Fri, 26 Sep 2014 17:48:10 -0400
8047125: (ref) More phantom object references
Reviewed-by: mchung, dfuchs, ahgross, jmasa, brutisso, mgerdin
Contributed-by: kim.barrett@oracle.com
1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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25 #ifndef SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
26 #define SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
28 #include "memory/referencePolicy.hpp"
29 #include "memory/referenceProcessorStats.hpp"
30 #include "memory/referenceType.hpp"
31 #include "oops/instanceRefKlass.hpp"
33 class GCTimer;
35 // ReferenceProcessor class encapsulates the per-"collector" processing
36 // of java.lang.Reference objects for GC. The interface is useful for supporting
37 // a generational abstraction, in particular when there are multiple
38 // generations that are being independently collected -- possibly
39 // concurrently and/or incrementally. Note, however, that the
40 // ReferenceProcessor class abstracts away from a generational setting
41 // by using only a heap interval (called "span" below), thus allowing
42 // its use in a straightforward manner in a general, non-generational
43 // setting.
44 //
45 // The basic idea is that each ReferenceProcessor object concerns
46 // itself with ("weak") reference processing in a specific "span"
47 // of the heap of interest to a specific collector. Currently,
48 // the span is a convex interval of the heap, but, efficiency
49 // apart, there seems to be no reason it couldn't be extended
50 // (with appropriate modifications) to any "non-convex interval".
52 // forward references
53 class ReferencePolicy;
54 class AbstractRefProcTaskExecutor;
56 // List of discovered references.
57 class DiscoveredList {
58 public:
59 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
60 oop head() const {
61 return UseCompressedOops ? oopDesc::decode_heap_oop(_compressed_head) :
62 _oop_head;
63 }
64 HeapWord* adr_head() {
65 return UseCompressedOops ? (HeapWord*)&_compressed_head :
66 (HeapWord*)&_oop_head;
67 }
68 void set_head(oop o) {
69 if (UseCompressedOops) {
70 // Must compress the head ptr.
71 _compressed_head = oopDesc::encode_heap_oop(o);
72 } else {
73 _oop_head = o;
74 }
75 }
76 bool is_empty() const { return head() == NULL; }
77 size_t length() { return _len; }
78 void set_length(size_t len) { _len = len; }
79 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
80 void dec_length(size_t dec) { _len -= dec; }
81 private:
82 // Set value depending on UseCompressedOops. This could be a template class
83 // but then we have to fix all the instantiations and declarations that use this class.
84 oop _oop_head;
85 narrowOop _compressed_head;
86 size_t _len;
87 };
89 // Iterator for the list of discovered references.
90 class DiscoveredListIterator {
91 private:
92 DiscoveredList& _refs_list;
93 HeapWord* _prev_next;
94 oop _prev;
95 oop _ref;
96 HeapWord* _discovered_addr;
97 oop _next;
98 HeapWord* _referent_addr;
99 oop _referent;
100 OopClosure* _keep_alive;
101 BoolObjectClosure* _is_alive;
103 DEBUG_ONLY(
104 oop _first_seen; // cyclic linked list check
105 )
107 NOT_PRODUCT(
108 size_t _processed;
109 size_t _removed;
110 )
112 public:
113 inline DiscoveredListIterator(DiscoveredList& refs_list,
114 OopClosure* keep_alive,
115 BoolObjectClosure* is_alive):
116 _refs_list(refs_list),
117 _prev_next(refs_list.adr_head()),
118 _prev(NULL),
119 _ref(refs_list.head()),
120 #ifdef ASSERT
121 _first_seen(refs_list.head()),
122 #endif
123 #ifndef PRODUCT
124 _processed(0),
125 _removed(0),
126 #endif
127 _next(NULL),
128 _keep_alive(keep_alive),
129 _is_alive(is_alive)
130 { }
132 // End Of List.
133 inline bool has_next() const { return _ref != NULL; }
135 // Get oop to the Reference object.
136 inline oop obj() const { return _ref; }
138 // Get oop to the referent object.
139 inline oop referent() const { return _referent; }
141 // Returns true if referent is alive.
142 inline bool is_referent_alive() const {
143 return _is_alive->do_object_b(_referent);
144 }
146 // Loads data for the current reference.
147 // The "allow_null_referent" argument tells us to allow for the possibility
148 // of a NULL referent in the discovered Reference object. This typically
149 // happens in the case of concurrent collectors that may have done the
150 // discovery concurrently, or interleaved, with mutator execution.
151 void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
153 // Move to the next discovered reference.
154 inline void next() {
155 _prev_next = _discovered_addr;
156 _prev = _ref;
157 move_to_next();
158 }
160 // Remove the current reference from the list
161 void remove();
163 // Make the Reference object active again.
164 void make_active();
166 // Make the referent alive.
167 inline void make_referent_alive() {
168 if (UseCompressedOops) {
169 _keep_alive->do_oop((narrowOop*)_referent_addr);
170 } else {
171 _keep_alive->do_oop((oop*)_referent_addr);
172 }
173 }
175 // Update the discovered field.
176 inline void update_discovered() {
177 // First _prev_next ref actually points into DiscoveredList (gross).
178 if (UseCompressedOops) {
179 if (!oopDesc::is_null(*(narrowOop*)_prev_next)) {
180 _keep_alive->do_oop((narrowOop*)_prev_next);
181 }
182 } else {
183 if (!oopDesc::is_null(*(oop*)_prev_next)) {
184 _keep_alive->do_oop((oop*)_prev_next);
185 }
186 }
187 }
189 // NULL out referent pointer.
190 void clear_referent();
192 // Statistics
193 NOT_PRODUCT(
194 inline size_t processed() const { return _processed; }
195 inline size_t removed() const { return _removed; }
196 )
198 inline void move_to_next() {
199 if (_ref == _next) {
200 // End of the list.
201 _ref = NULL;
202 } else {
203 _ref = _next;
204 }
205 assert(_ref != _first_seen, "cyclic ref_list found");
206 NOT_PRODUCT(_processed++);
207 }
208 };
210 class ReferenceProcessor : public CHeapObj<mtGC> {
212 private:
213 size_t total_count(DiscoveredList lists[]);
215 protected:
216 // Compatibility with pre-4965777 JDK's
217 static bool _pending_list_uses_discovered_field;
219 // The SoftReference master timestamp clock
220 static jlong _soft_ref_timestamp_clock;
222 MemRegion _span; // (right-open) interval of heap
223 // subject to wkref discovery
225 bool _discovering_refs; // true when discovery enabled
226 bool _discovery_is_atomic; // if discovery is atomic wrt
227 // other collectors in configuration
228 bool _discovery_is_mt; // true if reference discovery is MT.
230 bool _enqueuing_is_done; // true if all weak references enqueued
231 bool _processing_is_mt; // true during phases when
232 // reference processing is MT.
233 uint _next_id; // round-robin mod _num_q counter in
234 // support of work distribution
236 // For collectors that do not keep GC liveness information
237 // in the object header, this field holds a closure that
238 // helps the reference processor determine the reachability
239 // of an oop. It is currently initialized to NULL for all
240 // collectors except for CMS and G1.
241 BoolObjectClosure* _is_alive_non_header;
243 // Soft ref clearing policies
244 // . the default policy
245 static ReferencePolicy* _default_soft_ref_policy;
246 // . the "clear all" policy
247 static ReferencePolicy* _always_clear_soft_ref_policy;
248 // . the current policy below is either one of the above
249 ReferencePolicy* _current_soft_ref_policy;
251 // The discovered ref lists themselves
253 // The active MT'ness degree of the queues below
254 uint _num_q;
255 // The maximum MT'ness degree of the queues below
256 uint _max_num_q;
258 // Master array of discovered oops
259 DiscoveredList* _discovered_refs;
261 // Arrays of lists of oops, one per thread (pointers into master array above)
262 DiscoveredList* _discoveredSoftRefs;
263 DiscoveredList* _discoveredWeakRefs;
264 DiscoveredList* _discoveredFinalRefs;
265 DiscoveredList* _discoveredPhantomRefs;
266 DiscoveredList* _discoveredCleanerRefs;
268 public:
269 static int number_of_subclasses_of_ref() { return (REF_CLEANER - REF_OTHER); }
271 uint num_q() { return _num_q; }
272 uint max_num_q() { return _max_num_q; }
273 void set_active_mt_degree(uint v) { _num_q = v; }
275 DiscoveredList* discovered_refs() { return _discovered_refs; }
277 ReferencePolicy* setup_policy(bool always_clear) {
278 _current_soft_ref_policy = always_clear ?
279 _always_clear_soft_ref_policy : _default_soft_ref_policy;
280 _current_soft_ref_policy->setup(); // snapshot the policy threshold
281 return _current_soft_ref_policy;
282 }
284 // Process references with a certain reachability level.
285 size_t process_discovered_reflist(DiscoveredList refs_lists[],
286 ReferencePolicy* policy,
287 bool clear_referent,
288 BoolObjectClosure* is_alive,
289 OopClosure* keep_alive,
290 VoidClosure* complete_gc,
291 AbstractRefProcTaskExecutor* task_executor);
293 void process_phaseJNI(BoolObjectClosure* is_alive,
294 OopClosure* keep_alive,
295 VoidClosure* complete_gc);
297 // Work methods used by the method process_discovered_reflist
298 // Phase1: keep alive all those referents that are otherwise
299 // dead but which must be kept alive by policy (and their closure).
300 void process_phase1(DiscoveredList& refs_list,
301 ReferencePolicy* policy,
302 BoolObjectClosure* is_alive,
303 OopClosure* keep_alive,
304 VoidClosure* complete_gc);
305 // Phase2: remove all those references whose referents are
306 // reachable.
307 inline void process_phase2(DiscoveredList& refs_list,
308 BoolObjectClosure* is_alive,
309 OopClosure* keep_alive,
310 VoidClosure* complete_gc) {
311 if (discovery_is_atomic()) {
312 // complete_gc is ignored in this case for this phase
313 pp2_work(refs_list, is_alive, keep_alive);
314 } else {
315 assert(complete_gc != NULL, "Error");
316 pp2_work_concurrent_discovery(refs_list, is_alive,
317 keep_alive, complete_gc);
318 }
319 }
320 // Work methods in support of process_phase2
321 void pp2_work(DiscoveredList& refs_list,
322 BoolObjectClosure* is_alive,
323 OopClosure* keep_alive);
324 void pp2_work_concurrent_discovery(
325 DiscoveredList& refs_list,
326 BoolObjectClosure* is_alive,
327 OopClosure* keep_alive,
328 VoidClosure* complete_gc);
329 // Phase3: process the referents by either clearing them
330 // or keeping them alive (and their closure)
331 void process_phase3(DiscoveredList& refs_list,
332 bool clear_referent,
333 BoolObjectClosure* is_alive,
334 OopClosure* keep_alive,
335 VoidClosure* complete_gc);
337 // Enqueue references with a certain reachability level
338 void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr);
340 // "Preclean" all the discovered reference lists
341 // by removing references with strongly reachable referents.
342 // The first argument is a predicate on an oop that indicates
343 // its (strong) reachability and the second is a closure that
344 // may be used to incrementalize or abort the precleaning process.
345 // The caller is responsible for taking care of potential
346 // interference with concurrent operations on these lists
347 // (or predicates involved) by other threads. Currently
348 // only used by the CMS collector.
349 void preclean_discovered_references(BoolObjectClosure* is_alive,
350 OopClosure* keep_alive,
351 VoidClosure* complete_gc,
352 YieldClosure* yield,
353 GCTimer* gc_timer);
355 // Delete entries in the discovered lists that have
356 // either a null referent or are not active. Such
357 // Reference objects can result from the clearing
358 // or enqueueing of Reference objects concurrent
359 // with their discovery by a (concurrent) collector.
360 // For a definition of "active" see java.lang.ref.Reference;
361 // Refs are born active, become inactive when enqueued,
362 // and never become active again. The state of being
363 // active is encoded as follows: A Ref is active
364 // if and only if its "next" field is NULL.
365 void clean_up_discovered_references();
366 void clean_up_discovered_reflist(DiscoveredList& refs_list);
368 // Returns the name of the discovered reference list
369 // occupying the i / _num_q slot.
370 const char* list_name(uint i);
372 void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);
374 protected:
375 // "Preclean" the given discovered reference list
376 // by removing references with strongly reachable referents.
377 // Currently used in support of CMS only.
378 void preclean_discovered_reflist(DiscoveredList& refs_list,
379 BoolObjectClosure* is_alive,
380 OopClosure* keep_alive,
381 VoidClosure* complete_gc,
382 YieldClosure* yield);
384 // round-robin mod _num_q (not: _not_ mode _max_num_q)
385 uint next_id() {
386 uint id = _next_id;
387 if (++_next_id == _num_q) {
388 _next_id = 0;
389 }
390 return id;
391 }
392 DiscoveredList* get_discovered_list(ReferenceType rt);
393 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
394 HeapWord* discovered_addr);
395 void verify_ok_to_handle_reflists() PRODUCT_RETURN;
397 void clear_discovered_references(DiscoveredList& refs_list);
398 void abandon_partial_discovered_list(DiscoveredList& refs_list);
400 // Calculate the number of jni handles.
401 unsigned int count_jni_refs();
403 // Balances reference queues.
404 void balance_queues(DiscoveredList ref_lists[]);
406 // Update (advance) the soft ref master clock field.
407 void update_soft_ref_master_clock();
409 public:
410 // Default parameters give you a vanilla reference processor.
411 ReferenceProcessor(MemRegion span,
412 bool mt_processing = false, uint mt_processing_degree = 1,
413 bool mt_discovery = false, uint mt_discovery_degree = 1,
414 bool atomic_discovery = true,
415 BoolObjectClosure* is_alive_non_header = NULL);
417 // RefDiscoveryPolicy values
418 enum DiscoveryPolicy {
419 ReferenceBasedDiscovery = 0,
420 ReferentBasedDiscovery = 1,
421 DiscoveryPolicyMin = ReferenceBasedDiscovery,
422 DiscoveryPolicyMax = ReferentBasedDiscovery
423 };
425 static void init_statics();
427 public:
428 // get and set "is_alive_non_header" field
429 BoolObjectClosure* is_alive_non_header() {
430 return _is_alive_non_header;
431 }
432 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
433 _is_alive_non_header = is_alive_non_header;
434 }
436 // get and set span
437 MemRegion span() { return _span; }
438 void set_span(MemRegion span) { _span = span; }
440 // start and stop weak ref discovery
441 void enable_discovery(bool verify_disabled, bool check_no_refs);
442 void disable_discovery() { _discovering_refs = false; }
443 bool discovery_enabled() { return _discovering_refs; }
445 // whether discovery is atomic wrt other collectors
446 bool discovery_is_atomic() const { return _discovery_is_atomic; }
447 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
449 // whether the JDK in which we are embedded is a pre-4965777 JDK,
450 // and thus whether or not it uses the discovered field to chain
451 // the entries in the pending list.
452 static bool pending_list_uses_discovered_field() {
453 return _pending_list_uses_discovered_field;
454 }
456 // whether discovery is done by multiple threads same-old-timeously
457 bool discovery_is_mt() const { return _discovery_is_mt; }
458 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
460 // Whether we are in a phase when _processing_ is MT.
461 bool processing_is_mt() const { return _processing_is_mt; }
462 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
464 // whether all enqueuing of weak references is complete
465 bool enqueuing_is_done() { return _enqueuing_is_done; }
466 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
468 // iterate over oops
469 void weak_oops_do(OopClosure* f); // weak roots
471 // Balance each of the discovered lists.
472 void balance_all_queues();
473 void verify_list(DiscoveredList& ref_list);
475 // Discover a Reference object, using appropriate discovery criteria
476 bool discover_reference(oop obj, ReferenceType rt);
478 // Process references found during GC (called by the garbage collector)
479 ReferenceProcessorStats
480 process_discovered_references(BoolObjectClosure* is_alive,
481 OopClosure* keep_alive,
482 VoidClosure* complete_gc,
483 AbstractRefProcTaskExecutor* task_executor,
484 GCTimer *gc_timer);
486 // Enqueue references at end of GC (called by the garbage collector)
487 bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
489 // If a discovery is in process that is being superceded, abandon it: all
490 // the discovered lists will be empty, and all the objects on them will
491 // have NULL discovered fields. Must be called only at a safepoint.
492 void abandon_partial_discovery();
494 // debugging
495 void verify_no_references_recorded() PRODUCT_RETURN;
496 void verify_referent(oop obj) PRODUCT_RETURN;
498 // clear the discovered lists (unlinking each entry).
499 void clear_discovered_references() PRODUCT_RETURN;
500 };
502 // A utility class to disable reference discovery in
503 // the scope which contains it, for given ReferenceProcessor.
504 class NoRefDiscovery: StackObj {
505 private:
506 ReferenceProcessor* _rp;
507 bool _was_discovering_refs;
508 public:
509 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
510 _was_discovering_refs = _rp->discovery_enabled();
511 if (_was_discovering_refs) {
512 _rp->disable_discovery();
513 }
514 }
516 ~NoRefDiscovery() {
517 if (_was_discovering_refs) {
518 _rp->enable_discovery(true /*verify_disabled*/, false /*check_no_refs*/);
519 }
520 }
521 };
524 // A utility class to temporarily mutate the span of the
525 // given ReferenceProcessor in the scope that contains it.
526 class ReferenceProcessorSpanMutator: StackObj {
527 private:
528 ReferenceProcessor* _rp;
529 MemRegion _saved_span;
531 public:
532 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
533 MemRegion span):
534 _rp(rp) {
535 _saved_span = _rp->span();
536 _rp->set_span(span);
537 }
539 ~ReferenceProcessorSpanMutator() {
540 _rp->set_span(_saved_span);
541 }
542 };
544 // A utility class to temporarily change the MT'ness of
545 // reference discovery for the given ReferenceProcessor
546 // in the scope that contains it.
547 class ReferenceProcessorMTDiscoveryMutator: StackObj {
548 private:
549 ReferenceProcessor* _rp;
550 bool _saved_mt;
552 public:
553 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
554 bool mt):
555 _rp(rp) {
556 _saved_mt = _rp->discovery_is_mt();
557 _rp->set_mt_discovery(mt);
558 }
560 ~ReferenceProcessorMTDiscoveryMutator() {
561 _rp->set_mt_discovery(_saved_mt);
562 }
563 };
566 // A utility class to temporarily change the disposition
567 // of the "is_alive_non_header" closure field of the
568 // given ReferenceProcessor in the scope that contains it.
569 class ReferenceProcessorIsAliveMutator: StackObj {
570 private:
571 ReferenceProcessor* _rp;
572 BoolObjectClosure* _saved_cl;
574 public:
575 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
576 BoolObjectClosure* cl):
577 _rp(rp) {
578 _saved_cl = _rp->is_alive_non_header();
579 _rp->set_is_alive_non_header(cl);
580 }
582 ~ReferenceProcessorIsAliveMutator() {
583 _rp->set_is_alive_non_header(_saved_cl);
584 }
585 };
587 // A utility class to temporarily change the disposition
588 // of the "discovery_is_atomic" field of the
589 // given ReferenceProcessor in the scope that contains it.
590 class ReferenceProcessorAtomicMutator: StackObj {
591 private:
592 ReferenceProcessor* _rp;
593 bool _saved_atomic_discovery;
595 public:
596 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
597 bool atomic):
598 _rp(rp) {
599 _saved_atomic_discovery = _rp->discovery_is_atomic();
600 _rp->set_atomic_discovery(atomic);
601 }
603 ~ReferenceProcessorAtomicMutator() {
604 _rp->set_atomic_discovery(_saved_atomic_discovery);
605 }
606 };
609 // A utility class to temporarily change the MT processing
610 // disposition of the given ReferenceProcessor instance
611 // in the scope that contains it.
612 class ReferenceProcessorMTProcMutator: StackObj {
613 private:
614 ReferenceProcessor* _rp;
615 bool _saved_mt;
617 public:
618 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
619 bool mt):
620 _rp(rp) {
621 _saved_mt = _rp->processing_is_mt();
622 _rp->set_mt_processing(mt);
623 }
625 ~ReferenceProcessorMTProcMutator() {
626 _rp->set_mt_processing(_saved_mt);
627 }
628 };
631 // This class is an interface used to implement task execution for the
632 // reference processing.
633 class AbstractRefProcTaskExecutor {
634 public:
636 // Abstract tasks to execute.
637 class ProcessTask;
638 class EnqueueTask;
640 // Executes a task using worker threads.
641 virtual void execute(ProcessTask& task) = 0;
642 virtual void execute(EnqueueTask& task) = 0;
644 // Switch to single threaded mode.
645 virtual void set_single_threaded_mode() { };
646 };
648 // Abstract reference processing task to execute.
649 class AbstractRefProcTaskExecutor::ProcessTask {
650 protected:
651 ProcessTask(ReferenceProcessor& ref_processor,
652 DiscoveredList refs_lists[],
653 bool marks_oops_alive)
654 : _ref_processor(ref_processor),
655 _refs_lists(refs_lists),
656 _marks_oops_alive(marks_oops_alive)
657 { }
659 public:
660 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
661 OopClosure& keep_alive,
662 VoidClosure& complete_gc) = 0;
664 // Returns true if a task marks some oops as alive.
665 bool marks_oops_alive() const
666 { return _marks_oops_alive; }
668 protected:
669 ReferenceProcessor& _ref_processor;
670 DiscoveredList* _refs_lists;
671 const bool _marks_oops_alive;
672 };
674 // Abstract reference processing task to execute.
675 class AbstractRefProcTaskExecutor::EnqueueTask {
676 protected:
677 EnqueueTask(ReferenceProcessor& ref_processor,
678 DiscoveredList refs_lists[],
679 HeapWord* pending_list_addr,
680 int n_queues)
681 : _ref_processor(ref_processor),
682 _refs_lists(refs_lists),
683 _pending_list_addr(pending_list_addr),
684 _n_queues(n_queues)
685 { }
687 public:
688 virtual void work(unsigned int work_id) = 0;
690 protected:
691 ReferenceProcessor& _ref_processor;
692 DiscoveredList* _refs_lists;
693 HeapWord* _pending_list_addr;
694 int _n_queues;
695 };
697 #endif // SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP