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