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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  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
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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 "oops/instanceRefKlass.hpp"
  30 
  31 // ReferenceProcessor class encapsulates the per-"collector" processing
  32 // of java.lang.Reference objects for GC. The interface is useful for supporting
  33 // a generational abstraction, in particular when there are multiple
  34 // generations that are being independently collected -- possibly
  35 // concurrently and/or incrementally.  Note, however, that the
  36 // ReferenceProcessor class abstracts away from a generational setting
  37 // by using only a heap interval (called "span" below), thus allowing
  38 // its use in a straightforward manner in a general, non-generational
  39 // setting.
  40 //
  41 // The basic idea is that each ReferenceProcessor object concerns
  42 // itself with ("weak") reference processing in a specific "span"
  43 // of the heap of interest to a specific collector. Currently,
  44 // the span is a convex interval of the heap, but, efficiency
  45 // apart, there seems to be no reason it couldn't be extended
  46 // (with appropriate modifications) to any "non-convex interval".
  47 
  48 // forward references
  49 class ReferencePolicy;
  50 class AbstractRefProcTaskExecutor;
  51 
  52 // List of discovered references.
  53 class DiscoveredList {
  54 public:
  55   DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
  56   oop head() const     {
  57      return UseCompressedOops ?  oopDesc::decode_heap_oop(_compressed_head) :
  58                                 _oop_head;
  59   }
  60   HeapWord* adr_head() {
  61     return UseCompressedOops ? (HeapWord*)&_compressed_head :
  62                                (HeapWord*)&_oop_head;
  63   }
  64   void set_head(oop o) {
  65     if (UseCompressedOops) {
  66       // Must compress the head ptr.
  67       _compressed_head = oopDesc::encode_heap_oop(o);
  68     } else {
  69       _oop_head = o;
  70     }
  71   }
  72   bool   is_empty() const       { return head() == NULL; }
  73   size_t length()               { return _len; }
  74   void   set_length(size_t len) { _len = len;  }
  75   void   inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
  76   void   dec_length(size_t dec) { _len -= dec; }
  77 private:
  78   // Set value depending on UseCompressedOops. This could be a template class
  79   // but then we have to fix all the instantiations and declarations that use this class.
  80   oop       _oop_head;
  81   narrowOop _compressed_head;
  82   size_t _len;
  83 };
  84 
  85 // Iterator for the list of discovered references.
  86 class DiscoveredListIterator {
  87 private:
  88   DiscoveredList&    _refs_list;
  89   HeapWord*          _prev_next;
  90   oop                _prev;
  91   oop                _ref;
  92   HeapWord*          _discovered_addr;
  93   oop                _next;
  94   HeapWord*          _referent_addr;
  95   oop                _referent;
  96   OopClosure*        _keep_alive;
  97   BoolObjectClosure* _is_alive;
  98 
  99   DEBUG_ONLY(
 100   oop                _first_seen; // cyclic linked list check
 101   )
 102 
 103   NOT_PRODUCT(
 104   size_t             _processed;
 105   size_t             _removed;
 106   )
 107 
 108 public:
 109   inline DiscoveredListIterator(DiscoveredList&    refs_list,
 110                                 OopClosure*        keep_alive,
 111                                 BoolObjectClosure* is_alive):
 112     _refs_list(refs_list),
 113     _prev_next(refs_list.adr_head()),
 114     _prev(NULL),
 115     _ref(refs_list.head()),
 116 #ifdef ASSERT
 117     _first_seen(refs_list.head()),
 118 #endif
 119 #ifndef PRODUCT
 120     _processed(0),
 121     _removed(0),
 122 #endif
 123     _next(NULL),
 124     _keep_alive(keep_alive),
 125     _is_alive(is_alive)
 126 { }
 127 
 128   // End Of List.
 129   inline bool has_next() const { return _ref != NULL; }
 130 
 131   // Get oop to the Reference object.
 132   inline oop obj() const { return _ref; }
 133 
 134   // Get oop to the referent object.
 135   inline oop referent() const { return _referent; }
 136 
 137   // Returns true if referent is alive.
 138   inline bool is_referent_alive() const {
 139     return _is_alive->do_object_b(_referent);
 140   }
 141 
 142   // Loads data for the current reference.
 143   // The "allow_null_referent" argument tells us to allow for the possibility
 144   // of a NULL referent in the discovered Reference object. This typically
 145   // happens in the case of concurrent collectors that may have done the
 146   // discovery concurrently, or interleaved, with mutator execution.
 147   void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
 148 
 149   // Move to the next discovered reference.
 150   inline void next() {
 151     _prev_next = _discovered_addr;
 152     _prev = _ref;
 153     move_to_next();
 154   }
 155 
 156   // Remove the current reference from the list
 157   void remove();
 158 
 159   // Make the Reference object active again.
 160   void make_active();
 161 
 162   // Make the referent alive.
 163   inline void make_referent_alive() {
 164     if (UseCompressedOops) {
 165       _keep_alive->do_oop((narrowOop*)_referent_addr);
 166     } else {
 167       _keep_alive->do_oop((oop*)_referent_addr);
 168     }
 169   }
 170 
 171   // Update the discovered field.
 172   inline void update_discovered() {
 173     // First _prev_next ref actually points into DiscoveredList (gross).
 174     if (UseCompressedOops) {
 175       if (!oopDesc::is_null(*(narrowOop*)_prev_next)) {
 176         _keep_alive->do_oop((narrowOop*)_prev_next);
 177       }
 178     } else {
 179       if (!oopDesc::is_null(*(oop*)_prev_next)) {
 180         _keep_alive->do_oop((oop*)_prev_next);
 181       }
 182     }
 183   }
 184 
 185   // NULL out referent pointer.
 186   void clear_referent();
 187 
 188   // Statistics
 189   NOT_PRODUCT(
 190   inline size_t processed() const { return _processed; }
 191   inline size_t removed() const   { return _removed; }
 192   )
 193 
 194   inline void move_to_next() {
 195     if (_ref == _next) {
 196       // End of the list.
 197       _ref = NULL;
 198     } else {
 199       _ref = _next;
 200     }
 201     assert(_ref != _first_seen, "cyclic ref_list found");
 202     NOT_PRODUCT(_processed++);
 203   }
 204 };
 205 
 206 class ReferenceProcessor : public CHeapObj<mtGC> {
 207  protected:
 208   // Compatibility with pre-4965777 JDK's
 209   static bool _pending_list_uses_discovered_field;
 210 
 211   // The SoftReference master timestamp clock
 212   static jlong _soft_ref_timestamp_clock;
 213 
 214   MemRegion   _span;                    // (right-open) interval of heap
 215                                         // subject to wkref discovery
 216 
 217   bool        _discovering_refs;        // true when discovery enabled
 218   bool        _discovery_is_atomic;     // if discovery is atomic wrt
 219                                         // other collectors in configuration
 220   bool        _discovery_is_mt;         // true if reference discovery is MT.
 221 
 222   // If true, setting "next" field of a discovered refs list requires
 223   // write barrier(s).  (Must be true if used in a collector in which
 224   // elements of a discovered list may be moved during discovery: for
 225   // example, a collector like Garbage-First that moves objects during a
 226   // long-term concurrent marking phase that does weak reference
 227   // discovery.)
 228   bool        _discovered_list_needs_barrier;
 229 
 230   BarrierSet* _bs;                      // Cached copy of BarrierSet.
 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 
 268  public:
 269   static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); }
 270 
 271   uint num_q()                             { return _num_q; }
 272   uint max_num_q()                         { return _max_num_q; }
 273   void set_active_mt_degree(uint v)        { _num_q = v; }
 274 
 275   DiscoveredList* discovered_refs()        { return _discovered_refs; }
 276 
 277   ReferencePolicy* setup_policy(bool always_clear) {
 278     _current_soft_ref_policy = always_clear ?
 279       _always_clear_soft_ref_policy : _default_soft_ref_policy;
 280     _current_soft_ref_policy->setup();   // snapshot the policy threshold
 281     return _current_soft_ref_policy;
 282   }
 283 
 284   // Process references with a certain reachability level.
 285   void process_discovered_reflist(DiscoveredList               refs_lists[],
 286                                   ReferencePolicy*             policy,
 287                                   bool                         clear_referent,
 288                                   BoolObjectClosure*           is_alive,
 289                                   OopClosure*                  keep_alive,
 290                                   VoidClosure*                 complete_gc,
 291                                   AbstractRefProcTaskExecutor* task_executor);
 292 
 293   void process_phaseJNI(BoolObjectClosure* is_alive,
 294                         OopClosure*        keep_alive,
 295                         VoidClosure*       complete_gc);
 296 
 297   // Work methods used by the method process_discovered_reflist
 298   // Phase1: keep alive all those referents that are otherwise
 299   // dead but which must be kept alive by policy (and their closure).
 300   void process_phase1(DiscoveredList&     refs_list,
 301                       ReferencePolicy*    policy,
 302                       BoolObjectClosure*  is_alive,
 303                       OopClosure*         keep_alive,
 304                       VoidClosure*        complete_gc);
 305   // Phase2: remove all those references whose referents are
 306   // reachable.
 307   inline void process_phase2(DiscoveredList&    refs_list,
 308                              BoolObjectClosure* is_alive,
 309                              OopClosure*        keep_alive,
 310                              VoidClosure*       complete_gc) {
 311     if (discovery_is_atomic()) {
 312       // complete_gc is ignored in this case for this phase
 313       pp2_work(refs_list, is_alive, keep_alive);
 314     } else {
 315       assert(complete_gc != NULL, "Error");
 316       pp2_work_concurrent_discovery(refs_list, is_alive,
 317                                     keep_alive, complete_gc);
 318     }
 319   }
 320   // Work methods in support of process_phase2
 321   void pp2_work(DiscoveredList&    refs_list,
 322                 BoolObjectClosure* is_alive,
 323                 OopClosure*        keep_alive);
 324   void pp2_work_concurrent_discovery(
 325                 DiscoveredList&    refs_list,
 326                 BoolObjectClosure* is_alive,
 327                 OopClosure*        keep_alive,
 328                 VoidClosure*       complete_gc);
 329   // Phase3: process the referents by either clearing them
 330   // or keeping them alive (and their closure)
 331   void process_phase3(DiscoveredList&    refs_list,
 332                       bool               clear_referent,
 333                       BoolObjectClosure* is_alive,
 334                       OopClosure*        keep_alive,
 335                       VoidClosure*       complete_gc);
 336 
 337   // Enqueue references with a certain reachability level
 338   void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr);
 339 
 340   // "Preclean" all the discovered reference lists
 341   // by removing references with strongly reachable referents.
 342   // The first argument is a predicate on an oop that indicates
 343   // its (strong) reachability and the second is a closure that
 344   // may be used to incrementalize or abort the precleaning process.
 345   // The caller is responsible for taking care of potential
 346   // interference with concurrent operations on these lists
 347   // (or predicates involved) by other threads. Currently
 348   // only used by the CMS collector.
 349   void preclean_discovered_references(BoolObjectClosure* is_alive,
 350                                       OopClosure*        keep_alive,
 351                                       VoidClosure*       complete_gc,
 352                                       YieldClosure*      yield);
 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   // Set the 'discovered' field of the given reference to
 375   // the given value - emitting barriers depending upon
 376   // the value of _discovered_list_needs_barrier.
 377   void set_discovered(oop ref, oop value);
 378 
 379   // "Preclean" the given discovered reference list
 380   // by removing references with strongly reachable referents.
 381   // Currently used in support of CMS only.
 382   void preclean_discovered_reflist(DiscoveredList&    refs_list,
 383                                    BoolObjectClosure* is_alive,
 384                                    OopClosure*        keep_alive,
 385                                    VoidClosure*       complete_gc,
 386                                    YieldClosure*      yield);
 387 
 388   // round-robin mod _num_q (not: _not_ mode _max_num_q)
 389   uint next_id() {
 390     uint id = _next_id;
 391     if (++_next_id == _num_q) {
 392       _next_id = 0;
 393     }
 394     return id;
 395   }
 396   DiscoveredList* get_discovered_list(ReferenceType rt);
 397   inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
 398                                         HeapWord* discovered_addr);
 399   void verify_ok_to_handle_reflists() PRODUCT_RETURN;
 400 
 401   void clear_discovered_references(DiscoveredList& refs_list);
 402   void abandon_partial_discovered_list(DiscoveredList& refs_list);
 403 
 404   // Calculate the number of jni handles.
 405   unsigned int count_jni_refs();
 406 
 407   // Balances reference queues.
 408   void balance_queues(DiscoveredList ref_lists[]);
 409 
 410   // Update (advance) the soft ref master clock field.
 411   void update_soft_ref_master_clock();
 412 
 413  public:
 414   // constructor
 415   ReferenceProcessor():
 416     _span((HeapWord*)NULL, (HeapWord*)NULL),
 417     _discovered_refs(NULL),
 418     _discoveredSoftRefs(NULL),  _discoveredWeakRefs(NULL),
 419     _discoveredFinalRefs(NULL), _discoveredPhantomRefs(NULL),
 420     _discovering_refs(false),
 421     _discovery_is_atomic(true),
 422     _enqueuing_is_done(false),
 423     _discovery_is_mt(false),
 424     _discovered_list_needs_barrier(false),
 425     _bs(NULL),
 426     _is_alive_non_header(NULL),
 427     _num_q(0),
 428     _max_num_q(0),
 429     _processing_is_mt(false),
 430     _next_id(0)
 431   { }
 432 
 433   // Default parameters give you a vanilla reference processor.
 434   ReferenceProcessor(MemRegion span,
 435                      bool mt_processing = false, uint mt_processing_degree = 1,
 436                      bool mt_discovery  = false, uint mt_discovery_degree  = 1,
 437                      bool atomic_discovery = true,
 438                      BoolObjectClosure* is_alive_non_header = NULL,
 439                      bool discovered_list_needs_barrier = false);
 440 
 441   // RefDiscoveryPolicy values
 442   enum DiscoveryPolicy {
 443     ReferenceBasedDiscovery = 0,
 444     ReferentBasedDiscovery  = 1,
 445     DiscoveryPolicyMin      = ReferenceBasedDiscovery,
 446     DiscoveryPolicyMax      = ReferentBasedDiscovery
 447   };
 448 
 449   static void init_statics();
 450 
 451  public:
 452   // get and set "is_alive_non_header" field
 453   BoolObjectClosure* is_alive_non_header() {
 454     return _is_alive_non_header;
 455   }
 456   void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {
 457     _is_alive_non_header = is_alive_non_header;
 458   }
 459 
 460   // get and set span
 461   MemRegion span()                   { return _span; }
 462   void      set_span(MemRegion span) { _span = span; }
 463 
 464   // start and stop weak ref discovery
 465   void enable_discovery(bool verify_disabled, bool check_no_refs);
 466   void disable_discovery()  { _discovering_refs = false; }
 467   bool discovery_enabled()  { return _discovering_refs;  }
 468 
 469   // whether discovery is atomic wrt other collectors
 470   bool discovery_is_atomic() const { return _discovery_is_atomic; }
 471   void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }
 472 
 473   // whether the JDK in which we are embedded is a pre-4965777 JDK,
 474   // and thus whether or not it uses the discovered field to chain
 475   // the entries in the pending list.
 476   static bool pending_list_uses_discovered_field() {
 477     return _pending_list_uses_discovered_field;
 478   }
 479 
 480   // whether discovery is done by multiple threads same-old-timeously
 481   bool discovery_is_mt() const { return _discovery_is_mt; }
 482   void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }
 483 
 484   // Whether we are in a phase when _processing_ is MT.
 485   bool processing_is_mt() const { return _processing_is_mt; }
 486   void set_mt_processing(bool mt) { _processing_is_mt = mt; }
 487 
 488   // whether all enqueuing of weak references is complete
 489   bool enqueuing_is_done()  { return _enqueuing_is_done; }
 490   void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }
 491 
 492   // iterate over oops
 493   void weak_oops_do(OopClosure* f);       // weak roots
 494 
 495   // Balance each of the discovered lists.
 496   void balance_all_queues();
 497   void verify_list(DiscoveredList& ref_list);
 498 
 499   // Discover a Reference object, using appropriate discovery criteria
 500   bool discover_reference(oop obj, ReferenceType rt);
 501 
 502   // Process references found during GC (called by the garbage collector)
 503   void process_discovered_references(BoolObjectClosure*           is_alive,
 504                                      OopClosure*                  keep_alive,
 505                                      VoidClosure*                 complete_gc,
 506                                      AbstractRefProcTaskExecutor* task_executor);
 507 
 508  public:
 509   // Enqueue references at end of GC (called by the garbage collector)
 510   bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);
 511 
 512   // If a discovery is in process that is being superceded, abandon it: all
 513   // the discovered lists will be empty, and all the objects on them will
 514   // have NULL discovered fields.  Must be called only at a safepoint.
 515   void abandon_partial_discovery();
 516 
 517   // debugging
 518   void verify_no_references_recorded() PRODUCT_RETURN;
 519   void verify_referent(oop obj)        PRODUCT_RETURN;
 520 
 521   // clear the discovered lists (unlinking each entry).
 522   void clear_discovered_references() PRODUCT_RETURN;
 523 };
 524 
 525 // A utility class to disable reference discovery in
 526 // the scope which contains it, for given ReferenceProcessor.
 527 class NoRefDiscovery: StackObj {
 528  private:
 529   ReferenceProcessor* _rp;
 530   bool _was_discovering_refs;
 531  public:
 532   NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {
 533     _was_discovering_refs = _rp->discovery_enabled();
 534     if (_was_discovering_refs) {
 535       _rp->disable_discovery();
 536     }
 537   }
 538 
 539   ~NoRefDiscovery() {
 540     if (_was_discovering_refs) {
 541       _rp->enable_discovery(true /*verify_disabled*/, false /*check_no_refs*/);
 542     }
 543   }
 544 };
 545 
 546 
 547 // A utility class to temporarily mutate the span of the
 548 // given ReferenceProcessor in the scope that contains it.
 549 class ReferenceProcessorSpanMutator: StackObj {
 550  private:
 551   ReferenceProcessor* _rp;
 552   MemRegion           _saved_span;
 553 
 554  public:
 555   ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
 556                                 MemRegion span):
 557     _rp(rp) {
 558     _saved_span = _rp->span();
 559     _rp->set_span(span);
 560   }
 561 
 562   ~ReferenceProcessorSpanMutator() {
 563     _rp->set_span(_saved_span);
 564   }
 565 };
 566 
 567 // A utility class to temporarily change the MT'ness of
 568 // reference discovery for the given ReferenceProcessor
 569 // in the scope that contains it.
 570 class ReferenceProcessorMTDiscoveryMutator: StackObj {
 571  private:
 572   ReferenceProcessor* _rp;
 573   bool                _saved_mt;
 574 
 575  public:
 576   ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,
 577                                        bool mt):
 578     _rp(rp) {
 579     _saved_mt = _rp->discovery_is_mt();
 580     _rp->set_mt_discovery(mt);
 581   }
 582 
 583   ~ReferenceProcessorMTDiscoveryMutator() {
 584     _rp->set_mt_discovery(_saved_mt);
 585   }
 586 };
 587 
 588 
 589 // A utility class to temporarily change the disposition
 590 // of the "is_alive_non_header" closure field of the
 591 // given ReferenceProcessor in the scope that contains it.
 592 class ReferenceProcessorIsAliveMutator: StackObj {
 593  private:
 594   ReferenceProcessor* _rp;
 595   BoolObjectClosure*  _saved_cl;
 596 
 597  public:
 598   ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,
 599                                    BoolObjectClosure*  cl):
 600     _rp(rp) {
 601     _saved_cl = _rp->is_alive_non_header();
 602     _rp->set_is_alive_non_header(cl);
 603   }
 604 
 605   ~ReferenceProcessorIsAliveMutator() {
 606     _rp->set_is_alive_non_header(_saved_cl);
 607   }
 608 };
 609 
 610 // A utility class to temporarily change the disposition
 611 // of the "discovery_is_atomic" field of the
 612 // given ReferenceProcessor in the scope that contains it.
 613 class ReferenceProcessorAtomicMutator: StackObj {
 614  private:
 615   ReferenceProcessor* _rp;
 616   bool                _saved_atomic_discovery;
 617 
 618  public:
 619   ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,
 620                                   bool atomic):
 621     _rp(rp) {
 622     _saved_atomic_discovery = _rp->discovery_is_atomic();
 623     _rp->set_atomic_discovery(atomic);
 624   }
 625 
 626   ~ReferenceProcessorAtomicMutator() {
 627     _rp->set_atomic_discovery(_saved_atomic_discovery);
 628   }
 629 };
 630 
 631 
 632 // A utility class to temporarily change the MT processing
 633 // disposition of the given ReferenceProcessor instance
 634 // in the scope that contains it.
 635 class ReferenceProcessorMTProcMutator: StackObj {
 636  private:
 637   ReferenceProcessor* _rp;
 638   bool  _saved_mt;
 639 
 640  public:
 641   ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,
 642                                   bool mt):
 643     _rp(rp) {
 644     _saved_mt = _rp->processing_is_mt();
 645     _rp->set_mt_processing(mt);
 646   }
 647 
 648   ~ReferenceProcessorMTProcMutator() {
 649     _rp->set_mt_processing(_saved_mt);
 650   }
 651 };
 652 
 653 
 654 // This class is an interface used to implement task execution for the
 655 // reference processing.
 656 class AbstractRefProcTaskExecutor {
 657 public:
 658 
 659   // Abstract tasks to execute.
 660   class ProcessTask;
 661   class EnqueueTask;
 662 
 663   // Executes a task using worker threads.
 664   virtual void execute(ProcessTask& task) = 0;
 665   virtual void execute(EnqueueTask& task) = 0;
 666 
 667   // Switch to single threaded mode.
 668   virtual void set_single_threaded_mode() { };
 669 };
 670 
 671 // Abstract reference processing task to execute.
 672 class AbstractRefProcTaskExecutor::ProcessTask {
 673 protected:
 674   ProcessTask(ReferenceProcessor& ref_processor,
 675               DiscoveredList      refs_lists[],
 676               bool                marks_oops_alive)
 677     : _ref_processor(ref_processor),
 678       _refs_lists(refs_lists),
 679       _marks_oops_alive(marks_oops_alive)
 680   { }
 681 
 682 public:
 683   virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,
 684                     OopClosure& keep_alive,
 685                     VoidClosure& complete_gc) = 0;
 686 
 687   // Returns true if a task marks some oops as alive.
 688   bool marks_oops_alive() const
 689   { return _marks_oops_alive; }
 690 
 691 protected:
 692   ReferenceProcessor& _ref_processor;
 693   DiscoveredList*     _refs_lists;
 694   const bool          _marks_oops_alive;
 695 };
 696 
 697 // Abstract reference processing task to execute.
 698 class AbstractRefProcTaskExecutor::EnqueueTask {
 699 protected:
 700   EnqueueTask(ReferenceProcessor& ref_processor,
 701               DiscoveredList      refs_lists[],
 702               HeapWord*           pending_list_addr,
 703               int                 n_queues)
 704     : _ref_processor(ref_processor),
 705       _refs_lists(refs_lists),
 706       _pending_list_addr(pending_list_addr),
 707       _n_queues(n_queues)
 708   { }
 709 
 710 public:
 711   virtual void work(unsigned int work_id) = 0;
 712 
 713 protected:
 714   ReferenceProcessor& _ref_processor;
 715   DiscoveredList*     _refs_lists;
 716   HeapWord*           _pending_list_addr;
 717   int                 _n_queues;
 718 };
 719 
 720 #endif // SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP