1 /*
2 * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/javaClasses.inline.hpp"
27 #include "classfile/systemDictionary.hpp"
28 #include "gc/shared/collectedHeap.hpp"
29 #include "gc/shared/collectedHeap.inline.hpp"
30 #include "gc/shared/gcTimer.hpp"
31 #include "gc/shared/gcTraceTime.inline.hpp"
32 #include "gc/shared/referencePolicy.hpp"
33 #include "gc/shared/referenceProcessor.inline.hpp"
34 #include "logging/log.hpp"
35 #include "memory/allocation.hpp"
36 #include "memory/resourceArea.hpp"
37 #include "oops/oop.inline.hpp"
38 #include "runtime/java.hpp"
39 #include "runtime/jniHandles.hpp"
40
41 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
42 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
43 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0;
44
45 void referenceProcessor_init() {
46 ReferenceProcessor::init_statics();
47 }
48
49 void ReferenceProcessor::init_statics() {
50 // We need a monotonically non-decreasing time in ms but
51 // os::javaTimeMillis() does not guarantee monotonicity.
52 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
53
54 // Initialize the soft ref timestamp clock.
55 _soft_ref_timestamp_clock = now;
56 // Also update the soft ref clock in j.l.r.SoftReference
57 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock);
58
59 _always_clear_soft_ref_policy = new AlwaysClearPolicy();
60 if (is_server_compilation_mode_vm()) {
61 _default_soft_ref_policy = new LRUMaxHeapPolicy();
62 } else {
63 _default_soft_ref_policy = new LRUCurrentHeapPolicy();
64 }
65 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
66 vm_exit_during_initialization("Could not allocate reference policy object");
67 }
68 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
69 RefDiscoveryPolicy == ReferentBasedDiscovery,
70 "Unrecognized RefDiscoveryPolicy");
71 }
72
73 void ReferenceProcessor::enable_discovery(bool check_no_refs) {
74 #ifdef ASSERT
75 // Verify that we're not currently discovering refs
76 assert(!_discovering_refs, "nested call?");
77
78 if (check_no_refs) {
79 // Verify that the discovered lists are empty
80 verify_no_references_recorded();
81 }
82 #endif // ASSERT
83
84 // Someone could have modified the value of the static
85 // field in the j.l.r.SoftReference class that holds the
86 // soft reference timestamp clock using reflection or
87 // Unsafe between GCs. Unconditionally update the static
88 // field in ReferenceProcessor here so that we use the new
89 // value during reference discovery.
90
91 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
92 _discovering_refs = true;
93 }
94
95 ReferenceProcessor::ReferenceProcessor(MemRegion span,
96 bool mt_processing,
97 uint mt_processing_degree,
98 bool mt_discovery,
99 uint mt_discovery_degree,
100 bool atomic_discovery,
101 BoolObjectClosure* is_alive_non_header) :
102 _discovering_refs(false),
103 _enqueuing_is_done(false),
104 _is_alive_non_header(is_alive_non_header),
105 _processing_is_mt(mt_processing),
106 _next_id(0)
107 {
108 _span = span;
109 _discovery_is_atomic = atomic_discovery;
110 _discovery_is_mt = mt_discovery;
111 _num_q = MAX2(1U, mt_processing_degree);
112 _max_num_q = MAX2(_num_q, mt_discovery_degree);
113 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
114 _max_num_q * number_of_subclasses_of_ref(), mtGC);
115
116 if (_discovered_refs == NULL) {
117 vm_exit_during_initialization("Could not allocated RefProc Array");
118 }
119 _discoveredSoftRefs = &_discovered_refs[0];
120 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q];
121 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q];
122 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q];
123
124 // Initialize all entries to NULL
125 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
126 _discovered_refs[i].set_head(NULL);
127 _discovered_refs[i].set_length(0);
128 }
129
130 setup_policy(false /* default soft ref policy */);
131 }
132
133 #ifndef PRODUCT
134 void ReferenceProcessor::verify_no_references_recorded() {
135 guarantee(!_discovering_refs, "Discovering refs?");
136 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
137 guarantee(_discovered_refs[i].is_empty(),
138 "Found non-empty discovered list at %u", i);
139 }
140 }
141 #endif
142
143 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
144 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
145 if (UseCompressedOops) {
146 f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
147 } else {
148 f->do_oop((oop*)_discovered_refs[i].adr_head());
149 }
150 }
151 }
152
153 void ReferenceProcessor::update_soft_ref_master_clock() {
154 // Update (advance) the soft ref master clock field. This must be done
155 // after processing the soft ref list.
156
157 // We need a monotonically non-decreasing time in ms but
158 // os::javaTimeMillis() does not guarantee monotonicity.
159 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
160 jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
161 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
162
163 NOT_PRODUCT(
164 if (now < _soft_ref_timestamp_clock) {
165 log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT,
166 _soft_ref_timestamp_clock, now);
167 }
168 )
169 // The values of now and _soft_ref_timestamp_clock are set using
170 // javaTimeNanos(), which is guaranteed to be monotonically
171 // non-decreasing provided the underlying platform provides such
172 // a time source (and it is bug free).
173 // In product mode, however, protect ourselves from non-monotonicity.
174 if (now > _soft_ref_timestamp_clock) {
175 _soft_ref_timestamp_clock = now;
176 java_lang_ref_SoftReference::set_clock(now);
177 }
178 // Else leave clock stalled at its old value until time progresses
179 // past clock value.
180 }
181
182 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) {
183 size_t total = 0;
184 for (uint i = 0; i < _max_num_q; ++i) {
185 total += lists[i].length();
186 }
187 return total;
188 }
189
190 ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
191 BoolObjectClosure* is_alive,
192 OopClosure* keep_alive,
193 VoidClosure* complete_gc,
194 AbstractRefProcTaskExecutor* task_executor,
195 GCTimer* gc_timer) {
196
197 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
198 // Stop treating discovered references specially.
199 disable_discovery();
200
201 // If discovery was concurrent, someone could have modified
202 // the value of the static field in the j.l.r.SoftReference
203 // class that holds the soft reference timestamp clock using
204 // reflection or Unsafe between when discovery was enabled and
205 // now. Unconditionally update the static field in ReferenceProcessor
206 // here so that we use the new value during processing of the
207 // discovered soft refs.
208
209 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
210
211 ReferenceProcessorStats stats(
212 total_count(_discoveredSoftRefs),
213 total_count(_discoveredWeakRefs),
214 total_count(_discoveredFinalRefs),
215 total_count(_discoveredPhantomRefs));
216
217 // Soft references
218 {
219 GCTraceTime(Debug, gc, ref) tt("SoftReference", gc_timer);
220 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
221 is_alive, keep_alive, complete_gc, task_executor);
222 }
223
224 update_soft_ref_master_clock();
225
226 // Weak references
227 {
228 GCTraceTime(Debug, gc, ref) tt("WeakReference", gc_timer);
229 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
230 is_alive, keep_alive, complete_gc, task_executor);
231 }
232
233 // Final references
234 {
235 GCTraceTime(Debug, gc, ref) tt("FinalReference", gc_timer);
236 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
237 is_alive, keep_alive, complete_gc, task_executor);
238 }
239
240 // Phantom references
241 {
242 GCTraceTime(Debug, gc, ref) tt("PhantomReference", gc_timer);
243 process_discovered_reflist(_discoveredPhantomRefs, NULL, true,
244 is_alive, keep_alive, complete_gc, task_executor);
245 }
246
247 // Weak global JNI references. It would make more sense (semantically) to
248 // traverse these simultaneously with the regular weak references above, but
249 // that is not how the JDK1.2 specification is. See #4126360. Native code can
250 // thus use JNI weak references to circumvent the phantom references and
251 // resurrect a "post-mortem" object.
252 {
253 GCTraceTime(Debug, gc, ref) tt("JNI Weak Reference", gc_timer);
254 if (task_executor != NULL) {
255 task_executor->set_single_threaded_mode();
256 }
257 process_phaseJNI(is_alive, keep_alive, complete_gc);
258 }
259
260 HeapMonitoring::do_weak_oops(task_executor, is_alive, keep_alive, complete_gc);
261 log_debug(gc, ref)("Ref Counts: Soft: " SIZE_FORMAT " Weak: " SIZE_FORMAT " Final: " SIZE_FORMAT " Phantom: " SIZE_FORMAT,
262 stats.soft_count(), stats.weak_count(), stats.final_count(), stats.phantom_count());
263 log_develop_trace(gc, ref)("JNI Weak Reference count: " SIZE_FORMAT, count_jni_refs());
264
265 return stats;
266 }
267
268 #ifndef PRODUCT
269 // Calculate the number of jni handles.
270 size_t ReferenceProcessor::count_jni_refs() {
271 class CountHandleClosure: public OopClosure {
272 private:
273 size_t _count;
274 public:
275 CountHandleClosure(): _count(0) {}
276 void do_oop(oop* unused) { _count++; }
277 void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
278 size_t count() { return _count; }
279 };
280 CountHandleClosure global_handle_count;
281 JNIHandles::weak_oops_do(&global_handle_count);
282 return global_handle_count.count();
283 }
284 #endif
285
286 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
287 OopClosure* keep_alive,
288 VoidClosure* complete_gc) {
289 JNIHandles::weak_oops_do(is_alive, keep_alive);
290 complete_gc->do_void();
291 }
292
293 void ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
294 // Enqueue references that are not made active again, and
295 // clear the decks for the next collection (cycle).
296 enqueue_discovered_reflists(task_executor);
297
298 // Stop treating discovered references specially.
299 disable_discovery();
300 }
301
302 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list) {
303 // Given a list of refs linked through the "discovered" field
304 // (java.lang.ref.Reference.discovered), self-loop their "next" field
305 // thus distinguishing them from active References, then
306 // prepend them to the pending list.
307 //
308 // The Java threads will see the Reference objects linked together through
309 // the discovered field. Instead of trying to do the write barrier updates
310 // in all places in the reference processor where we manipulate the discovered
311 // field we make sure to do the barrier here where we anyway iterate through
312 // all linked Reference objects. Note that it is important to not dirty any
313 // cards during reference processing since this will cause card table
314 // verification to fail for G1.
315 log_develop_trace(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(&refs_list));
316
317 oop obj = NULL;
318 oop next_d = refs_list.head();
319 // Walk down the list, self-looping the next field
320 // so that the References are not considered active.
321 while (obj != next_d) {
322 obj = next_d;
323 assert(obj->is_instance(), "should be an instance object");
324 assert(InstanceKlass::cast(obj->klass())->is_reference_instance_klass(), "should be reference object");
325 next_d = java_lang_ref_Reference::discovered(obj);
326 log_develop_trace(gc, ref)(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, p2i(obj), p2i(next_d));
327 assert(java_lang_ref_Reference::next(obj) == NULL,
328 "Reference not active; should not be discovered");
329 // Self-loop next, so as to make Ref not active.
330 java_lang_ref_Reference::set_next_raw(obj, obj);
331 if (next_d != obj) {
332 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
333 } else {
334 // This is the last object.
335 // Swap refs_list into pending list and set obj's
336 // discovered to what we read from the pending list.
337 oop old = Universe::swap_reference_pending_list(refs_list.head());
338 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
339 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
340 }
341 }
342 }
343
344 // Parallel enqueue task
345 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
346 public:
347 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
348 DiscoveredList discovered_refs[],
349 int n_queues)
350 : EnqueueTask(ref_processor, discovered_refs, n_queues)
351 { }
352
353 virtual void work(unsigned int work_id) {
354 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
355 // Simplest first cut: static partitioning.
356 int index = work_id;
357 // The increment on "index" must correspond to the maximum number of queues
358 // (n_queues) with which that ReferenceProcessor was created. That
359 // is because of the "clever" way the discovered references lists were
360 // allocated and are indexed into.
361 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
362 for (int j = 0;
363 j < ReferenceProcessor::number_of_subclasses_of_ref();
364 j++, index += _n_queues) {
365 _ref_processor.enqueue_discovered_reflist(_refs_lists[index]);
366 _refs_lists[index].set_head(NULL);
367 _refs_lists[index].set_length(0);
368 }
369 }
370 };
371
372 // Enqueue references that are not made active again
373 void ReferenceProcessor::enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor) {
374 if (_processing_is_mt && task_executor != NULL) {
375 // Parallel code
376 RefProcEnqueueTask tsk(*this, _discovered_refs, _max_num_q);
377 task_executor->execute(tsk);
378 } else {
379 // Serial code: call the parent class's implementation
380 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
381 enqueue_discovered_reflist(_discovered_refs[i]);
382 _discovered_refs[i].set_head(NULL);
383 _discovered_refs[i].set_length(0);
384 }
385 }
386 }
387
388 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
389 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
390 oop discovered = java_lang_ref_Reference::discovered(_ref);
391 assert(_discovered_addr && discovered->is_oop_or_null(),
392 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
393 _next = discovered;
394 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
395 _referent = java_lang_ref_Reference::referent(_ref);
396 assert(Universe::heap()->is_in_reserved_or_null(_referent),
397 "Wrong oop found in java.lang.Reference object");
398 assert(allow_null_referent ?
399 _referent->is_oop_or_null()
400 : _referent->is_oop(),
401 "Expected an oop%s for referent field at " PTR_FORMAT,
402 (allow_null_referent ? " or NULL" : ""),
403 p2i(_referent));
404 }
405
406 void DiscoveredListIterator::remove() {
407 assert(_ref->is_oop(), "Dropping a bad reference");
408 oop_store_raw(_discovered_addr, NULL);
409
410 // First _prev_next ref actually points into DiscoveredList (gross).
411 oop new_next;
412 if (_next == _ref) {
413 // At the end of the list, we should make _prev point to itself.
414 // If _ref is the first ref, then _prev_next will be in the DiscoveredList,
415 // and _prev will be NULL.
416 new_next = _prev;
417 } else {
418 new_next = _next;
419 }
420 // Remove Reference object from discovered list. Note that G1 does not need a
421 // pre-barrier here because we know the Reference has already been found/marked,
422 // that's how it ended up in the discovered list in the first place.
423 oop_store_raw(_prev_next, new_next);
424 NOT_PRODUCT(_removed++);
425 _refs_list.dec_length(1);
426 }
427
428 void DiscoveredListIterator::clear_referent() {
429 oop_store_raw(_referent_addr, NULL);
430 }
431
432 // NOTE: process_phase*() are largely similar, and at a high level
433 // merely iterate over the extant list applying a predicate to
434 // each of its elements and possibly removing that element from the
435 // list and applying some further closures to that element.
436 // We should consider the possibility of replacing these
437 // process_phase*() methods by abstracting them into
438 // a single general iterator invocation that receives appropriate
439 // closures that accomplish this work.
440
441 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
442 // referents are not alive, but that should be kept alive for policy reasons.
443 // Keep alive the transitive closure of all such referents.
444 void
445 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
446 ReferencePolicy* policy,
447 BoolObjectClosure* is_alive,
448 OopClosure* keep_alive,
449 VoidClosure* complete_gc) {
450 assert(policy != NULL, "Must have a non-NULL policy");
451 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
452 // Decide which softly reachable refs should be kept alive.
453 while (iter.has_next()) {
454 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
455 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
456 if (referent_is_dead &&
457 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
458 log_develop_trace(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
459 p2i(iter.obj()), iter.obj()->klass()->internal_name());
460 // Remove Reference object from list
461 iter.remove();
462 // keep the referent around
463 iter.make_referent_alive();
464 iter.move_to_next();
465 } else {
466 iter.next();
467 }
468 }
469 // Close the reachable set
470 complete_gc->do_void();
471 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT,
472 iter.removed(), iter.processed(), p2i(&refs_list));
473 }
474
475 // Traverse the list and remove any Refs that are not active, or
476 // whose referents are either alive or NULL.
477 void
478 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
479 BoolObjectClosure* is_alive,
480 OopClosure* keep_alive) {
481 assert(discovery_is_atomic(), "Error");
482 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
483 while (iter.has_next()) {
484 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
485 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
486 assert(next == NULL, "Should not discover inactive Reference");
487 if (iter.is_referent_alive()) {
488 log_develop_trace(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
489 p2i(iter.obj()), iter.obj()->klass()->internal_name());
490 // The referent is reachable after all.
491 // Remove Reference object from list.
492 iter.remove();
493 // Update the referent pointer as necessary: Note that this
494 // should not entail any recursive marking because the
495 // referent must already have been traversed.
496 iter.make_referent_alive();
497 iter.move_to_next();
498 } else {
499 iter.next();
500 }
501 }
502 NOT_PRODUCT(
503 if (iter.processed() > 0) {
504 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
505 " Refs in discovered list " INTPTR_FORMAT,
506 iter.removed(), iter.processed(), p2i(&refs_list));
507 }
508 )
509 }
510
511 void
512 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
513 BoolObjectClosure* is_alive,
514 OopClosure* keep_alive,
515 VoidClosure* complete_gc) {
516 assert(!discovery_is_atomic(), "Error");
517 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
518 while (iter.has_next()) {
519 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
520 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
521 oop next = java_lang_ref_Reference::next(iter.obj());
522 if ((iter.referent() == NULL || iter.is_referent_alive() ||
523 next != NULL)) {
524 assert(next->is_oop_or_null(), "Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next));
525 // Remove Reference object from list
526 iter.remove();
527 // Trace the cohorts
528 iter.make_referent_alive();
529 if (UseCompressedOops) {
530 keep_alive->do_oop((narrowOop*)next_addr);
531 } else {
532 keep_alive->do_oop((oop*)next_addr);
533 }
534 iter.move_to_next();
535 } else {
536 iter.next();
537 }
538 }
539 // Now close the newly reachable set
540 complete_gc->do_void();
541 NOT_PRODUCT(
542 if (iter.processed() > 0) {
543 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
544 " Refs in discovered list " INTPTR_FORMAT,
545 iter.removed(), iter.processed(), p2i(&refs_list));
546 }
547 )
548 }
549
550 // Traverse the list and process the referents, by either
551 // clearing them or keeping them (and their reachable
552 // closure) alive.
553 void
554 ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
555 bool clear_referent,
556 BoolObjectClosure* is_alive,
557 OopClosure* keep_alive,
558 VoidClosure* complete_gc) {
559 ResourceMark rm;
560 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
561 while (iter.has_next()) {
562 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
563 if (clear_referent) {
564 // NULL out referent pointer
565 iter.clear_referent();
566 } else {
567 // keep the referent around
568 iter.make_referent_alive();
569 }
570 log_develop_trace(gc, ref)("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
571 clear_referent ? "cleared " : "", p2i(iter.obj()), iter.obj()->klass()->internal_name());
572 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
573 iter.next();
574 }
575 // Close the reachable set
576 complete_gc->do_void();
577 }
578
579 void
580 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
581 oop obj = NULL;
582 oop next = refs_list.head();
583 while (next != obj) {
584 obj = next;
585 next = java_lang_ref_Reference::discovered(obj);
586 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
587 }
588 refs_list.set_head(NULL);
589 refs_list.set_length(0);
590 }
591
592 void ReferenceProcessor::abandon_partial_discovery() {
593 // loop over the lists
594 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
595 if ((i % _max_num_q) == 0) {
596 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i));
597 }
598 clear_discovered_references(_discovered_refs[i]);
599 }
600 }
601
602 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
603 public:
604 RefProcPhase1Task(ReferenceProcessor& ref_processor,
605 DiscoveredList refs_lists[],
606 ReferencePolicy* policy,
607 bool marks_oops_alive)
608 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
609 _policy(policy)
610 { }
611 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
612 OopClosure& keep_alive,
613 VoidClosure& complete_gc)
614 {
615 _ref_processor.process_phase1(_refs_lists[i], _policy,
616 &is_alive, &keep_alive, &complete_gc);
617 }
618 private:
619 ReferencePolicy* _policy;
620 };
621
622 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
623 public:
624 RefProcPhase2Task(ReferenceProcessor& ref_processor,
625 DiscoveredList refs_lists[],
626 bool marks_oops_alive)
627 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
628 { }
629 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
630 OopClosure& keep_alive,
631 VoidClosure& complete_gc)
632 {
633 _ref_processor.process_phase2(_refs_lists[i],
634 &is_alive, &keep_alive, &complete_gc);
635 }
636 };
637
638 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
639 public:
640 RefProcPhase3Task(ReferenceProcessor& ref_processor,
641 DiscoveredList refs_lists[],
642 bool clear_referent,
643 bool marks_oops_alive)
644 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
645 _clear_referent(clear_referent)
646 { }
647 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
648 OopClosure& keep_alive,
649 VoidClosure& complete_gc)
650 {
651 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
652 &is_alive, &keep_alive, &complete_gc);
653 }
654 private:
655 bool _clear_referent;
656 };
657
658 #ifndef PRODUCT
659 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_refs) {
660 if (!log_is_enabled(Trace, gc, ref)) {
661 return;
662 }
663
664 stringStream st;
665 for (uint i = 0; i < active_length; ++i) {
666 st.print(SIZE_FORMAT " ", ref_lists[i].length());
667 }
668 log_develop_trace(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs);
669 #ifdef ASSERT
670 for (uint i = active_length; i < _max_num_q; i++) {
671 assert(ref_lists[i].length() == 0, SIZE_FORMAT " unexpected References in %u",
672 ref_lists[i].length(), i);
673 }
674 #endif
675 }
676 #endif
677
678 void ReferenceProcessor::set_active_mt_degree(uint v) {
679 _num_q = v;
680 _next_id = 0;
681 }
682
683 // Balances reference queues.
684 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
685 // queues[0, 1, ..., _num_q-1] because only the first _num_q
686 // corresponding to the active workers will be processed.
687 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
688 {
689 // calculate total length
690 size_t total_refs = 0;
691 log_develop_trace(gc, ref)("Balance ref_lists ");
692
693 for (uint i = 0; i < _max_num_q; ++i) {
694 total_refs += ref_lists[i].length();
695 }
696 log_reflist_counts(ref_lists, _max_num_q, total_refs);
697 size_t avg_refs = total_refs / _num_q + 1;
698 uint to_idx = 0;
699 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) {
700 bool move_all = false;
701 if (from_idx >= _num_q) {
702 move_all = ref_lists[from_idx].length() > 0;
703 }
704 while ((ref_lists[from_idx].length() > avg_refs) ||
705 move_all) {
706 assert(to_idx < _num_q, "Sanity Check!");
707 if (ref_lists[to_idx].length() < avg_refs) {
708 // move superfluous refs
709 size_t refs_to_move;
710 // Move all the Ref's if the from queue will not be processed.
711 if (move_all) {
712 refs_to_move = MIN2(ref_lists[from_idx].length(),
713 avg_refs - ref_lists[to_idx].length());
714 } else {
715 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
716 avg_refs - ref_lists[to_idx].length());
717 }
718
719 assert(refs_to_move > 0, "otherwise the code below will fail");
720
721 oop move_head = ref_lists[from_idx].head();
722 oop move_tail = move_head;
723 oop new_head = move_head;
724 // find an element to split the list on
725 for (size_t j = 0; j < refs_to_move; ++j) {
726 move_tail = new_head;
727 new_head = java_lang_ref_Reference::discovered(new_head);
728 }
729
730 // Add the chain to the to list.
731 if (ref_lists[to_idx].head() == NULL) {
732 // to list is empty. Make a loop at the end.
733 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
734 } else {
735 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
736 }
737 ref_lists[to_idx].set_head(move_head);
738 ref_lists[to_idx].inc_length(refs_to_move);
739
740 // Remove the chain from the from list.
741 if (move_tail == new_head) {
742 // We found the end of the from list.
743 ref_lists[from_idx].set_head(NULL);
744 } else {
745 ref_lists[from_idx].set_head(new_head);
746 }
747 ref_lists[from_idx].dec_length(refs_to_move);
748 if (ref_lists[from_idx].length() == 0) {
749 break;
750 }
751 } else {
752 to_idx = (to_idx + 1) % _num_q;
753 }
754 }
755 }
756 #ifdef ASSERT
757 size_t balanced_total_refs = 0;
758 for (uint i = 0; i < _num_q; ++i) {
759 balanced_total_refs += ref_lists[i].length();
760 }
761 log_reflist_counts(ref_lists, _num_q, balanced_total_refs);
762 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
763 #endif
764 }
765
766 void ReferenceProcessor::balance_all_queues() {
767 balance_queues(_discoveredSoftRefs);
768 balance_queues(_discoveredWeakRefs);
769 balance_queues(_discoveredFinalRefs);
770 balance_queues(_discoveredPhantomRefs);
771 }
772
773 void ReferenceProcessor::process_discovered_reflist(
774 DiscoveredList refs_lists[],
775 ReferencePolicy* policy,
776 bool clear_referent,
777 BoolObjectClosure* is_alive,
778 OopClosure* keep_alive,
779 VoidClosure* complete_gc,
780 AbstractRefProcTaskExecutor* task_executor)
781 {
782 bool mt_processing = task_executor != NULL && _processing_is_mt;
783 // If discovery used MT and a dynamic number of GC threads, then
784 // the queues must be balanced for correctness if fewer than the
785 // maximum number of queues were used. The number of queue used
786 // during discovery may be different than the number to be used
787 // for processing so don't depend of _num_q < _max_num_q as part
788 // of the test.
789 bool must_balance = _discovery_is_mt;
790
791 if ((mt_processing && ParallelRefProcBalancingEnabled) ||
792 must_balance) {
793 balance_queues(refs_lists);
794 }
795
796 // Phase 1 (soft refs only):
797 // . Traverse the list and remove any SoftReferences whose
798 // referents are not alive, but that should be kept alive for
799 // policy reasons. Keep alive the transitive closure of all
800 // such referents.
801 if (policy != NULL) {
802 if (mt_processing) {
803 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
804 task_executor->execute(phase1);
805 } else {
806 for (uint i = 0; i < _max_num_q; i++) {
807 process_phase1(refs_lists[i], policy,
808 is_alive, keep_alive, complete_gc);
809 }
810 }
811 } else { // policy == NULL
812 assert(refs_lists != _discoveredSoftRefs,
813 "Policy must be specified for soft references.");
814 }
815
816 // Phase 2:
817 // . Traverse the list and remove any refs whose referents are alive.
818 if (mt_processing) {
819 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
820 task_executor->execute(phase2);
821 } else {
822 for (uint i = 0; i < _max_num_q; i++) {
823 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
824 }
825 }
826
827 // Phase 3:
828 // . Traverse the list and process referents as appropriate.
829 if (mt_processing) {
830 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
831 task_executor->execute(phase3);
832 } else {
833 for (uint i = 0; i < _max_num_q; i++) {
834 process_phase3(refs_lists[i], clear_referent,
835 is_alive, keep_alive, complete_gc);
836 }
837 }
838 }
839
840 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
841 uint id = 0;
842 // Determine the queue index to use for this object.
843 if (_discovery_is_mt) {
844 // During a multi-threaded discovery phase,
845 // each thread saves to its "own" list.
846 Thread* thr = Thread::current();
847 id = thr->as_Worker_thread()->id();
848 } else {
849 // single-threaded discovery, we save in round-robin
850 // fashion to each of the lists.
851 if (_processing_is_mt) {
852 id = next_id();
853 }
854 }
855 assert(id < _max_num_q, "Id is out-of-bounds id %u and max id %u)", id, _max_num_q);
856
857 // Get the discovered queue to which we will add
858 DiscoveredList* list = NULL;
859 switch (rt) {
860 case REF_OTHER:
861 // Unknown reference type, no special treatment
862 break;
863 case REF_SOFT:
864 list = &_discoveredSoftRefs[id];
865 break;
866 case REF_WEAK:
867 list = &_discoveredWeakRefs[id];
868 break;
869 case REF_FINAL:
870 list = &_discoveredFinalRefs[id];
871 break;
872 case REF_PHANTOM:
873 list = &_discoveredPhantomRefs[id];
874 break;
875 case REF_NONE:
876 // we should not reach here if we are an InstanceRefKlass
877 default:
878 ShouldNotReachHere();
879 }
880 log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list));
881 return list;
882 }
883
884 inline void
885 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
886 oop obj,
887 HeapWord* discovered_addr) {
888 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
889 // First we must make sure this object is only enqueued once. CAS in a non null
890 // discovered_addr.
891 oop current_head = refs_list.head();
892 // The last ref must have its discovered field pointing to itself.
893 oop next_discovered = (current_head != NULL) ? current_head : obj;
894
895 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr,
896 NULL);
897 if (retest == NULL) {
898 // This thread just won the right to enqueue the object.
899 // We have separate lists for enqueueing, so no synchronization
900 // is necessary.
901 refs_list.set_head(obj);
902 refs_list.inc_length(1);
903
904 log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
905 p2i(obj), obj->klass()->internal_name());
906 } else {
907 // If retest was non NULL, another thread beat us to it:
908 // The reference has already been discovered...
909 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
910 p2i(obj), obj->klass()->internal_name());
911 }
912 }
913
914 #ifndef PRODUCT
915 // Non-atomic (i.e. concurrent) discovery might allow us
916 // to observe j.l.References with NULL referents, being those
917 // cleared concurrently by mutators during (or after) discovery.
918 void ReferenceProcessor::verify_referent(oop obj) {
919 bool da = discovery_is_atomic();
920 oop referent = java_lang_ref_Reference::referent(obj);
921 assert(da ? referent->is_oop() : referent->is_oop_or_null(),
922 "Bad referent " INTPTR_FORMAT " found in Reference "
923 INTPTR_FORMAT " during %satomic discovery ",
924 p2i(referent), p2i(obj), da ? "" : "non-");
925 }
926 #endif
927
928 // We mention two of several possible choices here:
929 // #0: if the reference object is not in the "originating generation"
930 // (or part of the heap being collected, indicated by our "span"
931 // we don't treat it specially (i.e. we scan it as we would
932 // a normal oop, treating its references as strong references).
933 // This means that references can't be discovered unless their
934 // referent is also in the same span. This is the simplest,
935 // most "local" and most conservative approach, albeit one
936 // that may cause weak references to be enqueued least promptly.
937 // We call this choice the "ReferenceBasedDiscovery" policy.
938 // #1: the reference object may be in any generation (span), but if
939 // the referent is in the generation (span) being currently collected
940 // then we can discover the reference object, provided
941 // the object has not already been discovered by
942 // a different concurrently running collector (as may be the
943 // case, for instance, if the reference object is in CMS and
944 // the referent in DefNewGeneration), and provided the processing
945 // of this reference object by the current collector will
946 // appear atomic to every other collector in the system.
947 // (Thus, for instance, a concurrent collector may not
948 // discover references in other generations even if the
949 // referent is in its own generation). This policy may,
950 // in certain cases, enqueue references somewhat sooner than
951 // might Policy #0 above, but at marginally increased cost
952 // and complexity in processing these references.
953 // We call this choice the "RefeferentBasedDiscovery" policy.
954 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
955 // Make sure we are discovering refs (rather than processing discovered refs).
956 if (!_discovering_refs || !RegisterReferences) {
957 return false;
958 }
959 // We only discover active references.
960 oop next = java_lang_ref_Reference::next(obj);
961 if (next != NULL) { // Ref is no longer active
962 return false;
963 }
964
965 HeapWord* obj_addr = (HeapWord*)obj;
966 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
967 !_span.contains(obj_addr)) {
968 // Reference is not in the originating generation;
969 // don't treat it specially (i.e. we want to scan it as a normal
970 // object with strong references).
971 return false;
972 }
973
974 // We only discover references whose referents are not (yet)
975 // known to be strongly reachable.
976 if (is_alive_non_header() != NULL) {
977 verify_referent(obj);
978 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
979 return false; // referent is reachable
980 }
981 }
982 if (rt == REF_SOFT) {
983 // For soft refs we can decide now if these are not
984 // current candidates for clearing, in which case we
985 // can mark through them now, rather than delaying that
986 // to the reference-processing phase. Since all current
987 // time-stamp policies advance the soft-ref clock only
988 // at a full collection cycle, this is always currently
989 // accurate.
990 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
991 return false;
992 }
993 }
994
995 ResourceMark rm; // Needed for tracing.
996
997 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
998 const oop discovered = java_lang_ref_Reference::discovered(obj);
999 assert(discovered->is_oop_or_null(), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
1000 if (discovered != NULL) {
1001 // The reference has already been discovered...
1002 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
1003 p2i(obj), obj->klass()->internal_name());
1004 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1005 // assumes that an object is not processed twice;
1006 // if it's been already discovered it must be on another
1007 // generation's discovered list; so we won't discover it.
1008 return false;
1009 } else {
1010 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1011 "Unrecognized policy");
1012 // Check assumption that an object is not potentially
1013 // discovered twice except by concurrent collectors that potentially
1014 // trace the same Reference object twice.
1015 assert(UseConcMarkSweepGC || UseG1GC,
1016 "Only possible with a concurrent marking collector");
1017 return true;
1018 }
1019 }
1020
1021 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1022 verify_referent(obj);
1023 // Discover if and only if EITHER:
1024 // .. reference is in our span, OR
1025 // .. we are an atomic collector and referent is in our span
1026 if (_span.contains(obj_addr) ||
1027 (discovery_is_atomic() &&
1028 _span.contains(java_lang_ref_Reference::referent(obj)))) {
1029 // should_enqueue = true;
1030 } else {
1031 return false;
1032 }
1033 } else {
1034 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1035 _span.contains(obj_addr), "code inconsistency");
1036 }
1037
1038 // Get the right type of discovered queue head.
1039 DiscoveredList* list = get_discovered_list(rt);
1040 if (list == NULL) {
1041 return false; // nothing special needs to be done
1042 }
1043
1044 if (_discovery_is_mt) {
1045 add_to_discovered_list_mt(*list, obj, discovered_addr);
1046 } else {
1047 // We do a raw store here: the field will be visited later when processing
1048 // the discovered references.
1049 oop current_head = list->head();
1050 // The last ref must have its discovered field pointing to itself.
1051 oop next_discovered = (current_head != NULL) ? current_head : obj;
1052
1053 assert(discovered == NULL, "control point invariant");
1054 oop_store_raw(discovered_addr, next_discovered);
1055 list->set_head(obj);
1056 list->inc_length(1);
1057
1058 log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name());
1059 }
1060 assert(obj->is_oop(), "Discovered a bad reference");
1061 verify_referent(obj);
1062 return true;
1063 }
1064
1065 bool ReferenceProcessor::has_discovered_references() {
1066 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
1067 if (!_discovered_refs[i].is_empty()) {
1068 return true;
1069 }
1070 }
1071 return false;
1072 }
1073
1074 // Preclean the discovered references by removing those
1075 // whose referents are alive, and by marking from those that
1076 // are not active. These lists can be handled here
1077 // in any order and, indeed, concurrently.
1078 void ReferenceProcessor::preclean_discovered_references(
1079 BoolObjectClosure* is_alive,
1080 OopClosure* keep_alive,
1081 VoidClosure* complete_gc,
1082 YieldClosure* yield,
1083 GCTimer* gc_timer) {
1084
1085 // Soft references
1086 {
1087 GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer);
1088 for (uint i = 0; i < _max_num_q; i++) {
1089 if (yield->should_return()) {
1090 return;
1091 }
1092 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1093 keep_alive, complete_gc, yield);
1094 }
1095 }
1096
1097 // Weak references
1098 {
1099 GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer);
1100 for (uint i = 0; i < _max_num_q; i++) {
1101 if (yield->should_return()) {
1102 return;
1103 }
1104 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1105 keep_alive, complete_gc, yield);
1106 }
1107 }
1108
1109 // Final references
1110 {
1111 GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer);
1112 for (uint i = 0; i < _max_num_q; i++) {
1113 if (yield->should_return()) {
1114 return;
1115 }
1116 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1117 keep_alive, complete_gc, yield);
1118 }
1119 }
1120
1121 // Phantom references
1122 {
1123 GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer);
1124 for (uint i = 0; i < _max_num_q; i++) {
1125 if (yield->should_return()) {
1126 return;
1127 }
1128 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1129 keep_alive, complete_gc, yield);
1130 }
1131 }
1132 }
1133
1134 // Walk the given discovered ref list, and remove all reference objects
1135 // whose referents are still alive, whose referents are NULL or which
1136 // are not active (have a non-NULL next field). NOTE: When we are
1137 // thus precleaning the ref lists (which happens single-threaded today),
1138 // we do not disable refs discovery to honor the correct semantics of
1139 // java.lang.Reference. As a result, we need to be careful below
1140 // that ref removal steps interleave safely with ref discovery steps
1141 // (in this thread).
1142 void
1143 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1144 BoolObjectClosure* is_alive,
1145 OopClosure* keep_alive,
1146 VoidClosure* complete_gc,
1147 YieldClosure* yield) {
1148 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1149 while (iter.has_next()) {
1150 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1151 oop obj = iter.obj();
1152 oop next = java_lang_ref_Reference::next(obj);
1153 if (iter.referent() == NULL || iter.is_referent_alive() ||
1154 next != NULL) {
1155 // The referent has been cleared, or is alive, or the Reference is not
1156 // active; we need to trace and mark its cohort.
1157 log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1158 p2i(iter.obj()), iter.obj()->klass()->internal_name());
1159 // Remove Reference object from list
1160 iter.remove();
1161 // Keep alive its cohort.
1162 iter.make_referent_alive();
1163 if (UseCompressedOops) {
1164 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
1165 keep_alive->do_oop(next_addr);
1166 } else {
1167 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
1168 keep_alive->do_oop(next_addr);
1169 }
1170 iter.move_to_next();
1171 } else {
1172 iter.next();
1173 }
1174 }
1175 // Close the reachable set
1176 complete_gc->do_void();
1177
1178 NOT_PRODUCT(
1179 if (iter.processed() > 0) {
1180 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT,
1181 iter.removed(), iter.processed(), p2i(&refs_list));
1182 }
1183 )
1184 }
1185
1186 const char* ReferenceProcessor::list_name(uint i) {
1187 assert(i <= _max_num_q * number_of_subclasses_of_ref(),
1188 "Out of bounds index");
1189
1190 int j = i / _max_num_q;
1191 switch (j) {
1192 case 0: return "SoftRef";
1193 case 1: return "WeakRef";
1194 case 2: return "FinalRef";
1195 case 3: return "PhantomRef";
1196 }
1197 ShouldNotReachHere();
1198 return NULL;
1199 }
1200