1208 if (UseCompressedOops) {
1209 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
1210 keep_alive->do_oop(next_addr);
1211 } else {
1212 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
1213 keep_alive->do_oop(next_addr);
1214 }
1215 iter.move_to_next();
1216 } else {
1217 iter.next();
1218 }
1219 }
1220 // Close the reachable set
1221 complete_gc->do_void();
1222
1223 NOT_PRODUCT(
1224 if (iter.processed() > 0) {
1225 log_develop(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT,
1226 iter.removed(), iter.processed(), p2i(refs_list.head()));
1227 }
1228 )
1229 }
1230
1231 const char* ReferenceProcessor::list_name(uint i) {
1232 assert(i <= _max_num_q * number_of_subclasses_of_ref(),
1233 "Out of bounds index");
1234
1235 int j = i / _max_num_q;
1236 switch (j) {
1237 case 0: return "SoftRef";
1238 case 1: return "WeakRef";
1239 case 2: return "FinalRef";
1240 case 3: return "PhantomRef";
1241 case 4: return "CleanerRef";
1242 }
1243 ShouldNotReachHere();
1244 return NULL;
1245 }
1246