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