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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  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_enqueue();
 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   // Phase3: process the referents by either clearing them
 266   // or keeping them alive (and their closure), and enqueuing them.
 267   void process_phase3(DiscoveredList&    refs_list,
 268                       bool               clear_referent,
 269                       BoolObjectClosure* is_alive,
 270                       OopClosure*        keep_alive,
 271                       VoidClosure*       complete_gc);
 272 
 273   // "Preclean" all the discovered reference lists
 274   // by removing references with strongly reachable referents.
 275   // The first argument is a predicate on an oop that indicates
 276   // its (strong) reachability and the second is a closure that
 277   // may be used to incrementalize or abort the precleaning process.
 278   // The caller is responsible for taking care of potential
 279   // interference with concurrent operations on these lists
 280   // (or predicates involved) by other threads. Currently
 281   // only used by the CMS collector.
 282   void preclean_discovered_references(BoolObjectClosure* is_alive,
 283                                       OopClosure*        keep_alive,
 284                                       VoidClosure*       complete_gc,
 285                                       YieldClosure*      yield,
 286                                       GCTimer*           gc_timer);
 287 
 288   // Returns the name of the discovered reference list
 289   // occupying the i / _num_queues slot.
 290   const char* list_name(uint i);
 291 
 292   // "Preclean" the given discovered reference list
 293   // by removing references with strongly reachable referents.
 294   // Currently used in support of CMS only.
 295   void preclean_discovered_reflist(DiscoveredList&    refs_list,
 296                                    BoolObjectClosure* is_alive,
 297                                    OopClosure*        keep_alive,
 298                                    VoidClosure*       complete_gc,
 299                                    YieldClosure*      yield);
 300 private:
 301   // round-robin mod _num_queues (not: _not_ mod _max_num_queues)
 302   uint next_id() {
 303     uint id = _next_id;
 304     assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
 305     if (++_next_id == _num_queues) {
 306       _next_id = 0;
 307     }
 308     assert(_next_id < _num_queues, "_next_id %u _num_queues %u _max_num_queues %u", _next_id, _num_queues, _max_num_queues);
 309     return id;
 310   }
 311   DiscoveredList* get_discovered_list(ReferenceType rt);
 312   inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
 313                                         HeapWord* discovered_addr);
 314 
 315   void clear_discovered_references(DiscoveredList& refs_list);
 316 
 317   void log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_count) PRODUCT_RETURN;
 318 
 319   // Balances reference queues.
 320   void balance_queues(DiscoveredList ref_lists[]);
 321 
 322   // Update (advance) the soft ref master clock field.
 323   void update_soft_ref_master_clock();
 324 
 325   bool is_subject_to_discovery(oop const obj) const;
 326 
 327 public:
 328   // Default parameters give you a vanilla reference processor.
 329   ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery,
 330                      bool mt_processing = false, uint mt_processing_degree = 1,
 331                      bool mt_discovery  = false, uint mt_discovery_degree  = 1,
 332                      bool atomic_discovery = true,
 333                      BoolObjectClosure* is_alive_non_header = NULL);
 334 
 335   // RefDiscoveryPolicy values
 336   enum DiscoveryPolicy {
 337     ReferenceBasedDiscovery = 0,
 338     ReferentBasedDiscovery  = 1,
 339     DiscoveryPolicyMin      = ReferenceBasedDiscovery,
 340     DiscoveryPolicyMax      = ReferentBasedDiscovery
 341   };
 342 
 343   static void init_statics();
 344 
 345  public:
 346   // get and set "is_alive_non_header" field
 347   BoolObjectClosure* is_alive_non_header() {
 348     return _is_alive_non_header;
 349   }
 350   void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
 351     _is_alive_non_header = is_alive_non_header;
 352   }
 353 
 354   BoolObjectClosure* is_subject_to_discovery_closure() const { return _is_subject_to_discovery; }
 355   void set_is_subject_to_discovery_closure(BoolObjectClosure* cl) { _is_subject_to_discovery = cl; }
 356 
 357   // start and stop weak ref discovery
 358   void enable_discovery(bool check_no_refs = true);
 359   void disable_discovery()  { _discovering_refs = false; }
 360   bool discovery_enabled()  { return _discovering_refs;  }
 361 
 362   // whether discovery is atomic wrt other collectors
 363   bool discovery_is_atomic() const { return _discovery_is_atomic; }
 364   void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
 365 
 366   // whether discovery is done by multiple threads same-old-timeously
 367   bool discovery_is_mt() const { return _discovery_is_mt; }
 368   void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
 369 
 370   // Whether we are in a phase when _processing_ is MT.
 371   bool processing_is_mt() const { return _processing_is_mt; }
 372   void set_mt_processing(bool mt) { _processing_is_mt = mt; }
 373 
 374   // whether all enqueueing of weak references is complete
 375   bool enqueuing_is_done()  { return _enqueuing_is_done; }
 376   void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
 377 
 378   // iterate over oops
 379   void weak_oops_do(OopClosure* f);       // weak roots
 380 
 381   void verify_list(DiscoveredList& ref_list);
 382 
 383   // Discover a Reference object, using appropriate discovery criteria
 384   virtual bool discover_reference(oop obj, ReferenceType rt);
 385 
 386   // Has discovered references that need handling
 387   bool has_discovered_references();
 388 
 389   // Process references found during GC (called by the garbage collector)
 390   ReferenceProcessorStats
 391   process_discovered_references(BoolObjectClosure*            is_alive,
 392                                 OopClosure*                   keep_alive,
 393                                 VoidClosure*                  complete_gc,
 394                                 AbstractRefProcTaskExecutor*  task_executor,
 395                                 ReferenceProcessorPhaseTimes* phase_times);
 396 
 397   // If a discovery is in process that is being superceded, abandon it: all
 398   // the discovered lists will be empty, and all the objects on them will
 399   // have NULL discovered fields.  Must be called only at a safepoint.
 400   void abandon_partial_discovery();
 401 
 402   size_t total_reference_count(ReferenceType rt) const;
 403 
 404   // debugging
 405   void verify_no_references_recorded() PRODUCT_RETURN;
 406   void verify_referent(oop obj)        PRODUCT_RETURN;
 407 };
 408 
 409 // A subject-to-discovery closure that uses a single memory span to determine the area that
 410 // is subject to discovery. Useful for collectors which have contiguous generations.
 411 class SpanSubjectToDiscoveryClosure : public BoolObjectClosure {
 412   MemRegion _span;
 413 
 414 public:
 415   SpanSubjectToDiscoveryClosure() : BoolObjectClosure(), _span() { }
 416   SpanSubjectToDiscoveryClosure(MemRegion span) : BoolObjectClosure(), _span(span) { }
 417 
 418   MemRegion span() const { return _span; }
 419 
 420   void set_span(MemRegion mr) {
 421     _span = mr;
 422   }
 423 
 424   virtual bool do_object_b(oop obj) {
 425     return _span.contains(obj);
 426   }
 427 };
 428 
 429 // A utility class to disable reference discovery in
 430 // the scope which contains it, for given ReferenceProcessor.
 431 class NoRefDiscovery: StackObj {
 432  private:
 433   ReferenceProcessor* _rp;
 434   bool _was_discovering_refs;
 435  public:
 436   NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
 437     _was_discovering_refs = _rp->discovery_enabled();
 438     if (_was_discovering_refs) {
 439       _rp->disable_discovery();
 440     }
 441   }
 442 
 443   ~NoRefDiscovery() {
 444     if (_was_discovering_refs) {
 445       _rp->enable_discovery(false /*check_no_refs*/);
 446     }
 447   }
 448 };
 449 
 450 // A utility class to temporarily mutate the subject discovery closure of the
 451 // given ReferenceProcessor in the scope that contains it.
 452 class ReferenceProcessorSubjectToDiscoveryMutator : StackObj {
 453   ReferenceProcessor* _rp;
 454   BoolObjectClosure* _saved_cl;
 455 
 456 public:
 457   ReferenceProcessorSubjectToDiscoveryMutator(ReferenceProcessor* rp, BoolObjectClosure* cl):
 458     _rp(rp) {
 459     _saved_cl = _rp->is_subject_to_discovery_closure();
 460     _rp->set_is_subject_to_discovery_closure(cl);
 461   }
 462 
 463   ~ReferenceProcessorSubjectToDiscoveryMutator() {
 464     _rp->set_is_subject_to_discovery_closure(_saved_cl);
 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   ReferenceProcessor* _rp;
 472   SpanSubjectToDiscoveryClosure _discoverer;
 473   BoolObjectClosure* _old_discoverer;
 474 
 475 public:
 476   ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
 477                                 MemRegion span):
 478     _rp(rp),
 479     _discoverer(span),
 480     _old_discoverer(rp->is_subject_to_discovery_closure()) {
 481 
 482     rp->set_is_subject_to_discovery_closure(&_discoverer);
 483   }
 484 
 485   ~ReferenceProcessorSpanMutator() {
 486     _rp->set_is_subject_to_discovery_closure(_old_discoverer);
 487   }
 488 };
 489 
 490 // A utility class to temporarily change the MT'ness of
 491 // reference discovery for the given ReferenceProcessor
 492 // in the scope that contains it.
 493 class ReferenceProcessorMTDiscoveryMutator: StackObj {
 494  private:
 495   ReferenceProcessor* _rp;
 496   bool                _saved_mt;
 497 
 498  public:
 499   ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
 500                                        bool mt):
 501     _rp(rp) {
 502     _saved_mt = _rp->discovery_is_mt();
 503     _rp->set_mt_discovery(mt);
 504   }
 505 
 506   ~ReferenceProcessorMTDiscoveryMutator() {
 507     _rp->set_mt_discovery(_saved_mt);
 508   }
 509 };
 510 
 511 // A utility class to temporarily change the disposition
 512 // of the "is_alive_non_header" closure field of the
 513 // given ReferenceProcessor in the scope that contains it.
 514 class ReferenceProcessorIsAliveMutator: StackObj {
 515  private:
 516   ReferenceProcessor* _rp;
 517   BoolObjectClosure*  _saved_cl;
 518 
 519  public:
 520   ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
 521                                    BoolObjectClosure*  cl):
 522     _rp(rp) {
 523     _saved_cl = _rp->is_alive_non_header();
 524     _rp->set_is_alive_non_header(cl);
 525   }
 526 
 527   ~ReferenceProcessorIsAliveMutator() {
 528     _rp->set_is_alive_non_header(_saved_cl);
 529   }
 530 };
 531 
 532 // A utility class to temporarily change the disposition
 533 // of the "discovery_is_atomic" field of the
 534 // given ReferenceProcessor in the scope that contains it.
 535 class ReferenceProcessorAtomicMutator: StackObj {
 536  private:
 537   ReferenceProcessor* _rp;
 538   bool                _saved_atomic_discovery;
 539 
 540  public:
 541   ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
 542                                   bool atomic):
 543     _rp(rp) {
 544     _saved_atomic_discovery = _rp->discovery_is_atomic();
 545     _rp->set_atomic_discovery(atomic);
 546   }
 547 
 548   ~ReferenceProcessorAtomicMutator() {
 549     _rp->set_atomic_discovery(_saved_atomic_discovery);
 550   }
 551 };
 552 
 553 
 554 // A utility class to temporarily change the MT processing
 555 // disposition of the given ReferenceProcessor instance
 556 // in the scope that contains it.
 557 class ReferenceProcessorMTProcMutator: StackObj {
 558  private:
 559   ReferenceProcessor* _rp;
 560   bool  _saved_mt;
 561 
 562  public:
 563   ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
 564                                   bool mt):
 565     _rp(rp) {
 566     _saved_mt = _rp->processing_is_mt();
 567     _rp->set_mt_processing(mt);
 568   }
 569 
 570   ~ReferenceProcessorMTProcMutator() {
 571     _rp->set_mt_processing(_saved_mt);
 572   }
 573 };
 574 
 575 
 576 // This class is an interface used to implement task execution for the
 577 // reference processing.
 578 class AbstractRefProcTaskExecutor {
 579 public:
 580 
 581   // Abstract tasks to execute.
 582   class ProcessTask;
 583 
 584   // Executes a task using worker threads.
 585   virtual void execute(ProcessTask& task) = 0;
 586 
 587   // Switch to single threaded mode.
 588   virtual void set_single_threaded_mode() { };
 589 };
 590 
 591 // Abstract reference processing task to execute.
 592 class AbstractRefProcTaskExecutor::ProcessTask {
 593 protected:
 594   ProcessTask(ReferenceProcessor&           ref_processor,
 595               DiscoveredList                refs_lists[],
 596               bool                          marks_oops_alive,
 597               ReferenceProcessorPhaseTimes* phase_times)
 598     : _ref_processor(ref_processor),
 599       _refs_lists(refs_lists),
 600       _phase_times(phase_times),
 601       _marks_oops_alive(marks_oops_alive)
 602   { }
 603 
 604 public:
 605   virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
 606                     OopClosure& keep_alive,
 607                     VoidClosure& complete_gc) = 0;
 608 
 609   // Returns true if a task marks some oops as alive.
 610   bool marks_oops_alive() const
 611   { return _marks_oops_alive; }
 612 
 613 protected:
 614   ReferenceProcessor&           _ref_processor;
 615   DiscoveredList*               _refs_lists;
 616   ReferenceProcessorPhaseTimes* _phase_times;
 617   const bool                    _marks_oops_alive;
 618 };
 619 
 620 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP