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  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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  *

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  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

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  * 2 along with this work; if not, write to the Free Software Foundation,

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 #ifndef SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP

 #define SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP

 #include "memory/referencePolicy.hpp"

 #include "oops/instanceRefKlass.hpp"

 // ReferenceProcessor class encapsulates the per-"collector" processing

 // of java.lang.Reference objects for GC. The interface is useful for supporting

 // a generational abstraction, in particular when there are multiple

 // generations that are being independently collected -- possibly

 // concurrently and/or incrementally.  Note, however, that the

 // ReferenceProcessor class abstracts away from a generational setting

 // by using only a heap interval (called "span" below), thus allowing

 // its use in a straightforward manner in a general, non-generational

 // setting.

 //

 // The basic idea is that each ReferenceProcessor object concerns

 // itself with ("weak") reference processing in a specific "span"

 // of the heap of interest to a specific collector. Currently,

 // the span is a convex interval of the heap, but, efficiency

 // apart, there seems to be no reason it couldn't be extended

 // (with appropriate modifications) to any "non-convex interval".

 // forward references

 class ReferencePolicy;

 class AbstractRefProcTaskExecutor;

 // List of discovered references.

 class DiscoveredList {

 public:

   DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }

   oop head() const     {

      return UseCompressedOops ?  oopDesc::decode_heap_oop(_compressed_head) :

                                 _oop_head;

   }

   HeapWord* adr_head() {

     return UseCompressedOops ? (HeapWord*)&_compressed_head :

                                (HeapWord*)&_oop_head;

   }

   void set_head(oop o) {

     if (UseCompressedOops) {

       // Must compress the head ptr.

       _compressed_head = oopDesc::encode_heap_oop(o);

     } else {

       _oop_head = o;

     }

   }

   bool   is_empty() const       { return head() == NULL; }

   size_t length()               { return _len; }

   void   set_length(size_t len) { _len = len;  }

   void   inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }

   void   dec_length(size_t dec) { _len -= dec; }

 private:

   // Set value depending on UseCompressedOops. This could be a template class

   // but then we have to fix all the instantiations and declarations that use this class.

   oop       _oop_head;

   narrowOop _compressed_head;

   size_t _len;

 };

 // Iterator for the list of discovered references.

 class DiscoveredListIterator {

 private:

   DiscoveredList&    _refs_list;

   HeapWord*          _prev_next;

   oop                _prev;

   oop                _ref;

   HeapWord*          _discovered_addr;

   oop                _next;

   HeapWord*          _referent_addr;

   oop                _referent;

   OopClosure*        _keep_alive;

   BoolObjectClosure* _is_alive;

   DEBUG_ONLY(

   oop                _first_seen; // cyclic linked list check

   )

   NOT_PRODUCT(

   size_t             _processed;

   size_t             _removed;

   )

 public:

   inline DiscoveredListIterator(DiscoveredList&    refs_list,

                                 OopClosure*        keep_alive,

                                 BoolObjectClosure* is_alive):

     _refs_list(refs_list),

     _prev_next(refs_list.adr_head()),

     _prev(NULL),

     _ref(refs_list.head()),

 #ifdef ASSERT

     _first_seen(refs_list.head()),

 #endif

 #ifndef PRODUCT

     _processed(0),

     _removed(0),

 #endif

     _next(NULL),

     _keep_alive(keep_alive),

     _is_alive(is_alive)

 { }

   // End Of List.

   inline bool has_next() const { return _ref != NULL; }

   // Get oop to the Reference object.

   inline oop obj() const { return _ref; }

   // Get oop to the referent object.

   inline oop referent() const { return _referent; }

   // Returns true if referent is alive.

   inline bool is_referent_alive() const {

     return _is_alive->do_object_b(_referent);

   }

   // Loads data for the current reference.

   // The "allow_null_referent" argument tells us to allow for the possibility

   // of a NULL referent in the discovered Reference object. This typically

   // happens in the case of concurrent collectors that may have done the

   // discovery concurrently, or interleaved, with mutator execution.

   void load_ptrs(DEBUG_ONLY(bool allow_null_referent));

   // Move to the next discovered reference.

   inline void next() {

     _prev_next = _discovered_addr;

     _prev = _ref;

     move_to_next();

   }

   // Remove the current reference from the list

   void remove();

   // Make the Reference object active again.

   void make_active();

   // Make the referent alive.

   inline void make_referent_alive() {

     if (UseCompressedOops) {

       _keep_alive->do_oop((narrowOop*)_referent_addr);

     } else {

       _keep_alive->do_oop((oop*)_referent_addr);

     }

   }

   // Update the discovered field.

   inline void update_discovered() {

     // First _prev_next ref actually points into DiscoveredList (gross).

     if (UseCompressedOops) {

       if (!oopDesc::is_null(*(narrowOop*)_prev_next)) {

         _keep_alive->do_oop((narrowOop*)_prev_next);

       }

     } else {

       if (!oopDesc::is_null(*(oop*)_prev_next)) {

         _keep_alive->do_oop((oop*)_prev_next);

       }

     }

   }

   // NULL out referent pointer.

   void clear_referent();

   // Statistics

   NOT_PRODUCT(

   inline size_t processed() const { return _processed; }

   inline size_t removed() const   { return _removed; }

   )

   inline void move_to_next() {

     if (_ref == _next) {

       // End of the list.

       _ref = NULL;

     } else {

       _ref = _next;

     }

     assert(_ref != _first_seen, "cyclic ref_list found");

     NOT_PRODUCT(_processed++);

   }

 };

 class ReferenceProcessor : public CHeapObj<mtGC> {

  protected:

   // Compatibility with pre-4965777 JDK's

   static bool _pending_list_uses_discovered_field;

   // The SoftReference master timestamp clock

   static jlong _soft_ref_timestamp_clock;

   MemRegion   _span;                    // (right-open) interval of heap

                                         // subject to wkref discovery

   bool        _discovering_refs;        // true when discovery enabled

   bool        _discovery_is_atomic;     // if discovery is atomic wrt

                                         // other collectors in configuration

   bool        _discovery_is_mt;         // true if reference discovery is MT.

   // If true, setting "next" field of a discovered refs list requires

   // write barrier(s).  (Must be true if used in a collector in which

   // elements of a discovered list may be moved during discovery: for

   // example, a collector like Garbage-First that moves objects during a

   // long-term concurrent marking phase that does weak reference

   // discovery.)

   bool        _discovered_list_needs_barrier;

   BarrierSet* _bs;                      // Cached copy of BarrierSet.

   bool        _enqueuing_is_done;       // true if all weak references enqueued

   bool        _processing_is_mt;        // true during phases when

                                         // reference processing is MT.

   uint        _next_id;                 // round-robin mod _num_q counter in

                                         // support of work distribution

   // For collectors that do not keep GC liveness information

   // in the object header, this field holds a closure that

   // helps the reference processor determine the reachability

   // of an oop. It is currently initialized to NULL for all

   // collectors except for CMS and G1.

   BoolObjectClosure* _is_alive_non_header;

   // Soft ref clearing policies

   // . the default policy

   static ReferencePolicy*   _default_soft_ref_policy;

   // . the "clear all" policy

   static ReferencePolicy*   _always_clear_soft_ref_policy;

   // . the current policy below is either one of the above

   ReferencePolicy*          _current_soft_ref_policy;

   // The discovered ref lists themselves

   // The active MT'ness degree of the queues below

   uint             _num_q;

   // The maximum MT'ness degree of the queues below

   uint             _max_num_q;

   // Master array of discovered oops

   DiscoveredList* _discovered_refs;

   // Arrays of lists of oops, one per thread (pointers into master array above)

   DiscoveredList* _discoveredSoftRefs;

   DiscoveredList* _discoveredWeakRefs;

   DiscoveredList* _discoveredFinalRefs;

   DiscoveredList* _discoveredPhantomRefs;

  public:

   static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); }

   uint num_q()                             { return _num_q; }

   uint max_num_q()                         { return _max_num_q; }

   void set_active_mt_degree(uint v)        { _num_q = v; }

   DiscoveredList* discovered_refs()        { return _discovered_refs; }

   ReferencePolicy* setup_policy(bool always_clear) {

     _current_soft_ref_policy = always_clear ?

       _always_clear_soft_ref_policy : _default_soft_ref_policy;

     _current_soft_ref_policy->setup();   // snapshot the policy threshold

     return _current_soft_ref_policy;

   }

   // Process references with a certain reachability level.

   void process_discovered_reflist(DiscoveredList               refs_lists[],

                                   ReferencePolicy*             policy,

                                   bool                         clear_referent,

                                   BoolObjectClosure*           is_alive,

                                   OopClosure*                  keep_alive,

                                   VoidClosure*                 complete_gc,

                                   AbstractRefProcTaskExecutor* task_executor);

   void process_phaseJNI(BoolObjectClosure* is_alive,

                         OopClosure*        keep_alive,

                         VoidClosure*       complete_gc);

   // Work methods used by the method process_discovered_reflist

   // Phase1: keep alive all those referents that are otherwise

   // dead but which must be kept alive by policy (and their closure).

   void process_phase1(DiscoveredList&     refs_list,

                       ReferencePolicy*    policy,

                       BoolObjectClosure*  is_alive,

                       OopClosure*         keep_alive,

                       VoidClosure*        complete_gc);

   // Phase2: remove all those references whose referents are

   // reachable.

   inline void process_phase2(DiscoveredList&    refs_list,

                              BoolObjectClosure* is_alive,

                              OopClosure*        keep_alive,

                              VoidClosure*       complete_gc) {

     if (discovery_is_atomic()) {

       // complete_gc is ignored in this case for this phase

       pp2_work(refs_list, is_alive, keep_alive);

     } else {

       assert(complete_gc != NULL, "Error");

       pp2_work_concurrent_discovery(refs_list, is_alive,

                                     keep_alive, complete_gc);

     }

   }

   // Work methods in support of process_phase2

   void pp2_work(DiscoveredList&    refs_list,

                 BoolObjectClosure* is_alive,

                 OopClosure*        keep_alive);

   void pp2_work_concurrent_discovery(

                 DiscoveredList&    refs_list,

                 BoolObjectClosure* is_alive,

                 OopClosure*        keep_alive,

                 VoidClosure*       complete_gc);

   // Phase3: process the referents by either clearing them

   // or keeping them alive (and their closure)

   void process_phase3(DiscoveredList&    refs_list,

                       bool               clear_referent,

                       BoolObjectClosure* is_alive,

                       OopClosure*        keep_alive,

                       VoidClosure*       complete_gc);

   // Enqueue references with a certain reachability level

   void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr);

   // "Preclean" all the discovered reference lists

   // by removing references with strongly reachable referents.

   // The first argument is a predicate on an oop that indicates

   // its (strong) reachability and the second is a closure that

   // may be used to incrementalize or abort the precleaning process.

   // The caller is responsible for taking care of potential

   // interference with concurrent operations on these lists

   // (or predicates involved) by other threads. Currently

   // only used by the CMS collector.

   void preclean_discovered_references(BoolObjectClosure* is_alive,

                                       OopClosure*        keep_alive,

                                       VoidClosure*       complete_gc,

                                       YieldClosure*      yield);

   // Delete entries in the discovered lists that have

   // either a null referent or are not active. Such

   // Reference objects can result from the clearing

   // or enqueueing of Reference objects concurrent

   // with their discovery by a (concurrent) collector.

   // For a definition of "active" see java.lang.ref.Reference;

   // Refs are born active, become inactive when enqueued,

   // and never become active again. The state of being

   // active is encoded as follows: A Ref is active

   // if and only if its "next" field is NULL.

   void clean_up_discovered_references();

   void clean_up_discovered_reflist(DiscoveredList& refs_list);

   // Returns the name of the discovered reference list

   // occupying the i / _num_q slot.

   const char* list_name(uint i);

   void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor);

  protected:

   // Set the 'discovered' field of the given reference to

   // the given value - emitting barriers depending upon

   // the value of _discovered_list_needs_barrier.

   void set_discovered(oop ref, oop value);

   // "Preclean" the given discovered reference list

   // by removing references with strongly reachable referents.

   // Currently used in support of CMS only.

   void preclean_discovered_reflist(DiscoveredList&    refs_list,

                                    BoolObjectClosure* is_alive,

                                    OopClosure*        keep_alive,

                                    VoidClosure*       complete_gc,

                                    YieldClosure*      yield);

   // round-robin mod _num_q (not: _not_ mode _max_num_q)

   uint next_id() {

     uint id = _next_id;

     if (++_next_id == _num_q) {

       _next_id = 0;

     }

     return id;

   }

   DiscoveredList* get_discovered_list(ReferenceType rt);

   inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,

                                         HeapWord* discovered_addr);

   void verify_ok_to_handle_reflists() PRODUCT_RETURN;

   void clear_discovered_references(DiscoveredList& refs_list);

   void abandon_partial_discovered_list(DiscoveredList& refs_list);

   // Calculate the number of jni handles.

   unsigned int count_jni_refs();

   // Balances reference queues.

   void balance_queues(DiscoveredList ref_lists[]);

   // Update (advance) the soft ref master clock field.

   void update_soft_ref_master_clock();

  public:

   // constructor

   ReferenceProcessor():

     _span((HeapWord*)NULL, (HeapWord*)NULL),

     _discovered_refs(NULL),

     _discoveredSoftRefs(NULL),  _discoveredWeakRefs(NULL),

     _discoveredFinalRefs(NULL), _discoveredPhantomRefs(NULL),

     _discovering_refs(false),

     _discovery_is_atomic(true),

     _enqueuing_is_done(false),

     _discovery_is_mt(false),

     _discovered_list_needs_barrier(false),

     _bs(NULL),

     _is_alive_non_header(NULL),

     _num_q(0),

     _max_num_q(0),

     _processing_is_mt(false),

     _next_id(0)

   { }

   // Default parameters give you a vanilla reference processor.

   ReferenceProcessor(MemRegion span,

                      bool mt_processing = false, uint mt_processing_degree = 1,

                      bool mt_discovery  = false, uint mt_discovery_degree  = 1,

                      bool atomic_discovery = true,

                      BoolObjectClosure* is_alive_non_header = NULL,

                      bool discovered_list_needs_barrier = false);

   // RefDiscoveryPolicy values

   enum DiscoveryPolicy {

     ReferenceBasedDiscovery = 0,

     ReferentBasedDiscovery  = 1,

     DiscoveryPolicyMin      = ReferenceBasedDiscovery,

     DiscoveryPolicyMax      = ReferentBasedDiscovery

   };

   static void init_statics();

  public:

   // get and set "is_alive_non_header" field

   BoolObjectClosure* is_alive_non_header() {

     return _is_alive_non_header;

   }

   void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) {

     _is_alive_non_header = is_alive_non_header;

   }

   // get and set span

   MemRegion span()                   { return _span; }

   void      set_span(MemRegion span) { _span = span; }

   // start and stop weak ref discovery

   void enable_discovery(bool verify_disabled, bool check_no_refs);

   void disable_discovery()  { _discovering_refs = false; }

   bool discovery_enabled()  { return _discovering_refs;  }

   // whether discovery is atomic wrt other collectors

   bool discovery_is_atomic() const { return _discovery_is_atomic; }

   void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; }

   // whether the JDK in which we are embedded is a pre-4965777 JDK,

   // and thus whether or not it uses the discovered field to chain

   // the entries in the pending list.

   static bool pending_list_uses_discovered_field() {

     return _pending_list_uses_discovered_field;

   }

   // whether discovery is done by multiple threads same-old-timeously

   bool discovery_is_mt() const { return _discovery_is_mt; }

   void set_mt_discovery(bool mt) { _discovery_is_mt = mt; }

   // Whether we are in a phase when _processing_ is MT.

   bool processing_is_mt() const { return _processing_is_mt; }

   void set_mt_processing(bool mt) { _processing_is_mt = mt; }

   // whether all enqueuing of weak references is complete

   bool enqueuing_is_done()  { return _enqueuing_is_done; }

   void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; }

   // iterate over oops

   void weak_oops_do(OopClosure* f);       // weak roots

   // Balance each of the discovered lists.

   void balance_all_queues();

   void verify_list(DiscoveredList& ref_list);

   // Discover a Reference object, using appropriate discovery criteria

   bool discover_reference(oop obj, ReferenceType rt);

   // Process references found during GC (called by the garbage collector)

   void process_discovered_references(BoolObjectClosure*           is_alive,

                                      OopClosure*                  keep_alive,

                                      VoidClosure*                 complete_gc,

                                      AbstractRefProcTaskExecutor* task_executor);

  public:

   // Enqueue references at end of GC (called by the garbage collector)

   bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL);

   // If a discovery is in process that is being superceded, abandon it: all

   // the discovered lists will be empty, and all the objects on them will

   // have NULL discovered fields.  Must be called only at a safepoint.

   void abandon_partial_discovery();

   // debugging

   void verify_no_references_recorded() PRODUCT_RETURN;

   void verify_referent(oop obj)        PRODUCT_RETURN;

   // clear the discovered lists (unlinking each entry).

   void clear_discovered_references() PRODUCT_RETURN;

 };

 // A utility class to disable reference discovery in

 // the scope which contains it, for given ReferenceProcessor.

 class NoRefDiscovery: StackObj {

  private:

   ReferenceProcessor* _rp;

   bool _was_discovering_refs;

  public:

   NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) {

     _was_discovering_refs = _rp->discovery_enabled();

     if (_was_discovering_refs) {

       _rp->disable_discovery();

     }

   }

   ~NoRefDiscovery() {

     if (_was_discovering_refs) {

       _rp->enable_discovery(true /*verify_disabled*/, false /*check_no_refs*/);

     }

   }

 };

 // A utility class to temporarily mutate the span of the

 // given ReferenceProcessor in the scope that contains it.

 class ReferenceProcessorSpanMutator: StackObj {

  private:

   ReferenceProcessor* _rp;

   MemRegion           _saved_span;

  public:

   ReferenceProcessorSpanMutator(ReferenceProcessor* rp,

                                 MemRegion span):

     _rp(rp) {

     _saved_span = _rp->span();

     _rp->set_span(span);

   }

   ~ReferenceProcessorSpanMutator() {

     _rp->set_span(_saved_span);

   }

 };

 // A utility class to temporarily change the MT'ness of

 // reference discovery for the given ReferenceProcessor

 // in the scope that contains it.

 class ReferenceProcessorMTDiscoveryMutator: StackObj {

  private:

   ReferenceProcessor* _rp;

   bool                _saved_mt;

  public:

   ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp,

                                        bool mt):

     _rp(rp) {

     _saved_mt = _rp->discovery_is_mt();

     _rp->set_mt_discovery(mt);

   }

   ~ReferenceProcessorMTDiscoveryMutator() {

     _rp->set_mt_discovery(_saved_mt);

   }

 };

 // A utility class to temporarily change the disposition

 // of the "is_alive_non_header" closure field of the

 // given ReferenceProcessor in the scope that contains it.

 class ReferenceProcessorIsAliveMutator: StackObj {

  private:

   ReferenceProcessor* _rp;

   BoolObjectClosure*  _saved_cl;

  public:

   ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp,

                                    BoolObjectClosure*  cl):

     _rp(rp) {

     _saved_cl = _rp->is_alive_non_header();

     _rp->set_is_alive_non_header(cl);

   }

   ~ReferenceProcessorIsAliveMutator() {

     _rp->set_is_alive_non_header(_saved_cl);

   }

 };

 // A utility class to temporarily change the disposition

 // of the "discovery_is_atomic" field of the

 // given ReferenceProcessor in the scope that contains it.

 class ReferenceProcessorAtomicMutator: StackObj {

  private:

   ReferenceProcessor* _rp;

   bool                _saved_atomic_discovery;

  public:

   ReferenceProcessorAtomicMutator(ReferenceProcessor* rp,

                                   bool atomic):

     _rp(rp) {

     _saved_atomic_discovery = _rp->discovery_is_atomic();

     _rp->set_atomic_discovery(atomic);

   }

   ~ReferenceProcessorAtomicMutator() {

     _rp->set_atomic_discovery(_saved_atomic_discovery);

   }

 };

 // A utility class to temporarily change the MT processing

 // disposition of the given ReferenceProcessor instance

 // in the scope that contains it.

 class ReferenceProcessorMTProcMutator: StackObj {

  private:

   ReferenceProcessor* _rp;

   bool  _saved_mt;

  public:

   ReferenceProcessorMTProcMutator(ReferenceProcessor* rp,

                                   bool mt):

     _rp(rp) {

     _saved_mt = _rp->processing_is_mt();

     _rp->set_mt_processing(mt);

   }

   ~ReferenceProcessorMTProcMutator() {

     _rp->set_mt_processing(_saved_mt);

   }

 };

 // This class is an interface used to implement task execution for the

 // reference processing.

 class AbstractRefProcTaskExecutor {

 public:

   // Abstract tasks to execute.

   class ProcessTask;

   class EnqueueTask;

   // Executes a task using worker threads.

   virtual void execute(ProcessTask& task) = 0;

   virtual void execute(EnqueueTask& task) = 0;

   // Switch to single threaded mode.

   virtual void set_single_threaded_mode() { };

 };

 // Abstract reference processing task to execute.

 class AbstractRefProcTaskExecutor::ProcessTask {

 protected:

   ProcessTask(ReferenceProcessor& ref_processor,

               DiscoveredList      refs_lists[],

               bool                marks_oops_alive)

     : _ref_processor(ref_processor),

       _refs_lists(refs_lists),

       _marks_oops_alive(marks_oops_alive)

   { }

 public:

   virtual void work(unsigned int work_id, BoolObjectClosure& is_alive,

                     OopClosure& keep_alive,

                     VoidClosure& complete_gc) = 0;

   // Returns true if a task marks some oops as alive.

   bool marks_oops_alive() const

   { return _marks_oops_alive; }

 protected:

   ReferenceProcessor& _ref_processor;

   DiscoveredList*     _refs_lists;

   const bool          _marks_oops_alive;

 };

 // Abstract reference processing task to execute.

 class AbstractRefProcTaskExecutor::EnqueueTask {

 protected:

   EnqueueTask(ReferenceProcessor& ref_processor,

               DiscoveredList      refs_lists[],

               HeapWord*           pending_list_addr,

               int                 n_queues)

     : _ref_processor(ref_processor),

       _refs_lists(refs_lists),

       _pending_list_addr(pending_list_addr),

       _n_queues(n_queues)

   { }

 public:

   virtual void work(unsigned int work_id) = 0;

 protected:

   ReferenceProcessor& _ref_processor;

   DiscoveredList*     _refs_lists;

   HeapWord*           _pending_list_addr;

   int                 _n_queues;

 };

 #endif // SHARE_VM_MEMORY_REFERENCEPROCESSOR_HPP