jdk/src/hotspot/share/gc/shared/referenceProcessor.hpp

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#ifndef SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP
#define SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP

#include "gc/shared/referenceDiscoverer.hpp"
#include "gc/shared/referencePolicy.hpp"
#include "gc/shared/referenceProcessorPhaseTimes.hpp"
#include "gc/shared/referenceProcessorStats.hpp"
#include "memory/referenceType.hpp"
#include "oops/instanceRefKlass.hpp"

class GCTimer;

// 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.
// ReferenceProcessor class abstracts away from a generational setting
// by using a closure that determines whether a given reference or referent are
// subject to this ReferenceProcessor's discovery, thus allowing its use in a
// straightforward manner in a general, non-generational, non-contiguous generation
// (or heap) setting.
//

// forward references
class ReferencePolicy;
class AbstractRefProcTaskExecutor;

// List of discovered references.
class DiscoveredList {
public:
  DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
  inline oop head() const;
  HeapWord* adr_head() {
    return UseCompressedOops ? (HeapWord*)&_compressed_head :
                               (HeapWord*)&_oop_head;
  }
  inline void set_head(oop o);
  inline bool is_empty() const;
  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_discovered_addr;
  oop                _prev_discovered;
  oop                _current_discovered;
  HeapWord*          _current_discovered_addr;
  oop                _next_discovered;

  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);

  // End Of List.
  inline bool has_next() const { return _current_discovered != NULL; }

  // Get oop to the Reference object.
  inline oop obj() const { return _current_discovered; }

  // 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_discovered_addr = _current_discovered_addr;
    _prev_discovered = _current_discovered;
    move_to_next();
  }

  // Remove the current reference from the list
  void remove();

  // 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);
    }
  }

  // Do enqueuing work, i.e. notifying the GC about the changed discovered pointers.
  void enqueue();

  // Move enqueued references to the reference pending list.
  void complete_enqueue();

  // 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 (_current_discovered == _next_discovered) {
      // End of the list.
      _current_discovered = NULL;
    } else {
      _current_discovered = _next_discovered;
    }
    assert(_current_discovered != _first_seen, "cyclic ref_list found");
    NOT_PRODUCT(_processed++);
  }
};

class ReferenceProcessor : public ReferenceDiscoverer {
  size_t total_count(DiscoveredList lists[]) const;

  // The SoftReference master timestamp clock
  static jlong _soft_ref_timestamp_clock;

  BoolObjectClosure* _is_subject_to_discovery; // determines whether a given oop is subject
                                               // to this ReferenceProcessor's discovery
                                               // (and further processing).

  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.

  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_queues 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_queues;
  // The maximum MT'ness degree of the queues below
  uint            _max_num_queues;

  // 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_queues() const                  { return _num_queues; }
  uint max_num_queues() const              { return _max_num_queues; }
  void set_active_mt_degree(uint 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,
                                  ReferenceProcessorPhaseTimes* phase_times);

  // 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.
  void process_phase2(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), and enqueuing them.
  void process_phase3(DiscoveredList&    refs_list,
                      bool               clear_referent,
                      BoolObjectClosure* is_alive,
                      OopClosure*        keep_alive,
                      VoidClosure*       complete_gc);

  // "Preclean" all the discovered reference lists by removing references that
  // are active (e.g. due to the mutator calling enqueue()) or with NULL or
  // strongly reachable referents.
  // The first argument is a predicate on an oop that indicates
  // its (strong) reachability and the fourth 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.
  void preclean_discovered_references(BoolObjectClosure* is_alive,
                                      OopClosure*        keep_alive,
                                      VoidClosure*       complete_gc,
                                      YieldClosure*      yield,
                                      GCTimer*           gc_timer);

  // Returns the name of the discovered reference list
  // occupying the i / _num_queues slot.
  const char* list_name(uint i);

private:
  // "Preclean" the given discovered reference list by removing references with
  // the attributes mentioned in preclean_discovered_references().
  // Supports both normal and fine grain yielding.
  // Returns whether the operation should be aborted.
  bool preclean_discovered_reflist(DiscoveredList&    refs_list,
                                   BoolObjectClosure* is_alive,
                                   OopClosure*        keep_alive,
                                   VoidClosure*       complete_gc,
                                   YieldClosure*      yield);

  // round-robin mod _num_queues (not: _not_ mod _max_num_queues)
  uint next_id() {
    uint id = _next_id;
    assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
    if (++_next_id == _num_queues) {
      _next_id = 0;
    }
    assert(_next_id < _num_queues, "_next_id %u _num_queues %u _max_num_queues %u", _next_id, _num_queues, _max_num_queues);
    return id;
  }
  DiscoveredList* get_discovered_list(ReferenceType rt);
  inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj,
                                        HeapWord* discovered_addr);

  void clear_discovered_references(DiscoveredList& refs_list);

  void log_reflist(const char* prefix, DiscoveredList list[], uint num_active_queues);
  void log_reflist_counts(DiscoveredList ref_lists[], uint num_active_queues) PRODUCT_RETURN;

  // Balances reference queues.
  void balance_queues(DiscoveredList refs_lists[]);
  bool need_balance_queues(DiscoveredList refs_lists[]);

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

  bool is_subject_to_discovery(oop const obj) const;

public:
  // Default parameters give you a vanilla reference processor.
  ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery,
                     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);

  // 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;
  }

  BoolObjectClosure* is_subject_to_discovery_closure() const { return _is_subject_to_discovery; }
  void set_is_subject_to_discovery_closure(BoolObjectClosure* cl) { _is_subject_to_discovery = cl; }

  // start and stop weak ref discovery
  void enable_discovery(bool check_no_refs = true);
  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 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 enqueueing 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

  void verify_list(DiscoveredList& ref_list);

  // Discover a Reference object, using appropriate discovery criteria
  virtual bool discover_reference(oop obj, ReferenceType rt);

  // Has discovered references that need handling
  bool has_discovered_references();

  // Process references found during GC (called by the garbage collector)
  ReferenceProcessorStats
  process_discovered_references(BoolObjectClosure*            is_alive,
                                OopClosure*                   keep_alive,
                                VoidClosure*                  complete_gc,
                                AbstractRefProcTaskExecutor*  task_executor,
                                ReferenceProcessorPhaseTimes* phase_times);

  // 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();

  size_t total_reference_count(ReferenceType rt) const;

  // debugging
  void verify_no_references_recorded() PRODUCT_RETURN;
  void verify_referent(oop obj)        PRODUCT_RETURN;
};

// A subject-to-discovery closure that uses a single memory span to determine the area that
// is subject to discovery. Useful for collectors which have contiguous generations.
class SpanSubjectToDiscoveryClosure : public BoolObjectClosure {
  MemRegion _span;

public:
  SpanSubjectToDiscoveryClosure() : BoolObjectClosure(), _span() { }
  SpanSubjectToDiscoveryClosure(MemRegion span) : BoolObjectClosure(), _span(span) { }

  MemRegion span() const { return _span; }

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

  virtual bool do_object_b(oop obj) {
    return _span.contains(obj);
  }
};

// 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(false /*check_no_refs*/);
    }
  }
};

// A utility class to temporarily mutate the subject discovery closure of the
// given ReferenceProcessor in the scope that contains it.
class ReferenceProcessorSubjectToDiscoveryMutator : StackObj {
  ReferenceProcessor* _rp;
  BoolObjectClosure* _saved_cl;

public:
  ReferenceProcessorSubjectToDiscoveryMutator(ReferenceProcessor* rp, BoolObjectClosure* cl):
    _rp(rp) {
    _saved_cl = _rp->is_subject_to_discovery_closure();
    _rp->set_is_subject_to_discovery_closure(cl);
  }

  ~ReferenceProcessorSubjectToDiscoveryMutator() {
    _rp->set_is_subject_to_discovery_closure(_saved_cl);
  }
};

// A utility class to temporarily mutate the span of the
// given ReferenceProcessor in the scope that contains it.
class ReferenceProcessorSpanMutator : StackObj {
  ReferenceProcessor* _rp;
  SpanSubjectToDiscoveryClosure _discoverer;
  BoolObjectClosure* _old_discoverer;

public:
  ReferenceProcessorSpanMutator(ReferenceProcessor* rp,
                                MemRegion span):
    _rp(rp),
    _discoverer(span),
    _old_discoverer(rp->is_subject_to_discovery_closure()) {

    rp->set_is_subject_to_discovery_closure(&_discoverer);
  }

  ~ReferenceProcessorSpanMutator() {
    _rp->set_is_subject_to_discovery_closure(_old_discoverer);
  }
};

// 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;

  // Executes a task using worker threads.
  virtual void execute(ProcessTask& 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,
              ReferenceProcessorPhaseTimes* phase_times)
    : _ref_processor(ref_processor),
      _refs_lists(refs_lists),
      _phase_times(phase_times),
      _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;
  ReferenceProcessorPhaseTimes* _phase_times;
  const bool                    _marks_oops_alive;
};

#endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP