1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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13 * accompanied this code).
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23 */
24
25 #ifndef SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP
26 #define SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP
27
28 #include "gc/shared/gcTrace.hpp"
29 #include "gc/shared/referencePolicy.hpp"
30 #include "gc/shared/referenceProcessorStats.hpp"
31 #include "memory/referenceType.hpp"
32 #include "oops/instanceRefKlass.hpp"
33
34 class GCTimer;
35
36 // ReferenceProcessor class encapsulates the per-"collector" processing
37 // of java.lang.Reference objects for GC. The interface is useful for supporting
38 // a generational abstraction, in particular when there are multiple
39 // generations that are being independently collected -- possibly
40 // concurrently and/or incrementally. Note, however, that the
41 // ReferenceProcessor class abstracts away from a generational setting
42 // by using only a heap interval (called "span" below), thus allowing
43 // its use in a straightforward manner in a general, non-generational
44 // setting.
45 //
46 // The basic idea is that each ReferenceProcessor object concerns
47 // itself with ("weak") reference processing in a specific "span"
48 // of the heap of interest to a specific collector. Currently,
49 // the span is a convex interval of the heap, but, efficiency
50 // apart, there seems to be no reason it couldn't be extended
51 // (with appropriate modifications) to any "non-convex interval".
52
53 // forward references
54 class ReferencePolicy;
55 class AbstractRefProcTaskExecutor;
56
57 // List of discovered references.
58 class DiscoveredList {
59 public:
60 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
61 oop head() const {
62 return UseCompressedOops ? oopDesc::decode_heap_oop(_compressed_head) :
63 _oop_head;
64 }
65 HeapWord* adr_head() {
66 return UseCompressedOops ? (HeapWord*)&_compressed_head :
67 (HeapWord*)&_oop_head;
68 }
69 void set_head(oop o) {
70 if (UseCompressedOops) {
71 // Must compress the head ptr.
72 _compressed_head = oopDesc::encode_heap_oop(o);
73 } else {
74 _oop_head = o;
75 }
76 }
77 bool is_empty() const { return head() == NULL; }
78 size_t length() { return _len; }
79 void set_length(size_t len) { _len = len; }
80 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
81 void dec_length(size_t dec) { _len -= dec; }
82 private:
83 // Set value depending on UseCompressedOops. This could be a template class
84 // but then we have to fix all the instantiations and declarations that use this class.
85 oop _oop_head;
86 narrowOop _compressed_head;
87 size_t _len;
88 };
89
90 // Iterator for the list of discovered references.
91 class DiscoveredListIterator {
92 private:
93 DiscoveredList& _refs_list;
94 HeapWord* _prev_next;
95 oop _prev;
96 oop _ref;
97 HeapWord* _discovered_addr;
98 oop _next;
99 HeapWord* _referent_addr;
100 oop _referent;
101 OopClosure* _keep_alive;
102 BoolObjectClosure* _is_alive;
103
104 DEBUG_ONLY(
105 oop _first_seen; // cyclic linked list check
106 )
107
108 NOT_PRODUCT(
109 size_t _processed;
110 size_t _removed;
111 )
112
113 public:
114 inline DiscoveredListIterator(DiscoveredList& refs_list,
115 OopClosure* keep_alive,
116 BoolObjectClosure* is_alive):
117 _refs_list(refs_list),
118 _prev_next(refs_list.adr_head()),
119 _prev(NULL),
120 _ref(refs_list.head()),
121 #ifdef ASSERT
122 _first_seen(refs_list.head()),
123 #endif
124 #ifndef PRODUCT
125 _processed(0),
126 _removed(0),
127 #endif
128 _next(NULL),
129 _keep_alive(keep_alive),
130 _is_alive(is_alive)
131 { }
132
133 // End Of List.
134 inline bool has_next() const { return _ref != NULL; }
135
136 // Get oop to the Reference object.
137 inline oop obj() const { return _ref; }
138
139 // Get oop to the referent object.
140 inline oop referent() const { return _referent; }
141
142 // Returns true if referent is alive.
143 inline bool is_referent_alive() const {
144 return _is_alive->do_object_b(_referent);
145 }
146
147 // Loads data for the current reference.
148 // The "allow_null_referent" argument tells us to allow for the possibility
149 // of a NULL referent in the discovered Reference object. This typically
150 // happens in the case of concurrent collectors that may have done the
151 // discovery concurrently, or interleaved, with mutator execution.
152 void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
153
154 // Move to the next discovered reference.
155 inline void next() {
156 _prev_next = _discovered_addr;
157 _prev = _ref;
158 move_to_next();
159 }
160
161 // Remove the current reference from the list
162 void remove();
163
164 // Make the referent alive.
165 inline void make_referent_alive() {
166 if (UseCompressedOops) {
167 _keep_alive->do_oop((narrowOop*)_referent_addr);
168 } else {
169 _keep_alive->do_oop((oop*)_referent_addr);
170 }
171 }
172
173 // NULL out referent pointer.
174 void clear_referent();
175
176 // Statistics
177 NOT_PRODUCT(
178 inline size_t processed() const { return _processed; }
179 inline size_t removed() const { return _removed; }
180 )
181
182 inline void move_to_next() {
183 if (_ref == _next) {
184 // End of the list.
185 _ref = NULL;
186 } else {
187 _ref = _next;
188 }
189 assert(_ref != _first_seen, "cyclic ref_list found");
190 NOT_PRODUCT(_processed++);
191 }
192 };
193
194 class ReferenceProcessor : public CHeapObj<mtGC> {
195
196 private:
197 size_t total_count(DiscoveredList lists[]);
198
199 protected:
200 // The SoftReference master timestamp clock
201 static jlong _soft_ref_timestamp_clock;
202
203 MemRegion _span; // (right-open) interval of heap
204 // subject to wkref discovery
205
206 bool _discovering_refs; // true when discovery enabled
207 bool _discovery_is_atomic; // if discovery is atomic wrt
208 // other collectors in configuration
209 bool _discovery_is_mt; // true if reference discovery is MT.
210
211 bool _enqueuing_is_done; // true if all weak references enqueued
212 bool _processing_is_mt; // true during phases when
213 // reference processing is MT.
214 uint _next_id; // round-robin mod _num_q counter in
215 // support of work distribution
216
217 // For collectors that do not keep GC liveness information
218 // in the object header, this field holds a closure that
219 // helps the reference processor determine the reachability
220 // of an oop. It is currently initialized to NULL for all
221 // collectors except for CMS and G1.
222 BoolObjectClosure* _is_alive_non_header;
223
224 // Soft ref clearing policies
225 // . the default policy
226 static ReferencePolicy* _default_soft_ref_policy;
227 // . the "clear all" policy
228 static ReferencePolicy* _always_clear_soft_ref_policy;
229 // . the current policy below is either one of the above
230 ReferencePolicy* _current_soft_ref_policy;
231
232 // The discovered ref lists themselves
233
234 // The active MT'ness degree of the queues below
235 uint _num_q;
236 // The maximum MT'ness degree of the queues below
237 uint _max_num_q;
238
239 // Master array of discovered oops
240 DiscoveredList* _discovered_refs;
241
242 // Arrays of lists of oops, one per thread (pointers into master array above)
243 DiscoveredList* _discoveredSoftRefs;
244 DiscoveredList* _discoveredWeakRefs;
245 DiscoveredList* _discoveredFinalRefs;
246 DiscoveredList* _discoveredPhantomRefs;
247
248 public:
249 static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); }
250
251 uint num_q() { return _num_q; }
252 uint max_num_q() { return _max_num_q; }
253 void set_active_mt_degree(uint v) { _num_q = v; }
254
255 DiscoveredList* discovered_refs() { return _discovered_refs; }
256
257 ReferencePolicy* setup_policy(bool always_clear) {
258 _current_soft_ref_policy = always_clear ?
259 _always_clear_soft_ref_policy : _default_soft_ref_policy;
260 _current_soft_ref_policy->setup(); // snapshot the policy threshold
261 return _current_soft_ref_policy;
262 }
263
264 // Process references with a certain reachability level.
265 void process_discovered_reflist(DiscoveredList refs_lists[],
266 ReferencePolicy* policy,
267 bool clear_referent,
268 BoolObjectClosure* is_alive,
269 OopClosure* keep_alive,
270 VoidClosure* complete_gc,
271 AbstractRefProcTaskExecutor* task_executor);
272
273 void process_phaseJNI(BoolObjectClosure* is_alive,
274 OopClosure* keep_alive,
275 VoidClosure* complete_gc);
276
277 // Work methods used by the method process_discovered_reflist
278 // Phase1: keep alive all those referents that are otherwise
279 // dead but which must be kept alive by policy (and their closure).
280 void process_phase1(DiscoveredList& refs_list,
281 ReferencePolicy* policy,
282 BoolObjectClosure* is_alive,
283 OopClosure* keep_alive,
284 VoidClosure* complete_gc);
285 // Phase2: remove all those references whose referents are
286 // reachable.
287 inline void process_phase2(DiscoveredList& refs_list,
288 BoolObjectClosure* is_alive,
289 OopClosure* keep_alive,
290 VoidClosure* complete_gc) {
291 if (discovery_is_atomic()) {
292 // complete_gc is ignored in this case for this phase
293 pp2_work(refs_list, is_alive, keep_alive);
294 } else {
295 assert(complete_gc != NULL, "Error");
296 pp2_work_concurrent_discovery(refs_list, is_alive,
297 keep_alive, complete_gc);
298 }
299 }
300 // Work methods in support of process_phase2
301 void pp2_work(DiscoveredList& refs_list,
302 BoolObjectClosure* is_alive,
303 OopClosure* keep_alive);
304 void pp2_work_concurrent_discovery(
305 DiscoveredList& refs_list,
306 BoolObjectClosure* is_alive,
307 OopClosure* keep_alive,
308 VoidClosure* complete_gc);
309 // Phase3: process the referents by either clearing them
310 // or keeping them alive (and their closure)
311 void process_phase3(DiscoveredList& refs_list,
312 bool clear_referent,
313 BoolObjectClosure* is_alive,
314 OopClosure* keep_alive,
315 VoidClosure* complete_gc);
316
317 // Enqueue references with a certain reachability level
318 void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr);
319
320 // "Preclean" all the discovered reference lists
321 // by removing references with strongly reachable referents.
322 // The first argument is a predicate on an oop that indicates
323 // its (strong) reachability and the second is a closure that
324 // may be used to incrementalize or abort the precleaning process.
325 // The caller is responsible for taking care of potential
326 // interference with concurrent operations on these lists
327 // (or predicates involved) by other threads. Currently
328 // only used by the CMS collector.
329 void preclean_discovered_references(BoolObjectClosure* is_alive,
330 OopClosure* keep_alive,
331 VoidClosure* complete_gc,
332 YieldClosure* yield,
333 GCTimer* gc_timer);
334
335 // Returns the name of the discovered reference list
336 // occupying the i / _num_q slot.
337 const char* list_name(uint i);
338
339 void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);
340
341 protected:
342 // "Preclean" the given discovered reference list
343 // by removing references with strongly reachable referents.
344 // Currently used in support of CMS only.
345 void preclean_discovered_reflist(DiscoveredList& refs_list,
346 BoolObjectClosure* is_alive,
347 OopClosure* keep_alive,
348 VoidClosure* complete_gc,
349 YieldClosure* yield);
350
351 // round-robin mod _num_q (not: _not_ mode _max_num_q)
352 uint next_id() {
353 uint id = _next_id;
354 if (++_next_id == _num_q) {
355 _next_id = 0;
356 }
357 return id;
358 }
359 DiscoveredList* get_discovered_list(ReferenceType rt);
360 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
361 HeapWord* discovered_addr);
362
363 void clear_discovered_references(DiscoveredList& refs_list);
364
365 // Calculate the number of jni handles.
366 size_t count_jni_refs();
367
368 void log_reflist_counts(DiscoveredList ref_lists[], size_t total_count) PRODUCT_RETURN;
369
370 // Balances reference queues.
371 void balance_queues(DiscoveredList ref_lists[]);
372
373 // Update (advance) the soft ref master clock field.
374 void update_soft_ref_master_clock();
375
376 public:
377 // Default parameters give you a vanilla reference processor.
378 ReferenceProcessor(MemRegion span,
379 bool mt_processing = false, uint mt_processing_degree = 1,
380 bool mt_discovery = false, uint mt_discovery_degree = 1,
381 bool atomic_discovery = true,
382 BoolObjectClosure* is_alive_non_header = NULL);
383
384 // RefDiscoveryPolicy values
385 enum DiscoveryPolicy {
386 ReferenceBasedDiscovery = 0,
387 ReferentBasedDiscovery = 1,
388 DiscoveryPolicyMin = ReferenceBasedDiscovery,
389 DiscoveryPolicyMax = ReferentBasedDiscovery
390 };
391
392 static void init_statics();
393
394 public:
395 // get and set "is_alive_non_header" field
396 BoolObjectClosure* is_alive_non_header() {
397 return _is_alive_non_header;
398 }
399 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
400 _is_alive_non_header = is_alive_non_header;
401 }
402
403 // get and set span
404 MemRegion span() { return _span; }
405 void set_span(MemRegion span) { _span = span; }
406
407 // start and stop weak ref discovery
408 void enable_discovery(bool check_no_refs = true);
409 void disable_discovery() { _discovering_refs = false; }
410 bool discovery_enabled() { return _discovering_refs; }
411
412 // whether discovery is atomic wrt other collectors
413 bool discovery_is_atomic() const { return _discovery_is_atomic; }
414 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
415
416 // whether discovery is done by multiple threads same-old-timeously
417 bool discovery_is_mt() const { return _discovery_is_mt; }
418 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
419
420 // Whether we are in a phase when _processing_ is MT.
421 bool processing_is_mt() const { return _processing_is_mt; }
422 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
423
424 // whether all enqueueing of weak references is complete
425 bool enqueuing_is_done() { return _enqueuing_is_done; }
426 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
427
428 // iterate over oops
429 void weak_oops_do(OopClosure* f); // weak roots
430
431 // Balance each of the discovered lists.
432 void balance_all_queues();
433 void verify_list(DiscoveredList& ref_list);
434
435 // Discover a Reference object, using appropriate discovery criteria
436 bool discover_reference(oop obj, ReferenceType rt);
437
438 // Process references found during GC (called by the garbage collector)
439 ReferenceProcessorStats
440 process_discovered_references(BoolObjectClosure* is_alive,
441 OopClosure* keep_alive,
442 VoidClosure* complete_gc,
443 AbstractRefProcTaskExecutor* task_executor,
444 GCTimer *gc_timer);
445
446 // Enqueue references at end of GC (called by the garbage collector)
447 bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
448
449 // If a discovery is in process that is being superceded, abandon it: all
450 // the discovered lists will be empty, and all the objects on them will
451 // have NULL discovered fields. Must be called only at a safepoint.
452 void abandon_partial_discovery();
453
454 // debugging
455 void verify_no_references_recorded() PRODUCT_RETURN;
456 void verify_referent(oop obj) PRODUCT_RETURN;
457 };
458
459 // A utility class to disable reference discovery in
460 // the scope which contains it, for given ReferenceProcessor.
461 class NoRefDiscovery: StackObj {
462 private:
463 ReferenceProcessor* _rp;
464 bool _was_discovering_refs;
465 public:
466 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
467 _was_discovering_refs = _rp->discovery_enabled();
468 if (_was_discovering_refs) {
469 _rp->disable_discovery();
470 }
471 }
472
473 ~NoRefDiscovery() {
474 if (_was_discovering_refs) {
475 _rp->enable_discovery(false /*check_no_refs*/);
476 }
477 }
478 };
479
480
481 // A utility class to temporarily mutate the span of the
482 // given ReferenceProcessor in the scope that contains it.
483 class ReferenceProcessorSpanMutator: StackObj {
484 private:
485 ReferenceProcessor* _rp;
486 MemRegion _saved_span;
487
488 public:
489 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
490 MemRegion span):
491 _rp(rp) {
492 _saved_span = _rp->span();
493 _rp->set_span(span);
494 }
495
496 ~ReferenceProcessorSpanMutator() {
497 _rp->set_span(_saved_span);
498 }
499 };
500
501 // A utility class to temporarily change the MT'ness of
502 // reference discovery for the given ReferenceProcessor
503 // in the scope that contains it.
504 class ReferenceProcessorMTDiscoveryMutator: StackObj {
505 private:
506 ReferenceProcessor* _rp;
507 bool _saved_mt;
508
509 public:
510 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
511 bool mt):
512 _rp(rp) {
513 _saved_mt = _rp->discovery_is_mt();
514 _rp->set_mt_discovery(mt);
515 }
516
517 ~ReferenceProcessorMTDiscoveryMutator() {
518 _rp->set_mt_discovery(_saved_mt);
519 }
520 };
521
522
523 // A utility class to temporarily change the disposition
524 // of the "is_alive_non_header" closure field of the
525 // given ReferenceProcessor in the scope that contains it.
526 class ReferenceProcessorIsAliveMutator: StackObj {
527 private:
528 ReferenceProcessor* _rp;
529 BoolObjectClosure* _saved_cl;
530
531 public:
532 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
533 BoolObjectClosure* cl):
534 _rp(rp) {
535 _saved_cl = _rp->is_alive_non_header();
536 _rp->set_is_alive_non_header(cl);
537 }
538
539 ~ReferenceProcessorIsAliveMutator() {
540 _rp->set_is_alive_non_header(_saved_cl);
541 }
542 };
543
544 // A utility class to temporarily change the disposition
545 // of the "discovery_is_atomic" field of the
546 // given ReferenceProcessor in the scope that contains it.
547 class ReferenceProcessorAtomicMutator: StackObj {
548 private:
549 ReferenceProcessor* _rp;
550 bool _saved_atomic_discovery;
551
552 public:
553 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
554 bool atomic):
555 _rp(rp) {
556 _saved_atomic_discovery = _rp->discovery_is_atomic();
557 _rp->set_atomic_discovery(atomic);
558 }
559
560 ~ReferenceProcessorAtomicMutator() {
561 _rp->set_atomic_discovery(_saved_atomic_discovery);
562 }
563 };
564
565
566 // A utility class to temporarily change the MT processing
567 // disposition of the given ReferenceProcessor instance
568 // in the scope that contains it.
569 class ReferenceProcessorMTProcMutator: StackObj {
570 private:
571 ReferenceProcessor* _rp;
572 bool _saved_mt;
573
574 public:
575 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
576 bool mt):
577 _rp(rp) {
578 _saved_mt = _rp->processing_is_mt();
579 _rp->set_mt_processing(mt);
580 }
581
582 ~ReferenceProcessorMTProcMutator() {
583 _rp->set_mt_processing(_saved_mt);
584 }
585 };
586
587
588 // This class is an interface used to implement task execution for the
589 // reference processing.
590 class AbstractRefProcTaskExecutor {
591 public:
592
593 // Abstract tasks to execute.
594 class ProcessTask;
595 class EnqueueTask;
596
597 // Executes a task using worker threads.
598 virtual void execute(ProcessTask& task) = 0;
599 virtual void execute(EnqueueTask& task) = 0;
600
601 // Switch to single threaded mode.
602 virtual void set_single_threaded_mode() { };
603 };
604
605 // Abstract reference processing task to execute.
606 class AbstractRefProcTaskExecutor::ProcessTask {
607 protected:
608 ProcessTask(ReferenceProcessor& ref_processor,
609 DiscoveredList refs_lists[],
610 bool marks_oops_alive)
611 : _ref_processor(ref_processor),
612 _refs_lists(refs_lists),
613 _marks_oops_alive(marks_oops_alive)
614 { }
615
616 public:
617 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
618 OopClosure& keep_alive,
619 VoidClosure& complete_gc) = 0;
620
621 // Returns true if a task marks some oops as alive.
622 bool marks_oops_alive() const
623 { return _marks_oops_alive; }
624
625 protected:
626 ReferenceProcessor& _ref_processor;
627 DiscoveredList* _refs_lists;
628 const bool _marks_oops_alive;
629 };
630
631 // Abstract reference processing task to execute.
632 class AbstractRefProcTaskExecutor::EnqueueTask {
633 protected:
634 EnqueueTask(ReferenceProcessor& ref_processor,
635 DiscoveredList refs_lists[],
636 HeapWord* pending_list_addr,
637 int n_queues)
638 : _ref_processor(ref_processor),
639 _refs_lists(refs_lists),
640 _pending_list_addr(pending_list_addr),
641 _n_queues(n_queues)
642 { }
643
644 public:
645 virtual void work(unsigned int work_id) = 0;
646
647 protected:
648 ReferenceProcessor& _ref_processor;
649 DiscoveredList* _refs_lists;
650 HeapWord* _pending_list_addr;
651 int _n_queues;
652 };
653
654 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP