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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 // End of list marker
56 static oop _sentinelRef;
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 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 void set_mt_degree(int v) { _num_q = v; }
107 DiscoveredList* discovered_soft_refs() { return _discoveredSoftRefs; }
108 static oop sentinel_ref() { return _sentinelRef; }
109 static oop* adr_sentinel_ref() { return &_sentinelRef; }
110 ReferencePolicy* setup_policy(bool always_clear) {
111 _current_soft_ref_policy = always_clear ?
112 _always_clear_soft_ref_policy : _default_soft_ref_policy;
113 _current_soft_ref_policy->setup(); // snapshot the policy threshold
114 return _current_soft_ref_policy;
115 }
116
117 public:
118 // Process references with a certain reachability level.
119 void process_discovered_reflist(DiscoveredList refs_lists[],
120 ReferencePolicy* policy,
121 bool clear_referent,
122 BoolObjectClosure* is_alive,
123 OopClosure* keep_alive,
124 VoidClosure* complete_gc,
125 AbstractRefProcTaskExecutor* task_executor);
126
127 void process_phaseJNI(BoolObjectClosure* is_alive,
128 OopClosure* keep_alive,
129 VoidClosure* complete_gc);
130
131 // Work methods used by the method process_discovered_reflist
132 // Phase1: keep alive all those referents that are otherwise
133 // dead but which must be kept alive by policy (and their closure).
134 void process_phase1(DiscoveredList& refs_list,
135 ReferencePolicy* policy,
136 BoolObjectClosure* is_alive,
137 OopClosure* keep_alive,
138 VoidClosure* complete_gc);
139 // Phase2: remove all those references whose referents are
140 // reachable.
141 inline void process_phase2(DiscoveredList& refs_list,
142 BoolObjectClosure* is_alive,
143 OopClosure* keep_alive,
144 VoidClosure* complete_gc) {
145 if (discovery_is_atomic()) {
146 // complete_gc is ignored in this case for this phase
147 pp2_work(refs_list, is_alive, keep_alive);
148 } else {
149 assert(complete_gc != NULL, "Error");
150 pp2_work_concurrent_discovery(refs_list, is_alive,
151 keep_alive, complete_gc);
152 }
153 }
154 // Work methods in support of process_phase2
155 void pp2_work(DiscoveredList& refs_list,
156 BoolObjectClosure* is_alive,
157 OopClosure* keep_alive);
158 void pp2_work_concurrent_discovery(
159 DiscoveredList& refs_list,
160 BoolObjectClosure* is_alive,
161 OopClosure* keep_alive,
162 VoidClosure* complete_gc);
163 // Phase3: process the referents by either clearing them
164 // or keeping them alive (and their closure)
165 void process_phase3(DiscoveredList& refs_list,
166 bool clear_referent,
167 BoolObjectClosure* is_alive,
168 OopClosure* keep_alive,
169 VoidClosure* complete_gc);
170
171 // Enqueue references with a certain reachability level
172 void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr);
173
174 // "Preclean" all the discovered reference lists
175 // by removing references with strongly reachable referents.
176 // The first argument is a predicate on an oop that indicates
177 // its (strong) reachability and the second is a closure that
178 // may be used to incrementalize or abort the precleaning process.
179 // The caller is responsible for taking care of potential
180 // interference with concurrent operations on these lists
181 // (or predicates involved) by other threads. Currently
182 // only used by the CMS collector. should_unload_classes is
183 // used to aid assertion checking when classes are collected.
184 void preclean_discovered_references(BoolObjectClosure* is_alive,
185 OopClosure* keep_alive,
186 VoidClosure* complete_gc,
187 YieldClosure* yield,
188 bool should_unload_classes);
189
190 // Delete entries in the discovered lists that have
191 // either a null referent or are not active. Such
192 // Reference objects can result from the clearing
193 // or enqueueing of Reference objects concurrent
194 // with their discovery by a (concurrent) collector.
195 // For a definition of "active" see java.lang.ref.Reference;
196 // Refs are born active, become inactive when enqueued,
197 // and never become active again. The state of being
198 // active is encoded as follows: A Ref is active
199 // if and only if its "next" field is NULL.
200 void clean_up_discovered_references();
201 void clean_up_discovered_reflist(DiscoveredList& refs_list);
202
203 // Returns the name of the discovered reference list
204 // occupying the i / _num_q slot.
205 const char* list_name(int i);
206
207 void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);
208
209 protected:
210 // "Preclean" the given discovered reference list
211 // by removing references with strongly reachable referents.
212 // Currently used in support of CMS only.
213 void preclean_discovered_reflist(DiscoveredList& refs_list,
214 BoolObjectClosure* is_alive,
215 OopClosure* keep_alive,
216 VoidClosure* complete_gc,
217 YieldClosure* yield);
218
219 int next_id() {
220 int id = _next_id;
221 if (++_next_id == _num_q) {
222 _next_id = 0;
223 }
224 return id;
225 }
226 DiscoveredList* get_discovered_list(ReferenceType rt);
227 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
228 HeapWord* discovered_addr);
229 void verify_ok_to_handle_reflists() PRODUCT_RETURN;
230
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 discovery is done by multiple threads same-old-timeously
302 bool discovery_is_mt() const { return _discovery_is_mt; }
303 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
304
305 // Whether we are in a phase when _processing_ is MT.
306 bool processing_is_mt() const { return _processing_is_mt; }
307 void set_mt_processing(bool mt) { _processing_is_mt = mt; }
308
309 // whether all enqueuing of weak references is complete
310 bool enqueuing_is_done() { return _enqueuing_is_done; }
311 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
312
313 // iterate over oops
314 void weak_oops_do(OopClosure* f); // weak roots
315 static void oops_do(OopClosure* f); // strong root(s)
316
317 // Balance each of the discovered lists.
318 void balance_all_queues();
319
320 // Discover a Reference object, using appropriate discovery criteria
321 bool discover_reference(oop obj, ReferenceType rt);
322
323 // Process references found during GC (called by the garbage collector)
324 void process_discovered_references(BoolObjectClosure* is_alive,
325 OopClosure* keep_alive,
326 VoidClosure* complete_gc,
327 AbstractRefProcTaskExecutor* task_executor);
328
329 public:
330 // Enqueue references at end of GC (called by the garbage collector)
331 bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
332
333 // If a discovery is in process that is being superceded, abandon it: all
334 // the discovered lists will be empty, and all the objects on them will
335 // have NULL discovered fields. Must be called only at a safepoint.
336 void abandon_partial_discovery();
337
338 // debugging
339 void verify_no_references_recorded() PRODUCT_RETURN;
340 void verify_referent(oop obj) PRODUCT_RETURN;
341 static void verify();
342
343 // clear the discovered lists (unlinking each entry).
344 void clear_discovered_references() PRODUCT_RETURN;
345 };
346
347 // A utility class to disable reference discovery in
348 // the scope which contains it, for given ReferenceProcessor.
349 class NoRefDiscovery: StackObj {
350 private:
351 ReferenceProcessor* _rp;
352 bool _was_discovering_refs;
353 public:
354 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
355 _was_discovering_refs = _rp->discovery_enabled();
356 if (_was_discovering_refs) {
357 _rp->disable_discovery();
358 }
359 }
360
361 ~NoRefDiscovery() {
362 if (_was_discovering_refs) {
363 _rp->enable_discovery();
364 }
365 }
366 };
367
368
369 // A utility class to temporarily mutate the span of the
370 // given ReferenceProcessor in the scope that contains it.
371 class ReferenceProcessorSpanMutator: StackObj {
372 private:
373 ReferenceProcessor* _rp;
374 MemRegion _saved_span;
375
376 public:
377 ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
378 MemRegion span):
379 _rp(rp) {
380 _saved_span = _rp->span();
381 _rp->set_span(span);
382 }
383
384 ~ReferenceProcessorSpanMutator() {
385 _rp->set_span(_saved_span);
386 }
387 };
388
389 // A utility class to temporarily change the MT'ness of
390 // reference discovery for the given ReferenceProcessor
391 // in the scope that contains it.
392 class ReferenceProcessorMTMutator: StackObj {
393 private:
394 ReferenceProcessor* _rp;
395 bool _saved_mt;
396
397 public:
398 ReferenceProcessorMTMutator(ReferenceProcessor* rp,
399 bool mt):
400 _rp(rp) {
401 _saved_mt = _rp->discovery_is_mt();
402 _rp->set_mt_discovery(mt);
403 }
404
405 ~ReferenceProcessorMTMutator() {
406 _rp->set_mt_discovery(_saved_mt);
407 }
408 };
409
410
411 // A utility class to temporarily change the disposition
412 // of the "is_alive_non_header" closure field of the
413 // given ReferenceProcessor in the scope that contains it.
414 class ReferenceProcessorIsAliveMutator: StackObj {
415 private:
416 ReferenceProcessor* _rp;
417 BoolObjectClosure* _saved_cl;
418
419 public:
420 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
421 BoolObjectClosure* cl):
422 _rp(rp) {
423 _saved_cl = _rp->is_alive_non_header();
424 _rp->set_is_alive_non_header(cl);
425 }
426
427 ~ReferenceProcessorIsAliveMutator() {
428 _rp->set_is_alive_non_header(_saved_cl);
429 }
430 };
431
432 // A utility class to temporarily change the disposition
433 // of the "discovery_is_atomic" field of the
434 // given ReferenceProcessor in the scope that contains it.
435 class ReferenceProcessorAtomicMutator: StackObj {
436 private:
437 ReferenceProcessor* _rp;
438 bool _saved_atomic_discovery;
439
440 public:
441 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
442 bool atomic):
443 _rp(rp) {
444 _saved_atomic_discovery = _rp->discovery_is_atomic();
445 _rp->set_atomic_discovery(atomic);
446 }
447
448 ~ReferenceProcessorAtomicMutator() {
449 _rp->set_atomic_discovery(_saved_atomic_discovery);
450 }
451 };
452
453
454 // A utility class to temporarily change the MT processing
455 // disposition of the given ReferenceProcessor instance
456 // in the scope that contains it.
457 class ReferenceProcessorMTProcMutator: StackObj {
458 private:
459 ReferenceProcessor* _rp;
460 bool _saved_mt;
461
462 public:
463 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
464 bool mt):
465 _rp(rp) {
466 _saved_mt = _rp->processing_is_mt();
467 _rp->set_mt_processing(mt);
468 }
469
470 ~ReferenceProcessorMTProcMutator() {
471 _rp->set_mt_processing(_saved_mt);
472 }
473 };
474
475
476 // This class is an interface used to implement task execution for the
477 // reference processing.
478 class AbstractRefProcTaskExecutor {
479 public:
480
481 // Abstract tasks to execute.
482 class ProcessTask;
483 class EnqueueTask;
484
485 // Executes a task using worker threads.
486 virtual void execute(ProcessTask& task) = 0;
487 virtual void execute(EnqueueTask& task) = 0;
488
489 // Switch to single threaded mode.
490 virtual void set_single_threaded_mode() { };
491 };
492
493 // Abstract reference processing task to execute.
494 class AbstractRefProcTaskExecutor::ProcessTask {
495 protected:
496 ProcessTask(ReferenceProcessor& ref_processor,
497 DiscoveredList refs_lists[],
498 bool marks_oops_alive)
499 : _ref_processor(ref_processor),
500 _refs_lists(refs_lists),
501 _marks_oops_alive(marks_oops_alive)
502 { }
503
504 public:
505 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
506 OopClosure& keep_alive,
507 VoidClosure& complete_gc) = 0;
508
509 // Returns true if a task marks some oops as alive.
510 bool marks_oops_alive() const
511 { return _marks_oops_alive; }
512
513 protected:
514 ReferenceProcessor& _ref_processor;
515 DiscoveredList* _refs_lists;
516 const bool _marks_oops_alive;
517 };
518
519 // Abstract reference processing task to execute.
520 class AbstractRefProcTaskExecutor::EnqueueTask {
521 protected:
522 EnqueueTask(ReferenceProcessor& ref_processor,
523 DiscoveredList refs_lists[],
524 HeapWord* pending_list_addr,
525 oop sentinel_ref,
526 int n_queues)
527 : _ref_processor(ref_processor),
528 _refs_lists(refs_lists),
529 _pending_list_addr(pending_list_addr),
530 _sentinel_ref(sentinel_ref),
531 _n_queues(n_queues)
532 { }
533
534 public:
535 virtual void work(unsigned int work_id) = 0;
536
537 protected:
538 ReferenceProcessor& _ref_processor;
539 DiscoveredList* _refs_lists;
540 HeapWord* _pending_list_addr;
541 oop _sentinel_ref;
542 int _n_queues;
543 };
544
545 #endif // SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP