/*

 * Copyright (c) 2001, 2011, Oracle and/or its affiliates. All rights reserved.

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

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * 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).

 *

 * You should have received a copy of the GNU General Public License version

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

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 *

 */

#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 {

 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.

                                        // 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

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

  // 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); }

  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.  should_unload_classes is

  // used to aid assertion checking when classes are collected.

  void preclean_discovered_references(BoolObjectClosure* is_alive,

                                      OopClosure*        keep_alive,

                                      VoidClosure*       complete_gc,

                                      YieldClosure*      yield,

                                      bool               should_unload_classes);

  // 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.

  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)

    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 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();

  // 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)