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_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/referenceProcessorStats.hpp"
  31 #include "memory/referenceType.hpp"
  32 #include "oops/instanceRefKlass.hpp"
  33 
  34 class AbstractRefProcTaskExecutor;
  35 class GCTimer;
  36 class ReferencePolicy;
  37 class ReferenceProcessorPhaseTimes;
  38 
  39 // List of discovered references.
  40 class DiscoveredList {
  41 public:
  42   DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
  43   inline oop head() const;
  44   HeapWord* adr_head() {
  45     return UseCompressedOops ? (HeapWord*)&_compressed_head :
  46                                (HeapWord*)&_oop_head;
  47   }
  48   inline void set_head(oop o);
  49   inline bool is_empty() const;
  50   size_t length()               { return _len; }
  51   void   set_length(size_t len) { _len = len;  }
  52   void   inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
  53   void   dec_length(size_t dec) { _len -= dec; }
  54 
  55   inline void clear();
  56 private:
  57   // Set value depending on UseCompressedOops. This could be a template class
  58   // but then we have to fix all the instantiations and declarations that use this class.
  59   oop       _oop_head;
  60   narrowOop _compressed_head;
  61   size_t _len;
  62 };
  63 
  64 // Iterator for the list of discovered references.
  65 class DiscoveredListIterator {
  66 private:
  67   DiscoveredList&    _refs_list;
  68   HeapWord*          _prev_discovered_addr;
  69   oop                _prev_discovered;
  70   oop                _current_discovered;
  71   HeapWord*          _current_discovered_addr;
  72   oop                _next_discovered;
  73 
  74   HeapWord*          _referent_addr;
  75   oop                _referent;
  76 
  77   OopClosure*        _keep_alive;
  78   BoolObjectClosure* _is_alive;
  79 
  80   DEBUG_ONLY(
  81   oop                _first_seen; // cyclic linked list check
  82   )
  83 
  84   size_t             _processed;
  85   size_t             _removed;
  86 
  87 public:
  88   inline DiscoveredListIterator(DiscoveredList&    refs_list,
  89                                 OopClosure*        keep_alive,
  90                                 BoolObjectClosure* is_alive);
  91 
  92   // End Of List.
  93   inline bool has_next() const { return _current_discovered != NULL; }
  94 
  95   // Get oop to the Reference object.
  96   inline oop obj() const { return _current_discovered; }
  97 
  98   // Get oop to the referent object.
  99   inline oop referent() const { return _referent; }
 100 
 101   // Returns true if referent is alive.
 102   inline bool is_referent_alive() const {
 103     return _is_alive->do_object_b(_referent);
 104   }
 105 
 106   // Loads data for the current reference.
 107   // The "allow_null_referent" argument tells us to allow for the possibility
 108   // of a NULL referent in the discovered Reference object. This typically
 109   // happens in the case of concurrent collectors that may have done the
 110   // discovery concurrently, or interleaved, with mutator execution.
 111   void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
 112 
 113   // Move to the next discovered reference.
 114   inline void next() {
 115     _prev_discovered_addr = _current_discovered_addr;
 116     _prev_discovered = _current_discovered;
 117     move_to_next();
 118   }
 119 
 120   // Remove the current reference from the list
 121   void remove();
 122 
 123   // Make the referent alive.
 124   inline void make_referent_alive() {
 125     if (UseCompressedOops) {
 126       _keep_alive->do_oop((narrowOop*)_referent_addr);
 127     } else {
 128       _keep_alive->do_oop((oop*)_referent_addr);
 129     }
 130   }
 131 
 132   // Do enqueuing work, i.e. notifying the GC about the changed discovered pointers.
 133   void enqueue();
 134 
 135   // Move enqueued references to the reference pending list.
 136   void complete_enqueue();
 137 
 138   // NULL out referent pointer.
 139   void clear_referent();
 140 
 141   // Statistics
 142   inline size_t processed() const { return _processed; }
 143   inline size_t removed() const { return _removed; }
 144 
 145   inline void move_to_next() {
 146     if (oopDesc::unsafe_equals(_current_discovered, _next_discovered)) {
 147       // End of the list.
 148       _current_discovered = NULL;
 149     } else {
 150       _current_discovered = _next_discovered;
 151     }
 152     assert(! oopDesc::unsafe_equals(_current_discovered, _first_seen), "cyclic ref_list found");
 153     _processed++;
 154   }
 155 };
 156 
 157 // The ReferenceProcessor class encapsulates the per-"collector" processing
 158 // of java.lang.Reference objects for GC. The interface is useful for supporting
 159 // a generational abstraction, in particular when there are multiple
 160 // generations that are being independently collected -- possibly
 161 // concurrently and/or incrementally.
 162 // ReferenceProcessor class abstracts away from a generational setting
 163 // by using a closure that determines whether a given reference or referent are
 164 // subject to this ReferenceProcessor's discovery, thus allowing its use in a
 165 // straightforward manner in a general, non-generational, non-contiguous generation
 166 // (or heap) setting.
 167 class ReferenceProcessor : public ReferenceDiscoverer {
 168   friend class RefProcPhase1Task;
 169   friend class RefProcPhase2Task;
 170   friend class RefProcPhase3Task;
 171   friend class RefProcPhase4Task;
 172 public:
 173   // Names of sub-phases of reference processing. Indicates the type of the reference
 174   // processed and the associated phase number at the end.
 175   enum RefProcSubPhases {
 176     SoftRefSubPhase1,
 177     SoftRefSubPhase2,
 178     WeakRefSubPhase2,
 179     FinalRefSubPhase2,
 180     FinalRefSubPhase3,
 181     PhantomRefSubPhase4,
 182     RefSubPhaseMax
 183   };
 184 
 185   // Main phases of reference processing.
 186   enum RefProcPhases {
 187     RefPhase1,
 188     RefPhase2,
 189     RefPhase3,
 190     RefPhase4,
 191     RefPhaseMax
 192   };
 193 
 194 private:
 195   size_t total_count(DiscoveredList lists[]) const;
 196   void verify_total_count_zero(DiscoveredList lists[], const char* type) NOT_DEBUG_RETURN;
 197 
 198   // The SoftReference master timestamp clock
 199   static jlong _soft_ref_timestamp_clock;
 200 
 201   BoolObjectClosure* _is_subject_to_discovery; // determines whether a given oop is subject
 202                                                // to this ReferenceProcessor's discovery
 203                                                // (and further processing).
 204 
 205   bool        _discovering_refs;        // true when discovery enabled
 206   bool        _discovery_is_atomic;     // if discovery is atomic wrt
 207                                         // other collectors in configuration
 208   bool        _discovery_is_mt;         // true if reference discovery is MT.
 209 
 210   bool        _enqueuing_is_done;       // true if all weak references enqueued
 211   bool        _processing_is_mt;        // true during phases when
 212                                         // reference processing is MT.
 213   uint        _next_id;                 // round-robin mod _num_queues counter in
 214                                         // support of work distribution
 215 
 216   bool        _adjust_no_of_processing_threads; // allow dynamic adjustment of processing threads
 217   // For collectors that do not keep GC liveness information
 218   // in the object header, this field holds a closure that
 219   // helps the reference processor determine the reachability
 220   // of an oop. It is currently initialized to NULL for all
 221   // collectors except for CMS and G1.
 222   BoolObjectClosure* _is_alive_non_header;
 223 
 224   // Soft ref clearing policies
 225   // . the default policy
 226   static ReferencePolicy*   _default_soft_ref_policy;
 227   // . the "clear all" policy
 228   static ReferencePolicy*   _always_clear_soft_ref_policy;
 229   // . the current policy below is either one of the above
 230   ReferencePolicy*          _current_soft_ref_policy;
 231 
 232   // The discovered ref lists themselves
 233 
 234   // The active MT'ness degree of the queues below
 235   uint            _num_queues;
 236   // The maximum MT'ness degree of the queues below
 237   uint            _max_num_queues;
 238 
 239   // Master array of discovered oops
 240   DiscoveredList* _discovered_refs;
 241 
 242   // Arrays of lists of oops, one per thread (pointers into master array above)
 243   DiscoveredList* _discoveredSoftRefs;
 244   DiscoveredList* _discoveredWeakRefs;
 245   DiscoveredList* _discoveredFinalRefs;
 246   DiscoveredList* _discoveredPhantomRefs;
 247 
 248   // Phase 1: Re-evaluate soft ref policy.
 249   void process_soft_ref_reconsider(BoolObjectClosure* is_alive,
 250                                    OopClosure* keep_alive,
 251                                    VoidClosure* complete_gc,
 252                                    AbstractRefProcTaskExecutor*  task_executor,
 253                                    ReferenceProcessorPhaseTimes* phase_times);
 254 
 255   // Phase 2: Drop Soft/Weak/Final references with a NULL or live referent, and clear
 256   // and enqueue non-Final references.
 257   void process_soft_weak_final_refs(BoolObjectClosure* is_alive,
 258                                     OopClosure* keep_alive,
 259                                     VoidClosure* complete_gc,
 260                                     AbstractRefProcTaskExecutor*  task_executor,
 261                                     ReferenceProcessorPhaseTimes* phase_times);
 262 
 263   // Phase 3: Keep alive followers of Final references, and enqueue.
 264   void process_final_keep_alive(OopClosure* keep_alive,
 265                                 VoidClosure* complete_gc,
 266                                 AbstractRefProcTaskExecutor*  task_executor,
 267                                 ReferenceProcessorPhaseTimes* phase_times);
 268 
 269   // Phase 4: Drop and keep alive live Phantom references, or clear and enqueue if dead.
 270   void process_phantom_refs(BoolObjectClosure* is_alive,
 271                             OopClosure* keep_alive,
 272                             VoidClosure* complete_gc,
 273                             AbstractRefProcTaskExecutor*  task_executor,
 274                             ReferenceProcessorPhaseTimes* phase_times);
 275 
 276   // Work methods used by the process_* methods. All methods return the number of
 277   // removed elements.
 278 
 279   // (SoftReferences only) Traverse the list and remove any SoftReferences whose
 280   // referents are not alive, but that should be kept alive for policy reasons.
 281   // Keep alive the transitive closure of all such referents.
 282   size_t process_soft_ref_reconsider_work(DiscoveredList&     refs_list,
 283                                           ReferencePolicy*    policy,
 284                                           BoolObjectClosure*  is_alive,
 285                                           OopClosure*         keep_alive,
 286                                           VoidClosure*        complete_gc);
 287 
 288   // Traverse the list and remove any Refs whose referents are alive,
 289   // or NULL if discovery is not atomic. Enqueue and clear the reference for
 290   // others if do_enqueue_and_clear is set.
 291   size_t process_soft_weak_final_refs_work(DiscoveredList&    refs_list,
 292                                            BoolObjectClosure* is_alive,
 293                                            OopClosure*        keep_alive,
 294                                            bool               do_enqueue_and_clear);
 295 
 296   // Keep alive followers of referents for FinalReferences. Must only be called for
 297   // those.
 298   size_t process_final_keep_alive_work(DiscoveredList&    refs_list,
 299                                        OopClosure*        keep_alive,
 300                                        VoidClosure*       complete_gc);
 301 
 302   size_t process_phantom_refs_work(DiscoveredList&    refs_list,
 303                                    BoolObjectClosure* is_alive,
 304                                    OopClosure*        keep_alive,
 305                                    VoidClosure*       complete_gc);
 306 
 307 public:
 308   static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); }
 309 
 310   uint num_queues() const                  { return _num_queues; }
 311   uint max_num_queues() const              { return _max_num_queues; }
 312   void set_active_mt_degree(uint v);
 313 
 314   ReferencePolicy* setup_policy(bool always_clear) {
 315     _current_soft_ref_policy = always_clear ?
 316       _always_clear_soft_ref_policy : _default_soft_ref_policy;
 317     _current_soft_ref_policy->setup();   // snapshot the policy threshold
 318     return _current_soft_ref_policy;
 319   }
 320 
 321   // "Preclean" all the discovered reference lists by removing references that
 322   // are active (e.g. due to the mutator calling enqueue()) or with NULL or
 323   // strongly reachable referents.
 324   // The first argument is a predicate on an oop that indicates
 325   // its (strong) reachability and the fourth is a closure that
 326   // may be used to incrementalize or abort the precleaning process.
 327   // The caller is responsible for taking care of potential
 328   // interference with concurrent operations on these lists
 329   // (or predicates involved) by other threads.
 330   void preclean_discovered_references(BoolObjectClosure* is_alive,
 331                                       OopClosure*        keep_alive,
 332                                       VoidClosure*       complete_gc,
 333                                       YieldClosure*      yield,
 334                                       GCTimer*           gc_timer);
 335 
 336 private:
 337   // Returns the name of the discovered reference list
 338   // occupying the i / _num_queues slot.
 339   const char* list_name(uint i);
 340 
 341   // "Preclean" the given discovered reference list by removing references with
 342   // the attributes mentioned in preclean_discovered_references().
 343   // Supports both normal and fine grain yielding.
 344   // Returns whether the operation should be aborted.
 345   bool preclean_discovered_reflist(DiscoveredList&    refs_list,
 346                                    BoolObjectClosure* is_alive,
 347                                    OopClosure*        keep_alive,
 348                                    VoidClosure*       complete_gc,
 349                                    YieldClosure*      yield);
 350 
 351   // round-robin mod _num_queues (not: _not_ mod _max_num_queues)
 352   uint next_id() {
 353     uint id = _next_id;
 354     assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
 355     if (++_next_id == _num_queues) {
 356       _next_id = 0;
 357     }
 358     assert(_next_id < _num_queues, "_next_id %u _num_queues %u _max_num_queues %u", _next_id, _num_queues, _max_num_queues);
 359     return id;
 360   }
 361   DiscoveredList* get_discovered_list(ReferenceType rt);
 362   inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
 363                                         HeapWord* discovered_addr);
 364 
 365   void clear_discovered_references(DiscoveredList& refs_list);
 366 
 367   void log_reflist(const char* prefix, DiscoveredList list[], uint num_active_queues);
 368   void log_reflist_counts(DiscoveredList ref_lists[], uint num_active_queues) PRODUCT_RETURN;
 369 
 370   // Balances reference queues.
 371   void balance_queues(DiscoveredList refs_lists[]);
 372   bool need_balance_queues(DiscoveredList refs_lists[]);
 373 
 374   // If there is need to balance the given queue, do it.
 375   void maybe_balance_queues(DiscoveredList refs_lists[]);
 376 
 377   // Update (advance) the soft ref master clock field.
 378   void update_soft_ref_master_clock();
 379 
 380   bool is_subject_to_discovery(oop const obj) const;
 381 
 382   bool is_mt_processing_set_up(AbstractRefProcTaskExecutor* task_executor) const;
 383 
 384 public:
 385   // Default parameters give you a vanilla reference processor.
 386   ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery,
 387                      bool mt_processing = false, uint mt_processing_degree = 1,
 388                      bool mt_discovery  = false, uint mt_discovery_degree  = 1,
 389                      bool atomic_discovery = true,
 390                      BoolObjectClosure* is_alive_non_header = NULL,
 391                      bool adjust_no_of_processing_threads = false);
 392 
 393   // RefDiscoveryPolicy values
 394   enum DiscoveryPolicy {
 395     ReferenceBasedDiscovery = 0,
 396     ReferentBasedDiscovery  = 1,
 397     DiscoveryPolicyMin      = ReferenceBasedDiscovery,
 398     DiscoveryPolicyMax      = ReferentBasedDiscovery
 399   };
 400 
 401   static void init_statics();
 402 
 403   // get and set "is_alive_non_header" field
 404   BoolObjectClosure* is_alive_non_header() {
 405     return _is_alive_non_header;
 406   }
 407   void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
 408     _is_alive_non_header = is_alive_non_header;
 409   }
 410 
 411   BoolObjectClosure* is_subject_to_discovery_closure() const { return _is_subject_to_discovery; }
 412   void set_is_subject_to_discovery_closure(BoolObjectClosure* cl) { _is_subject_to_discovery = cl; }
 413 
 414   // start and stop weak ref discovery
 415   void enable_discovery(bool check_no_refs = true);
 416   void disable_discovery()  { _discovering_refs = false; }
 417   bool discovery_enabled()  { return _discovering_refs;  }
 418 
 419   // whether discovery is atomic wrt other collectors
 420   bool discovery_is_atomic() const { return _discovery_is_atomic; }
 421   void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
 422 
 423   // whether discovery is done by multiple threads same-old-timeously
 424   bool discovery_is_mt() const { return _discovery_is_mt; }
 425   void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
 426 
 427   // Whether we are in a phase when _processing_ is MT.
 428   bool processing_is_mt() const { return _processing_is_mt; }
 429   void set_mt_processing(bool mt) { _processing_is_mt = mt; }
 430 
 431   // whether all enqueueing of weak references is complete
 432   bool enqueuing_is_done()  { return _enqueuing_is_done; }
 433   void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
 434 
 435   // iterate over oops
 436   void weak_oops_do(OopClosure* f);       // weak roots
 437 
 438   void verify_list(DiscoveredList& ref_list);
 439 
 440   // Discover a Reference object, using appropriate discovery criteria
 441   virtual bool discover_reference(oop obj, ReferenceType rt);
 442 
 443   // Has discovered references that need handling
 444   bool has_discovered_references();
 445 
 446   // Process references found during GC (called by the garbage collector)
 447   ReferenceProcessorStats
 448   process_discovered_references(BoolObjectClosure*            is_alive,
 449                                 OopClosure*                   keep_alive,
 450                                 VoidClosure*                  complete_gc,
 451                                 AbstractRefProcTaskExecutor*  task_executor,
 452                                 ReferenceProcessorPhaseTimes* phase_times);
 453 
 454   // If a discovery is in process that is being superceded, abandon it: all
 455   // the discovered lists will be empty, and all the objects on them will
 456   // have NULL discovered fields.  Must be called only at a safepoint.
 457   void abandon_partial_discovery();
 458 
 459   size_t total_reference_count(ReferenceType rt) const;
 460 
 461   // debugging
 462   void verify_no_references_recorded() PRODUCT_RETURN;
 463   void verify_referent(oop obj)        PRODUCT_RETURN;
 464 
 465   bool adjust_no_of_processing_threads() const { return _adjust_no_of_processing_threads; }
 466 };
 467 
 468 // A subject-to-discovery closure that uses a single memory span to determine the area that
 469 // is subject to discovery. Useful for collectors which have contiguous generations.
 470 class SpanSubjectToDiscoveryClosure : public BoolObjectClosure {
 471   MemRegion _span;
 472 
 473 public:
 474   SpanSubjectToDiscoveryClosure() : BoolObjectClosure(), _span() { }
 475   SpanSubjectToDiscoveryClosure(MemRegion span) : BoolObjectClosure(), _span(span) { }
 476 
 477   MemRegion span() const { return _span; }
 478 
 479   void set_span(MemRegion mr) {
 480     _span = mr;
 481   }
 482 
 483   virtual bool do_object_b(oop obj) {
 484     return _span.contains(obj);
 485   }
 486 };
 487 
 488 // A utility class to disable reference discovery in
 489 // the scope which contains it, for given ReferenceProcessor.
 490 class NoRefDiscovery: StackObj {
 491  private:
 492   ReferenceProcessor* _rp;
 493   bool _was_discovering_refs;
 494  public:
 495   NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
 496     _was_discovering_refs = _rp->discovery_enabled();
 497     if (_was_discovering_refs) {
 498       _rp->disable_discovery();
 499     }
 500   }
 501 
 502   ~NoRefDiscovery() {
 503     if (_was_discovering_refs) {
 504       _rp->enable_discovery(false /*check_no_refs*/);
 505     }
 506   }
 507 };
 508 
 509 // A utility class to temporarily mutate the subject discovery closure of the
 510 // given ReferenceProcessor in the scope that contains it.
 511 class ReferenceProcessorSubjectToDiscoveryMutator : StackObj {
 512   ReferenceProcessor* _rp;
 513   BoolObjectClosure* _saved_cl;
 514 
 515 public:
 516   ReferenceProcessorSubjectToDiscoveryMutator(ReferenceProcessor* rp, BoolObjectClosure* cl):
 517     _rp(rp) {
 518     _saved_cl = _rp->is_subject_to_discovery_closure();
 519     _rp->set_is_subject_to_discovery_closure(cl);
 520   }
 521 
 522   ~ReferenceProcessorSubjectToDiscoveryMutator() {
 523     _rp->set_is_subject_to_discovery_closure(_saved_cl);
 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   ReferenceProcessor* _rp;
 531   SpanSubjectToDiscoveryClosure _discoverer;
 532   BoolObjectClosure* _old_discoverer;
 533 
 534 public:
 535   ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
 536                                 MemRegion span):
 537     _rp(rp),
 538     _discoverer(span),
 539     _old_discoverer(rp->is_subject_to_discovery_closure()) {
 540 
 541     rp->set_is_subject_to_discovery_closure(&_discoverer);
 542   }
 543 
 544   ~ReferenceProcessorSpanMutator() {
 545     _rp->set_is_subject_to_discovery_closure(_old_discoverer);
 546   }
 547 };
 548 
 549 // A utility class to temporarily change the MT'ness of
 550 // reference discovery for the given ReferenceProcessor
 551 // in the scope that contains it.
 552 class ReferenceProcessorMTDiscoveryMutator: StackObj {
 553  private:
 554   ReferenceProcessor* _rp;
 555   bool                _saved_mt;
 556 
 557  public:
 558   ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
 559                                        bool mt):
 560     _rp(rp) {
 561     _saved_mt = _rp->discovery_is_mt();
 562     _rp->set_mt_discovery(mt);
 563   }
 564 
 565   ~ReferenceProcessorMTDiscoveryMutator() {
 566     _rp->set_mt_discovery(_saved_mt);
 567   }
 568 };
 569 
 570 // A utility class to temporarily change the disposition
 571 // of the "is_alive_non_header" closure field of the
 572 // given ReferenceProcessor in the scope that contains it.
 573 class ReferenceProcessorIsAliveMutator: StackObj {
 574  private:
 575   ReferenceProcessor* _rp;
 576   BoolObjectClosure*  _saved_cl;
 577 
 578  public:
 579   ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
 580                                    BoolObjectClosure*  cl):
 581     _rp(rp) {
 582     _saved_cl = _rp->is_alive_non_header();
 583     _rp->set_is_alive_non_header(cl);
 584   }
 585 
 586   ~ReferenceProcessorIsAliveMutator() {
 587     _rp->set_is_alive_non_header(_saved_cl);
 588   }
 589 };
 590 
 591 // A utility class to temporarily change the disposition
 592 // of the "discovery_is_atomic" field of the
 593 // given ReferenceProcessor in the scope that contains it.
 594 class ReferenceProcessorAtomicMutator: StackObj {
 595  private:
 596   ReferenceProcessor* _rp;
 597   bool                _saved_atomic_discovery;
 598 
 599  public:
 600   ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
 601                                   bool atomic):
 602     _rp(rp) {
 603     _saved_atomic_discovery = _rp->discovery_is_atomic();
 604     _rp->set_atomic_discovery(atomic);
 605   }
 606 
 607   ~ReferenceProcessorAtomicMutator() {
 608     _rp->set_atomic_discovery(_saved_atomic_discovery);
 609   }
 610 };
 611 
 612 
 613 // A utility class to temporarily change the MT processing
 614 // disposition of the given ReferenceProcessor instance
 615 // in the scope that contains it.
 616 class ReferenceProcessorMTProcMutator: StackObj {
 617  private:
 618   ReferenceProcessor* _rp;
 619   bool  _saved_mt;
 620 
 621  public:
 622   ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
 623                                   bool mt):
 624     _rp(rp) {
 625     _saved_mt = _rp->processing_is_mt();
 626     _rp->set_mt_processing(mt);
 627   }
 628 
 629   ~ReferenceProcessorMTProcMutator() {
 630     _rp->set_mt_processing(_saved_mt);
 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 
 642   // Executes a task using worker threads.
 643   virtual void execute(ProcessTask& task, uint ergo_workers) = 0;
 644 
 645   // Switch to single threaded mode.
 646   virtual void set_single_threaded_mode() { };
 647 };
 648 
 649 // Abstract reference processing task to execute.
 650 class AbstractRefProcTaskExecutor::ProcessTask {
 651 protected:
 652   ReferenceProcessor&           _ref_processor;
 653   // Indicates whether the phase could generate work that should be balanced across
 654   // threads after execution.
 655   bool                          _marks_oops_alive;
 656   ReferenceProcessorPhaseTimes* _phase_times;
 657 
 658   ProcessTask(ReferenceProcessor& ref_processor,
 659               bool marks_oops_alive,
 660               ReferenceProcessorPhaseTimes* phase_times)
 661     : _ref_processor(ref_processor),
 662       _marks_oops_alive(marks_oops_alive),
 663       _phase_times(phase_times)
 664   { }
 665 
 666 public:
 667   virtual void work(uint worker_id,
 668                     BoolObjectClosure& is_alive,
 669                     OopClosure& keep_alive,
 670                     VoidClosure& complete_gc) = 0;
 671 
 672   bool marks_oops_alive() const { return _marks_oops_alive; }
 673 };
 674 
 675 // Temporarily change the number of workers based on given reference count.
 676 // This ergonomically decided worker count will be used to activate worker threads.
 677 class RefProcMTDegreeAdjuster : public StackObj {
 678   typedef ReferenceProcessor::RefProcPhases RefProcPhases;
 679 
 680   ReferenceProcessor* _rp;
 681   bool                _saved_mt_processing;
 682   uint                _saved_num_queues;
 683 
 684   // Calculate based on total of references.
 685   uint ergo_proc_thread_count(size_t ref_count,
 686                               uint max_threads,
 687                               RefProcPhases phase) const;
 688 
 689   bool use_max_threads(RefProcPhases phase) const;
 690 
 691 public:
 692   RefProcMTDegreeAdjuster(ReferenceProcessor* rp,
 693                           RefProcPhases phase,
 694                           size_t ref_count);
 695   ~RefProcMTDegreeAdjuster();
 696 };
 697 
 698 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP