1 /*
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   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.
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  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).
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  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP
  26 #define SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP
  27 
  28 #include "gc/shared/referencePolicy.hpp"
  29 #include "gc/shared/referenceProcessorPhaseTimes.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.
  41 // ReferenceProcessor class abstracts away from a generational setting
  42 // by using a closure that determines whether a given reference or referent are
  43 // subject to this ReferenceProcessor's discovery, thus allowing its use in a
  44 // straightforward manner in a general, non-generational, non-contiguous generation
  45 // (or heap) setting.
  46 //
  47 
  48 // forward references
  49 class ReferencePolicy;
  50 class AbstractRefProcTaskExecutor;
  51 
  52 // List of discovered references.
  53 class DiscoveredList {
  54 public:
  55   DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
  56   inline oop head() const;
  57   HeapWord* adr_head() {
  58     return UseCompressedOops ? (HeapWord*)&_compressed_head :
  59                                (HeapWord*)&_oop_head;
  60   }
  61   inline void set_head(oop o);
  62   inline bool is_empty() const;
  63   size_t length()               { return _len; }
  64   void   set_length(size_t len) { _len = len;  }
  65   void   inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
  66   void   dec_length(size_t dec) { _len -= dec; }
  67 private:
  68   // Set value depending on UseCompressedOops. This could be a template class
  69   // but then we have to fix all the instantiations and declarations that use this class.
  70   oop       _oop_head;
  71   narrowOop _compressed_head;
  72   size_t _len;
  73 };
  74 
  75 // Iterator for the list of discovered references.
  76 class DiscoveredListIterator {
  77 private:
  78   DiscoveredList&    _refs_list;
  79   HeapWord*          _prev_next;
  80   oop                _prev;
  81   oop                _ref;
  82   HeapWord*          _discovered_addr;
  83   oop                _next;
  84   HeapWord*          _referent_addr;
  85   oop                _referent;
  86   OopClosure*        _keep_alive;
  87   BoolObjectClosure* _is_alive;
  88 
  89   DEBUG_ONLY(
  90   oop                _first_seen; // cyclic linked list check
  91   )
  92 
  93   NOT_PRODUCT(
  94   size_t             _processed;
  95   size_t             _removed;
  96   )
  97 
  98 public:
  99   inline DiscoveredListIterator(DiscoveredList&    refs_list,
 100                                 OopClosure*        keep_alive,
 101                                 BoolObjectClosure* is_alive);
 102 
 103   // End Of List.
 104   inline bool has_next() const { return _ref != NULL; }
 105 
 106   // Get oop to the Reference object.
 107   inline oop obj() const { return _ref; }
 108 
 109   // Get oop to the referent object.
 110   inline oop referent() const { return _referent; }
 111 
 112   // Returns true if referent is alive.
 113   inline bool is_referent_alive() const {
 114     return _is_alive->do_object_b(_referent);
 115   }
 116 
 117   // Loads data for the current reference.
 118   // The "allow_null_referent" argument tells us to allow for the possibility
 119   // of a NULL referent in the discovered Reference object. This typically
 120   // happens in the case of concurrent collectors that may have done the
 121   // discovery concurrently, or interleaved, with mutator execution.
 122   void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
 123 
 124   // Move to the next discovered reference.
 125   inline void next() {
 126     _prev_next = _discovered_addr;
 127     _prev = _ref;
 128     move_to_next();
 129   }
 130 
 131   // Remove the current reference from the list
 132   void remove();
 133 
 134   // Make the referent alive.
 135   inline void make_referent_alive() {
 136     if (UseCompressedOops) {
 137       _keep_alive->do_oop((narrowOop*)_referent_addr);
 138     } else {
 139       _keep_alive->do_oop((oop*)_referent_addr);
 140     }
 141   }
 142 
 143   // NULL out referent pointer.
 144   void clear_referent();
 145 
 146   // Statistics
 147   NOT_PRODUCT(
 148   inline size_t processed() const { return _processed; }
 149   inline size_t removed() const   { return _removed; }
 150   )
 151 
 152   inline void move_to_next() {
 153     if (_ref == _next) {
 154       // End of the list.
 155       _ref = NULL;
 156     } else {
 157       _ref = _next;
 158     }
 159     assert(_ref != _first_seen, "cyclic ref_list found");
 160     NOT_PRODUCT(_processed++);
 161   }
 162 };
 163 
 164 class ReferenceProcessor : public CHeapObj<mtGC> {
 165   size_t total_count(DiscoveredList lists[]) const;
 166 
 167   // The SoftReference master timestamp clock
 168   static jlong _soft_ref_timestamp_clock;
 169 
 170   BoolObjectClosure* _is_subject_to_discovery; // determines whether a given oop is subject
 171                                                // to this ReferenceProcessor's discovery
 172                                                // (and further processing).
 173 
 174   bool        _discovering_refs;        // true when discovery enabled
 175   bool        _discovery_is_atomic;     // if discovery is atomic wrt
 176                                         // other collectors in configuration
 177   bool        _discovery_is_mt;         // true if reference discovery is MT.
 178 
 179   bool        _enqueuing_is_done;       // true if all weak references enqueued
 180   bool        _processing_is_mt;        // true during phases when
 181                                         // reference processing is MT.
 182   uint        _next_id;                 // round-robin mod _num_q counter in
 183                                         // support of work distribution
 184 
 185   // For collectors that do not keep GC liveness information
 186   // in the object header, this field holds a closure that
 187   // helps the reference processor determine the reachability
 188   // of an oop. It is currently initialized to NULL for all
 189   // collectors except for CMS and G1.
 190   BoolObjectClosure* _is_alive_non_header;
 191 
 192   // Soft ref clearing policies
 193   // . the default policy
 194   static ReferencePolicy*   _default_soft_ref_policy;
 195   // . the "clear all" policy
 196   static ReferencePolicy*   _always_clear_soft_ref_policy;
 197   // . the current policy below is either one of the above
 198   ReferencePolicy*          _current_soft_ref_policy;
 199 
 200   // The discovered ref lists themselves
 201 
 202   // The active MT'ness degree of the queues below
 203   uint             _num_q;
 204   // The maximum MT'ness degree of the queues below
 205   uint             _max_num_q;
 206 
 207   // Master array of discovered oops
 208   DiscoveredList* _discovered_refs;
 209 
 210   // Arrays of lists of oops, one per thread (pointers into master array above)
 211   DiscoveredList* _discoveredSoftRefs;
 212   DiscoveredList* _discoveredWeakRefs;
 213   DiscoveredList* _discoveredFinalRefs;
 214   DiscoveredList* _discoveredPhantomRefs;
 215 
 216  public:
 217   static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); }
 218 
 219   uint num_q()                             { return _num_q; }
 220   uint max_num_q()                         { return _max_num_q; }
 221   void set_active_mt_degree(uint v);
 222 
 223   DiscoveredList* discovered_refs()        { return _discovered_refs; }
 224 
 225   ReferencePolicy* setup_policy(bool always_clear) {
 226     _current_soft_ref_policy = always_clear ?
 227       _always_clear_soft_ref_policy : _default_soft_ref_policy;
 228     _current_soft_ref_policy->setup();   // snapshot the policy threshold
 229     return _current_soft_ref_policy;
 230   }
 231 
 232   // Process references with a certain reachability level.
 233   void process_discovered_reflist(DiscoveredList                refs_lists[],
 234                                   ReferencePolicy*              policy,
 235                                   bool                          clear_referent,
 236                                   BoolObjectClosure*            is_alive,
 237                                   OopClosure*                   keep_alive,
 238                                   VoidClosure*                  complete_gc,
 239                                   AbstractRefProcTaskExecutor*  task_executor,
 240                                   ReferenceProcessorPhaseTimes* phase_times);
 241 
 242   // Work methods used by the method process_discovered_reflist
 243   // Phase1: keep alive all those referents that are otherwise
 244   // dead but which must be kept alive by policy (and their closure).
 245   void process_phase1(DiscoveredList&     refs_list,
 246                       ReferencePolicy*    policy,
 247                       BoolObjectClosure*  is_alive,
 248                       OopClosure*         keep_alive,
 249                       VoidClosure*        complete_gc);
 250   // Phase2: remove all those references whose referents are
 251   // reachable.
 252   void process_phase2(DiscoveredList&    refs_list,
 253                       BoolObjectClosure* is_alive,
 254                       OopClosure*        keep_alive,
 255                       VoidClosure*       complete_gc);
 256   // Work methods in support of process_phase2
 257   void pp2_work(DiscoveredList&    refs_list,
 258                 BoolObjectClosure* is_alive,
 259                 OopClosure*        keep_alive);
 260   void pp2_work_concurrent_discovery(
 261                 DiscoveredList&    refs_list,
 262                 BoolObjectClosure* is_alive,
 263                 OopClosure*        keep_alive,
 264                 VoidClosure*       complete_gc);
 265   // Phase3: process the referents by either clearing them
 266   // or keeping them alive (and their closure)
 267   void process_phase3(DiscoveredList&    refs_list,
 268                       bool               clear_referent,
 269                       BoolObjectClosure* is_alive,
 270                       OopClosure*        keep_alive,
 271                       VoidClosure*       complete_gc);
 272 
 273   // Enqueue references with a certain reachability level
 274   void enqueue_discovered_reflist(DiscoveredList& refs_list);
 275 
 276   // "Preclean" all the discovered reference lists
 277   // by removing references with strongly reachable referents.
 278   // The first argument is a predicate on an oop that indicates
 279   // its (strong) reachability and the second is a closure that
 280   // may be used to incrementalize or abort the precleaning process.
 281   // The caller is responsible for taking care of potential
 282   // interference with concurrent operations on these lists
 283   // (or predicates involved) by other threads. Currently
 284   // only used by the CMS collector.
 285   void preclean_discovered_references(BoolObjectClosure* is_alive,
 286                                       OopClosure*        keep_alive,
 287                                       VoidClosure*       complete_gc,
 288                                       YieldClosure*      yield,
 289                                       GCTimer*           gc_timer);
 290 
 291   // Returns the name of the discovered reference list
 292   // occupying the i / _num_q slot.
 293   const char* list_name(uint i);
 294 
 295   void enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor,
 296                                    ReferenceProcessorPhaseTimes* phase_times);
 297 
 298   // "Preclean" the given discovered reference list
 299   // by removing references with strongly reachable referents.
 300   // Currently used in support of CMS only.
 301   void preclean_discovered_reflist(DiscoveredList&    refs_list,
 302                                    BoolObjectClosure* is_alive,
 303                                    OopClosure*        keep_alive,
 304                                    VoidClosure*       complete_gc,
 305                                    YieldClosure*      yield);
 306 private:
 307   // round-robin mod _num_q (not: _not_ mode _max_num_q)
 308   uint next_id() {
 309     uint id = _next_id;
 310     assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
 311     if (++_next_id == _num_q) {
 312       _next_id = 0;
 313     }
 314     assert(_next_id < _num_q, "_next_id %u _num_q %u _max_num_q %u", _next_id, _num_q, _max_num_q);
 315     return id;
 316   }
 317   DiscoveredList* get_discovered_list(ReferenceType rt);
 318   inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
 319                                         HeapWord* discovered_addr);
 320 
 321   void clear_discovered_references(DiscoveredList& refs_list);
 322 
 323   void log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_count) PRODUCT_RETURN;
 324 
 325   // Balances reference queues.
 326   void balance_queues(DiscoveredList ref_lists[]);
 327 
 328   // Update (advance) the soft ref master clock field.
 329   void update_soft_ref_master_clock();
 330 
 331   template <class T>
 332   bool is_subject_to_discovery(T const obj) const;
 333 public:
 334   // Default parameters give you a vanilla reference processor.
 335   ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery,
 336                      bool mt_processing = false, uint mt_processing_degree = 1,
 337                      bool mt_discovery  = false, uint mt_discovery_degree  = 1,
 338                      bool atomic_discovery = true,
 339                      BoolObjectClosure* is_alive_non_header = NULL);
 340 
 341   // RefDiscoveryPolicy values
 342   enum DiscoveryPolicy {
 343     ReferenceBasedDiscovery = 0,
 344     ReferentBasedDiscovery  = 1,
 345     DiscoveryPolicyMin      = ReferenceBasedDiscovery,
 346     DiscoveryPolicyMax      = ReferentBasedDiscovery
 347   };
 348 
 349   static void init_statics();
 350 
 351  public:
 352   // get and set "is_alive_non_header" field
 353   BoolObjectClosure* is_alive_non_header() {
 354     return _is_alive_non_header;
 355   }
 356   void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
 357     _is_alive_non_header = is_alive_non_header;
 358   }
 359 
 360   BoolObjectClosure* is_subject_to_discovery_closure() const { return _is_subject_to_discovery; }
 361   void set_is_subject_to_discovery_closure(BoolObjectClosure* cl) { _is_subject_to_discovery = cl; }
 362 
 363   // start and stop weak ref discovery
 364   void enable_discovery(bool check_no_refs = true);
 365   void disable_discovery()  { _discovering_refs = false; }
 366   bool discovery_enabled()  { return _discovering_refs;  }
 367 
 368   // whether discovery is atomic wrt other collectors
 369   bool discovery_is_atomic() const { return _discovery_is_atomic; }
 370   void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
 371 
 372   // whether discovery is done by multiple threads same-old-timeously
 373   bool discovery_is_mt() const { return _discovery_is_mt; }
 374   void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
 375 
 376   // Whether we are in a phase when _processing_ is MT.
 377   bool processing_is_mt() const { return _processing_is_mt; }
 378   void set_mt_processing(bool mt) { _processing_is_mt = mt; }
 379 
 380   // whether all enqueueing of weak references is complete
 381   bool enqueuing_is_done()  { return _enqueuing_is_done; }
 382   void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
 383 
 384   // iterate over oops
 385   void weak_oops_do(OopClosure* f);       // weak roots
 386 
 387   // Balance each of the discovered lists.
 388   void balance_all_queues();
 389   void verify_list(DiscoveredList& ref_list);
 390 
 391   // Discover a Reference object, using appropriate discovery criteria
 392   bool discover_reference(oop obj, ReferenceType rt);
 393 
 394   // Has discovered references that need handling
 395   bool has_discovered_references();
 396 
 397   // Process references found during GC (called by the garbage collector)
 398   ReferenceProcessorStats
 399   process_discovered_references(BoolObjectClosure*            is_alive,
 400                                 OopClosure*                   keep_alive,
 401                                 VoidClosure*                  complete_gc,
 402                                 AbstractRefProcTaskExecutor*  task_executor,
 403                                 ReferenceProcessorPhaseTimes* phase_times);
 404 
 405   // Enqueue references at end of GC (called by the garbage collector)
 406   void enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor,
 407                                      ReferenceProcessorPhaseTimes* phase_times);
 408 
 409   // If a discovery is in process that is being superceded, abandon it: all
 410   // the discovered lists will be empty, and all the objects on them will
 411   // have NULL discovered fields.  Must be called only at a safepoint.
 412   void abandon_partial_discovery();
 413 
 414   size_t total_reference_count(ReferenceType rt) const;
 415 
 416   // debugging
 417   void verify_no_references_recorded() PRODUCT_RETURN;
 418   void verify_referent(oop obj)        PRODUCT_RETURN;
 419 };
 420 
 421 // A reference processor that uses a single memory span to determine the area that
 422 // is subject to discovery. Useful for collectors which have contiguous generations.
 423 class SpanReferenceProcessor : public ReferenceProcessor {
 424   class SpanBasedDiscoverer : public BoolObjectClosure {
 425   public:
 426     MemRegion _span;
 427 
 428     SpanBasedDiscoverer(MemRegion span) : BoolObjectClosure(), _span(span) { }
 429 
 430     virtual bool do_object_b(oop obj) {
 431       return _span.contains(obj);
 432     }
 433   };
 434 
 435   SpanBasedDiscoverer _span_based_discoverer;
 436 public:
 437   SpanReferenceProcessor(MemRegion span,
 438                               bool mt_processing = false, uint mt_processing_degree = 1,
 439                               bool mt_discovery  = false, uint mt_discovery_degree  = 1,
 440                               bool atomic_discovery = true,
 441                               BoolObjectClosure* is_alive_non_header = NULL);
 442 
 443   // get and set span
 444   MemRegion span()                   { return _span_based_discoverer._span; }
 445   void      set_span(MemRegion span) { _span_based_discoverer._span = span; }
 446 };
 447 
 448 // A utility class to disable reference discovery in
 449 // the scope which contains it, for given ReferenceProcessor.
 450 class NoRefDiscovery: StackObj {
 451  private:
 452   ReferenceProcessor* _rp;
 453   bool _was_discovering_refs;
 454  public:
 455   NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
 456     _was_discovering_refs = _rp->discovery_enabled();
 457     if (_was_discovering_refs) {
 458       _rp->disable_discovery();
 459     }
 460   }
 461 
 462   ~NoRefDiscovery() {
 463     if (_was_discovering_refs) {
 464       _rp->enable_discovery(false /*check_no_refs*/);
 465     }
 466   }
 467 };
 468 
 469 // A utility class to temporarily mutate the subject discovery closure of the
 470 // given ReferenceProcessor in the scope that contains it.
 471 class ReferenceProcessorSubjectToDiscoveryMutator : StackObj {
 472  private:
 473   ReferenceProcessor* _rp;
 474   BoolObjectClosure* _saved_cl;
 475 
 476  public:
 477   ReferenceProcessorSubjectToDiscoveryMutator(ReferenceProcessor* rp, BoolObjectClosure* cl):
 478     _rp(rp) {
 479     _saved_cl = _rp->is_subject_to_discovery_closure();
 480     _rp->set_is_subject_to_discovery_closure(cl);
 481   }
 482 
 483   ~ReferenceProcessorSubjectToDiscoveryMutator() {
 484     _rp->set_is_subject_to_discovery_closure(_saved_cl);
 485   }
 486 };
 487 
 488 // A utility class to temporarily mutate the span of the
 489 // given ReferenceProcessor in the scope that contains it.
 490 class ReferenceProcessorSpanMutator: StackObj {
 491  private:
 492   SpanReferenceProcessor* _rp;
 493   MemRegion _saved_span;
 494 
 495  public:
 496   ReferenceProcessorSpanMutator(SpanReferenceProcessor* rp,
 497                                 MemRegion span):
 498     _rp(rp) {
 499     _saved_span = _rp->span();
 500     _rp->set_span(span);
 501   }
 502 
 503   ~ReferenceProcessorSpanMutator() {
 504     _rp->set_span(_saved_span);
 505   }
 506 };
 507 
 508 // A utility class to temporarily change the MT'ness of
 509 // reference discovery for the given ReferenceProcessor
 510 // in the scope that contains it.
 511 class ReferenceProcessorMTDiscoveryMutator: StackObj {
 512  private:
 513   ReferenceProcessor* _rp;
 514   bool                _saved_mt;
 515 
 516  public:
 517   ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
 518                                        bool mt):
 519     _rp(rp) {
 520     _saved_mt = _rp->discovery_is_mt();
 521     _rp->set_mt_discovery(mt);
 522   }
 523 
 524   ~ReferenceProcessorMTDiscoveryMutator() {
 525     _rp->set_mt_discovery(_saved_mt);
 526   }
 527 };
 528 
 529 // A utility class to temporarily change the disposition
 530 // of the "is_alive_non_header" closure field of the
 531 // given ReferenceProcessor in the scope that contains it.
 532 class ReferenceProcessorIsAliveMutator: StackObj {
 533  private:
 534   ReferenceProcessor* _rp;
 535   BoolObjectClosure*  _saved_cl;
 536 
 537  public:
 538   ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
 539                                    BoolObjectClosure*  cl):
 540     _rp(rp) {
 541     _saved_cl = _rp->is_alive_non_header();
 542     _rp->set_is_alive_non_header(cl);
 543   }
 544 
 545   ~ReferenceProcessorIsAliveMutator() {
 546     _rp->set_is_alive_non_header(_saved_cl);
 547   }
 548 };
 549 
 550 // A utility class to temporarily change the disposition
 551 // of the "discovery_is_atomic" field of the
 552 // given ReferenceProcessor in the scope that contains it.
 553 class ReferenceProcessorAtomicMutator: StackObj {
 554  private:
 555   ReferenceProcessor* _rp;
 556   bool                _saved_atomic_discovery;
 557 
 558  public:
 559   ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
 560                                   bool atomic):
 561     _rp(rp) {
 562     _saved_atomic_discovery = _rp->discovery_is_atomic();
 563     _rp->set_atomic_discovery(atomic);
 564   }
 565 
 566   ~ReferenceProcessorAtomicMutator() {
 567     _rp->set_atomic_discovery(_saved_atomic_discovery);
 568   }
 569 };
 570 
 571 
 572 // A utility class to temporarily change the MT processing
 573 // disposition of the given ReferenceProcessor instance
 574 // in the scope that contains it.
 575 class ReferenceProcessorMTProcMutator: StackObj {
 576  private:
 577   ReferenceProcessor* _rp;
 578   bool  _saved_mt;
 579 
 580  public:
 581   ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
 582                                   bool mt):
 583     _rp(rp) {
 584     _saved_mt = _rp->processing_is_mt();
 585     _rp->set_mt_processing(mt);
 586   }
 587 
 588   ~ReferenceProcessorMTProcMutator() {
 589     _rp->set_mt_processing(_saved_mt);
 590   }
 591 };
 592 
 593 
 594 // This class is an interface used to implement task execution for the
 595 // reference processing.
 596 class AbstractRefProcTaskExecutor {
 597 public:
 598 
 599   // Abstract tasks to execute.
 600   class ProcessTask;
 601   class EnqueueTask;
 602 
 603   // Executes a task using worker threads.
 604   virtual void execute(ProcessTask& task) = 0;
 605   virtual void execute(EnqueueTask& task) = 0;
 606 
 607   // Switch to single threaded mode.
 608   virtual void set_single_threaded_mode() { };
 609 };
 610 
 611 // Abstract reference processing task to execute.
 612 class AbstractRefProcTaskExecutor::ProcessTask {
 613 protected:
 614   ProcessTask(ReferenceProcessor&           ref_processor,
 615               DiscoveredList                refs_lists[],
 616               bool                          marks_oops_alive,
 617               ReferenceProcessorPhaseTimes* phase_times)
 618     : _ref_processor(ref_processor),
 619       _refs_lists(refs_lists),
 620       _phase_times(phase_times),
 621       _marks_oops_alive(marks_oops_alive)
 622   { }
 623 
 624 public:
 625   virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
 626                     OopClosure& keep_alive,
 627                     VoidClosure& complete_gc) = 0;
 628 
 629   // Returns true if a task marks some oops as alive.
 630   bool marks_oops_alive() const
 631   { return _marks_oops_alive; }
 632 
 633 protected:
 634   ReferenceProcessor&           _ref_processor;
 635   DiscoveredList*               _refs_lists;
 636   ReferenceProcessorPhaseTimes* _phase_times;
 637   const bool                    _marks_oops_alive;
 638 };
 639 
 640 // Abstract reference processing task to execute.
 641 class AbstractRefProcTaskExecutor::EnqueueTask {
 642 protected:
 643   EnqueueTask(ReferenceProcessor&           ref_processor,
 644               DiscoveredList                refs_lists[],
 645               int                           n_queues,
 646               ReferenceProcessorPhaseTimes* phase_times)
 647     : _ref_processor(ref_processor),
 648       _refs_lists(refs_lists),
 649       _n_queues(n_queues),
 650       _phase_times(phase_times)
 651   { }
 652 
 653 public:
 654   virtual void work(unsigned int work_id) = 0;
 655 
 656 protected:
 657   ReferenceProcessor&           _ref_processor;
 658   DiscoveredList*               _refs_lists;
 659   ReferenceProcessorPhaseTimes* _phase_times;
 660   int                           _n_queues;
 661 };
 662 
 663 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP