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/heapMonitoring.hpp"
39 #include "runtime/java.hpp"
40 #include "runtime/jniHandles.hpp"
41
42 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
43 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
44 jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0;
45
46 void referenceProcessor_init() {
47 ReferenceProcessor::init_statics();
48 }
49
50 void ReferenceProcessor::init_statics() {
51 // We need a monotonically non-decreasing time in ms but
52 // os::javaTimeMillis() does not guarantee monotonicity.
53 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
54
55 // Initialize the soft ref timestamp clock.
56 _soft_ref_timestamp_clock = now;
57 // Also update the soft ref clock in j.l.r.SoftReference
58 java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock);
59
60 _always_clear_soft_ref_policy = new AlwaysClearPolicy();
61 if (is_server_compilation_mode_vm()) {
62 _default_soft_ref_policy = new LRUMaxHeapPolicy();
63 } else {
64 _default_soft_ref_policy = new LRUCurrentHeapPolicy();
65 }
66 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
67 vm_exit_during_initialization("Could not allocate reference policy object");
68 }
69 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
70 RefDiscoveryPolicy == ReferentBasedDiscovery,
71 "Unrecognized RefDiscoveryPolicy");
72 }
73
74 void ReferenceProcessor::enable_discovery(bool check_no_refs) {
75 #ifdef ASSERT
76 // Verify that we're not currently discovering refs
77 assert(!_discovering_refs, "nested call?");
78
79 if (check_no_refs) {
80 // Verify that the discovered lists are empty
81 verify_no_references_recorded();
82 }
83 #endif // ASSERT
84
85 // Someone could have modified the value of the static
86 // field in the j.l.r.SoftReference class that holds the
87 // soft reference timestamp clock using reflection or
88 // Unsafe between GCs. Unconditionally update the static
89 // field in ReferenceProcessor here so that we use the new
90 // value during reference discovery.
91
92 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
93 _discovering_refs = true;
94 }
95
96 ReferenceProcessor::ReferenceProcessor(MemRegion span,
97 bool mt_processing,
98 uint mt_processing_degree,
99 bool mt_discovery,
100 uint mt_discovery_degree,
101 bool atomic_discovery,
102 BoolObjectClosure* is_alive_non_header) :
103 _discovering_refs(false),
104 _enqueuing_is_done(false),
105 _is_alive_non_header(is_alive_non_header),
106 _processing_is_mt(mt_processing),
107 _next_id(0)
108 {
109 _span = span;
110 _discovery_is_atomic = atomic_discovery;
111 _discovery_is_mt = mt_discovery;
112 _num_q = MAX2(1U, mt_processing_degree);
113 _max_num_q = MAX2(_num_q, mt_discovery_degree);
114 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
115 _max_num_q * number_of_subclasses_of_ref(), mtGC);
116
117 if (_discovered_refs == NULL) {
118 vm_exit_during_initialization("Could not allocated RefProc Array");
119 }
120 _discoveredSoftRefs = &_discovered_refs[0];
121 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q];
122 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q];
123 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q];
124
125 // Initialize all entries to NULL
126 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
127 _discovered_refs[i].set_head(NULL);
128 _discovered_refs[i].set_length(0);
129 }
130
131 setup_policy(false /* default soft ref policy */);
132 }
133
134 #ifndef PRODUCT
135 void ReferenceProcessor::verify_no_references_recorded() {
136 guarantee(!_discovering_refs, "Discovering refs?");
137 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
138 guarantee(_discovered_refs[i].is_empty(),
139 "Found non-empty discovered list at %u", i);
140 }
141 }
142 #endif
143
144 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
145 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
146 if (UseCompressedOops) {
147 f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
148 } else {
149 f->do_oop((oop*)_discovered_refs[i].adr_head());
150 }
151 }
152 }
153
154 void ReferenceProcessor::update_soft_ref_master_clock() {
155 // Update (advance) the soft ref master clock field. This must be done
156 // after processing the soft ref list.
157
158 // We need a monotonically non-decreasing time in ms but
159 // os::javaTimeMillis() does not guarantee monotonicity.
160 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
161 jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
162 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
163
164 NOT_PRODUCT(
165 if (now < _soft_ref_timestamp_clock) {
166 log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT,
167 _soft_ref_timestamp_clock, now);
168 }
169 )
170 // The values of now and _soft_ref_timestamp_clock are set using
171 // javaTimeNanos(), which is guaranteed to be monotonically
172 // non-decreasing provided the underlying platform provides such
173 // a time source (and it is bug free).
174 // In product mode, however, protect ourselves from non-monotonicity.
175 if (now > _soft_ref_timestamp_clock) {
176 _soft_ref_timestamp_clock = now;
177 java_lang_ref_SoftReference::set_clock(now);
178 }
179 // Else leave clock stalled at its old value until time progresses
180 // past clock value.
181 }
182
183 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) {
184 size_t total = 0;
185 for (uint i = 0; i < _max_num_q; ++i) {
186 total += lists[i].length();
187 }
188 return total;
189 }
190
191 ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
192 BoolObjectClosure* is_alive,
193 OopClosure* keep_alive,
194 VoidClosure* complete_gc,
195 AbstractRefProcTaskExecutor* task_executor,
196 GCTimer* gc_timer) {
197
198 assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
199 // Stop treating discovered references specially.
200 disable_discovery();
201
202 // If discovery was concurrent, someone could have modified
203 // the value of the static field in the j.l.r.SoftReference
204 // class that holds the soft reference timestamp clock using
205 // reflection or Unsafe between when discovery was enabled and
206 // now. Unconditionally update the static field in ReferenceProcessor
207 // here so that we use the new value during processing of the
208 // discovered soft refs.
209
210 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
211
212 ReferenceProcessorStats stats(
213 total_count(_discoveredSoftRefs),
214 total_count(_discoveredWeakRefs),
215 total_count(_discoveredFinalRefs),
216 total_count(_discoveredPhantomRefs));
217
218 // Soft references
219 {
220 GCTraceTime(Debug, gc, ref) tt("SoftReference", gc_timer);
221 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
222 is_alive, keep_alive, complete_gc, task_executor);
223 }
224
225 update_soft_ref_master_clock();
226
227 // Weak references
228 {
229 GCTraceTime(Debug, gc, ref) tt("WeakReference", gc_timer);
230 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
231 is_alive, keep_alive, complete_gc, task_executor);
232 }
233
234 // Final references
235 {
236 GCTraceTime(Debug, gc, ref) tt("FinalReference", gc_timer);
237 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
238 is_alive, keep_alive, complete_gc, task_executor);
239 }
240
241 // Phantom references
242 {
243 GCTraceTime(Debug, gc, ref) tt("PhantomReference", gc_timer);
244 process_discovered_reflist(_discoveredPhantomRefs, NULL, true,
245 is_alive, keep_alive, complete_gc, task_executor);
246 }
247
248 // Weak global JNI references. It would make more sense (semantically) to
249 // traverse these simultaneously with the regular weak references above, but
250 // that is not how the JDK1.2 specification is. See #4126360. Native code can
251 // thus use JNI weak references to circumvent the phantom references and
252 // resurrect a "post-mortem" object.
253 {
254 GCTraceTime(Debug, gc, ref) tt("JNI Weak Reference", gc_timer);
255 if (task_executor != NULL) {
256 task_executor->set_single_threaded_mode();
257 }
258 process_phaseJNI(is_alive, keep_alive, complete_gc);
259 }
260
261 HeapMonitoring::weak_oops_do(task_executor, is_alive, keep_alive, complete_gc);
262 log_debug(gc, ref)("Ref Counts: Soft: " SIZE_FORMAT " Weak: " SIZE_FORMAT " Final: " SIZE_FORMAT " Phantom: " SIZE_FORMAT,
263 stats.soft_count(), stats.weak_count(), stats.final_count(), stats.phantom_count());
264 log_develop_trace(gc, ref)("JNI Weak Reference count: " SIZE_FORMAT, count_jni_refs());
265
266 return stats;
267 }
268
269 #ifndef PRODUCT
270 // Calculate the number of jni handles.
271 size_t ReferenceProcessor::count_jni_refs() {
272 class CountHandleClosure: public OopClosure {
273 private:
274 size_t _count;
275 public:
276 CountHandleClosure(): _count(0) {}
277 void do_oop(oop* unused) { _count++; }
278 void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
279 size_t count() { return _count; }
280 };
281 CountHandleClosure global_handle_count;
282 JNIHandles::weak_oops_do(&global_handle_count);
283 return global_handle_count.count();
284 }
285 #endif
286
287 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
288 OopClosure* keep_alive,
289 VoidClosure* complete_gc) {
290 JNIHandles::weak_oops_do(is_alive, keep_alive);
291 complete_gc->do_void();
292 }
293
294 void ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
295 // Enqueue references that are not made active again, and
296 // clear the decks for the next collection (cycle).
297 enqueue_discovered_reflists(task_executor);
298
299 // Stop treating discovered references specially.
300 disable_discovery();
301 }
302
303 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list) {
304 // Given a list of refs linked through the "discovered" field
305 // (java.lang.ref.Reference.discovered), self-loop their "next" field
306 // thus distinguishing them from active References, then
307 // prepend them to the pending list.
308 //
309 // The Java threads will see the Reference objects linked together through
310 // the discovered field. Instead of trying to do the write barrier updates
311 // in all places in the reference processor where we manipulate the discovered
312 // field we make sure to do the barrier here where we anyway iterate through
313 // all linked Reference objects. Note that it is important to not dirty any
314 // cards during reference processing since this will cause card table
315 // verification to fail for G1.
316 log_develop_trace(gc, ref)("ReferenceProcessor::enqueue_discovered_reflist list " INTPTR_FORMAT, p2i(&refs_list));
317
318 oop obj = NULL;
319 oop next_d = refs_list.head();
320 // Walk down the list, self-looping the next field
321 // so that the References are not considered active.
322 while (obj != next_d) {
323 obj = next_d;
324 assert(obj->is_instance(), "should be an instance object");
325 assert(InstanceKlass::cast(obj->klass())->is_reference_instance_klass(), "should be reference object");
326 next_d = java_lang_ref_Reference::discovered(obj);
327 log_develop_trace(gc, ref)(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT, p2i(obj), p2i(next_d));
328 assert(java_lang_ref_Reference::next(obj) == NULL,
329 "Reference not active; should not be discovered");
330 // Self-loop next, so as to make Ref not active.
331 java_lang_ref_Reference::set_next_raw(obj, obj);
332 if (next_d != obj) {
333 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
334 } else {
335 // This is the last object.
336 // Swap refs_list into pending list and set obj's
337 // discovered to what we read from the pending list.
338 oop old = Universe::swap_reference_pending_list(refs_list.head());
339 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
340 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
341 }
342 }
343 }
344
345 // Parallel enqueue task
346 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
347 public:
348 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
349 DiscoveredList discovered_refs[],
350 int n_queues)
351 : EnqueueTask(ref_processor, discovered_refs, n_queues)
352 { }
353
354 virtual void work(unsigned int work_id) {
355 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
356 // Simplest first cut: static partitioning.
357 int index = work_id;
358 // The increment on "index" must correspond to the maximum number of queues
359 // (n_queues) with which that ReferenceProcessor was created. That
360 // is because of the "clever" way the discovered references lists were
361 // allocated and are indexed into.
362 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
363 for (int j = 0;
364 j < ReferenceProcessor::number_of_subclasses_of_ref();
365 j++, index += _n_queues) {
366 _ref_processor.enqueue_discovered_reflist(_refs_lists[index]);
367 _refs_lists[index].set_head(NULL);
368 _refs_lists[index].set_length(0);
369 }
370 }
371 };
372
373 // Enqueue references that are not made active again
374 void ReferenceProcessor::enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor) {
375 if (_processing_is_mt && task_executor != NULL) {
376 // Parallel code
377 RefProcEnqueueTask tsk(*this, _discovered_refs, _max_num_q);
378 task_executor->execute(tsk);
379 } else {
380 // Serial code: call the parent class's implementation
381 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
382 enqueue_discovered_reflist(_discovered_refs[i]);
383 _discovered_refs[i].set_head(NULL);
384 _discovered_refs[i].set_length(0);
385 }
386 }
387 }
388
389 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
390 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
391 oop discovered = java_lang_ref_Reference::discovered(_ref);
392 assert(_discovered_addr && discovered->is_oop_or_null(),
393 "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
394 _next = discovered;
395 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
396 _referent = java_lang_ref_Reference::referent(_ref);
397 assert(Universe::heap()->is_in_reserved_or_null(_referent),
398 "Wrong oop found in java.lang.Reference object");
399 assert(allow_null_referent ?
400 _referent->is_oop_or_null()
401 : _referent->is_oop(),
402 "Expected an oop%s for referent field at " PTR_FORMAT,
403 (allow_null_referent ? " or NULL" : ""),
404 p2i(_referent));
405 }
406
407 void DiscoveredListIterator::remove() {
408 assert(_ref->is_oop(), "Dropping a bad reference");
409 oop_store_raw(_discovered_addr, NULL);
410
411 // First _prev_next ref actually points into DiscoveredList (gross).
412 oop new_next;
413 if (_next == _ref) {
414 // At the end of the list, we should make _prev point to itself.
415 // If _ref is the first ref, then _prev_next will be in the DiscoveredList,
416 // and _prev will be NULL.
417 new_next = _prev;
418 } else {
419 new_next = _next;
420 }
421 // Remove Reference object from discovered list. Note that G1 does not need a
422 // pre-barrier here because we know the Reference has already been found/marked,
423 // that's how it ended up in the discovered list in the first place.
424 oop_store_raw(_prev_next, new_next);
425 NOT_PRODUCT(_removed++);
426 _refs_list.dec_length(1);
427 }
428
429 void DiscoveredListIterator::clear_referent() {
430 oop_store_raw(_referent_addr, NULL);
431 }
432
433 // NOTE: process_phase*() are largely similar, and at a high level
434 // merely iterate over the extant list applying a predicate to
435 // each of its elements and possibly removing that element from the
436 // list and applying some further closures to that element.
437 // We should consider the possibility of replacing these
438 // process_phase*() methods by abstracting them into
439 // a single general iterator invocation that receives appropriate
440 // closures that accomplish this work.
441
442 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
443 // referents are not alive, but that should be kept alive for policy reasons.
444 // Keep alive the transitive closure of all such referents.
445 void
446 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
447 ReferencePolicy* policy,
448 BoolObjectClosure* is_alive,
449 OopClosure* keep_alive,
450 VoidClosure* complete_gc) {
451 assert(policy != NULL, "Must have a non-NULL policy");
452 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
453 // Decide which softly reachable refs should be kept alive.
454 while (iter.has_next()) {
455 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
456 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
457 if (referent_is_dead &&
458 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
459 log_develop_trace(gc, ref)("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
460 p2i(iter.obj()), iter.obj()->klass()->internal_name());
461 // Remove Reference object from list
462 iter.remove();
463 // keep the referent around
464 iter.make_referent_alive();
465 iter.move_to_next();
466 } else {
467 iter.next();
468 }
469 }
470 // Close the reachable set
471 complete_gc->do_void();
472 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT,
473 iter.removed(), iter.processed(), p2i(&refs_list));
474 }
475
476 // Traverse the list and remove any Refs that are not active, or
477 // whose referents are either alive or NULL.
478 void
479 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
480 BoolObjectClosure* is_alive,
481 OopClosure* keep_alive) {
482 assert(discovery_is_atomic(), "Error");
483 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
484 while (iter.has_next()) {
485 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
486 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
487 assert(next == NULL, "Should not discover inactive Reference");
488 if (iter.is_referent_alive()) {
489 log_develop_trace(gc, ref)("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
490 p2i(iter.obj()), iter.obj()->klass()->internal_name());
491 // The referent is reachable after all.
492 // Remove Reference object from list.
493 iter.remove();
494 // Update the referent pointer as necessary: Note that this
495 // should not entail any recursive marking because the
496 // referent must already have been traversed.
497 iter.make_referent_alive();
498 iter.move_to_next();
499 } else {
500 iter.next();
501 }
502 }
503 NOT_PRODUCT(
504 if (iter.processed() > 0) {
505 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
506 " Refs in discovered list " INTPTR_FORMAT,
507 iter.removed(), iter.processed(), p2i(&refs_list));
508 }
509 )
510 }
511
512 void
513 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
514 BoolObjectClosure* is_alive,
515 OopClosure* keep_alive,
516 VoidClosure* complete_gc) {
517 assert(!discovery_is_atomic(), "Error");
518 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
519 while (iter.has_next()) {
520 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
521 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
522 oop next = java_lang_ref_Reference::next(iter.obj());
523 if ((iter.referent() == NULL || iter.is_referent_alive() ||
524 next != NULL)) {
525 assert(next->is_oop_or_null(), "Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next));
526 // Remove Reference object from list
527 iter.remove();
528 // Trace the cohorts
529 iter.make_referent_alive();
530 if (UseCompressedOops) {
531 keep_alive->do_oop((narrowOop*)next_addr);
532 } else {
533 keep_alive->do_oop((oop*)next_addr);
534 }
535 iter.move_to_next();
536 } else {
537 iter.next();
538 }
539 }
540 // Now close the newly reachable set
541 complete_gc->do_void();
542 NOT_PRODUCT(
543 if (iter.processed() > 0) {
544 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
545 " Refs in discovered list " INTPTR_FORMAT,
546 iter.removed(), iter.processed(), p2i(&refs_list));
547 }
548 )
549 }
550
551 // Traverse the list and process the referents, by either
552 // clearing them or keeping them (and their reachable
553 // closure) alive.
554 void
555 ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
556 bool clear_referent,
557 BoolObjectClosure* is_alive,
558 OopClosure* keep_alive,
559 VoidClosure* complete_gc) {
560 ResourceMark rm;
561 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
562 while (iter.has_next()) {
563 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
564 if (clear_referent) {
565 // NULL out referent pointer
566 iter.clear_referent();
567 } else {
568 // keep the referent around
569 iter.make_referent_alive();
570 }
571 log_develop_trace(gc, ref)("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
572 clear_referent ? "cleared " : "", p2i(iter.obj()), iter.obj()->klass()->internal_name());
573 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
574 iter.next();
575 }
576 // Close the reachable set
577 complete_gc->do_void();
578 }
579
580 void
581 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
582 oop obj = NULL;
583 oop next = refs_list.head();
584 while (next != obj) {
585 obj = next;
586 next = java_lang_ref_Reference::discovered(obj);
587 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
588 }
589 refs_list.set_head(NULL);
590 refs_list.set_length(0);
591 }
592
593 void ReferenceProcessor::abandon_partial_discovery() {
594 // loop over the lists
595 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
596 if ((i % _max_num_q) == 0) {
597 log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i));
598 }
599 clear_discovered_references(_discovered_refs[i]);
600 }
601 }
602
603 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
604 public:
605 RefProcPhase1Task(ReferenceProcessor& ref_processor,
606 DiscoveredList refs_lists[],
607 ReferencePolicy* policy,
608 bool marks_oops_alive)
609 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
610 _policy(policy)
611 { }
612 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
613 OopClosure& keep_alive,
614 VoidClosure& complete_gc)
615 {
616 _ref_processor.process_phase1(_refs_lists[i], _policy,
617 &is_alive, &keep_alive, &complete_gc);
618 }
619 private:
620 ReferencePolicy* _policy;
621 };
622
623 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
624 public:
625 RefProcPhase2Task(ReferenceProcessor& ref_processor,
626 DiscoveredList refs_lists[],
627 bool marks_oops_alive)
628 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
629 { }
630 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
631 OopClosure& keep_alive,
632 VoidClosure& complete_gc)
633 {
634 _ref_processor.process_phase2(_refs_lists[i],
635 &is_alive, &keep_alive, &complete_gc);
636 }
637 };
638
639 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
640 public:
641 RefProcPhase3Task(ReferenceProcessor& ref_processor,
642 DiscoveredList refs_lists[],
643 bool clear_referent,
644 bool marks_oops_alive)
645 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
646 _clear_referent(clear_referent)
647 { }
648 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
649 OopClosure& keep_alive,
650 VoidClosure& complete_gc)
651 {
652 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
653 &is_alive, &keep_alive, &complete_gc);
654 }
655 private:
656 bool _clear_referent;
657 };
658
659 #ifndef PRODUCT
660 void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_refs) {
661 if (!log_is_enabled(Trace, gc, ref)) {
662 return;
663 }
664
665 stringStream st;
666 for (uint i = 0; i < active_length; ++i) {
667 st.print(SIZE_FORMAT " ", ref_lists[i].length());
668 }
669 log_develop_trace(gc, ref)("%s= " SIZE_FORMAT, st.as_string(), total_refs);
670 #ifdef ASSERT
671 for (uint i = active_length; i < _max_num_q; i++) {
672 assert(ref_lists[i].length() == 0, SIZE_FORMAT " unexpected References in %u",
673 ref_lists[i].length(), i);
674 }
675 #endif
676 }
677 #endif
678
679 void ReferenceProcessor::set_active_mt_degree(uint v) {
680 _num_q = v;
681 _next_id = 0;
682 }
683
684 // Balances reference queues.
685 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
686 // queues[0, 1, ..., _num_q-1] because only the first _num_q
687 // corresponding to the active workers will be processed.
688 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
689 {
690 // calculate total length
691 size_t total_refs = 0;
692 log_develop_trace(gc, ref)("Balance ref_lists ");
693
694 for (uint i = 0; i < _max_num_q; ++i) {
695 total_refs += ref_lists[i].length();
696 }
697 log_reflist_counts(ref_lists, _max_num_q, total_refs);
698 size_t avg_refs = total_refs / _num_q + 1;
699 uint to_idx = 0;
700 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) {
701 bool move_all = false;
702 if (from_idx >= _num_q) {
703 move_all = ref_lists[from_idx].length() > 0;
704 }
705 while ((ref_lists[from_idx].length() > avg_refs) ||
706 move_all) {
707 assert(to_idx < _num_q, "Sanity Check!");
708 if (ref_lists[to_idx].length() < avg_refs) {
709 // move superfluous refs
710 size_t refs_to_move;
711 // Move all the Ref's if the from queue will not be processed.
712 if (move_all) {
713 refs_to_move = MIN2(ref_lists[from_idx].length(),
714 avg_refs - ref_lists[to_idx].length());
715 } else {
716 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
717 avg_refs - ref_lists[to_idx].length());
718 }
719
720 assert(refs_to_move > 0, "otherwise the code below will fail");
721
722 oop move_head = ref_lists[from_idx].head();
723 oop move_tail = move_head;
724 oop new_head = move_head;
725 // find an element to split the list on
726 for (size_t j = 0; j < refs_to_move; ++j) {
727 move_tail = new_head;
728 new_head = java_lang_ref_Reference::discovered(new_head);
729 }
730
731 // Add the chain to the to list.
732 if (ref_lists[to_idx].head() == NULL) {
733 // to list is empty. Make a loop at the end.
734 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
735 } else {
736 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
737 }
738 ref_lists[to_idx].set_head(move_head);
739 ref_lists[to_idx].inc_length(refs_to_move);
740
741 // Remove the chain from the from list.
742 if (move_tail == new_head) {
743 // We found the end of the from list.
744 ref_lists[from_idx].set_head(NULL);
745 } else {
746 ref_lists[from_idx].set_head(new_head);
747 }
748 ref_lists[from_idx].dec_length(refs_to_move);
749 if (ref_lists[from_idx].length() == 0) {
750 break;
751 }
752 } else {
753 to_idx = (to_idx + 1) % _num_q;
754 }
755 }
756 }
757 #ifdef ASSERT
758 size_t balanced_total_refs = 0;
759 for (uint i = 0; i < _num_q; ++i) {
760 balanced_total_refs += ref_lists[i].length();
761 }
762 log_reflist_counts(ref_lists, _num_q, balanced_total_refs);
763 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
764 #endif
765 }
766
767 void ReferenceProcessor::balance_all_queues() {
768 balance_queues(_discoveredSoftRefs);
769 balance_queues(_discoveredWeakRefs);
770 balance_queues(_discoveredFinalRefs);
771 balance_queues(_discoveredPhantomRefs);
772 }
773
774 void ReferenceProcessor::process_discovered_reflist(
775 DiscoveredList refs_lists[],
776 ReferencePolicy* policy,
777 bool clear_referent,
778 BoolObjectClosure* is_alive,
779 OopClosure* keep_alive,
780 VoidClosure* complete_gc,
781 AbstractRefProcTaskExecutor* task_executor)
782 {
783 bool mt_processing = task_executor != NULL && _processing_is_mt;
784 // If discovery used MT and a dynamic number of GC threads, then
785 // the queues must be balanced for correctness if fewer than the
786 // maximum number of queues were used. The number of queue used
787 // during discovery may be different than the number to be used
788 // for processing so don't depend of _num_q < _max_num_q as part
789 // of the test.
790 bool must_balance = _discovery_is_mt;
791
792 if ((mt_processing && ParallelRefProcBalancingEnabled) ||
793 must_balance) {
794 balance_queues(refs_lists);
795 }
796
797 // Phase 1 (soft refs only):
798 // . Traverse the list and remove any SoftReferences whose
799 // referents are not alive, but that should be kept alive for
800 // policy reasons. Keep alive the transitive closure of all
801 // such referents.
802 if (policy != NULL) {
803 if (mt_processing) {
804 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
805 task_executor->execute(phase1);
806 } else {
807 for (uint i = 0; i < _max_num_q; i++) {
808 process_phase1(refs_lists[i], policy,
809 is_alive, keep_alive, complete_gc);
810 }
811 }
812 } else { // policy == NULL
813 assert(refs_lists != _discoveredSoftRefs,
814 "Policy must be specified for soft references.");
815 }
816
817 // Phase 2:
818 // . Traverse the list and remove any refs whose referents are alive.
819 if (mt_processing) {
820 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
821 task_executor->execute(phase2);
822 } else {
823 for (uint i = 0; i < _max_num_q; i++) {
824 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
825 }
826 }
827
828 // Phase 3:
829 // . Traverse the list and process referents as appropriate.
830 if (mt_processing) {
831 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
832 task_executor->execute(phase3);
833 } else {
834 for (uint i = 0; i < _max_num_q; i++) {
835 process_phase3(refs_lists[i], clear_referent,
836 is_alive, keep_alive, complete_gc);
837 }
838 }
839 }
840
841 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
842 uint id = 0;
843 // Determine the queue index to use for this object.
844 if (_discovery_is_mt) {
845 // During a multi-threaded discovery phase,
846 // each thread saves to its "own" list.
847 Thread* thr = Thread::current();
848 id = thr->as_Worker_thread()->id();
849 } else {
850 // single-threaded discovery, we save in round-robin
851 // fashion to each of the lists.
852 if (_processing_is_mt) {
853 id = next_id();
854 }
855 }
856 assert(id < _max_num_q, "Id is out-of-bounds id %u and max id %u)", id, _max_num_q);
857
858 // Get the discovered queue to which we will add
859 DiscoveredList* list = NULL;
860 switch (rt) {
861 case REF_OTHER:
862 // Unknown reference type, no special treatment
863 break;
864 case REF_SOFT:
865 list = &_discoveredSoftRefs[id];
866 break;
867 case REF_WEAK:
868 list = &_discoveredWeakRefs[id];
869 break;
870 case REF_FINAL:
871 list = &_discoveredFinalRefs[id];
872 break;
873 case REF_PHANTOM:
874 list = &_discoveredPhantomRefs[id];
875 break;
876 case REF_NONE:
877 // we should not reach here if we are an InstanceRefKlass
878 default:
879 ShouldNotReachHere();
880 }
881 log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list));
882 return list;
883 }
884
885 inline void
886 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
887 oop obj,
888 HeapWord* discovered_addr) {
889 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
890 // First we must make sure this object is only enqueued once. CAS in a non null
891 // discovered_addr.
892 oop current_head = refs_list.head();
893 // The last ref must have its discovered field pointing to itself.
894 oop next_discovered = (current_head != NULL) ? current_head : obj;
895
896 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr,
897 NULL);
898 if (retest == NULL) {
899 // This thread just won the right to enqueue the object.
900 // We have separate lists for enqueueing, so no synchronization
901 // is necessary.
902 refs_list.set_head(obj);
903 refs_list.inc_length(1);
904
905 log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
906 p2i(obj), obj->klass()->internal_name());
907 } else {
908 // If retest was non NULL, another thread beat us to it:
909 // The reference has already been discovered...
910 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
911 p2i(obj), obj->klass()->internal_name());
912 }
913 }
914
915 #ifndef PRODUCT
916 // Non-atomic (i.e. concurrent) discovery might allow us
917 // to observe j.l.References with NULL referents, being those
918 // cleared concurrently by mutators during (or after) discovery.
919 void ReferenceProcessor::verify_referent(oop obj) {
920 bool da = discovery_is_atomic();
921 oop referent = java_lang_ref_Reference::referent(obj);
922 assert(da ? referent->is_oop() : referent->is_oop_or_null(),
923 "Bad referent " INTPTR_FORMAT " found in Reference "
924 INTPTR_FORMAT " during %satomic discovery ",
925 p2i(referent), p2i(obj), da ? "" : "non-");
926 }
927 #endif
928
929 // We mention two of several possible choices here:
930 // #0: if the reference object is not in the "originating generation"
931 // (or part of the heap being collected, indicated by our "span"
932 // we don't treat it specially (i.e. we scan it as we would
933 // a normal oop, treating its references as strong references).
934 // This means that references can't be discovered unless their
935 // referent is also in the same span. This is the simplest,
936 // most "local" and most conservative approach, albeit one
937 // that may cause weak references to be enqueued least promptly.
938 // We call this choice the "ReferenceBasedDiscovery" policy.
939 // #1: the reference object may be in any generation (span), but if
940 // the referent is in the generation (span) being currently collected
941 // then we can discover the reference object, provided
942 // the object has not already been discovered by
943 // a different concurrently running collector (as may be the
944 // case, for instance, if the reference object is in CMS and
945 // the referent in DefNewGeneration), and provided the processing
946 // of this reference object by the current collector will
947 // appear atomic to every other collector in the system.
948 // (Thus, for instance, a concurrent collector may not
949 // discover references in other generations even if the
950 // referent is in its own generation). This policy may,
951 // in certain cases, enqueue references somewhat sooner than
952 // might Policy #0 above, but at marginally increased cost
953 // and complexity in processing these references.
954 // We call this choice the "RefeferentBasedDiscovery" policy.
955 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
956 // Make sure we are discovering refs (rather than processing discovered refs).
957 if (!_discovering_refs || !RegisterReferences) {
958 return false;
959 }
960 // We only discover active references.
961 oop next = java_lang_ref_Reference::next(obj);
962 if (next != NULL) { // Ref is no longer active
963 return false;
964 }
965
966 HeapWord* obj_addr = (HeapWord*)obj;
967 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
968 !_span.contains(obj_addr)) {
969 // Reference is not in the originating generation;
970 // don't treat it specially (i.e. we want to scan it as a normal
971 // object with strong references).
972 return false;
973 }
974
975 // We only discover references whose referents are not (yet)
976 // known to be strongly reachable.
977 if (is_alive_non_header() != NULL) {
978 verify_referent(obj);
979 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
980 return false; // referent is reachable
981 }
982 }
983 if (rt == REF_SOFT) {
984 // For soft refs we can decide now if these are not
985 // current candidates for clearing, in which case we
986 // can mark through them now, rather than delaying that
987 // to the reference-processing phase. Since all current
988 // time-stamp policies advance the soft-ref clock only
989 // at a full collection cycle, this is always currently
990 // accurate.
991 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
992 return false;
993 }
994 }
995
996 ResourceMark rm; // Needed for tracing.
997
998 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
999 const oop discovered = java_lang_ref_Reference::discovered(obj);
1000 assert(discovered->is_oop_or_null(), "Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered));
1001 if (discovered != NULL) {
1002 // The reference has already been discovered...
1003 log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)",
1004 p2i(obj), obj->klass()->internal_name());
1005 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1006 // assumes that an object is not processed twice;
1007 // if it's been already discovered it must be on another
1008 // generation's discovered list; so we won't discover it.
1009 return false;
1010 } else {
1011 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1012 "Unrecognized policy");
1013 // Check assumption that an object is not potentially
1014 // discovered twice except by concurrent collectors that potentially
1015 // trace the same Reference object twice.
1016 assert(UseConcMarkSweepGC || UseG1GC,
1017 "Only possible with a concurrent marking collector");
1018 return true;
1019 }
1020 }
1021
1022 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1023 verify_referent(obj);
1024 // Discover if and only if EITHER:
1025 // .. reference is in our span, OR
1026 // .. we are an atomic collector and referent is in our span
1027 if (_span.contains(obj_addr) ||
1028 (discovery_is_atomic() &&
1029 _span.contains(java_lang_ref_Reference::referent(obj)))) {
1030 // should_enqueue = true;
1031 } else {
1032 return false;
1033 }
1034 } else {
1035 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1036 _span.contains(obj_addr), "code inconsistency");
1037 }
1038
1039 // Get the right type of discovered queue head.
1040 DiscoveredList* list = get_discovered_list(rt);
1041 if (list == NULL) {
1042 return false; // nothing special needs to be done
1043 }
1044
1045 if (_discovery_is_mt) {
1046 add_to_discovered_list_mt(*list, obj, discovered_addr);
1047 } else {
1048 // We do a raw store here: the field will be visited later when processing
1049 // the discovered references.
1050 oop current_head = list->head();
1051 // The last ref must have its discovered field pointing to itself.
1052 oop next_discovered = (current_head != NULL) ? current_head : obj;
1053
1054 assert(discovered == NULL, "control point invariant");
1055 oop_store_raw(discovered_addr, next_discovered);
1056 list->set_head(obj);
1057 list->inc_length(1);
1058
1059 log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name());
1060 }
1061 assert(obj->is_oop(), "Discovered a bad reference");
1062 verify_referent(obj);
1063 return true;
1064 }
1065
1066 bool ReferenceProcessor::has_discovered_references() {
1067 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
1068 if (!_discovered_refs[i].is_empty()) {
1069 return true;
1070 }
1071 }
1072 return false;
1073 }
1074
1075 // Preclean the discovered references by removing those
1076 // whose referents are alive, and by marking from those that
1077 // are not active. These lists can be handled here
1078 // in any order and, indeed, concurrently.
1079 void ReferenceProcessor::preclean_discovered_references(
1080 BoolObjectClosure* is_alive,
1081 OopClosure* keep_alive,
1082 VoidClosure* complete_gc,
1083 YieldClosure* yield,
1084 GCTimer* gc_timer) {
1085
1086 // Soft references
1087 {
1088 GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer);
1089 for (uint i = 0; i < _max_num_q; i++) {
1090 if (yield->should_return()) {
1091 return;
1092 }
1093 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1094 keep_alive, complete_gc, yield);
1095 }
1096 }
1097
1098 // Weak references
1099 {
1100 GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer);
1101 for (uint i = 0; i < _max_num_q; i++) {
1102 if (yield->should_return()) {
1103 return;
1104 }
1105 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1106 keep_alive, complete_gc, yield);
1107 }
1108 }
1109
1110 // Final references
1111 {
1112 GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer);
1113 for (uint i = 0; i < _max_num_q; i++) {
1114 if (yield->should_return()) {
1115 return;
1116 }
1117 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1118 keep_alive, complete_gc, yield);
1119 }
1120 }
1121
1122 // Phantom references
1123 {
1124 GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer);
1125 for (uint i = 0; i < _max_num_q; i++) {
1126 if (yield->should_return()) {
1127 return;
1128 }
1129 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1130 keep_alive, complete_gc, yield);
1131 }
1132 }
1133 }
1134
1135 // Walk the given discovered ref list, and remove all reference objects
1136 // whose referents are still alive, whose referents are NULL or which
1137 // are not active (have a non-NULL next field). NOTE: When we are
1138 // thus precleaning the ref lists (which happens single-threaded today),
1139 // we do not disable refs discovery to honor the correct semantics of
1140 // java.lang.Reference. As a result, we need to be careful below
1141 // that ref removal steps interleave safely with ref discovery steps
1142 // (in this thread).
1143 void
1144 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1145 BoolObjectClosure* is_alive,
1146 OopClosure* keep_alive,
1147 VoidClosure* complete_gc,
1148 YieldClosure* yield) {
1149 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1150 while (iter.has_next()) {
1151 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1152 oop obj = iter.obj();
1153 oop next = java_lang_ref_Reference::next(obj);
1154 if (iter.referent() == NULL || iter.is_referent_alive() ||
1155 next != NULL) {
1156 // The referent has been cleared, or is alive, or the Reference is not
1157 // active; we need to trace and mark its cohort.
1158 log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1159 p2i(iter.obj()), iter.obj()->klass()->internal_name());
1160 // Remove Reference object from list
1161 iter.remove();
1162 // Keep alive its cohort.
1163 iter.make_referent_alive();
1164 if (UseCompressedOops) {
1165 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
1166 keep_alive->do_oop(next_addr);
1167 } else {
1168 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
1169 keep_alive->do_oop(next_addr);
1170 }
1171 iter.move_to_next();
1172 } else {
1173 iter.next();
1174 }
1175 }
1176 // Close the reachable set
1177 complete_gc->do_void();
1178
1179 NOT_PRODUCT(
1180 if (iter.processed() > 0) {
1181 log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_FORMAT,
1182 iter.removed(), iter.processed(), p2i(&refs_list));
1183 }
1184 )
1185 }
1186
1187 const char* ReferenceProcessor::list_name(uint i) {
1188 assert(i <= _max_num_q * number_of_subclasses_of_ref(),
1189 "Out of bounds index");
1190
1191 int j = i / _max_num_q;
1192 switch (j) {
1193 case 0: return "SoftRef";
1194 case 1: return "WeakRef";
1195 case 2: return "FinalRef";
1196 case 3: return "PhantomRef";
1197 }
1198 ShouldNotReachHere();
1199 return NULL;
1200 }
1201