1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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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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  24 
  25 #ifndef SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
  26 #define SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
  27 
  28 #include "gc_implementation/shared/gcTrace.hpp"
  29 #include "memory/referencePolicy.hpp"
  30 #include "memory/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   DiscoveredList* _discoveredCleanerRefs;
 248 
 249  public:
 250   static int number_of_subclasses_of_ref() { return (REF_CLEANER - REF_OTHER); }
 251 
 252   uint num_q()                             { return _num_q; }
 253   uint max_num_q()                         { return _max_num_q; }
 254   void set_active_mt_degree(uint v)        { _num_q = v; }
 255 
 256   DiscoveredList* discovered_refs()        { return _discovered_refs; }
 257 
 258   ReferencePolicy* setup_policy(bool always_clear) {
 259     _current_soft_ref_policy = always_clear ?
 260       _always_clear_soft_ref_policy : _default_soft_ref_policy;
 261     _current_soft_ref_policy->setup();   // snapshot the policy threshold
 262     return _current_soft_ref_policy;
 263   }
 264 
 265   // Process references with a certain reachability level.
 266   size_t process_discovered_reflist(DiscoveredList               refs_lists[],
 267                                     ReferencePolicy*             policy,
 268                                     bool                         clear_referent,
 269                                     BoolObjectClosure*           is_alive,
 270                                     OopClosure*                  keep_alive,
 271                                     VoidClosure*                 complete_gc,
 272                                     AbstractRefProcTaskExecutor* task_executor);
 273 
 274   void process_phaseJNI(BoolObjectClosure* is_alive,
 275                         OopClosure*        keep_alive,
 276                         VoidClosure*       complete_gc);
 277 
 278   // Work methods used by the method process_discovered_reflist
 279   // Phase1: keep alive all those referents that are otherwise
 280   // dead but which must be kept alive by policy (and their closure).
 281   void process_phase1(DiscoveredList&     refs_list,
 282                       ReferencePolicy*    policy,
 283                       BoolObjectClosure*  is_alive,
 284                       OopClosure*         keep_alive,
 285                       VoidClosure*        complete_gc);
 286   // Phase2: remove all those references whose referents are
 287   // reachable.
 288   inline void process_phase2(DiscoveredList&    refs_list,
 289                              BoolObjectClosure* is_alive,
 290                              OopClosure*        keep_alive,
 291                              VoidClosure*       complete_gc) {
 292     if (discovery_is_atomic()) {
 293       // complete_gc is ignored in this case for this phase
 294       pp2_work(refs_list, is_alive, keep_alive);
 295     } else {
 296       assert(complete_gc != NULL, "Error");
 297       pp2_work_concurrent_discovery(refs_list, is_alive,
 298                                     keep_alive, complete_gc);
 299     }
 300   }
 301   // Work methods in support of process_phase2
 302   void pp2_work(DiscoveredList&    refs_list,
 303                 BoolObjectClosure* is_alive,
 304                 OopClosure*        keep_alive);
 305   void pp2_work_concurrent_discovery(
 306                 DiscoveredList&    refs_list,
 307                 BoolObjectClosure* is_alive,
 308                 OopClosure*        keep_alive,
 309                 VoidClosure*       complete_gc);
 310   // Phase3: process the referents by either clearing them
 311   // or keeping them alive (and their closure)
 312   void process_phase3(DiscoveredList&    refs_list,
 313                       bool               clear_referent,
 314                       BoolObjectClosure* is_alive,
 315                       OopClosure*        keep_alive,
 316                       VoidClosure*       complete_gc);
 317 
 318   // Enqueue references with a certain reachability level
 319   void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr);
 320 
 321   // "Preclean" all the discovered reference lists
 322   // by removing references with strongly reachable referents.
 323   // The first argument is a predicate on an oop that indicates
 324   // its (strong) reachability and the second is a closure that
 325   // may be used to incrementalize or abort the precleaning process.
 326   // The caller is responsible for taking care of potential
 327   // interference with concurrent operations on these lists
 328   // (or predicates involved) by other threads. Currently
 329   // only used by the CMS collector.
 330   void preclean_discovered_references(BoolObjectClosure* is_alive,
 331                                       OopClosure*        keep_alive,
 332                                       VoidClosure*       complete_gc,
 333                                       YieldClosure*      yield,
 334                                       GCTimer*           gc_timer,
 335                                       GCId               gc_id);
 336 
 337   // Returns the name of the discovered reference list
 338   // occupying the i / _num_q slot.
 339   const char* list_name(uint i);
 340 
 341   void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);
 342 
 343  protected:
 344   // "Preclean" the given discovered reference list
 345   // by removing references with strongly reachable referents.
 346   // Currently used in support of CMS only.
 347   void preclean_discovered_reflist(DiscoveredList&    refs_list,
 348                                    BoolObjectClosure* is_alive,
 349                                    OopClosure*        keep_alive,
 350                                    VoidClosure*       complete_gc,
 351                                    YieldClosure*      yield);
 352 
 353   // round-robin mod _num_q (not: _not_ mode _max_num_q)
 354   uint next_id() {
 355     uint id = _next_id;
 356     if (++_next_id == _num_q) {
 357       _next_id = 0;
 358     }
 359     return id;
 360   }
 361   DiscoveredList* get_discovered_list(ReferenceType rt);
 362   inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
 363                                         HeapWord* discovered_addr);
 364   void verify_ok_to_handle_reflists() PRODUCT_RETURN;
 365 
 366   void clear_discovered_references(DiscoveredList& refs_list);
 367   void abandon_partial_discovered_list(DiscoveredList& refs_list);
 368 
 369   // Calculate the number of jni handles.
 370   unsigned int count_jni_refs();
 371 
 372   // Balances reference queues.
 373   void balance_queues(DiscoveredList ref_lists[]);
 374 
 375   // Update (advance) the soft ref master clock field.
 376   void update_soft_ref_master_clock();
 377 
 378  public:
 379   // Default parameters give you a vanilla reference processor.
 380   ReferenceProcessor(MemRegion span,
 381                      bool mt_processing = false, uint mt_processing_degree = 1,
 382                      bool mt_discovery  = false, uint mt_discovery_degree  = 1,
 383                      bool atomic_discovery = true,
 384                      BoolObjectClosure* is_alive_non_header = NULL);
 385 
 386   // RefDiscoveryPolicy values
 387   enum DiscoveryPolicy {
 388     ReferenceBasedDiscovery = 0,
 389     ReferentBasedDiscovery  = 1,
 390     DiscoveryPolicyMin      = ReferenceBasedDiscovery,
 391     DiscoveryPolicyMax      = ReferentBasedDiscovery
 392   };
 393 
 394   static void init_statics();
 395 
 396  public:
 397   // get and set "is_alive_non_header" field
 398   BoolObjectClosure* is_alive_non_header() {
 399     return _is_alive_non_header;
 400   }
 401   void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
 402     _is_alive_non_header = is_alive_non_header;
 403   }
 404 
 405   // get and set span
 406   MemRegion span()                   { return _span; }
 407   void      set_span(MemRegion span) { _span = span; }
 408 
 409   // start and stop weak ref discovery
 410   void enable_discovery(bool check_no_refs = true);
 411   void disable_discovery()  { _discovering_refs = false; }
 412   bool discovery_enabled()  { return _discovering_refs;  }
 413 
 414   // whether discovery is atomic wrt other collectors
 415   bool discovery_is_atomic() const { return _discovery_is_atomic; }
 416   void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
 417 
 418   // whether discovery is done by multiple threads same-old-timeously
 419   bool discovery_is_mt() const { return _discovery_is_mt; }
 420   void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
 421 
 422   // Whether we are in a phase when _processing_ is MT.
 423   bool processing_is_mt() const { return _processing_is_mt; }
 424   void set_mt_processing(bool mt) { _processing_is_mt = mt; }
 425 
 426   // whether all enqueueing of weak references is complete
 427   bool enqueuing_is_done()  { return _enqueuing_is_done; }
 428   void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
 429 
 430   // iterate over oops
 431   void weak_oops_do(OopClosure* f);       // weak roots
 432 
 433   // Balance each of the discovered lists.
 434   void balance_all_queues();
 435   void verify_list(DiscoveredList& ref_list);
 436 
 437   // Discover a Reference object, using appropriate discovery criteria
 438   bool discover_reference(oop obj, ReferenceType rt);
 439 
 440   // Process references found during GC (called by the garbage collector)
 441   ReferenceProcessorStats
 442   process_discovered_references(BoolObjectClosure*           is_alive,
 443                                 OopClosure*                  keep_alive,
 444                                 VoidClosure*                 complete_gc,
 445                                 AbstractRefProcTaskExecutor* task_executor,
 446                                 GCTimer *gc_timer,
 447                                 GCId    gc_id);
 448 
 449   // Enqueue references at end of GC (called by the garbage collector)
 450   bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
 451 
 452   // If a discovery is in process that is being superceded, abandon it: all
 453   // the discovered lists will be empty, and all the objects on them will
 454   // have NULL discovered fields.  Must be called only at a safepoint.
 455   void abandon_partial_discovery();
 456 
 457   // debugging
 458   void verify_no_references_recorded() PRODUCT_RETURN;
 459   void verify_referent(oop obj)        PRODUCT_RETURN;
 460 
 461   // clear the discovered lists (unlinking each entry).
 462   void clear_discovered_references() PRODUCT_RETURN;
 463 };
 464 
 465 // A utility class to disable reference discovery in
 466 // the scope which contains it, for given ReferenceProcessor.
 467 class NoRefDiscovery: StackObj {
 468  private:
 469   ReferenceProcessor* _rp;
 470   bool _was_discovering_refs;
 471  public:
 472   NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
 473     _was_discovering_refs = _rp->discovery_enabled();
 474     if (_was_discovering_refs) {
 475       _rp->disable_discovery();
 476     }
 477   }
 478 
 479   ~NoRefDiscovery() {
 480     if (_was_discovering_refs) {
 481       _rp->enable_discovery(false /*check_no_refs*/);
 482     }
 483   }
 484 };
 485 
 486 
 487 // A utility class to temporarily mutate the span of the
 488 // given ReferenceProcessor in the scope that contains it.
 489 class ReferenceProcessorSpanMutator: StackObj {
 490  private:
 491   ReferenceProcessor* _rp;
 492   MemRegion           _saved_span;
 493 
 494  public:
 495   ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
 496                                 MemRegion span):
 497     _rp(rp) {
 498     _saved_span = _rp->span();
 499     _rp->set_span(span);
 500   }
 501 
 502   ~ReferenceProcessorSpanMutator() {
 503     _rp->set_span(_saved_span);
 504   }
 505 };
 506 
 507 // A utility class to temporarily change the MT'ness of
 508 // reference discovery for the given ReferenceProcessor
 509 // in the scope that contains it.
 510 class ReferenceProcessorMTDiscoveryMutator: StackObj {
 511  private:
 512   ReferenceProcessor* _rp;
 513   bool                _saved_mt;
 514 
 515  public:
 516   ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
 517                                        bool mt):
 518     _rp(rp) {
 519     _saved_mt = _rp->discovery_is_mt();
 520     _rp->set_mt_discovery(mt);
 521   }
 522 
 523   ~ReferenceProcessorMTDiscoveryMutator() {
 524     _rp->set_mt_discovery(_saved_mt);
 525   }
 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     : _ref_processor(ref_processor),
 618       _refs_lists(refs_lists),
 619       _marks_oops_alive(marks_oops_alive)
 620   { }
 621 
 622 public:
 623   virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
 624                     OopClosure& keep_alive,
 625                     VoidClosure& complete_gc) = 0;
 626 
 627   // Returns true if a task marks some oops as alive.
 628   bool marks_oops_alive() const
 629   { return _marks_oops_alive; }
 630 
 631 protected:
 632   ReferenceProcessor& _ref_processor;
 633   DiscoveredList*     _refs_lists;
 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               HeapWord*           pending_list_addr,
 643               int                 n_queues)
 644     : _ref_processor(ref_processor),
 645       _refs_lists(refs_lists),
 646       _pending_list_addr(pending_list_addr),
 647       _n_queues(n_queues)
 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   HeapWord*           _pending_list_addr;
 657   int                 _n_queues;
 658 };
 659 
 660 #endif // SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP