1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
26 #define SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
27
28 #include "memory/referencePolicy.hpp"
29 #include "oops/instanceRefKlass.hpp"
30
31 // ReferenceProcessor class encapsulates the per-"collector" processing
32 // of java.lang.Reference objects for GC. The interface is useful for supporting
33 // a generational abstraction, in particular when there are multiple
34 // generations that are being independently collected -- possibly
35 // concurrently and/or incrementally. Note, however, that the
36 // ReferenceProcessor class abstracts away from a generational setting
37 // by using only a heap interval (called "span" below), thus allowing
38 // its use in a straightforward manner in a general, non-generational
39 // setting.
40 //
41 // The basic idea is that each ReferenceProcessor object concerns
42 // itself with ("weak") reference processing in a specific "span"
43 // of the heap of interest to a specific collector. Currently,
44 // the span is a convex interval of the heap, but, efficiency
45 // apart, there seems to be no reason it couldn't be extended
46 // (with appropriate modifications) to any "non-convex interval".
47
48 // forward references
49 class ReferencePolicy;
50 class AbstractRefProcTaskExecutor;
51 class DiscoveredList;
52
53 class ReferenceProcessor : public CHeapObj {
54 protected:
55 // Compatibility with pre-4965777 JDK's
56 static bool _pending_list_uses_discovered_field;
57 MemRegion _span; // (right-open) interval of heap
58 // subject to wkref discovery
59 bool _discovering_refs; // true when discovery enabled
60 bool _discovery_is_atomic; // if discovery is atomic wrt
61 // other collectors in configuration
62 bool _discovery_is_mt; // true if reference discovery is MT.
63 // If true, setting "next" field of a discovered refs list requires
64 // write barrier(s). (Must be true if used in a collector in which
65 // elements of a discovered list may be moved during discovery: for
66 // example, a collector like Garbage-First that moves objects during a
67 // long-term concurrent marking phase that does weak reference
68 // discovery.)
69 bool _discovered_list_needs_barrier;
70 BarrierSet* _bs; // Cached copy of BarrierSet.
71 bool _enqueuing_is_done; // true if all weak references enqueued
72 bool _processing_is_mt; // true during phases when
73 // reference processing is MT.
74 int _next_id; // round-robin mod _num_q counter in
75 // support of work distribution
76
77 // For collectors that do not keep GC marking information
78 // in the object header, this field holds a closure that
79 // helps the reference processor determine the reachability
80 // of an oop (the field is currently initialized to NULL for
81 // all collectors but the CMS collector).
82 BoolObjectClosure* _is_alive_non_header;
83
84 // Soft ref clearing policies
85 // . the default policy
86 static ReferencePolicy* _default_soft_ref_policy;
87 // . the "clear all" policy
88 static ReferencePolicy* _always_clear_soft_ref_policy;
89 // . the current policy below is either one of the above
90 ReferencePolicy* _current_soft_ref_policy;
91
92 // The discovered ref lists themselves
93
94 // The active MT'ness degree of the queues below
95 int _num_q;
96 // The maximum MT'ness degree of the queues below
97 int _max_num_q;
98 // Arrays of lists of oops, one per thread
99 DiscoveredList* _discoveredSoftRefs;
100 DiscoveredList* _discoveredWeakRefs;
101 DiscoveredList* _discoveredFinalRefs;
102 DiscoveredList* _discoveredPhantomRefs;
103
104 public:
105 int num_q() { return _num_q; }
106 int max_num_q() { return _max_num_q; }
107 void set_active_mt_degree(int v) { _num_q = v; }
108 DiscoveredList* discovered_soft_refs() { return _discoveredSoftRefs; }
109 ReferencePolicy* setup_policy(bool always_clear) {
110 _current_soft_ref_policy = always_clear ?
111 _always_clear_soft_ref_policy : _default_soft_ref_policy;
112 _current_soft_ref_policy->setup(); // snapshot the policy threshold
113 return _current_soft_ref_policy;
114 }
115
116 // Process references with a certain reachability level.
117 void process_discovered_reflist(DiscoveredList refs_lists[],
118 ReferencePolicy* policy,
119 bool clear_referent,
120 BoolObjectClosure* is_alive,
121 OopClosure* keep_alive,
122 VoidClosure* complete_gc,
123 AbstractRefProcTaskExecutor* task_executor);
124
125 void process_phaseJNI(BoolObjectClosure* is_alive,
126 OopClosure* keep_alive,
127 VoidClosure* complete_gc);
128
129 // Work methods used by the method process_discovered_reflist
130 // Phase1: keep alive all those referents that are otherwise
131 // dead but which must be kept alive by policy (and their closure).
132 void process_phase1(DiscoveredList& refs_list,
133 ReferencePolicy* policy,
134 BoolObjectClosure* is_alive,
135 OopClosure* keep_alive,
136 VoidClosure* complete_gc);
137 // Phase2: remove all those references whose referents are
138 // reachable.
139 inline void process_phase2(DiscoveredList& refs_list,
140 BoolObjectClosure* is_alive,
141 OopClosure* keep_alive,
142 VoidClosure* complete_gc) {
143 if (discovery_is_atomic()) {
144 // complete_gc is ignored in this case for this phase
145 pp2_work(refs_list, is_alive, keep_alive);
146 } else {
147 assert(complete_gc != NULL, "Error");
148 pp2_work_concurrent_discovery(refs_list, is_alive,
149 keep_alive, complete_gc);
150 }
151 }
152 // Work methods in support of process_phase2
153 void pp2_work(DiscoveredList& refs_list,
154 BoolObjectClosure* is_alive,
155 OopClosure* keep_alive);
156 void pp2_work_concurrent_discovery(
157 DiscoveredList& refs_list,
158 BoolObjectClosure* is_alive,
159 OopClosure* keep_alive,
160 VoidClosure* complete_gc);
161 // Phase3: process the referents by either clearing them
162 // or keeping them alive (and their closure)
163 void process_phase3(DiscoveredList& refs_list,
164 bool clear_referent,
165 BoolObjectClosure* is_alive,
166 OopClosure* keep_alive,
167 VoidClosure* complete_gc);
168
169 // Enqueue references with a certain reachability level
170 void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr);
171
172 // "Preclean" all the discovered reference lists
173 // by removing references with strongly reachable referents.
174 // The first argument is a predicate on an oop that indicates
175 // its (strong) reachability and the second is a closure that
176 // may be used to incrementalize or abort the precleaning process.
177 // The caller is responsible for taking care of potential
178 // interference with concurrent operations on these lists
179 // (or predicates involved) by other threads. Currently
180 // only used by the CMS collector. should_unload_classes is
181 // used to aid assertion checking when classes are collected.
182 void preclean_discovered_references(BoolObjectClosure* is_alive,
183 OopClosure* keep_alive,
184 VoidClosure* complete_gc,
185 YieldClosure* yield,
186 bool should_unload_classes);
187
188 // Delete entries in the discovered lists that have
189 // either a null referent or are not active. Such
190 // Reference objects can result from the clearing
191 // or enqueueing of Reference objects concurrent
192 // with their discovery by a (concurrent) collector.
193 // For a definition of "active" see java.lang.ref.Reference;
194 // Refs are born active, become inactive when enqueued,
195 // and never become active again. The state of being
196 // active is encoded as follows: A Ref is active
197 // if and only if its "next" field is NULL.
198 void clean_up_discovered_references();
199 void clean_up_discovered_reflist(DiscoveredList& refs_list);
200
201 // Returns the name of the discovered reference list
202 // occupying the i / _num_q slot.
203 const char* list_name(int i);
204
205 void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);
206
207 protected:
208 // "Preclean" the given discovered reference list
209 // by removing references with strongly reachable referents.
210 // Currently used in support of CMS only.
211 void preclean_discovered_reflist(DiscoveredList& refs_list,
212 BoolObjectClosure* is_alive,
213 OopClosure* keep_alive,
214 VoidClosure* complete_gc,
215 YieldClosure* yield);
216
217 // round-robin mod _num_q (not: _not_ mode _max_num_q)
218 int next_id() {
219 int id = _next_id;
220 if (++_next_id == _num_q) {
221 _next_id = 0;
222 }
223 return id;
224 }
225 DiscoveredList* get_discovered_list(ReferenceType rt);
226 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
227 HeapWord* discovered_addr);
228 void verify_ok_to_handle_reflists() PRODUCT_RETURN;
229
230 void clear_discovered_references(DiscoveredList& refs_list);
231 void abandon_partial_discovered_list(DiscoveredList& refs_list);
232
233 // Calculate the number of jni handles.
234 unsigned int count_jni_refs();
235
236 // Balances reference queues.
237 void balance_queues(DiscoveredList ref_lists[]);
238
239 // Update (advance) the soft ref master clock field.
240 void update_soft_ref_master_clock();
241
242 public:
243 // constructor
244 ReferenceProcessor():
245 _span((HeapWord*)NULL, (HeapWord*)NULL),
246 _discoveredSoftRefs(NULL), _discoveredWeakRefs(NULL),
247 _discoveredFinalRefs(NULL), _discoveredPhantomRefs(NULL),
248 _discovering_refs(false),
249 _discovery_is_atomic(true),
250 _enqueuing_is_done(false),
251 _discovery_is_mt(false),
252 _discovered_list_needs_barrier(false),
253 _bs(NULL),
254 _is_alive_non_header(NULL),
255 _num_q(0),
256 _max_num_q(0),
257 _processing_is_mt(false),
258 _next_id(0)
259 { }
260
261 // Default parameters give you a vanilla reference processor.
262 ReferenceProcessor(MemRegion span,
263 bool mt_processing = false, int mt_processing_degree = 1,
264 bool mt_discovery = false, int mt_discovery_degree = 1,
265 bool atomic_discovery = true,
266 BoolObjectClosure* is_alive_non_header = NULL,
267 bool discovered_list_needs_barrier = false);
268
269 // RefDiscoveryPolicy values
270 enum DiscoveryPolicy {
271 ReferenceBasedDiscovery = 0,
272 ReferentBasedDiscovery = 1,
273 DiscoveryPolicyMin = ReferenceBasedDiscovery,
274 DiscoveryPolicyMax = ReferentBasedDiscovery
275 };
276
277 static void init_statics();
278
279 public:
280 // get and set "is_alive_non_header" field
281 BoolObjectClosure* is_alive_non_header() {
282 return _is_alive_non_header;
283 }
284 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
285 _is_alive_non_header = is_alive_non_header;
286 }
287
288 // get and set span
289 MemRegion span() { return _span; }
290 void set_span(MemRegion span) { _span = span; }
291
292 // start and stop weak ref discovery
293 void enable_discovery() { _discovering_refs = true; }
294 void disable_discovery() { _discovering_refs = false; }
295 bool discovery_enabled() { return _discovering_refs; }
296
297 // whether discovery is atomic wrt other collectors
298 bool discovery_is_atomic() const { return _discovery_is_atomic; }
299 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
300
301 // whether the JDK in which we are embedded is a pre-4965777 JDK,
302 // and thus whether ir not it uses the discovered field to chain
303 // the entries in the pending list.
304 static bool pending_list_uses_discovered_field() {
305 return _pending_list_uses_discovered_field;
306 }
307
308 // whether discovery is done by multiple threads same-old-timeously
309 bool discovery_is_mt() const { return _discovery_is_mt; }
310 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
311
312 // Whether we are in a phase when _processing_ is MT.
313 bool processing_is_mt() const { return _processing_is_mt; }
314 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
315
316 // whether all enqueuing of weak references is complete
317 bool enqueuing_is_done() { return _enqueuing_is_done; }
318 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
319
320 // iterate over oops
321 void weak_oops_do(OopClosure* f); // weak roots
322
323 // Balance each of the discovered lists.
324 void balance_all_queues();
325
326 // Discover a Reference object, using appropriate discovery criteria
327 bool discover_reference(oop obj, ReferenceType rt);
328
329 // Process references found during GC (called by the garbage collector)
330 void process_discovered_references(BoolObjectClosure* is_alive,
331 OopClosure* keep_alive,
332 VoidClosure* complete_gc,
333 AbstractRefProcTaskExecutor* task_executor);
334
335 public:
336 // Enqueue references at end of GC (called by the garbage collector)
337 bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
338
339 // If a discovery is in process that is being superceded, abandon it: all
340 // the discovered lists will be empty, and all the objects on them will
341 // have NULL discovered fields. Must be called only at a safepoint.
342 void abandon_partial_discovery();
343
344 // debugging
345 void verify_no_references_recorded() PRODUCT_RETURN;
346 void verify_referent(oop obj) PRODUCT_RETURN;
347
348 // clear the discovered lists (unlinking each entry).
349 void clear_discovered_references() PRODUCT_RETURN;
350 };
351
352 // A utility class to disable reference discovery in
353 // the scope which contains it, for given ReferenceProcessor.
354 class NoRefDiscovery: StackObj {
355 private:
356 ReferenceProcessor* _rp;
357 bool _was_discovering_refs;
358 public:
359 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
360 _was_discovering_refs = _rp->discovery_enabled();
361 if (_was_discovering_refs) {
362 _rp->disable_discovery();
363 }
364 }
365
366 ~NoRefDiscovery() {
367 if (_was_discovering_refs) {
368 _rp->enable_discovery();
369 }
370 }
371 };
372
373
374 // A utility class to temporarily mutate the span of the
375 // given ReferenceProcessor in the scope that contains it.
376 class ReferenceProcessorSpanMutator: StackObj {
377 private:
378 ReferenceProcessor* _rp;
379 MemRegion _saved_span;
380
381 public:
382 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
383 MemRegion span):
384 _rp(rp) {
385 _saved_span = _rp->span();
386 _rp->set_span(span);
387 }
388
389 ~ReferenceProcessorSpanMutator() {
390 _rp->set_span(_saved_span);
391 }
392 };
393
394 // A utility class to temporarily change the MT'ness of
395 // reference discovery for the given ReferenceProcessor
396 // in the scope that contains it.
397 class ReferenceProcessorMTDiscoveryMutator: StackObj {
398 private:
399 ReferenceProcessor* _rp;
400 bool _saved_mt;
401
402 public:
403 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
404 bool mt):
405 _rp(rp) {
406 _saved_mt = _rp->discovery_is_mt();
407 _rp->set_mt_discovery(mt);
408 }
409
410 ~ReferenceProcessorMTDiscoveryMutator() {
411 _rp->set_mt_discovery(_saved_mt);
412 }
413 };
414
415
416 // A utility class to temporarily change the disposition
417 // of the "is_alive_non_header" closure field of the
418 // given ReferenceProcessor in the scope that contains it.
419 class ReferenceProcessorIsAliveMutator: StackObj {
420 private:
421 ReferenceProcessor* _rp;
422 BoolObjectClosure* _saved_cl;
423
424 public:
425 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
426 BoolObjectClosure* cl):
427 _rp(rp) {
428 _saved_cl = _rp->is_alive_non_header();
429 _rp->set_is_alive_non_header(cl);
430 }
431
432 ~ReferenceProcessorIsAliveMutator() {
433 _rp->set_is_alive_non_header(_saved_cl);
434 }
435 };
436
437 // A utility class to temporarily change the disposition
438 // of the "discovery_is_atomic" field of the
439 // given ReferenceProcessor in the scope that contains it.
440 class ReferenceProcessorAtomicMutator: StackObj {
441 private:
442 ReferenceProcessor* _rp;
443 bool _saved_atomic_discovery;
444
445 public:
446 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
447 bool atomic):
448 _rp(rp) {
449 _saved_atomic_discovery = _rp->discovery_is_atomic();
450 _rp->set_atomic_discovery(atomic);
451 }
452
453 ~ReferenceProcessorAtomicMutator() {
454 _rp->set_atomic_discovery(_saved_atomic_discovery);
455 }
456 };
457
458
459 // A utility class to temporarily change the MT processing
460 // disposition of the given ReferenceProcessor instance
461 // in the scope that contains it.
462 class ReferenceProcessorMTProcMutator: StackObj {
463 private:
464 ReferenceProcessor* _rp;
465 bool _saved_mt;
466
467 public:
468 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
469 bool mt):
470 _rp(rp) {
471 _saved_mt = _rp->processing_is_mt();
472 _rp->set_mt_processing(mt);
473 }
474
475 ~ReferenceProcessorMTProcMutator() {
476 _rp->set_mt_processing(_saved_mt);
477 }
478 };
479
480
481 // This class is an interface used to implement task execution for the
482 // reference processing.
483 class AbstractRefProcTaskExecutor {
484 public:
485
486 // Abstract tasks to execute.
487 class ProcessTask;
488 class EnqueueTask;
489
490 // Executes a task using worker threads.
491 virtual void execute(ProcessTask& task) = 0;
492 virtual void execute(EnqueueTask& task) = 0;
493
494 // Switch to single threaded mode.
495 virtual void set_single_threaded_mode() { };
496 };
497
498 // Abstract reference processing task to execute.
499 class AbstractRefProcTaskExecutor::ProcessTask {
500 protected:
501 ProcessTask(ReferenceProcessor& ref_processor,
502 DiscoveredList refs_lists[],
503 bool marks_oops_alive)
504 : _ref_processor(ref_processor),
505 _refs_lists(refs_lists),
506 _marks_oops_alive(marks_oops_alive)
507 { }
508
509 public:
510 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
511 OopClosure& keep_alive,
512 VoidClosure& complete_gc) = 0;
513
514 // Returns true if a task marks some oops as alive.
515 bool marks_oops_alive() const
516 { return _marks_oops_alive; }
517
518 protected:
519 ReferenceProcessor& _ref_processor;
520 DiscoveredList* _refs_lists;
521 const bool _marks_oops_alive;
522 };
523
524 // Abstract reference processing task to execute.
525 class AbstractRefProcTaskExecutor::EnqueueTask {
526 protected:
527 EnqueueTask(ReferenceProcessor& ref_processor,
528 DiscoveredList refs_lists[],
529 HeapWord* pending_list_addr,
530 int n_queues)
531 : _ref_processor(ref_processor),
532 _refs_lists(refs_lists),
533 _pending_list_addr(pending_list_addr),
534 _n_queues(n_queues)
535 { }
536
537 public:
538 virtual void work(unsigned int work_id) = 0;
539
540 protected:
541 ReferenceProcessor& _ref_processor;
542 DiscoveredList* _refs_lists;
543 HeapWord* _pending_list_addr;
544 int _n_queues;
545 };
546
547 #endif // SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP