1 /*
2 * Copyright (c) 2001, 2014, 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_implementation/shared/gcTimer.hpp"
29 #include "gc_implementation/shared/gcTraceTime.hpp"
30 #include "gc_interface/collectedHeap.hpp"
31 #include "gc_interface/collectedHeap.inline.hpp"
32 #include "memory/referencePolicy.hpp"
33 #include "memory/referenceProcessor.hpp"
34 #include "oops/oop.inline.hpp"
35 #include "runtime/java.hpp"
36 #include "runtime/jniHandles.hpp"
37
38 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
39
40 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
41 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
42 bool ReferenceProcessor::_pending_list_uses_discovered_field = false;
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-deccreasing 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 _default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy())
61 NOT_COMPILER2(LRUCurrentHeapPolicy());
62 if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
63 vm_exit_during_initialization("Could not allocate reference policy object");
64 }
65 guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
66 RefDiscoveryPolicy == ReferentBasedDiscovery,
67 "Unrecongnized RefDiscoveryPolicy");
68 _pending_list_uses_discovered_field = JDK_Version::current().pending_list_uses_discovered_field();
69 }
70
71 void ReferenceProcessor::enable_discovery(bool verify_disabled, bool check_no_refs) {
72 #ifdef ASSERT
73 // Verify that we're not currently discovering refs
74 assert(!verify_disabled || !_discovering_refs, "nested call?");
75
76 if (check_no_refs) {
77 // Verify that the discovered lists are empty
78 verify_no_references_recorded();
79 }
80 #endif // ASSERT
81
82 // Someone could have modified the value of the static
83 // field in the j.l.r.SoftReference class that holds the
84 // soft reference timestamp clock using reflection or
85 // Unsafe between GCs. Unconditionally update the static
86 // field in ReferenceProcessor here so that we use the new
87 // value during reference discovery.
88
89 _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
90 _discovering_refs = true;
91 }
92
93 ReferenceProcessor::ReferenceProcessor(MemRegion span,
94 bool mt_processing,
95 uint mt_processing_degree,
96 bool mt_discovery,
97 uint mt_discovery_degree,
98 bool atomic_discovery,
99 BoolObjectClosure* is_alive_non_header) :
100 _discovering_refs(false),
101 _enqueuing_is_done(false),
102 _is_alive_non_header(is_alive_non_header),
103 _processing_is_mt(mt_processing),
104 _next_id(0)
105 {
106 _span = span;
107 _discovery_is_atomic = atomic_discovery;
108 _discovery_is_mt = mt_discovery;
109 _num_q = MAX2(1U, mt_processing_degree);
110 _max_num_q = MAX2(_num_q, mt_discovery_degree);
111 _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
112 _max_num_q * number_of_subclasses_of_ref(), mtGC);
113
114 if (_discovered_refs == NULL) {
115 vm_exit_during_initialization("Could not allocated RefProc Array");
116 }
117 _discoveredSoftRefs = &_discovered_refs[0];
118 _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q];
119 _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q];
120 _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q];
121 _discoveredCleanerRefs = &_discoveredPhantomRefs[_max_num_q];
122
123 // Initialize all entries to NULL
124 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
125 _discovered_refs[i].set_head(NULL);
126 _discovered_refs[i].set_length(0);
127 }
128
129 setup_policy(false /* default soft ref policy */);
130 }
131
132 #ifndef PRODUCT
133 void ReferenceProcessor::verify_no_references_recorded() {
134 guarantee(!_discovering_refs, "Discovering refs?");
135 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
136 guarantee(_discovered_refs[i].is_empty(),
137 "Found non-empty discovered list");
138 }
139 }
140 #endif
141
142 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
143 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
144 if (UseCompressedOops) {
145 f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
146 } else {
147 f->do_oop((oop*)_discovered_refs[i].adr_head());
148 }
149 }
150 }
151
152 void ReferenceProcessor::update_soft_ref_master_clock() {
153 // Update (advance) the soft ref master clock field. This must be done
154 // after processing the soft ref list.
155
156 // We need a monotonically non-deccreasing time in ms but
157 // os::javaTimeMillis() does not guarantee monotonicity.
158 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
159 jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
160 assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
161
162 NOT_PRODUCT(
163 if (now < _soft_ref_timestamp_clock) {
164 warning("time warp: "INT64_FORMAT" to "INT64_FORMAT,
165 _soft_ref_timestamp_clock, now);
166 }
167 )
168 // The values of now and _soft_ref_timestamp_clock are set using
169 // javaTimeNanos(), which is guaranteed to be monotonically
170 // non-decreasing provided the underlying platform provides such
171 // a time source (and it is bug free).
172 // In product mode, however, protect ourselves from non-monotonicty.
173 if (now > _soft_ref_timestamp_clock) {
174 _soft_ref_timestamp_clock = now;
175 java_lang_ref_SoftReference::set_clock(now);
176 }
177 // Else leave clock stalled at its old value until time progresses
178 // past clock value.
179 }
180
181 size_t ReferenceProcessor::total_count(DiscoveredList lists[]) {
182 size_t total = 0;
183 for (uint i = 0; i < _max_num_q; ++i) {
184 total += lists[i].length();
185 }
186 return total;
187 }
188
189 ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
190 BoolObjectClosure* is_alive,
191 OopClosure* keep_alive,
192 VoidClosure* complete_gc,
193 AbstractRefProcTaskExecutor* task_executor,
194 GCTimer* gc_timer,
195 GCId gc_id) {
196 NOT_PRODUCT(verify_ok_to_handle_reflists());
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 bool trace_time = PrintGCDetails && PrintReferenceGC;
213
214 // Soft references
215 size_t soft_count = 0;
216 {
217 GCTraceTime tt("SoftReference", trace_time, false, gc_timer, gc_id);
218 soft_count =
219 process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
220 is_alive, keep_alive, complete_gc, task_executor);
221 }
222
223 update_soft_ref_master_clock();
224
225 // Weak references
226 size_t weak_count = 0;
227 {
228 GCTraceTime tt("WeakReference", trace_time, false, gc_timer, gc_id);
229 weak_count =
230 process_discovered_reflist(_discoveredWeakRefs, NULL, true,
231 is_alive, keep_alive, complete_gc, task_executor);
232 }
233
234 // Final references
235 size_t final_count = 0;
236 {
237 GCTraceTime tt("FinalReference", trace_time, false, gc_timer, gc_id);
238 final_count =
239 process_discovered_reflist(_discoveredFinalRefs, NULL, false,
240 is_alive, keep_alive, complete_gc, task_executor);
241 }
242
243 // Phantom references
244 size_t phantom_count = 0;
245 {
246 GCTraceTime tt("PhantomReference", trace_time, false, gc_timer, gc_id);
247 phantom_count =
248 process_discovered_reflist(_discoveredPhantomRefs, NULL, false,
249 is_alive, keep_alive, complete_gc, task_executor);
250
251 // Process cleaners, but include them in phantom statistics. We expect
252 // Cleaner references to be temporary, and don't want to deal with
253 // possible incompatibilities arising from making it more visible.
254 phantom_count +=
255 process_discovered_reflist(_discoveredCleanerRefs, NULL, true,
256 is_alive, keep_alive, complete_gc, task_executor);
257 }
258
259 // Weak global JNI references. It would make more sense (semantically) to
260 // traverse these simultaneously with the regular weak references above, but
261 // that is not how the JDK1.2 specification is. See #4126360. Native code can
262 // thus use JNI weak references to circumvent the phantom references and
263 // resurrect a "post-mortem" object.
264 {
265 GCTraceTime tt("JNI Weak Reference", trace_time, false, gc_timer, gc_id);
266 if (task_executor != NULL) {
267 task_executor->set_single_threaded_mode();
268 }
269 process_phaseJNI(is_alive, keep_alive, complete_gc);
270 }
271
272 return ReferenceProcessorStats(soft_count, weak_count, final_count, phantom_count);
273 }
274
275 #ifndef PRODUCT
276 // Calculate the number of jni handles.
277 uint ReferenceProcessor::count_jni_refs() {
278 class AlwaysAliveClosure: public BoolObjectClosure {
279 public:
280 virtual bool do_object_b(oop obj) { return true; }
281 };
282
283 class CountHandleClosure: public OopClosure {
284 private:
285 int _count;
286 public:
287 CountHandleClosure(): _count(0) {}
288 void do_oop(oop* unused) { _count++; }
289 void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
290 int count() { return _count; }
291 };
292 CountHandleClosure global_handle_count;
293 AlwaysAliveClosure always_alive;
294 JNIHandles::weak_oops_do(&always_alive, &global_handle_count);
295 return global_handle_count.count();
296 }
297 #endif
298
299 void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
300 OopClosure* keep_alive,
301 VoidClosure* complete_gc) {
302 #ifndef PRODUCT
303 if (PrintGCDetails && PrintReferenceGC) {
304 unsigned int count = count_jni_refs();
305 gclog_or_tty->print(", %u refs", count);
306 }
307 #endif
308 JNIHandles::weak_oops_do(is_alive, keep_alive);
309 complete_gc->do_void();
310 }
311
312
313 template <class T>
314 bool enqueue_discovered_ref_helper(ReferenceProcessor* ref,
315 AbstractRefProcTaskExecutor* task_executor) {
316
317 // Remember old value of pending references list
318 T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr();
319 T old_pending_list_value = *pending_list_addr;
320
321 // Enqueue references that are not made active again, and
322 // clear the decks for the next collection (cycle).
323 ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor);
324 // Do the post-barrier on pending_list_addr missed in
325 // enqueue_discovered_reflist.
326 oopDesc::bs()->write_ref_field(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr));
327
328 // Stop treating discovered references specially.
329 ref->disable_discovery();
330
331 // Return true if new pending references were added
332 return old_pending_list_value != *pending_list_addr;
333 }
334
335 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
336 NOT_PRODUCT(verify_ok_to_handle_reflists());
337 if (UseCompressedOops) {
338 return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
339 } else {
340 return enqueue_discovered_ref_helper<oop>(this, task_executor);
341 }
342 }
343
344 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
345 HeapWord* pending_list_addr) {
346 // Given a list of refs linked through the "discovered" field
347 // (java.lang.ref.Reference.discovered), self-loop their "next" field
348 // thus distinguishing them from active References, then
349 // prepend them to the pending list.
350 //
351 // The Java threads will see the Reference objects linked together through
352 // the discovered field. Instead of trying to do the write barrier updates
353 // in all places in the reference processor where we manipulate the discovered
354 // field we make sure to do the barrier here where we anyway iterate through
355 // all linked Reference objects. Note that it is important to not dirty any
356 // cards during reference processing since this will cause card table
357 // verification to fail for G1.
358 //
359 // BKWRD COMPATIBILITY NOTE: For older JDKs (prior to the fix for 4956777),
360 // the "next" field is used to chain the pending list, not the discovered
361 // field.
362 if (TraceReferenceGC && PrintGCDetails) {
363 gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list "
364 INTPTR_FORMAT, (address)refs_list.head());
365 }
366
367 oop obj = NULL;
368 oop next_d = refs_list.head();
369 if (pending_list_uses_discovered_field()) { // New behavior
370 // Walk down the list, self-looping the next field
371 // so that the References are not considered active.
372 while (obj != next_d) {
373 obj = next_d;
374 assert(obj->is_instanceRef(), "should be reference object");
375 next_d = java_lang_ref_Reference::discovered(obj);
376 if (TraceReferenceGC && PrintGCDetails) {
377 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT,
378 (void *)obj, (void *)next_d);
379 }
380 assert(java_lang_ref_Reference::next(obj) == NULL,
381 "Reference not active; should not be discovered");
382 // Self-loop next, so as to make Ref not active.
383 java_lang_ref_Reference::set_next_raw(obj, obj);
384 if (next_d != obj) {
385 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
386 } else {
387 // This is the last object.
388 // Swap refs_list into pending_list_addr and
389 // set obj's discovered to what we read from pending_list_addr.
390 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
391 // Need post-barrier on pending_list_addr. See enqueue_discovered_ref_helper() above.
392 java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
393 oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
394 }
395 }
396 } else { // Old behaviour
397 // Walk down the list, copying the discovered field into
398 // the next field and clearing the discovered field.
399 while (obj != next_d) {
400 obj = next_d;
401 assert(obj->is_instanceRef(), "should be reference object");
402 next_d = java_lang_ref_Reference::discovered(obj);
403 if (TraceReferenceGC && PrintGCDetails) {
404 gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT,
405 (void *)obj, (void *)next_d);
406 }
407 assert(java_lang_ref_Reference::next(obj) == NULL,
408 "The reference should not be enqueued");
409 if (next_d == obj) { // obj is last
410 // Swap refs_list into pendling_list_addr and
411 // set obj's next to what we read from pending_list_addr.
412 oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
413 // Need oop_check on pending_list_addr above;
414 // see special oop-check code at the end of
415 // enqueue_discovered_reflists() further below.
416 if (old == NULL) {
417 // obj should be made to point to itself, since
418 // pending list was empty.
419 java_lang_ref_Reference::set_next(obj, obj);
420 } else {
421 java_lang_ref_Reference::set_next(obj, old);
422 }
423 } else {
424 java_lang_ref_Reference::set_next(obj, next_d);
425 }
426 java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
427 }
428 }
429 }
430
431 // Parallel enqueue task
432 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
433 public:
434 RefProcEnqueueTask(ReferenceProcessor& ref_processor,
435 DiscoveredList discovered_refs[],
436 HeapWord* pending_list_addr,
437 int n_queues)
438 : EnqueueTask(ref_processor, discovered_refs,
439 pending_list_addr, n_queues)
440 { }
441
442 virtual void work(unsigned int work_id) {
443 assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
444 // Simplest first cut: static partitioning.
445 int index = work_id;
446 // The increment on "index" must correspond to the maximum number of queues
447 // (n_queues) with which that ReferenceProcessor was created. That
448 // is because of the "clever" way the discovered references lists were
449 // allocated and are indexed into.
450 assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
451 for (int j = 0;
452 j < ReferenceProcessor::number_of_subclasses_of_ref();
453 j++, index += _n_queues) {
454 _ref_processor.enqueue_discovered_reflist(
455 _refs_lists[index], _pending_list_addr);
456 _refs_lists[index].set_head(NULL);
457 _refs_lists[index].set_length(0);
458 }
459 }
460 };
461
462 // Enqueue references that are not made active again
463 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr,
464 AbstractRefProcTaskExecutor* task_executor) {
465 if (_processing_is_mt && task_executor != NULL) {
466 // Parallel code
467 RefProcEnqueueTask tsk(*this, _discovered_refs,
468 pending_list_addr, _max_num_q);
469 task_executor->execute(tsk);
470 } else {
471 // Serial code: call the parent class's implementation
472 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
473 enqueue_discovered_reflist(_discovered_refs[i], pending_list_addr);
474 _discovered_refs[i].set_head(NULL);
475 _discovered_refs[i].set_length(0);
476 }
477 }
478 }
479
480 void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
481 _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
482 oop discovered = java_lang_ref_Reference::discovered(_ref);
483 assert(_discovered_addr && discovered->is_oop_or_null(),
484 "discovered field is bad");
485 _next = discovered;
486 _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
487 _referent = java_lang_ref_Reference::referent(_ref);
488 assert(Universe::heap()->is_in_reserved_or_null(_referent),
489 "Wrong oop found in java.lang.Reference object");
490 assert(allow_null_referent ?
491 _referent->is_oop_or_null()
492 : _referent->is_oop(),
493 "bad referent");
494 }
495
496 void DiscoveredListIterator::remove() {
497 assert(_ref->is_oop(), "Dropping a bad reference");
498 oop_store_raw(_discovered_addr, NULL);
499
500 // First _prev_next ref actually points into DiscoveredList (gross).
501 oop new_next;
502 if (_next == _ref) {
503 // At the end of the list, we should make _prev point to itself.
504 // If _ref is the first ref, then _prev_next will be in the DiscoveredList,
505 // and _prev will be NULL.
506 new_next = _prev;
507 } else {
508 new_next = _next;
509 }
510 // Remove Reference object from discovered list. Note that G1 does not need a
511 // pre-barrier here because we know the Reference has already been found/marked,
512 // that's how it ended up in the discovered list in the first place.
513 oop_store_raw(_prev_next, new_next);
514 NOT_PRODUCT(_removed++);
515 _refs_list.dec_length(1);
516 }
517
518 // Make the Reference object active again.
519 void DiscoveredListIterator::make_active() {
520 // The pre barrier for G1 is probably just needed for the old
521 // reference processing behavior. Should we guard this with
522 // ReferenceProcessor::pending_list_uses_discovered_field() ?
523 if (UseG1GC) {
524 HeapWord* next_addr = java_lang_ref_Reference::next_addr(_ref);
525 if (UseCompressedOops) {
526 oopDesc::bs()->write_ref_field_pre((narrowOop*)next_addr, NULL);
527 } else {
528 oopDesc::bs()->write_ref_field_pre((oop*)next_addr, NULL);
529 }
530 }
531 java_lang_ref_Reference::set_next_raw(_ref, NULL);
532 }
533
534 void DiscoveredListIterator::clear_referent() {
535 oop_store_raw(_referent_addr, NULL);
536 }
537
538 // NOTE: process_phase*() are largely similar, and at a high level
539 // merely iterate over the extant list applying a predicate to
540 // each of its elements and possibly removing that element from the
541 // list and applying some further closures to that element.
542 // We should consider the possibility of replacing these
543 // process_phase*() methods by abstracting them into
544 // a single general iterator invocation that receives appropriate
545 // closures that accomplish this work.
546
547 // (SoftReferences only) Traverse the list and remove any SoftReferences whose
548 // referents are not alive, but that should be kept alive for policy reasons.
549 // Keep alive the transitive closure of all such referents.
550 void
551 ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
552 ReferencePolicy* policy,
553 BoolObjectClosure* is_alive,
554 OopClosure* keep_alive,
555 VoidClosure* complete_gc) {
556 assert(policy != NULL, "Must have a non-NULL policy");
557 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
558 // Decide which softly reachable refs should be kept alive.
559 while (iter.has_next()) {
560 iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
561 bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
562 if (referent_is_dead &&
563 !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
564 if (TraceReferenceGC) {
565 gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
566 (void *)iter.obj(), iter.obj()->klass()->internal_name());
567 }
568 // Remove Reference object from list
569 iter.remove();
570 // Make the Reference object active again
571 iter.make_active();
572 // keep the referent around
573 iter.make_referent_alive();
574 iter.move_to_next();
575 } else {
576 iter.next();
577 }
578 }
579 // Close the reachable set
580 complete_gc->do_void();
581 NOT_PRODUCT(
582 if (PrintGCDetails && TraceReferenceGC) {
583 gclog_or_tty->print_cr(" Dropped %d dead Refs out of %d "
584 "discovered Refs by policy, from list " INTPTR_FORMAT,
585 iter.removed(), iter.processed(), (address)refs_list.head());
586 }
587 )
588 }
589
590 // Traverse the list and remove any Refs that are not active, or
591 // whose referents are either alive or NULL.
592 void
593 ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
594 BoolObjectClosure* is_alive,
595 OopClosure* keep_alive) {
596 assert(discovery_is_atomic(), "Error");
597 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
598 while (iter.has_next()) {
599 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
600 DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
601 assert(next == NULL, "Should not discover inactive Reference");
602 if (iter.is_referent_alive()) {
603 if (TraceReferenceGC) {
604 gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
605 (void *)iter.obj(), iter.obj()->klass()->internal_name());
606 }
607 // The referent is reachable after all.
608 // Remove Reference object from list.
609 iter.remove();
610 // Update the referent pointer as necessary: Note that this
611 // should not entail any recursive marking because the
612 // referent must already have been traversed.
613 iter.make_referent_alive();
614 iter.move_to_next();
615 } else {
616 iter.next();
617 }
618 }
619 NOT_PRODUCT(
620 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) {
621 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d "
622 "Refs in discovered list " INTPTR_FORMAT,
623 iter.removed(), iter.processed(), (address)refs_list.head());
624 }
625 )
626 }
627
628 void
629 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
630 BoolObjectClosure* is_alive,
631 OopClosure* keep_alive,
632 VoidClosure* complete_gc) {
633 assert(!discovery_is_atomic(), "Error");
634 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
635 while (iter.has_next()) {
636 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
637 HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
638 oop next = java_lang_ref_Reference::next(iter.obj());
639 if ((iter.referent() == NULL || iter.is_referent_alive() ||
640 next != NULL)) {
641 assert(next->is_oop_or_null(), "bad next field");
642 // Remove Reference object from list
643 iter.remove();
644 // Trace the cohorts
645 iter.make_referent_alive();
646 if (UseCompressedOops) {
647 keep_alive->do_oop((narrowOop*)next_addr);
648 } else {
649 keep_alive->do_oop((oop*)next_addr);
650 }
651 iter.move_to_next();
652 } else {
653 iter.next();
654 }
655 }
656 // Now close the newly reachable set
657 complete_gc->do_void();
658 NOT_PRODUCT(
659 if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) {
660 gclog_or_tty->print_cr(" Dropped %d active Refs out of %d "
661 "Refs in discovered list " INTPTR_FORMAT,
662 iter.removed(), iter.processed(), (address)refs_list.head());
663 }
664 )
665 }
666
667 // Traverse the list and process the referents, by either
668 // clearing them or keeping them (and their reachable
669 // closure) alive.
670 void
671 ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
672 bool clear_referent,
673 BoolObjectClosure* is_alive,
674 OopClosure* keep_alive,
675 VoidClosure* complete_gc) {
676 ResourceMark rm;
677 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
678 while (iter.has_next()) {
679 iter.update_discovered();
680 iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
681 if (clear_referent) {
682 // NULL out referent pointer
683 iter.clear_referent();
684 } else {
685 // keep the referent around
686 iter.make_referent_alive();
687 }
688 if (TraceReferenceGC) {
689 gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
690 clear_referent ? "cleared " : "",
691 (void *)iter.obj(), iter.obj()->klass()->internal_name());
692 }
693 assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
694 iter.next();
695 }
696 // Remember to update the next pointer of the last ref.
697 iter.update_discovered();
698 // Close the reachable set
699 complete_gc->do_void();
700 }
701
702 void
703 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
704 oop obj = NULL;
705 oop next = refs_list.head();
706 while (next != obj) {
707 obj = next;
708 next = java_lang_ref_Reference::discovered(obj);
709 java_lang_ref_Reference::set_discovered_raw(obj, NULL);
710 }
711 refs_list.set_head(NULL);
712 refs_list.set_length(0);
713 }
714
715 void
716 ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) {
717 clear_discovered_references(refs_list);
718 }
719
720 void ReferenceProcessor::abandon_partial_discovery() {
721 // loop over the lists
722 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
723 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) {
724 gclog_or_tty->print_cr("\nAbandoning %s discovered list", list_name(i));
725 }
726 abandon_partial_discovered_list(_discovered_refs[i]);
727 }
728 }
729
730 class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
731 public:
732 RefProcPhase1Task(ReferenceProcessor& ref_processor,
733 DiscoveredList refs_lists[],
734 ReferencePolicy* policy,
735 bool marks_oops_alive)
736 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
737 _policy(policy)
738 { }
739 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
740 OopClosure& keep_alive,
741 VoidClosure& complete_gc)
742 {
743 Thread* thr = Thread::current();
744 int refs_list_index = ((WorkerThread*)thr)->id();
745 _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy,
746 &is_alive, &keep_alive, &complete_gc);
747 }
748 private:
749 ReferencePolicy* _policy;
750 };
751
752 class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
753 public:
754 RefProcPhase2Task(ReferenceProcessor& ref_processor,
755 DiscoveredList refs_lists[],
756 bool marks_oops_alive)
757 : ProcessTask(ref_processor, refs_lists, marks_oops_alive)
758 { }
759 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
760 OopClosure& keep_alive,
761 VoidClosure& complete_gc)
762 {
763 _ref_processor.process_phase2(_refs_lists[i],
764 &is_alive, &keep_alive, &complete_gc);
765 }
766 };
767
768 class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
769 public:
770 RefProcPhase3Task(ReferenceProcessor& ref_processor,
771 DiscoveredList refs_lists[],
772 bool clear_referent,
773 bool marks_oops_alive)
774 : ProcessTask(ref_processor, refs_lists, marks_oops_alive),
775 _clear_referent(clear_referent)
776 { }
777 virtual void work(unsigned int i, BoolObjectClosure& is_alive,
778 OopClosure& keep_alive,
779 VoidClosure& complete_gc)
780 {
781 // Don't use "refs_list_index" calculated in this way because
782 // balance_queues() has moved the Ref's into the first n queues.
783 // Thread* thr = Thread::current();
784 // int refs_list_index = ((WorkerThread*)thr)->id();
785 // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent,
786 _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
787 &is_alive, &keep_alive, &complete_gc);
788 }
789 private:
790 bool _clear_referent;
791 };
792
793 // Balances reference queues.
794 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
795 // queues[0, 1, ..., _num_q-1] because only the first _num_q
796 // corresponding to the active workers will be processed.
797 void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
798 {
799 // calculate total length
800 size_t total_refs = 0;
801 if (TraceReferenceGC && PrintGCDetails) {
802 gclog_or_tty->print_cr("\nBalance ref_lists ");
803 }
804
805 for (uint i = 0; i < _max_num_q; ++i) {
806 total_refs += ref_lists[i].length();
807 if (TraceReferenceGC && PrintGCDetails) {
808 gclog_or_tty->print("%d ", ref_lists[i].length());
809 }
810 }
811 if (TraceReferenceGC && PrintGCDetails) {
812 gclog_or_tty->print_cr(" = %d", total_refs);
813 }
814 size_t avg_refs = total_refs / _num_q + 1;
815 uint to_idx = 0;
816 for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) {
817 bool move_all = false;
818 if (from_idx >= _num_q) {
819 move_all = ref_lists[from_idx].length() > 0;
820 }
821 while ((ref_lists[from_idx].length() > avg_refs) ||
822 move_all) {
823 assert(to_idx < _num_q, "Sanity Check!");
824 if (ref_lists[to_idx].length() < avg_refs) {
825 // move superfluous refs
826 size_t refs_to_move;
827 // Move all the Ref's if the from queue will not be processed.
828 if (move_all) {
829 refs_to_move = MIN2(ref_lists[from_idx].length(),
830 avg_refs - ref_lists[to_idx].length());
831 } else {
832 refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
833 avg_refs - ref_lists[to_idx].length());
834 }
835
836 assert(refs_to_move > 0, "otherwise the code below will fail");
837
838 oop move_head = ref_lists[from_idx].head();
839 oop move_tail = move_head;
840 oop new_head = move_head;
841 // find an element to split the list on
842 for (size_t j = 0; j < refs_to_move; ++j) {
843 move_tail = new_head;
844 new_head = java_lang_ref_Reference::discovered(new_head);
845 }
846
847 // Add the chain to the to list.
848 if (ref_lists[to_idx].head() == NULL) {
849 // to list is empty. Make a loop at the end.
850 java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
851 } else {
852 java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
853 }
854 ref_lists[to_idx].set_head(move_head);
855 ref_lists[to_idx].inc_length(refs_to_move);
856
857 // Remove the chain from the from list.
858 if (move_tail == new_head) {
859 // We found the end of the from list.
860 ref_lists[from_idx].set_head(NULL);
861 } else {
862 ref_lists[from_idx].set_head(new_head);
863 }
864 ref_lists[from_idx].dec_length(refs_to_move);
865 if (ref_lists[from_idx].length() == 0) {
866 break;
867 }
868 } else {
869 to_idx = (to_idx + 1) % _num_q;
870 }
871 }
872 }
873 #ifdef ASSERT
874 size_t balanced_total_refs = 0;
875 for (uint i = 0; i < _max_num_q; ++i) {
876 balanced_total_refs += ref_lists[i].length();
877 if (TraceReferenceGC && PrintGCDetails) {
878 gclog_or_tty->print("%d ", ref_lists[i].length());
879 }
880 }
881 if (TraceReferenceGC && PrintGCDetails) {
882 gclog_or_tty->print_cr(" = %d", balanced_total_refs);
883 gclog_or_tty->flush();
884 }
885 assert(total_refs == balanced_total_refs, "Balancing was incomplete");
886 #endif
887 }
888
889 void ReferenceProcessor::balance_all_queues() {
890 balance_queues(_discoveredSoftRefs);
891 balance_queues(_discoveredWeakRefs);
892 balance_queues(_discoveredFinalRefs);
893 balance_queues(_discoveredPhantomRefs);
894 balance_queues(_discoveredCleanerRefs);
895 }
896
897 size_t
898 ReferenceProcessor::process_discovered_reflist(
899 DiscoveredList refs_lists[],
900 ReferencePolicy* policy,
901 bool clear_referent,
902 BoolObjectClosure* is_alive,
903 OopClosure* keep_alive,
904 VoidClosure* complete_gc,
905 AbstractRefProcTaskExecutor* task_executor)
906 {
907 bool mt_processing = task_executor != NULL && _processing_is_mt;
908 // If discovery used MT and a dynamic number of GC threads, then
909 // the queues must be balanced for correctness if fewer than the
910 // maximum number of queues were used. The number of queue used
911 // during discovery may be different than the number to be used
912 // for processing so don't depend of _num_q < _max_num_q as part
913 // of the test.
914 bool must_balance = _discovery_is_mt;
915
916 if ((mt_processing && ParallelRefProcBalancingEnabled) ||
917 must_balance) {
918 balance_queues(refs_lists);
919 }
920
921 size_t total_list_count = total_count(refs_lists);
922
923 if (PrintReferenceGC && PrintGCDetails) {
924 gclog_or_tty->print(", %u refs", total_list_count);
925 }
926
927 // Phase 1 (soft refs only):
928 // . Traverse the list and remove any SoftReferences whose
929 // referents are not alive, but that should be kept alive for
930 // policy reasons. Keep alive the transitive closure of all
931 // such referents.
932 if (policy != NULL) {
933 if (mt_processing) {
934 RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
935 task_executor->execute(phase1);
936 } else {
937 for (uint i = 0; i < _max_num_q; i++) {
938 process_phase1(refs_lists[i], policy,
939 is_alive, keep_alive, complete_gc);
940 }
941 }
942 } else { // policy == NULL
943 assert(refs_lists != _discoveredSoftRefs,
944 "Policy must be specified for soft references.");
945 }
946
947 // Phase 2:
948 // . Traverse the list and remove any refs whose referents are alive.
949 if (mt_processing) {
950 RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
951 task_executor->execute(phase2);
952 } else {
953 for (uint i = 0; i < _max_num_q; i++) {
954 process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
955 }
956 }
957
958 // Phase 3:
959 // . Traverse the list and process referents as appropriate.
960 if (mt_processing) {
961 RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
962 task_executor->execute(phase3);
963 } else {
964 for (uint i = 0; i < _max_num_q; i++) {
965 process_phase3(refs_lists[i], clear_referent,
966 is_alive, keep_alive, complete_gc);
967 }
968 }
969
970 return total_list_count;
971 }
972
973 void ReferenceProcessor::clean_up_discovered_references() {
974 // loop over the lists
975 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
976 if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) {
977 gclog_or_tty->print_cr(
978 "\nScrubbing %s discovered list of Null referents",
979 list_name(i));
980 }
981 clean_up_discovered_reflist(_discovered_refs[i]);
982 }
983 }
984
985 void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) {
986 assert(!discovery_is_atomic(), "Else why call this method?");
987 DiscoveredListIterator iter(refs_list, NULL, NULL);
988 while (iter.has_next()) {
989 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
990 oop next = java_lang_ref_Reference::next(iter.obj());
991 assert(next->is_oop_or_null(), "bad next field");
992 // If referent has been cleared or Reference is not active,
993 // drop it.
994 if (iter.referent() == NULL || next != NULL) {
995 debug_only(
996 if (PrintGCDetails && TraceReferenceGC) {
997 gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: "
998 INTPTR_FORMAT " with next field: " INTPTR_FORMAT
999 " and referent: " INTPTR_FORMAT,
1000 (void *)iter.obj(), (void *)next, (void *)iter.referent());
1001 }
1002 )
1003 // Remove Reference object from list
1004 iter.remove();
1005 iter.move_to_next();
1006 } else {
1007 iter.next();
1008 }
1009 }
1010 NOT_PRODUCT(
1011 if (PrintGCDetails && TraceReferenceGC) {
1012 gclog_or_tty->print(
1013 " Removed %d Refs with NULL referents out of %d discovered Refs",
1014 iter.removed(), iter.processed());
1015 }
1016 )
1017 }
1018
1019 inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
1020 uint id = 0;
1021 // Determine the queue index to use for this object.
1022 if (_discovery_is_mt) {
1023 // During a multi-threaded discovery phase,
1024 // each thread saves to its "own" list.
1025 Thread* thr = Thread::current();
1026 id = thr->as_Worker_thread()->id();
1027 } else {
1028 // single-threaded discovery, we save in round-robin
1029 // fashion to each of the lists.
1030 if (_processing_is_mt) {
1031 id = next_id();
1032 }
1033 }
1034 assert(0 <= id && id < _max_num_q, "Id is out-of-bounds (call Freud?)");
1035
1036 // Get the discovered queue to which we will add
1037 DiscoveredList* list = NULL;
1038 switch (rt) {
1039 case REF_OTHER:
1040 // Unknown reference type, no special treatment
1041 break;
1042 case REF_SOFT:
1043 list = &_discoveredSoftRefs[id];
1044 break;
1045 case REF_WEAK:
1046 list = &_discoveredWeakRefs[id];
1047 break;
1048 case REF_FINAL:
1049 list = &_discoveredFinalRefs[id];
1050 break;
1051 case REF_PHANTOM:
1052 list = &_discoveredPhantomRefs[id];
1053 break;
1054 case REF_CLEANER:
1055 list = &_discoveredCleanerRefs[id];
1056 break;
1057 case REF_NONE:
1058 // we should not reach here if we are an InstanceRefKlass
1059 default:
1060 ShouldNotReachHere();
1061 }
1062 if (TraceReferenceGC && PrintGCDetails) {
1063 gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, id, list);
1064 }
1065 return list;
1066 }
1067
1068 inline void
1069 ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
1070 oop obj,
1071 HeapWord* discovered_addr) {
1072 assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
1073 // First we must make sure this object is only enqueued once. CAS in a non null
1074 // discovered_addr.
1075 oop current_head = refs_list.head();
1076 // The last ref must have its discovered field pointing to itself.
1077 oop next_discovered = (current_head != NULL) ? current_head : obj;
1078
1079 oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr,
1080 NULL);
1081 if (retest == NULL) {
1082 // This thread just won the right to enqueue the object.
1083 // We have separate lists for enqueueing, so no synchronization
1084 // is necessary.
1085 refs_list.set_head(obj);
1086 refs_list.inc_length(1);
1087
1088 if (TraceReferenceGC) {
1089 gclog_or_tty->print_cr("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
1090 (void *)obj, obj->klass()->internal_name());
1091 }
1092 } else {
1093 // If retest was non NULL, another thread beat us to it:
1094 // The reference has already been discovered...
1095 if (TraceReferenceGC) {
1096 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)",
1097 (void *)obj, obj->klass()->internal_name());
1098 }
1099 }
1100 }
1101
1102 #ifndef PRODUCT
1103 // Non-atomic (i.e. concurrent) discovery might allow us
1104 // to observe j.l.References with NULL referents, being those
1105 // cleared concurrently by mutators during (or after) discovery.
1106 void ReferenceProcessor::verify_referent(oop obj) {
1107 bool da = discovery_is_atomic();
1108 oop referent = java_lang_ref_Reference::referent(obj);
1109 assert(da ? referent->is_oop() : referent->is_oop_or_null(),
1110 err_msg("Bad referent " INTPTR_FORMAT " found in Reference "
1111 INTPTR_FORMAT " during %satomic discovery ",
1112 (void *)referent, (void *)obj, da ? "" : "non-"));
1113 }
1114 #endif
1115
1116 // We mention two of several possible choices here:
1117 // #0: if the reference object is not in the "originating generation"
1118 // (or part of the heap being collected, indicated by our "span"
1119 // we don't treat it specially (i.e. we scan it as we would
1120 // a normal oop, treating its references as strong references).
1121 // This means that references can't be discovered unless their
1122 // referent is also in the same span. This is the simplest,
1123 // most "local" and most conservative approach, albeit one
1124 // that may cause weak references to be enqueued least promptly.
1125 // We call this choice the "ReferenceBasedDiscovery" policy.
1126 // #1: the reference object may be in any generation (span), but if
1127 // the referent is in the generation (span) being currently collected
1128 // then we can discover the reference object, provided
1129 // the object has not already been discovered by
1130 // a different concurrently running collector (as may be the
1131 // case, for instance, if the reference object is in CMS and
1132 // the referent in DefNewGeneration), and provided the processing
1133 // of this reference object by the current collector will
1134 // appear atomic to every other collector in the system.
1135 // (Thus, for instance, a concurrent collector may not
1136 // discover references in other generations even if the
1137 // referent is in its own generation). This policy may,
1138 // in certain cases, enqueue references somewhat sooner than
1139 // might Policy #0 above, but at marginally increased cost
1140 // and complexity in processing these references.
1141 // We call this choice the "RefeferentBasedDiscovery" policy.
1142 bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
1143 // Make sure we are discovering refs (rather than processing discovered refs).
1144 if (!_discovering_refs || !RegisterReferences) {
1145 return false;
1146 }
1147 // We only discover active references.
1148 oop next = java_lang_ref_Reference::next(obj);
1149 if (next != NULL) { // Ref is no longer active
1150 return false;
1151 }
1152
1153 HeapWord* obj_addr = (HeapWord*)obj;
1154 if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1155 !_span.contains(obj_addr)) {
1156 // Reference is not in the originating generation;
1157 // don't treat it specially (i.e. we want to scan it as a normal
1158 // object with strong references).
1159 return false;
1160 }
1161
1162 // We only discover references whose referents are not (yet)
1163 // known to be strongly reachable.
1164 if (is_alive_non_header() != NULL) {
1165 verify_referent(obj);
1166 if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
1167 return false; // referent is reachable
1168 }
1169 }
1170 if (rt == REF_SOFT) {
1171 // For soft refs we can decide now if these are not
1172 // current candidates for clearing, in which case we
1173 // can mark through them now, rather than delaying that
1174 // to the reference-processing phase. Since all current
1175 // time-stamp policies advance the soft-ref clock only
1176 // at a major collection cycle, this is always currently
1177 // accurate.
1178 if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
1179 return false;
1180 }
1181 }
1182
1183 ResourceMark rm; // Needed for tracing.
1184
1185 HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
1186 const oop discovered = java_lang_ref_Reference::discovered(obj);
1187 assert(discovered->is_oop_or_null(), "bad discovered field");
1188 if (discovered != NULL) {
1189 // The reference has already been discovered...
1190 if (TraceReferenceGC) {
1191 gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)",
1192 (void *)obj, obj->klass()->internal_name());
1193 }
1194 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1195 // assumes that an object is not processed twice;
1196 // if it's been already discovered it must be on another
1197 // generation's discovered list; so we won't discover it.
1198 return false;
1199 } else {
1200 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
1201 "Unrecognized policy");
1202 // Check assumption that an object is not potentially
1203 // discovered twice except by concurrent collectors that potentially
1204 // trace the same Reference object twice.
1205 assert(UseConcMarkSweepGC || UseG1GC,
1206 "Only possible with a concurrent marking collector");
1207 return true;
1208 }
1209 }
1210
1211 if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
1212 verify_referent(obj);
1213 // Discover if and only if EITHER:
1214 // .. reference is in our span, OR
1215 // .. we are an atomic collector and referent is in our span
1216 if (_span.contains(obj_addr) ||
1217 (discovery_is_atomic() &&
1218 _span.contains(java_lang_ref_Reference::referent(obj)))) {
1219 // should_enqueue = true;
1220 } else {
1221 return false;
1222 }
1223 } else {
1224 assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
1225 _span.contains(obj_addr), "code inconsistency");
1226 }
1227
1228 // Get the right type of discovered queue head.
1229 DiscoveredList* list = get_discovered_list(rt);
1230 if (list == NULL) {
1231 return false; // nothing special needs to be done
1232 }
1233
1234 if (_discovery_is_mt) {
1235 add_to_discovered_list_mt(*list, obj, discovered_addr);
1236 } else {
1237 // We do a raw store here: the field will be visited later when processing
1238 // the discovered references.
1239 oop current_head = list->head();
1240 // The last ref must have its discovered field pointing to itself.
1241 oop next_discovered = (current_head != NULL) ? current_head : obj;
1242
1243 assert(discovered == NULL, "control point invariant");
1244 oop_store_raw(discovered_addr, next_discovered);
1245 list->set_head(obj);
1246 list->inc_length(1);
1247
1248 if (TraceReferenceGC) {
1249 gclog_or_tty->print_cr("Discovered reference (" INTPTR_FORMAT ": %s)",
1250 (void *)obj, obj->klass()->internal_name());
1251 }
1252 }
1253 assert(obj->is_oop(), "Discovered a bad reference");
1254 verify_referent(obj);
1255 return true;
1256 }
1257
1258 // Preclean the discovered references by removing those
1259 // whose referents are alive, and by marking from those that
1260 // are not active. These lists can be handled here
1261 // in any order and, indeed, concurrently.
1262 void ReferenceProcessor::preclean_discovered_references(
1263 BoolObjectClosure* is_alive,
1264 OopClosure* keep_alive,
1265 VoidClosure* complete_gc,
1266 YieldClosure* yield,
1267 GCTimer* gc_timer,
1268 GCId gc_id) {
1269
1270 NOT_PRODUCT(verify_ok_to_handle_reflists());
1271
1272 // Soft references
1273 {
1274 GCTraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC,
1275 false, gc_timer, gc_id);
1276 for (uint i = 0; i < _max_num_q; i++) {
1277 if (yield->should_return()) {
1278 return;
1279 }
1280 preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
1281 keep_alive, complete_gc, yield);
1282 }
1283 }
1284
1285 // Weak references
1286 {
1287 GCTraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC,
1288 false, gc_timer, gc_id);
1289 for (uint i = 0; i < _max_num_q; i++) {
1290 if (yield->should_return()) {
1291 return;
1292 }
1293 preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
1294 keep_alive, complete_gc, yield);
1295 }
1296 }
1297
1298 // Final references
1299 {
1300 GCTraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC,
1301 false, gc_timer, gc_id);
1302 for (uint i = 0; i < _max_num_q; i++) {
1303 if (yield->should_return()) {
1304 return;
1305 }
1306 preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
1307 keep_alive, complete_gc, yield);
1308 }
1309 }
1310
1311 // Phantom references
1312 {
1313 GCTraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC,
1314 false, gc_timer, gc_id);
1315 for (uint i = 0; i < _max_num_q; i++) {
1316 if (yield->should_return()) {
1317 return;
1318 }
1319 preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
1320 keep_alive, complete_gc, yield);
1321 }
1322
1323 // Cleaner references. Included in timing for phantom references. We
1324 // expect Cleaner references to be temporary, and don't want to deal with
1325 // possible incompatibilities arising from making it more visible.
1326 for (uint i = 0; i < _max_num_q; i++) {
1327 if (yield->should_return()) {
1328 return;
1329 }
1330 preclean_discovered_reflist(_discoveredCleanerRefs[i], is_alive,
1331 keep_alive, complete_gc, yield);
1332 }
1333 }
1334 }
1335
1336 // Walk the given discovered ref list, and remove all reference objects
1337 // whose referents are still alive, whose referents are NULL or which
1338 // are not active (have a non-NULL next field). NOTE: When we are
1339 // thus precleaning the ref lists (which happens single-threaded today),
1340 // we do not disable refs discovery to honour the correct semantics of
1341 // java.lang.Reference. As a result, we need to be careful below
1342 // that ref removal steps interleave safely with ref discovery steps
1343 // (in this thread).
1344 void
1345 ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
1346 BoolObjectClosure* is_alive,
1347 OopClosure* keep_alive,
1348 VoidClosure* complete_gc,
1349 YieldClosure* yield) {
1350 DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
1351 while (iter.has_next()) {
1352 iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
1353 oop obj = iter.obj();
1354 oop next = java_lang_ref_Reference::next(obj);
1355 if (iter.referent() == NULL || iter.is_referent_alive() ||
1356 next != NULL) {
1357 // The referent has been cleared, or is alive, or the Reference is not
1358 // active; we need to trace and mark its cohort.
1359 if (TraceReferenceGC) {
1360 gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)",
1361 (void *)iter.obj(), iter.obj()->klass()->internal_name());
1362 }
1363 // Remove Reference object from list
1364 iter.remove();
1365 // Keep alive its cohort.
1366 iter.make_referent_alive();
1367 if (UseCompressedOops) {
1368 narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
1369 keep_alive->do_oop(next_addr);
1370 } else {
1371 oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
1372 keep_alive->do_oop(next_addr);
1373 }
1374 iter.move_to_next();
1375 } else {
1376 iter.next();
1377 }
1378 }
1379 // Close the reachable set
1380 complete_gc->do_void();
1381
1382 NOT_PRODUCT(
1383 if (PrintGCDetails && PrintReferenceGC && (iter.processed() > 0)) {
1384 gclog_or_tty->print_cr(" Dropped %d Refs out of %d "
1385 "Refs in discovered list " INTPTR_FORMAT,
1386 iter.removed(), iter.processed(), (address)refs_list.head());
1387 }
1388 )
1389 }
1390
1391 const char* ReferenceProcessor::list_name(uint i) {
1392 assert(i >= 0 && i <= _max_num_q * number_of_subclasses_of_ref(),
1393 "Out of bounds index");
1394
1395 int j = i / _max_num_q;
1396 switch (j) {
1397 case 0: return "SoftRef";
1398 case 1: return "WeakRef";
1399 case 2: return "FinalRef";
1400 case 3: return "PhantomRef";
1401 case 4: return "CleanerRef";
1402 }
1403 ShouldNotReachHere();
1404 return NULL;
1405 }
1406
1407 #ifndef PRODUCT
1408 void ReferenceProcessor::verify_ok_to_handle_reflists() {
1409 // empty for now
1410 }
1411 #endif
1412
1413 #ifndef PRODUCT
1414 void ReferenceProcessor::clear_discovered_references() {
1415 guarantee(!_discovering_refs, "Discovering refs?");
1416 for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
1417 clear_discovered_references(_discovered_refs[i]);
1418 }
1419 }
1420
1421 #endif // PRODUCT