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




 670 
 671 protected:
 672   ReferenceProcessor& _ref_processor;
 673   DiscoveredList*     _refs_lists;
 674   const bool          _marks_oops_alive;
 675 };
 676 
 677 // Abstract reference processing task to execute.
 678 class AbstractRefProcTaskExecutor::EnqueueTask {
 679 protected:
 680   EnqueueTask(ReferenceProcessor& ref_processor,
 681               DiscoveredList      refs_lists[],
 682               HeapWord*           pending_list_addr,
 683               int                 n_queues)
 684     : _ref_processor(ref_processor),
 685       _refs_lists(refs_lists),
 686       _pending_list_addr(pending_list_addr),
 687       _n_queues(n_queues)
 688   { }
 689 
 690 public:
 691   virtual void work(unsigned int work_id) = 0;
 692 
 693 protected:
 694   ReferenceProcessor& _ref_processor;
 695   DiscoveredList*     _refs_lists;
 696   HeapWord*           _pending_list_addr;
 697   int                 _n_queues;
 698 };
 699 
 700 #endif // SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP
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