1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
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   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
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  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
  26 #define SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
  27 
  28 #include "memory/referencePolicy.hpp"
  29 #include "memory/referenceProcessorStats.hpp"
  30 #include "memory/referenceType.hpp"
  31 #include "oops/instanceRefKlass.hpp"
  32 
  33 class GCTimer;
  34 
  35 // ReferenceProcessor class encapsulates the per-"collector" processing
  36 // of java.lang.Reference objects for GC. The interface is useful for supporting
  37 // a generational abstraction, in particular when there are multiple
  38 // generations that are being independently collected -- possibly
  39 // concurrently and/or incrementally.  Note, however, that the
  40 // ReferenceProcessor class abstracts away from a generational setting
  41 // by using only a heap interval (called "span" below), thus allowing
  42 // its use in a straightforward manner in a general, non-generational
  43 // setting.
  44 //
  45 // The basic idea is that each ReferenceProcessor object concerns
  46 // itself with ("weak") reference processing in a specific "span"
  47 // of the heap of interest to a specific collector. Currently,
  48 // the span is a convex interval of the heap, but, efficiency
  49 // apart, there seems to be no reason it couldn't be extended
  50 // (with appropriate modifications) to any "non-convex interval".
  51 
  52 // forward references
  53 class ReferencePolicy;
  54 class AbstractRefProcTaskExecutor;
  55 
  56 // List of discovered references.
  57 class DiscoveredList {
  58 public:
  59   DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
  60   oop head() const     {
  61      return UseCompressedOops ?  oopDesc::decode_heap_oop(_compressed_head) :
  62                                 _oop_head;
  63   }
  64   HeapWord* adr_head() {
  65     return UseCompressedOops ? (HeapWord*)&_compressed_head :
  66                                (HeapWord*)&_oop_head;
  67   }
  68   void set_head(oop o) {
  69     if (UseCompressedOops) {
  70       // Must compress the head ptr.
  71       _compressed_head = oopDesc::encode_heap_oop(o);
  72     } else {
  73       _oop_head = o;
  74     }
  75   }
  76   bool   is_empty() const       { return head() == NULL; }
  77   size_t length()               { return _len; }
  78   void   set_length(size_t len) { _len = len;  }
  79   void   inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
  80   void   dec_length(size_t dec) { _len -= dec; }
  81 private:
  82   // Set value depending on UseCompressedOops. This could be a template class
  83   // but then we have to fix all the instantiations and declarations that use this class.
  84   oop       _oop_head;
  85   narrowOop _compressed_head;
  86   size_t _len;
  87 };
  88 
  89 // Iterator for the list of discovered references.
  90 class DiscoveredListIterator {
  91 private:
  92   DiscoveredList&    _refs_list;
  93   HeapWord*          _prev_next;
  94   oop                _prev;
  95   oop                _ref;
  96   HeapWord*          _discovered_addr;
  97   oop                _next;
  98   HeapWord*          _referent_addr;
  99   oop                _referent;
 100   OopClosure*        _keep_alive;
 101   BoolObjectClosure* _is_alive;
 102 
 103   DEBUG_ONLY(
 104   oop                _first_seen; // cyclic linked list check
 105   )
 106 
 107   NOT_PRODUCT(
 108   size_t             _processed;
 109   size_t             _removed;
 110   )
 111 
 112 public:
 113   inline DiscoveredListIterator(DiscoveredList&    refs_list,
 114                                 OopClosure*        keep_alive,
 115                                 BoolObjectClosure* is_alive):
 116     _refs_list(refs_list),
 117     _prev_next(refs_list.adr_head()),
 118     _prev(NULL),
 119     _ref(refs_list.head()),
 120 #ifdef ASSERT
 121     _first_seen(refs_list.head()),
 122 #endif
 123 #ifndef PRODUCT
 124     _processed(0),
 125     _removed(0),
 126 #endif
 127     _next(NULL),
 128     _keep_alive(keep_alive),
 129     _is_alive(is_alive)
 130 { }
 131 
 132   // End Of List.
 133   inline bool has_next() const { return _ref != NULL; }
 134 
 135   // Get oop to the Reference object.
 136   inline oop obj() const { return _ref; }
 137 
 138   // Get oop to the referent object.
 139   inline oop referent() const { return _referent; }
 140 
 141   // Returns true if referent is alive.
 142   inline bool is_referent_alive() const {
 143     return _is_alive->do_object_b(_referent);
 144   }
 145 
 146   // Loads data for the current reference.
 147   // The "allow_null_referent" argument tells us to allow for the possibility
 148   // of a NULL referent in the discovered Reference object. This typically
 149   // happens in the case of concurrent collectors that may have done the
 150   // discovery concurrently, or interleaved, with mutator execution.
 151   void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
 152 
 153   // Move to the next discovered reference.
 154   inline void next() {
 155     _prev_next = _discovered_addr;
 156     _prev = _ref;
 157     move_to_next();
 158   }
 159 
 160   // Remove the current reference from the list
 161   void remove();
 162 
 163   // Make the Reference object active again.
 164   void make_active();
 165 
 166   // Make the referent alive.
 167   inline void make_referent_alive() {
 168     if (UseCompressedOops) {
 169       _keep_alive->do_oop((narrowOop*)_referent_addr);
 170     } else {
 171       _keep_alive->do_oop((oop*)_referent_addr);
 172     }
 173   }
 174 
 175   // Update the discovered field.
 176   inline void update_discovered() {
 177     // First _prev_next ref actually points into DiscoveredList (gross).
 178     if (UseCompressedOops) {
 179       if (!oopDesc::is_null(*(narrowOop*)_prev_next)) {
 180         _keep_alive->do_oop((narrowOop*)_prev_next);
 181       }
 182     } else {
 183       if (!oopDesc::is_null(*(oop*)_prev_next)) {
 184         _keep_alive->do_oop((oop*)_prev_next);
 185       }
 186     }
 187   }
 188 
 189   // NULL out referent pointer.
 190   void clear_referent();
 191 
 192   // Statistics
 193   NOT_PRODUCT(
 194   inline size_t processed() const { return _processed; }
 195   inline size_t removed() const   { return _removed; }
 196   )
 197 
 198   inline void move_to_next() {
 199     if (_ref == _next) {
 200       // End of the list.
 201       _ref = NULL;
 202     } else {
 203       _ref = _next;
 204     }
 205     assert(_ref != _first_seen, "cyclic ref_list found");
 206     NOT_PRODUCT(_processed++);
 207   }
 208 };
 209 
 210 class ReferenceProcessor : public CHeapObj<mtGC> {
 211 
 212  private:
 213   size_t total_count(DiscoveredList lists[]);
 214 
 215  protected:
 216   // Compatibility with pre-4965777 JDK's
 217   static bool _pending_list_uses_discovered_field;
 218 
 219   // The SoftReference master timestamp clock
 220   static jlong _soft_ref_timestamp_clock;
 221 
 222   MemRegion   _span;                    // (right-open) interval of heap
 223                                         // subject to wkref discovery
 224 
 225   bool        _discovering_refs;        // true when discovery enabled
 226   bool        _discovery_is_atomic;     // if discovery is atomic wrt
 227                                         // other collectors in configuration
 228   bool        _discovery_is_mt;         // true if reference discovery is MT.
 229 
 230   bool        _enqueuing_is_done;       // true if all weak references enqueued
 231   bool        _processing_is_mt;        // true during phases when
 232                                         // reference processing is MT.
 233   uint        _next_id;                 // round-robin mod _num_q counter in
 234                                         // support of work distribution
 235 
 236   // For collectors that do not keep GC liveness information
 237   // in the object header, this field holds a closure that
 238   // helps the reference processor determine the reachability
 239   // of an oop. It is currently initialized to NULL for all
 240   // collectors except for CMS and G1.
 241   BoolObjectClosure* _is_alive_non_header;
 242 
 243   // Soft ref clearing policies
 244   // . the default policy
 245   static ReferencePolicy*   _default_soft_ref_policy;
 246   // . the "clear all" policy
 247   static ReferencePolicy*   _always_clear_soft_ref_policy;
 248   // . the current policy below is either one of the above
 249   ReferencePolicy*          _current_soft_ref_policy;
 250 
 251   // The discovered ref lists themselves
 252 
 253   // The active MT'ness degree of the queues below
 254   uint             _num_q;
 255   // The maximum MT'ness degree of the queues below
 256   uint             _max_num_q;
 257 
 258   // Master array of discovered oops
 259   DiscoveredList* _discovered_refs;
 260 
 261   // Arrays of lists of oops, one per thread (pointers into master array above)
 262   DiscoveredList* _discoveredSoftRefs;
 263   DiscoveredList* _discoveredWeakRefs;
 264   DiscoveredList* _discoveredFinalRefs;
 265   DiscoveredList* _discoveredPhantomRefs;
 266 
 267  public:
 268   static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); }
 269 
 270   uint num_q()                             { return _num_q; }
 271   uint max_num_q()                         { return _max_num_q; }
 272   void set_active_mt_degree(uint v)        { _num_q = v; }
 273 
 274   DiscoveredList* discovered_refs()        { return _discovered_refs; }
 275 
 276   ReferencePolicy* setup_policy(bool always_clear) {
 277     _current_soft_ref_policy = always_clear ?
 278       _always_clear_soft_ref_policy : _default_soft_ref_policy;
 279     _current_soft_ref_policy->setup();   // snapshot the policy threshold
 280     return _current_soft_ref_policy;
 281   }
 282 
 283   // Process references with a certain reachability level.
 284   size_t process_discovered_reflist(DiscoveredList               refs_lists[],
 285                                     ReferencePolicy*             policy,
 286                                     bool                         clear_referent,
 287                                     BoolObjectClosure*           is_alive,
 288                                     OopClosure*                  keep_alive,
 289                                     VoidClosure*                 complete_gc,
 290                                     AbstractRefProcTaskExecutor* task_executor);
 291 
 292   void process_phaseJNI(BoolObjectClosure* is_alive,
 293                         OopClosure*        keep_alive,
 294                         VoidClosure*       complete_gc);
 295 
 296   // Work methods used by the method process_discovered_reflist
 297   // Phase1: keep alive all those referents that are otherwise
 298   // dead but which must be kept alive by policy (and their closure).
 299   void process_phase1(DiscoveredList&     refs_list,
 300                       ReferencePolicy*    policy,
 301                       BoolObjectClosure*  is_alive,
 302                       OopClosure*         keep_alive,
 303                       VoidClosure*        complete_gc);
 304   // Phase2: remove all those references whose referents are
 305   // reachable.
 306   inline void process_phase2(DiscoveredList&    refs_list,
 307                              BoolObjectClosure* is_alive,
 308                              OopClosure*        keep_alive,
 309                              VoidClosure*       complete_gc) {
 310     if (discovery_is_atomic()) {
 311       // complete_gc is ignored in this case for this phase
 312       pp2_work(refs_list, is_alive, keep_alive);
 313     } else {
 314       assert(complete_gc != NULL, "Error");
 315       pp2_work_concurrent_discovery(refs_list, is_alive,
 316                                     keep_alive, complete_gc);
 317     }
 318   }
 319   // Work methods in support of process_phase2
 320   void pp2_work(DiscoveredList&    refs_list,
 321                 BoolObjectClosure* is_alive,
 322                 OopClosure*        keep_alive);
 323   void pp2_work_concurrent_discovery(
 324                 DiscoveredList&    refs_list,
 325                 BoolObjectClosure* is_alive,
 326                 OopClosure*        keep_alive,
 327                 VoidClosure*       complete_gc);
 328   // Phase3: process the referents by either clearing them
 329   // or keeping them alive (and their closure)
 330   void process_phase3(DiscoveredList&    refs_list,
 331                       bool               clear_referent,
 332                       BoolObjectClosure* is_alive,
 333                       OopClosure*        keep_alive,
 334                       VoidClosure*       complete_gc);
 335 
 336   // Enqueue references with a certain reachability level
 337   void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr);
 338 
 339   // "Preclean" all the discovered reference lists
 340   // by removing references with strongly reachable referents.
 341   // The first argument is a predicate on an oop that indicates
 342   // its (strong) reachability and the second is a closure that
 343   // may be used to incrementalize or abort the precleaning process.
 344   // The caller is responsible for taking care of potential
 345   // interference with concurrent operations on these lists
 346   // (or predicates involved) by other threads. Currently
 347   // only used by the CMS collector.
 348   void preclean_discovered_references(BoolObjectClosure* is_alive,
 349                                       OopClosure*        keep_alive,
 350                                       VoidClosure*       complete_gc,
 351                                       YieldClosure*      yield,
 352                                       GCTimer*           gc_timer);
 353 
 354   // Delete entries in the discovered lists that have
 355   // either a null referent or are not active. Such
 356   // Reference objects can result from the clearing
 357   // or enqueueing of Reference objects concurrent
 358   // with their discovery by a (concurrent) collector.
 359   // For a definition of "active" see java.lang.ref.Reference;
 360   // Refs are born active, become inactive when enqueued,
 361   // and never become active again. The state of being
 362   // active is encoded as follows: A Ref is active
 363   // if and only if its "next" field is NULL.
 364   void clean_up_discovered_references();
 365   void clean_up_discovered_reflist(DiscoveredList& refs_list);
 366 
 367   // Returns the name of the discovered reference list
 368   // occupying the i / _num_q slot.
 369   const char* list_name(uint i);
 370 
 371   void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);
 372 
 373  protected:
 374   // "Preclean" the given discovered reference list
 375   // by removing references with strongly reachable referents.
 376   // Currently used in support of CMS only.
 377   void preclean_discovered_reflist(DiscoveredList&    refs_list,
 378                                    BoolObjectClosure* is_alive,
 379                                    OopClosure*        keep_alive,
 380                                    VoidClosure*       complete_gc,
 381                                    YieldClosure*      yield);
 382 
 383   // round-robin mod _num_q (not: _not_ mode _max_num_q)
 384   uint next_id() {
 385     uint id = _next_id;
 386     if (++_next_id == _num_q) {
 387       _next_id = 0;
 388     }
 389     return id;
 390   }
 391   DiscoveredList* get_discovered_list(ReferenceType rt);
 392   inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
 393                                         HeapWord* discovered_addr);
 394   void verify_ok_to_handle_reflists() PRODUCT_RETURN;
 395 
 396   void clear_discovered_references(DiscoveredList& refs_list);
 397   void abandon_partial_discovered_list(DiscoveredList& refs_list);
 398 
 399   // Calculate the number of jni handles.
 400   unsigned int count_jni_refs();
 401 
 402   // Balances reference queues.
 403   void balance_queues(DiscoveredList ref_lists[]);
 404 
 405   // Update (advance) the soft ref master clock field.
 406   void update_soft_ref_master_clock();
 407 
 408  public:
 409   // Default parameters give you a vanilla reference processor.
 410   ReferenceProcessor(MemRegion span,
 411                      bool mt_processing = false, uint mt_processing_degree = 1,
 412                      bool mt_discovery  = false, uint mt_discovery_degree  = 1,
 413                      bool atomic_discovery = true,
 414                      BoolObjectClosure* is_alive_non_header = NULL);
 415 
 416   // RefDiscoveryPolicy values
 417   enum DiscoveryPolicy {
 418     ReferenceBasedDiscovery = 0,
 419     ReferentBasedDiscovery  = 1,
 420     DiscoveryPolicyMin      = ReferenceBasedDiscovery,
 421     DiscoveryPolicyMax      = ReferentBasedDiscovery
 422   };
 423 
 424   static void init_statics();
 425 
 426  public:
 427   // get and set "is_alive_non_header" field
 428   BoolObjectClosure* is_alive_non_header() {
 429     return _is_alive_non_header;
 430   }
 431   void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
 432     _is_alive_non_header = is_alive_non_header;
 433   }
 434 
 435   // get and set span
 436   MemRegion span()                   { return _span; }
 437   void      set_span(MemRegion span) { _span = span; }
 438 
 439   // start and stop weak ref discovery
 440   void enable_discovery(bool verify_disabled, bool check_no_refs);
 441   void disable_discovery()  { _discovering_refs = false; }
 442   bool discovery_enabled()  { return _discovering_refs;  }
 443 
 444   // whether discovery is atomic wrt other collectors
 445   bool discovery_is_atomic() const { return _discovery_is_atomic; }
 446   void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
 447 
 448   // whether the JDK in which we are embedded is a pre-4965777 JDK,
 449   // and thus whether or not it uses the discovered field to chain
 450   // the entries in the pending list.
 451   static bool pending_list_uses_discovered_field() {
 452     return _pending_list_uses_discovered_field;
 453   }
 454 
 455   // whether discovery is done by multiple threads same-old-timeously
 456   bool discovery_is_mt() const { return _discovery_is_mt; }
 457   void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
 458 
 459   // Whether we are in a phase when _processing_ is MT.
 460   bool processing_is_mt() const { return _processing_is_mt; }
 461   void set_mt_processing(bool mt) { _processing_is_mt = mt; }
 462 
 463   // whether all enqueueing of weak references is complete
 464   bool enqueuing_is_done()  { return _enqueuing_is_done; }
 465   void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
 466 
 467   // iterate over oops
 468   void weak_oops_do(OopClosure* f);       // weak roots
 469 
 470   // Balance each of the discovered lists.
 471   void balance_all_queues();
 472   void verify_list(DiscoveredList& ref_list);
 473 
 474   // Discover a Reference object, using appropriate discovery criteria
 475   bool discover_reference(oop obj, ReferenceType rt);
 476 
 477   // Process references found during GC (called by the garbage collector)
 478   ReferenceProcessorStats
 479   process_discovered_references(BoolObjectClosure*           is_alive,
 480                                 OopClosure*                  keep_alive,
 481                                 VoidClosure*                 complete_gc,
 482                                 AbstractRefProcTaskExecutor* task_executor,
 483                                 GCTimer *gc_timer);
 484 
 485   // Enqueue references at end of GC (called by the garbage collector)
 486   bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
 487 
 488   // If a discovery is in process that is being superceded, abandon it: all
 489   // the discovered lists will be empty, and all the objects on them will
 490   // have NULL discovered fields.  Must be called only at a safepoint.
 491   void abandon_partial_discovery();
 492 
 493   // debugging
 494   void verify_no_references_recorded() PRODUCT_RETURN;
 495   void verify_referent(oop obj)        PRODUCT_RETURN;
 496 
 497   // clear the discovered lists (unlinking each entry).
 498   void clear_discovered_references() PRODUCT_RETURN;
 499 };
 500 
 501 // A utility class to disable reference discovery in
 502 // the scope which contains it, for given ReferenceProcessor.
 503 class NoRefDiscovery: StackObj {
 504  private:
 505   ReferenceProcessor* _rp;
 506   bool _was_discovering_refs;
 507  public:
 508   NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
 509     _was_discovering_refs = _rp->discovery_enabled();
 510     if (_was_discovering_refs) {
 511       _rp->disable_discovery();
 512     }
 513   }
 514 
 515   ~NoRefDiscovery() {
 516     if (_was_discovering_refs) {
 517       _rp->enable_discovery(true /*verify_disabled*/, false /*check_no_refs*/);
 518     }
 519   }
 520 };
 521 
 522 
 523 // A utility class to temporarily mutate the span of the
 524 // given ReferenceProcessor in the scope that contains it.
 525 class ReferenceProcessorSpanMutator: StackObj {
 526  private:
 527   ReferenceProcessor* _rp;
 528   MemRegion           _saved_span;
 529 
 530  public:
 531   ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
 532                                 MemRegion span):
 533     _rp(rp) {
 534     _saved_span = _rp->span();
 535     _rp->set_span(span);
 536   }
 537 
 538   ~ReferenceProcessorSpanMutator() {
 539     _rp->set_span(_saved_span);
 540   }
 541 };
 542 
 543 // A utility class to temporarily change the MT'ness of
 544 // reference discovery for the given ReferenceProcessor
 545 // in the scope that contains it.
 546 class ReferenceProcessorMTDiscoveryMutator: StackObj {
 547  private:
 548   ReferenceProcessor* _rp;
 549   bool                _saved_mt;
 550 
 551  public:
 552   ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
 553                                        bool mt):
 554     _rp(rp) {
 555     _saved_mt = _rp->discovery_is_mt();
 556     _rp->set_mt_discovery(mt);
 557   }
 558 
 559   ~ReferenceProcessorMTDiscoveryMutator() {
 560     _rp->set_mt_discovery(_saved_mt);
 561   }
 562 };
 563 
 564 
 565 // A utility class to temporarily change the disposition
 566 // of the "is_alive_non_header" closure field of the
 567 // given ReferenceProcessor in the scope that contains it.
 568 class ReferenceProcessorIsAliveMutator: StackObj {
 569  private:
 570   ReferenceProcessor* _rp;
 571   BoolObjectClosure*  _saved_cl;
 572 
 573  public:
 574   ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
 575                                    BoolObjectClosure*  cl):
 576     _rp(rp) {
 577     _saved_cl = _rp->is_alive_non_header();
 578     _rp->set_is_alive_non_header(cl);
 579   }
 580 
 581   ~ReferenceProcessorIsAliveMutator() {
 582     _rp->set_is_alive_non_header(_saved_cl);
 583   }
 584 };
 585 
 586 // A utility class to temporarily change the disposition
 587 // of the "discovery_is_atomic" field of the
 588 // given ReferenceProcessor in the scope that contains it.
 589 class ReferenceProcessorAtomicMutator: StackObj {
 590  private:
 591   ReferenceProcessor* _rp;
 592   bool                _saved_atomic_discovery;
 593 
 594  public:
 595   ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
 596                                   bool atomic):
 597     _rp(rp) {
 598     _saved_atomic_discovery = _rp->discovery_is_atomic();
 599     _rp->set_atomic_discovery(atomic);
 600   }
 601 
 602   ~ReferenceProcessorAtomicMutator() {
 603     _rp->set_atomic_discovery(_saved_atomic_discovery);
 604   }
 605 };
 606 
 607 
 608 // A utility class to temporarily change the MT processing
 609 // disposition of the given ReferenceProcessor instance
 610 // in the scope that contains it.
 611 class ReferenceProcessorMTProcMutator: StackObj {
 612  private:
 613   ReferenceProcessor* _rp;
 614   bool  _saved_mt;
 615 
 616  public:
 617   ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
 618                                   bool mt):
 619     _rp(rp) {
 620     _saved_mt = _rp->processing_is_mt();
 621     _rp->set_mt_processing(mt);
 622   }
 623 
 624   ~ReferenceProcessorMTProcMutator() {
 625     _rp->set_mt_processing(_saved_mt);
 626   }
 627 };
 628 
 629 
 630 // This class is an interface used to implement task execution for the
 631 // reference processing.
 632 class AbstractRefProcTaskExecutor {
 633 public:
 634 
 635   // Abstract tasks to execute.
 636   class ProcessTask;
 637   class EnqueueTask;
 638 
 639   // Executes a task using worker threads.
 640   virtual void execute(ProcessTask& task) = 0;
 641   virtual void execute(EnqueueTask& task) = 0;
 642 
 643   // Switch to single threaded mode.
 644   virtual void set_single_threaded_mode() { };
 645 };
 646 
 647 // Abstract reference processing task to execute.
 648 class AbstractRefProcTaskExecutor::ProcessTask {
 649 protected:
 650   ProcessTask(ReferenceProcessor& ref_processor,
 651               DiscoveredList      refs_lists[],
 652               bool                marks_oops_alive)
 653     : _ref_processor(ref_processor),
 654       _refs_lists(refs_lists),
 655       _marks_oops_alive(marks_oops_alive)
 656   { }
 657 
 658 public:
 659   virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
 660                     OopClosure& keep_alive,
 661                     VoidClosure& complete_gc) = 0;
 662 
 663   // Returns true if a task marks some oops as alive.
 664   bool marks_oops_alive() const
 665   { return _marks_oops_alive; }
 666 
 667 protected:
 668   ReferenceProcessor& _ref_processor;
 669   DiscoveredList*     _refs_lists;
 670   const bool          _marks_oops_alive;
 671 };
 672 
 673 // Abstract reference processing task to execute.
 674 class AbstractRefProcTaskExecutor::EnqueueTask {
 675 protected:
 676   EnqueueTask(ReferenceProcessor& ref_processor,
 677               DiscoveredList      refs_lists[],
 678               HeapWord*           pending_list_addr,
 679               int                 n_queues)
 680     : _ref_processor(ref_processor),
 681       _refs_lists(refs_lists),
 682       _pending_list_addr(pending_list_addr),
 683       _n_queues(n_queues)
 684   { }
 685 
 686 public:
 687   virtual void work(unsigned int work_id) = 0;
 688 
 689 protected:
 690   ReferenceProcessor& _ref_processor;
 691   DiscoveredList*     _refs_lists;
 692   HeapWord*           _pending_list_addr;
 693   int                 _n_queues;
 694 };
 695 
 696 #endif // SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP