rev 49944 : imported patch 8201492-properly-implement-non-contiguous-reference-processing
rev 49945 : imported patch 8201492-stefanj-review
rev 49946 : imported patch 8201492-kim-review
rev 49949 : imported patch 8202021-cleanup-referenceprocessor
rev 49950 : imported patch 8202021-stefanj-review
rev 49951 : imported patch 8202017-reference-processor-remove-enqueue
rev 49953 : imported patch 8201491-precleaning
rev 49954 : [mq]: 8201491-kbarrett-review

   1 /*
   2  * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
   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.
   8  *
   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).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  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_enqeue();
 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   // Work methods in support of process_phase2
 266   void pp2_work(DiscoveredList&    refs_list,
 267                 BoolObjectClosure* is_alive,
 268                 OopClosure*        keep_alive);
 269   void pp2_work_concurrent_discovery(
 270                 DiscoveredList&    refs_list,
 271                 BoolObjectClosure* is_alive,
 272                 OopClosure*        keep_alive,
 273                 VoidClosure*       complete_gc);
 274   // Phase3: process the referents by either clearing them
 275   // or keeping them alive (and their closure), and enqueuing them.
 276   void process_phase3(DiscoveredList&    refs_list,
 277                       bool               clear_referent,
 278                       BoolObjectClosure* is_alive,
 279                       OopClosure*        keep_alive,
 280                       VoidClosure*       complete_gc);
 281 
 282   // "Preclean" all the discovered reference lists by removing references that
 283   // are active (e.g. due to the mutator calling enqueue()) or with NULL or
 284   // strongly reachable referents.
 285   // The first argument is a predicate on an oop that indicates
 286   // its (strong) reachability and the fourth is a closure that
 287   // may be used to incrementalize or abort the precleaning process.
 288   // The caller is responsible for taking care of potential
 289   // interference with concurrent operations on these lists
 290   // (or predicates involved) by other threads.

 291   void preclean_discovered_references(BoolObjectClosure* is_alive,
 292                                       OopClosure*        keep_alive,
 293                                       VoidClosure*       complete_gc,
 294                                       YieldClosure*      yield,
 295                                       GCTimer*           gc_timer);
 296 
 297   // Returns the name of the discovered reference list
 298   // occupying the i / _num_queues slot.
 299   const char* list_name(uint i);
 300 
 301 private:
 302   // "Preclean" the given discovered reference list by removing references with
 303   // the attributes mentioned in preclean_discovered_references().
 304   // Supports both normal and fine grain yielding.
 305   // Returns whether the operation should be aborted.
 306   bool preclean_discovered_reflist(DiscoveredList&    refs_list,
 307                                    BoolObjectClosure* is_alive,
 308                                    OopClosure*        keep_alive,
 309                                    VoidClosure*       complete_gc,
 310                                    YieldClosure*      yield);
 311 
 312   // round-robin mod _num_queues (not: _not_ mod _max_num_queues)
 313   uint next_id() {
 314     uint id = _next_id;
 315     assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
 316     if (++_next_id == _num_queues) {
 317       _next_id = 0;
 318     }
 319     assert(_next_id < _num_queues, "_next_id %u _num_queues %u _max_num_queues %u", _next_id, _num_queues, _max_num_queues);
 320     return id;
 321   }
 322   DiscoveredList* get_discovered_list(ReferenceType rt);
 323   inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
 324                                         HeapWord* discovered_addr);
 325 
 326   void clear_discovered_references(DiscoveredList& refs_list);
 327 
 328   void log_reflist(const char* prefix, DiscoveredList list[], uint num_active_queues);
 329   void log_reflist_counts(DiscoveredList ref_lists[], uint num_active_queues) PRODUCT_RETURN;
 330 
 331   // Balances reference queues.
 332   void balance_queues(DiscoveredList ref_lists[]);
 333 
 334   // Update (advance) the soft ref master clock field.
 335   void update_soft_ref_master_clock();
 336 
 337   bool is_subject_to_discovery(oop const obj) const;
 338 
 339 public:
 340   // Default parameters give you a vanilla reference processor.
 341   ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery,
 342                      bool mt_processing = false, uint mt_processing_degree = 1,
 343                      bool mt_discovery  = false, uint mt_discovery_degree  = 1,
 344                      bool atomic_discovery = true,
 345                      BoolObjectClosure* is_alive_non_header = NULL);
 346 
 347   // RefDiscoveryPolicy values
 348   enum DiscoveryPolicy {
 349     ReferenceBasedDiscovery = 0,
 350     ReferentBasedDiscovery  = 1,
 351     DiscoveryPolicyMin      = ReferenceBasedDiscovery,
 352     DiscoveryPolicyMax      = ReferentBasedDiscovery
 353   };
 354 
 355   static void init_statics();
 356 
 357  public:
 358   // get and set "is_alive_non_header" field
 359   BoolObjectClosure* is_alive_non_header() {
 360     return _is_alive_non_header;
 361   }
 362   void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
 363     _is_alive_non_header = is_alive_non_header;
 364   }
 365 
 366   BoolObjectClosure* is_subject_to_discovery_closure() const { return _is_subject_to_discovery; }
 367   void set_is_subject_to_discovery_closure(BoolObjectClosure* cl) { _is_subject_to_discovery = cl; }
 368 
 369   // start and stop weak ref discovery
 370   void enable_discovery(bool check_no_refs = true);
 371   void disable_discovery()  { _discovering_refs = false; }
 372   bool discovery_enabled()  { return _discovering_refs;  }
 373 
 374   // whether discovery is atomic wrt other collectors
 375   bool discovery_is_atomic() const { return _discovery_is_atomic; }
 376   void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
 377 
 378   // whether discovery is done by multiple threads same-old-timeously
 379   bool discovery_is_mt() const { return _discovery_is_mt; }
 380   void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
 381 
 382   // Whether we are in a phase when _processing_ is MT.
 383   bool processing_is_mt() const { return _processing_is_mt; }
 384   void set_mt_processing(bool mt) { _processing_is_mt = mt; }
 385 
 386   // whether all enqueueing of weak references is complete
 387   bool enqueuing_is_done()  { return _enqueuing_is_done; }
 388   void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
 389 
 390   // iterate over oops
 391   void weak_oops_do(OopClosure* f);       // weak roots
 392 
 393   void verify_list(DiscoveredList& ref_list);
 394 
 395   // Discover a Reference object, using appropriate discovery criteria
 396   virtual bool discover_reference(oop obj, ReferenceType rt);
 397 
 398   // Has discovered references that need handling
 399   bool has_discovered_references();
 400 
 401   // Process references found during GC (called by the garbage collector)
 402   ReferenceProcessorStats
 403   process_discovered_references(BoolObjectClosure*            is_alive,
 404                                 OopClosure*                   keep_alive,
 405                                 VoidClosure*                  complete_gc,
 406                                 AbstractRefProcTaskExecutor*  task_executor,
 407                                 ReferenceProcessorPhaseTimes* phase_times);
 408 
 409   // If a discovery is in process that is being superceded, abandon it: all
 410   // the discovered lists will be empty, and all the objects on them will
 411   // have NULL discovered fields.  Must be called only at a safepoint.
 412   void abandon_partial_discovery();
 413 
 414   size_t total_reference_count(ReferenceType rt) const;
 415 
 416   // debugging
 417   void verify_no_references_recorded() PRODUCT_RETURN;
 418   void verify_referent(oop obj)        PRODUCT_RETURN;
 419 };
 420 
 421 // A subject-to-discovery closure that uses a single memory span to determine the area that
 422 // is subject to discovery. Useful for collectors which have contiguous generations.
 423 class SpanSubjectToDiscoveryClosure : public BoolObjectClosure {
 424   MemRegion _span;
 425 
 426 public:
 427   SpanSubjectToDiscoveryClosure() : BoolObjectClosure(), _span() { }
 428   SpanSubjectToDiscoveryClosure(MemRegion span) : BoolObjectClosure(), _span(span) { }
 429 
 430   MemRegion span() const { return _span; }
 431 
 432   void set_span(MemRegion mr) {
 433     _span = mr;
 434   }
 435 
 436   virtual bool do_object_b(oop obj) {
 437     return _span.contains(obj);
 438   }
 439 };
 440 
 441 // A utility class to disable reference discovery in
 442 // the scope which contains it, for given ReferenceProcessor.
 443 class NoRefDiscovery: StackObj {
 444  private:
 445   ReferenceProcessor* _rp;
 446   bool _was_discovering_refs;
 447  public:
 448   NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
 449     _was_discovering_refs = _rp->discovery_enabled();
 450     if (_was_discovering_refs) {
 451       _rp->disable_discovery();
 452     }
 453   }
 454 
 455   ~NoRefDiscovery() {
 456     if (_was_discovering_refs) {
 457       _rp->enable_discovery(false /*check_no_refs*/);
 458     }
 459   }
 460 };
 461 
 462 // A utility class to temporarily mutate the subject discovery closure of the
 463 // given ReferenceProcessor in the scope that contains it.
 464 class ReferenceProcessorSubjectToDiscoveryMutator : StackObj {
 465   ReferenceProcessor* _rp;
 466   BoolObjectClosure* _saved_cl;
 467 
 468 public:
 469   ReferenceProcessorSubjectToDiscoveryMutator(ReferenceProcessor* rp, BoolObjectClosure* cl):
 470     _rp(rp) {
 471     _saved_cl = _rp->is_subject_to_discovery_closure();
 472     _rp->set_is_subject_to_discovery_closure(cl);
 473   }
 474 
 475   ~ReferenceProcessorSubjectToDiscoveryMutator() {
 476     _rp->set_is_subject_to_discovery_closure(_saved_cl);
 477   }
 478 };
 479 
 480 // A utility class to temporarily mutate the span of the
 481 // given ReferenceProcessor in the scope that contains it.
 482 class ReferenceProcessorSpanMutator : StackObj {
 483   ReferenceProcessor* _rp;
 484   SpanSubjectToDiscoveryClosure _discoverer;
 485   BoolObjectClosure* _old_discoverer;
 486 
 487 public:
 488   ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
 489                                 MemRegion span):
 490     _rp(rp),
 491     _discoverer(span),
 492     _old_discoverer(rp->is_subject_to_discovery_closure()) {
 493 
 494     rp->set_is_subject_to_discovery_closure(&_discoverer);
 495   }
 496 
 497   ~ReferenceProcessorSpanMutator() {
 498     _rp->set_is_subject_to_discovery_closure(_old_discoverer);
 499   }
 500 };
 501 
 502 // A utility class to temporarily change the MT'ness of
 503 // reference discovery for the given ReferenceProcessor
 504 // in the scope that contains it.
 505 class ReferenceProcessorMTDiscoveryMutator: StackObj {
 506  private:
 507   ReferenceProcessor* _rp;
 508   bool                _saved_mt;
 509 
 510  public:
 511   ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
 512                                        bool mt):
 513     _rp(rp) {
 514     _saved_mt = _rp->discovery_is_mt();
 515     _rp->set_mt_discovery(mt);
 516   }
 517 
 518   ~ReferenceProcessorMTDiscoveryMutator() {
 519     _rp->set_mt_discovery(_saved_mt);
 520   }
 521 };
 522 
 523 // A utility class to temporarily change the disposition
 524 // of the "is_alive_non_header" closure field of the
 525 // given ReferenceProcessor in the scope that contains it.
 526 class ReferenceProcessorIsAliveMutator: StackObj {
 527  private:
 528   ReferenceProcessor* _rp;
 529   BoolObjectClosure*  _saved_cl;
 530 
 531  public:
 532   ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
 533                                    BoolObjectClosure*  cl):
 534     _rp(rp) {
 535     _saved_cl = _rp->is_alive_non_header();
 536     _rp->set_is_alive_non_header(cl);
 537   }
 538 
 539   ~ReferenceProcessorIsAliveMutator() {
 540     _rp->set_is_alive_non_header(_saved_cl);
 541   }
 542 };
 543 
 544 // A utility class to temporarily change the disposition
 545 // of the "discovery_is_atomic" field of the
 546 // given ReferenceProcessor in the scope that contains it.
 547 class ReferenceProcessorAtomicMutator: StackObj {
 548  private:
 549   ReferenceProcessor* _rp;
 550   bool                _saved_atomic_discovery;
 551 
 552  public:
 553   ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
 554                                   bool atomic):
 555     _rp(rp) {
 556     _saved_atomic_discovery = _rp->discovery_is_atomic();
 557     _rp->set_atomic_discovery(atomic);
 558   }
 559 
 560   ~ReferenceProcessorAtomicMutator() {
 561     _rp->set_atomic_discovery(_saved_atomic_discovery);
 562   }
 563 };
 564 
 565 
 566 // A utility class to temporarily change the MT processing
 567 // disposition of the given ReferenceProcessor instance
 568 // in the scope that contains it.
 569 class ReferenceProcessorMTProcMutator: StackObj {
 570  private:
 571   ReferenceProcessor* _rp;
 572   bool  _saved_mt;
 573 
 574  public:
 575   ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
 576                                   bool mt):
 577     _rp(rp) {
 578     _saved_mt = _rp->processing_is_mt();
 579     _rp->set_mt_processing(mt);
 580   }
 581 
 582   ~ReferenceProcessorMTProcMutator() {
 583     _rp->set_mt_processing(_saved_mt);
 584   }
 585 };
 586 
 587 
 588 // This class is an interface used to implement task execution for the
 589 // reference processing.
 590 class AbstractRefProcTaskExecutor {
 591 public:
 592 
 593   // Abstract tasks to execute.
 594   class ProcessTask;
 595   class EnqueueTask;
 596 
 597   // Executes a task using worker threads.
 598   virtual void execute(ProcessTask& task) = 0;
 599   virtual void execute(EnqueueTask& task) = 0;
 600 
 601   // Switch to single threaded mode.
 602   virtual void set_single_threaded_mode() { };
 603 };
 604 
 605 // Abstract reference processing task to execute.
 606 class AbstractRefProcTaskExecutor::ProcessTask {
 607 protected:
 608   ProcessTask(ReferenceProcessor&           ref_processor,
 609               DiscoveredList                refs_lists[],
 610               bool                          marks_oops_alive,
 611               ReferenceProcessorPhaseTimes* phase_times)
 612     : _ref_processor(ref_processor),
 613       _refs_lists(refs_lists),
 614       _phase_times(phase_times),
 615       _marks_oops_alive(marks_oops_alive)
 616   { }
 617 
 618 public:
 619   virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
 620                     OopClosure& keep_alive,
 621                     VoidClosure& complete_gc) = 0;
 622 
 623   // Returns true if a task marks some oops as alive.
 624   bool marks_oops_alive() const
 625   { return _marks_oops_alive; }
 626 
 627 protected:
 628   ReferenceProcessor&           _ref_processor;
 629   DiscoveredList*               _refs_lists;
 630   ReferenceProcessorPhaseTimes* _phase_times;
 631   const bool                    _marks_oops_alive;
 632 };
 633 
 634 // Abstract reference processing task to execute.
 635 class AbstractRefProcTaskExecutor::EnqueueTask {
 636 protected:
 637   EnqueueTask(ReferenceProcessor&           ref_processor,
 638               DiscoveredList                refs_lists[],
 639               int                           n_queues,
 640               ReferenceProcessorPhaseTimes* phase_times)
 641     : _ref_processor(ref_processor),
 642       _refs_lists(refs_lists),
 643       _n_queues(n_queues),
 644       _phase_times(phase_times)
 645   { }
 646 
 647 public:
 648   virtual void work(unsigned int work_id) = 0;
 649 
 650 protected:
 651   ReferenceProcessor&           _ref_processor;
 652   DiscoveredList*               _refs_lists;
 653   ReferenceProcessorPhaseTimes* _phase_times;
 654   int                           _n_queues;
 655 };
 656 
 657 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP
--- EOF ---