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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   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  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/referenceDiscoverer.hpp"
  29 #include "gc/shared/referencePolicy.hpp"
  30 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
  31 #include "gc/shared/referenceProcessorStats.hpp"
  32 #include "memory/referenceType.hpp"
  33 #include "oops/instanceRefKlass.hpp"
  34 
  35 class GCTimer;
  36 
  37 // ReferenceProcessor class encapsulates the per-"collector" processing
  38 // of java.lang.Reference objects for GC. The interface is useful for supporting
  39 // a generational abstraction, in particular when there are multiple
  40 // generations that are being independently collected -- possibly
  41 // concurrently and/or incrementally.
  42 // ReferenceProcessor class abstracts away from a generational setting
  43 // by using a closure that determines whether a given reference or referent are
  44 // subject to this ReferenceProcessor's discovery, thus allowing its use in a
  45 // straightforward manner in a general, non-generational, non-contiguous generation
  46 // (or heap) setting.
  47 //
  48 
  49 // forward references
  50 class ReferencePolicy;
  51 class AbstractRefProcTaskExecutor;
  52 
  53 // List of discovered references.
  54 class DiscoveredList {
  55 public:
  56   DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
  57   inline oop head() const;
  58   HeapWord* adr_head() {
  59     return UseCompressedOops ? (HeapWord*)&_compressed_head :
  60                                (HeapWord*)&_oop_head;
  61   }
  62   inline void set_head(oop o);
  63   inline bool is_empty() const;
  64   size_t length()               { return _len; }
  65   void   set_length(size_t len) { _len = len;  }
  66   void   inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
  67   void   dec_length(size_t dec) { _len -= dec; }
  68 private:
  69   // Set value depending on UseCompressedOops. This could be a template class
  70   // but then we have to fix all the instantiations and declarations that use this class.
  71   oop       _oop_head;
  72   narrowOop _compressed_head;
  73   size_t _len;
  74 };
  75 
  76 // Iterator for the list of discovered references.
  77 class DiscoveredListIterator {
  78 private:
  79   DiscoveredList&    _refs_list;
  80   HeapWord*          _prev_discovered_addr;
  81   oop                _prev_discovered;
  82   oop                _current_discovered;
  83   HeapWord*          _current_discovered_addr;
  84   oop                _next_discovered;
  85 
  86   HeapWord*          _referent_addr;
  87   oop                _referent;
  88 
  89   OopClosure*        _keep_alive;
  90   BoolObjectClosure* _is_alive;
  91 
  92   DEBUG_ONLY(
  93   oop                _first_seen; // cyclic linked list check
  94   )
  95 
  96   NOT_PRODUCT(
  97   size_t             _processed;
  98   size_t             _removed;
  99   )
 100 
 101 public:
 102   inline DiscoveredListIterator(DiscoveredList&    refs_list,
 103                                 OopClosure*        keep_alive,
 104                                 BoolObjectClosure* is_alive);
 105 
 106   // End Of List.
 107   inline bool has_next() const { return _current_discovered != NULL; }
 108 
 109   // Get oop to the Reference object.
 110   inline oop obj() const { return _current_discovered; }
 111 
 112   // Get oop to the referent object.
 113   inline oop referent() const { return _referent; }
 114 
 115   // Returns true if referent is alive.
 116   inline bool is_referent_alive() const {
 117     return _is_alive->do_object_b(_referent);
 118   }
 119 
 120   // Loads data for the current reference.
 121   // The "allow_null_referent" argument tells us to allow for the possibility
 122   // of a NULL referent in the discovered Reference object. This typically
 123   // happens in the case of concurrent collectors that may have done the
 124   // discovery concurrently, or interleaved, with mutator execution.
 125   void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
 126 
 127   // Move to the next discovered reference.
 128   inline void next() {
 129     _prev_discovered_addr = _current_discovered_addr;
 130     _prev_discovered = _current_discovered;
 131     move_to_next();
 132   }
 133 
 134   // Remove the current reference from the list
 135   void remove();
 136 
 137   // Make the referent alive.
 138   inline void make_referent_alive() {
 139     if (UseCompressedOops) {
 140       _keep_alive->do_oop((narrowOop*)_referent_addr);
 141     } else {
 142       _keep_alive->do_oop((oop*)_referent_addr);
 143     }
 144   }
 145 
 146   // Do enqueuing work, i.e. notifying the GC about the changed discovered pointers.
 147   void enqueue();
 148 
 149   // Move enqueued references to the reference pending list.
 150   void complete_enqeue();
 151 
 152   // NULL out referent pointer.
 153   void clear_referent();
 154 
 155   // Statistics
 156   NOT_PRODUCT(
 157   inline size_t processed() const { return _processed; }
 158   inline size_t removed() const   { return _removed; }
 159   )
 160 
 161   inline void move_to_next() {
 162     if (_current_discovered == _next_discovered) {
 163       // End of the list.
 164       _current_discovered = NULL;
 165     } else {
 166       _current_discovered = _next_discovered;
 167     }
 168     assert(_current_discovered != _first_seen, "cyclic ref_list found");
 169     NOT_PRODUCT(_processed++);
 170   }
 171 };
 172 
 173 class ReferenceProcessor : public ReferenceDiscoverer {
 174   size_t total_count(DiscoveredList lists[]) const;
 175 
 176   // The SoftReference master timestamp clock
 177   static jlong _soft_ref_timestamp_clock;
 178 
 179   BoolObjectClosure* _is_subject_to_discovery; // determines whether a given oop is subject
 180                                                // to this ReferenceProcessor's discovery
 181                                                // (and further processing).
 182 
 183   bool        _discovering_refs;        // true when discovery enabled
 184   bool        _discovery_is_atomic;     // if discovery is atomic wrt
 185                                         // other collectors in configuration
 186   bool        _discovery_is_mt;         // true if reference discovery is MT.
 187 
 188   bool        _enqueuing_is_done;       // true if all weak references enqueued
 189   bool        _processing_is_mt;        // true during phases when
 190                                         // reference processing is MT.
 191   uint        _next_id;                 // round-robin mod _num_queues counter in
 192                                         // support of work distribution
 193 
 194   // For collectors that do not keep GC liveness information
 195   // in the object header, this field holds a closure that
 196   // helps the reference processor determine the reachability
 197   // of an oop. It is currently initialized to NULL for all
 198   // collectors except for CMS and G1.
 199   BoolObjectClosure* _is_alive_non_header;
 200 
 201   // Soft ref clearing policies
 202   // . the default policy
 203   static ReferencePolicy*   _default_soft_ref_policy;
 204   // . the "clear all" policy
 205   static ReferencePolicy*   _always_clear_soft_ref_policy;
 206   // . the current policy below is either one of the above
 207   ReferencePolicy*          _current_soft_ref_policy;
 208 
 209   // The discovered ref lists themselves
 210 
 211   // The active MT'ness degree of the queues below
 212   uint            _num_queues;
 213   // The maximum MT'ness degree of the queues below
 214   uint            _max_num_queues;
 215 
 216   // Master array of discovered oops
 217   DiscoveredList* _discovered_refs;
 218 
 219   // Arrays of lists of oops, one per thread (pointers into master array above)
 220   DiscoveredList* _discoveredSoftRefs;
 221   DiscoveredList* _discoveredWeakRefs;
 222   DiscoveredList* _discoveredFinalRefs;
 223   DiscoveredList* _discoveredPhantomRefs;
 224 
 225  public:
 226   static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); }
 227 
 228   uint num_queues() const                  { return _num_queues; }
 229   uint max_num_queues() const              { return _max_num_queues; }
 230   void set_active_mt_degree(uint v);
 231 
 232   DiscoveredList* discovered_refs()        { return _discovered_refs; }
 233 
 234   ReferencePolicy* setup_policy(bool always_clear) {
 235     _current_soft_ref_policy = always_clear ?
 236       _always_clear_soft_ref_policy : _default_soft_ref_policy;
 237     _current_soft_ref_policy->setup();   // snapshot the policy threshold
 238     return _current_soft_ref_policy;
 239   }
 240 
 241   // Process references with a certain reachability level.
 242   void process_discovered_reflist(DiscoveredList                refs_lists[],
 243                                   ReferencePolicy*              policy,
 244                                   bool                          clear_referent,
 245                                   BoolObjectClosure*            is_alive,
 246                                   OopClosure*                   keep_alive,
 247                                   VoidClosure*                  complete_gc,
 248                                   AbstractRefProcTaskExecutor*  task_executor,
 249                                   ReferenceProcessorPhaseTimes* phase_times);
 250 
 251   // Work methods used by the method process_discovered_reflist
 252   // Phase1: keep alive all those referents that are otherwise
 253   // dead but which must be kept alive by policy (and their closure).
 254   void process_phase1(DiscoveredList&     refs_list,
 255                       ReferencePolicy*    policy,
 256                       BoolObjectClosure*  is_alive,
 257                       OopClosure*         keep_alive,
 258                       VoidClosure*        complete_gc);
 259   // Phase2: remove all those references whose referents are
 260   // reachable.
 261   void process_phase2(DiscoveredList&    refs_list,
 262                       BoolObjectClosure* is_alive,
 263                       OopClosure*        keep_alive,
 264                       VoidClosure*       complete_gc);
 265   // Work methods in support of process_phase2
 266   void pp2_work(DiscoveredList&    refs_list,
 267                 BoolObjectClosure* is_alive,
 268                 OopClosure*        keep_alive);
 269   void pp2_work_concurrent_discovery(
 270                 DiscoveredList&    refs_list,
 271                 BoolObjectClosure* is_alive,
 272                 OopClosure*        keep_alive,
 273                 VoidClosure*       complete_gc);
 274   // Phase3: process the referents by either clearing them
 275   // or keeping them alive (and their closure), and enqueuing them.
 276   void process_phase3(DiscoveredList&    refs_list,
 277                       bool               clear_referent,
 278                       BoolObjectClosure* is_alive,
 279                       OopClosure*        keep_alive,
 280                       VoidClosure*       complete_gc);
 281 
 282   // "Preclean" all the discovered reference lists
 283   // by removing references with strongly reachable referents.
 284   // The first argument is a predicate on an oop that indicates
 285   // its (strong) reachability and the second is a closure that
 286   // may be used to incrementalize or abort the precleaning process.
 287   // The caller is responsible for taking care of potential
 288   // interference with concurrent operations on these lists
 289   // (or predicates involved) by other threads. Currently
 290   // only used by the CMS collector.
 291   void preclean_discovered_references(BoolObjectClosure* is_alive,
 292                                       OopClosure*        keep_alive,
 293                                       VoidClosure*       complete_gc,
 294                                       YieldClosure*      yield,
 295                                       GCTimer*           gc_timer);
 296 
 297   // Returns the name of the discovered reference list
 298   // occupying the i / _num_queues slot.
 299   const char* list_name(uint i);
 300 
 301   // "Preclean" the given discovered reference list
 302   // by removing references with strongly reachable referents.
 303   // Currently used in support of CMS only.
 304   void preclean_discovered_reflist(DiscoveredList&    refs_list,
 305                                    BoolObjectClosure* is_alive,
 306                                    OopClosure*        keep_alive,
 307                                    VoidClosure*       complete_gc,
 308                                    YieldClosure*      yield);
 309 private:
 310   // round-robin mod _num_queues (not: _not_ mod _max_num_queues)
 311   uint next_id() {
 312     uint id = _next_id;
 313     assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
 314     if (++_next_id == _num_queues) {
 315       _next_id = 0;
 316     }
 317     assert(_next_id < _num_queues, "_next_id %u _num_queues %u _max_num_queues %u", _next_id, _num_queues, _max_num_queues);
 318     return id;
 319   }
 320   DiscoveredList* get_discovered_list(ReferenceType rt);
 321   inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
 322                                         HeapWord* discovered_addr);
 323 
 324   void clear_discovered_references(DiscoveredList& refs_list);
 325 
 326   void log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_count) PRODUCT_RETURN;
 327 
 328   // Balances reference queues.
 329   void balance_queues(DiscoveredList ref_lists[]);
 330 
 331   // Update (advance) the soft ref master clock field.
 332   void update_soft_ref_master_clock();
 333 
 334   template <class T>
 335   bool is_subject_to_discovery(T const obj) const;
 336 public:
 337   // Default parameters give you a vanilla reference processor.
 338   ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery,
 339                      bool mt_processing = false, uint mt_processing_degree = 1,
 340                      bool mt_discovery  = false, uint mt_discovery_degree  = 1,
 341                      bool atomic_discovery = true,
 342                      BoolObjectClosure* is_alive_non_header = NULL);
 343 
 344   // RefDiscoveryPolicy values
 345   enum DiscoveryPolicy {
 346     ReferenceBasedDiscovery = 0,
 347     ReferentBasedDiscovery  = 1,
 348     DiscoveryPolicyMin      = ReferenceBasedDiscovery,
 349     DiscoveryPolicyMax      = ReferentBasedDiscovery
 350   };
 351 
 352   static void init_statics();
 353 
 354  public:
 355   // get and set "is_alive_non_header" field
 356   BoolObjectClosure* is_alive_non_header() {
 357     return _is_alive_non_header;
 358   }
 359   void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
 360     _is_alive_non_header = is_alive_non_header;
 361   }
 362 
 363   BoolObjectClosure* is_subject_to_discovery_closure() const { return _is_subject_to_discovery; }
 364   void set_is_subject_to_discovery_closure(BoolObjectClosure* cl) { _is_subject_to_discovery = cl; }
 365 
 366   // start and stop weak ref discovery
 367   void enable_discovery(bool check_no_refs = true);
 368   void disable_discovery()  { _discovering_refs = false; }
 369   bool discovery_enabled()  { return _discovering_refs;  }
 370 
 371   // whether discovery is atomic wrt other collectors
 372   bool discovery_is_atomic() const { return _discovery_is_atomic; }
 373   void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
 374 
 375   // whether discovery is done by multiple threads same-old-timeously
 376   bool discovery_is_mt() const { return _discovery_is_mt; }
 377   void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
 378 
 379   // Whether we are in a phase when _processing_ is MT.
 380   bool processing_is_mt() const { return _processing_is_mt; }
 381   void set_mt_processing(bool mt) { _processing_is_mt = mt; }
 382 
 383   // whether all enqueueing of weak references is complete
 384   bool enqueuing_is_done()  { return _enqueuing_is_done; }
 385   void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
 386 
 387   // iterate over oops
 388   void weak_oops_do(OopClosure* f);       // weak roots
 389 
 390   void verify_list(DiscoveredList& ref_list);
 391 
 392   // Discover a Reference object, using appropriate discovery criteria
 393   virtual bool discover_reference(oop obj, ReferenceType rt);
 394 
 395   // Has discovered references that need handling
 396   bool has_discovered_references();
 397 
 398   // Process references found during GC (called by the garbage collector)
 399   ReferenceProcessorStats
 400   process_discovered_references(BoolObjectClosure*            is_alive,
 401                                 OopClosure*                   keep_alive,
 402                                 VoidClosure*                  complete_gc,
 403                                 AbstractRefProcTaskExecutor*  task_executor,
 404                                 ReferenceProcessorPhaseTimes* phase_times);
 405 
 406   // If a discovery is in process that is being superceded, abandon it: all
 407   // the discovered lists will be empty, and all the objects on them will
 408   // have NULL discovered fields.  Must be called only at a safepoint.
 409   void abandon_partial_discovery();
 410 
 411   size_t total_reference_count(ReferenceType rt) const;
 412 
 413   // debugging
 414   void verify_no_references_recorded() PRODUCT_RETURN;
 415   void verify_referent(oop obj)        PRODUCT_RETURN;
 416 };
 417 
 418 // A reference processor that uses a single memory span to determine the area that
 419 // is subject to discovery. Useful for collectors which have contiguous generations.
 420 class SpanReferenceProcessor : public ReferenceProcessor {
 421   class SpanBasedDiscoverer : public BoolObjectClosure {
 422   public:
 423     MemRegion _span;
 424 
 425     SpanBasedDiscoverer(MemRegion span) : BoolObjectClosure(), _span(span) { }
 426 
 427     virtual bool do_object_b(oop obj) {
 428       return _span.contains(obj);
 429     }
 430   };
 431 
 432   SpanBasedDiscoverer _span_based_discoverer;
 433 public:
 434   SpanReferenceProcessor(MemRegion span,
 435                               bool mt_processing = false, uint mt_processing_degree = 1,
 436                               bool mt_discovery  = false, uint mt_discovery_degree  = 1,
 437                               bool atomic_discovery = true,
 438                               BoolObjectClosure* is_alive_non_header = NULL);
 439 
 440   // get and set span
 441   MemRegion span()                   { return _span_based_discoverer._span; }
 442   void      set_span(MemRegion span) { _span_based_discoverer._span = span; }
 443 };
 444 
 445 // A utility class to disable reference discovery in
 446 // the scope which contains it, for given ReferenceProcessor.
 447 class NoRefDiscovery: StackObj {
 448  private:
 449   ReferenceProcessor* _rp;
 450   bool _was_discovering_refs;
 451  public:
 452   NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
 453     _was_discovering_refs = _rp->discovery_enabled();
 454     if (_was_discovering_refs) {
 455       _rp->disable_discovery();
 456     }
 457   }
 458 
 459   ~NoRefDiscovery() {
 460     if (_was_discovering_refs) {
 461       _rp->enable_discovery(false /*check_no_refs*/);
 462     }
 463   }
 464 };
 465 
 466 // A utility class to temporarily mutate the subject discovery closure of the
 467 // given ReferenceProcessor in the scope that contains it.
 468 class ReferenceProcessorSubjectToDiscoveryMutator : StackObj {
 469  private:
 470   ReferenceProcessor* _rp;
 471   BoolObjectClosure* _saved_cl;
 472 
 473  public:
 474   ReferenceProcessorSubjectToDiscoveryMutator(ReferenceProcessor* rp, BoolObjectClosure* cl):
 475     _rp(rp) {
 476     _saved_cl = _rp->is_subject_to_discovery_closure();
 477     _rp->set_is_subject_to_discovery_closure(cl);
 478   }
 479 
 480   ~ReferenceProcessorSubjectToDiscoveryMutator() {
 481     _rp->set_is_subject_to_discovery_closure(_saved_cl);
 482   }
 483 };
 484 
 485 // A utility class to temporarily mutate the span of the
 486 // given ReferenceProcessor in the scope that contains it.
 487 class ReferenceProcessorSpanMutator: StackObj {
 488  private:
 489   SpanReferenceProcessor* _rp;
 490   MemRegion _saved_span;
 491 
 492  public:
 493   ReferenceProcessorSpanMutator(SpanReferenceProcessor* rp,
 494                                 MemRegion span):
 495     _rp(rp) {
 496     _saved_span = _rp->span();
 497     _rp->set_span(span);
 498   }
 499 
 500   ~ReferenceProcessorSpanMutator() {
 501     _rp->set_span(_saved_span);
 502   }
 503 };
 504 
 505 // A utility class to temporarily change the MT'ness of
 506 // reference discovery for the given ReferenceProcessor
 507 // in the scope that contains it.
 508 class ReferenceProcessorMTDiscoveryMutator: StackObj {
 509  private:
 510   ReferenceProcessor* _rp;
 511   bool                _saved_mt;
 512 
 513  public:
 514   ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
 515                                        bool mt):
 516     _rp(rp) {
 517     _saved_mt = _rp->discovery_is_mt();
 518     _rp->set_mt_discovery(mt);
 519   }
 520 
 521   ~ReferenceProcessorMTDiscoveryMutator() {
 522     _rp->set_mt_discovery(_saved_mt);
 523   }
 524 };
 525 
 526 // A utility class to temporarily change the disposition
 527 // of the "is_alive_non_header" closure field of the
 528 // given ReferenceProcessor in the scope that contains it.
 529 class ReferenceProcessorIsAliveMutator: StackObj {
 530  private:
 531   ReferenceProcessor* _rp;
 532   BoolObjectClosure*  _saved_cl;
 533 
 534  public:
 535   ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
 536                                    BoolObjectClosure*  cl):
 537     _rp(rp) {
 538     _saved_cl = _rp->is_alive_non_header();
 539     _rp->set_is_alive_non_header(cl);
 540   }
 541 
 542   ~ReferenceProcessorIsAliveMutator() {
 543     _rp->set_is_alive_non_header(_saved_cl);
 544   }
 545 };
 546 
 547 // A utility class to temporarily change the disposition
 548 // of the "discovery_is_atomic" field of the
 549 // given ReferenceProcessor in the scope that contains it.
 550 class ReferenceProcessorAtomicMutator: StackObj {
 551  private:
 552   ReferenceProcessor* _rp;
 553   bool                _saved_atomic_discovery;
 554 
 555  public:
 556   ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
 557                                   bool atomic):
 558     _rp(rp) {
 559     _saved_atomic_discovery = _rp->discovery_is_atomic();
 560     _rp->set_atomic_discovery(atomic);
 561   }
 562 
 563   ~ReferenceProcessorAtomicMutator() {
 564     _rp->set_atomic_discovery(_saved_atomic_discovery);
 565   }
 566 };
 567 
 568 
 569 // A utility class to temporarily change the MT processing
 570 // disposition of the given ReferenceProcessor instance
 571 // in the scope that contains it.
 572 class ReferenceProcessorMTProcMutator: StackObj {
 573  private:
 574   ReferenceProcessor* _rp;
 575   bool  _saved_mt;
 576 
 577  public:
 578   ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
 579                                   bool mt):
 580     _rp(rp) {
 581     _saved_mt = _rp->processing_is_mt();
 582     _rp->set_mt_processing(mt);
 583   }
 584 
 585   ~ReferenceProcessorMTProcMutator() {
 586     _rp->set_mt_processing(_saved_mt);
 587   }
 588 };
 589 
 590 
 591 // This class is an interface used to implement task execution for the
 592 // reference processing.
 593 class AbstractRefProcTaskExecutor {
 594 public:
 595 
 596   // Abstract tasks to execute.
 597   class ProcessTask;
 598   class EnqueueTask;
 599 
 600   // Executes a task using worker threads.
 601   virtual void execute(ProcessTask& task) = 0;
 602   virtual void execute(EnqueueTask& task) = 0;
 603 
 604   // Switch to single threaded mode.
 605   virtual void set_single_threaded_mode() { };
 606 };
 607 
 608 // Abstract reference processing task to execute.
 609 class AbstractRefProcTaskExecutor::ProcessTask {
 610 protected:
 611   ProcessTask(ReferenceProcessor&           ref_processor,
 612               DiscoveredList                refs_lists[],
 613               bool                          marks_oops_alive,
 614               ReferenceProcessorPhaseTimes* phase_times)
 615     : _ref_processor(ref_processor),
 616       _refs_lists(refs_lists),
 617       _phase_times(phase_times),
 618       _marks_oops_alive(marks_oops_alive)
 619   { }
 620 
 621 public:
 622   virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
 623                     OopClosure& keep_alive,
 624                     VoidClosure& complete_gc) = 0;
 625 
 626   // Returns true if a task marks some oops as alive.
 627   bool marks_oops_alive() const
 628   { return _marks_oops_alive; }
 629 
 630 protected:
 631   ReferenceProcessor&           _ref_processor;
 632   DiscoveredList*               _refs_lists;
 633   ReferenceProcessorPhaseTimes* _phase_times;
 634   const bool                    _marks_oops_alive;
 635 };
 636 
 637 // Abstract reference processing task to execute.
 638 class AbstractRefProcTaskExecutor::EnqueueTask {
 639 protected:
 640   EnqueueTask(ReferenceProcessor&           ref_processor,
 641               DiscoveredList                refs_lists[],
 642               int                           n_queues,
 643               ReferenceProcessorPhaseTimes* phase_times)
 644     : _ref_processor(ref_processor),
 645       _refs_lists(refs_lists),
 646       _n_queues(n_queues),
 647       _phase_times(phase_times)
 648   { }
 649 
 650 public:
 651   virtual void work(unsigned int work_id) = 0;
 652 
 653 protected:
 654   ReferenceProcessor&           _ref_processor;
 655   DiscoveredList*               _refs_lists;
 656   ReferenceProcessorPhaseTimes* _phase_times;
 657   int                           _n_queues;
 658 };
 659 
 660 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP