parNewGeneration.hpp

/*
 * Copyright 2001-2007 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
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class ChunkArray;
class ParScanWithoutBarrierClosure;
class ParScanWithBarrierClosure;
class ParRootScanWithoutBarrierClosure;
class ParRootScanWithBarrierTwoGensClosure;
class ParEvacuateFollowersClosure;

// It would be better if these types could be kept local to the .cpp file,
// but they must be here to allow ParScanClosure::do_oop_work to be defined
// in genOopClosures.inline.hpp.


typedef OopTaskQueue    ObjToScanQueue;
typedef OopTaskQueueSet ObjToScanQueueSet;

// Enable this to get push/pop/steal stats.
const int PAR_STATS_ENABLED = 0;

class ParKeepAliveClosure: public DefNewGeneration::KeepAliveClosure {
  ParScanWeakRefClosure* _par_cl;
 public:
  ParKeepAliveClosure(ParScanWeakRefClosure* cl);
  void do_oop(oop* p);
};

// The state needed by thread performing parallel young-gen collection.
class ParScanThreadState {
  friend class ParScanThreadStateSet;
  ObjToScanQueue *_work_queue;

  ParGCAllocBuffer _to_space_alloc_buffer;

  ParScanWithoutBarrierClosure         _to_space_closure; // scan_without_gc_barrier
  ParScanWithBarrierClosure            _old_gen_closure; // scan_with_gc_barrier
  ParRootScanWithoutBarrierClosure     _to_space_root_closure; // scan_root_without_gc_barrier
  // One of these two will be passed to process_strong_roots, which will
  // set its generation.  The first is for two-gen configs where the
  // old gen collects the perm gen; the second is for arbitrary configs.
  // The second isn't used right now (it used to be used for the train, an
  // incremental collector) but the declaration has been left as a reminder.
  ParRootScanWithBarrierTwoGensClosure _older_gen_closure;
  // This closure will always be bound to the old gen; it will be used
  // in evacuate_followers.
  ParRootScanWithBarrierTwoGensClosure _old_gen_root_closure; // scan_old_root_with_gc_barrier
  ParEvacuateFollowersClosure          _evacuate_followers;
  DefNewGeneration::IsAliveClosure     _is_alive_closure;
  ParScanWeakRefClosure                _scan_weak_ref_closure;
  ParKeepAliveClosure                  _keep_alive_closure;


  Space* _to_space;
  Space* to_space() { return _to_space; }

  Generation* _old_gen;
  Generation* old_gen() { return _old_gen; }

  HeapWord *_young_old_boundary;

  int _hash_seed;
  int _thread_num;
  ageTable _ageTable;

  bool _to_space_full;

  int _pushes, _pops, _steals, _steal_attempts, _term_attempts;
  int _overflow_pushes, _overflow_refills, _overflow_refill_objs;

  // Timing numbers.
  double _start;
  double _start_strong_roots;
  double _strong_roots_time;
  double _start_term;
  double _term_time;

  // Helper for trim_queues. Scans subset of an array and makes
  // remainder available for work stealing.
  void scan_partial_array_and_push_remainder(oop obj);

  // In support of CMS' parallel rescan of survivor space.
  ChunkArray* _survivor_chunk_array;
  ChunkArray* survivor_chunk_array() { return _survivor_chunk_array; }

  void record_survivor_plab(HeapWord* plab_start, size_t plab_word_size);

  ParScanThreadState(Space* to_space_, ParNewGeneration* gen_,
                     Generation* old_gen_, int thread_num_,
                     ObjToScanQueueSet* work_queue_set_, size_t desired_plab_sz_,
                     ParallelTaskTerminator& term_);

public:
  ageTable* age_table() {return &_ageTable;}

  ObjToScanQueue* work_queue() { return _work_queue; }

  ParGCAllocBuffer* to_space_alloc_buffer() {
    return &_to_space_alloc_buffer;
  }

  ParEvacuateFollowersClosure&      evacuate_followers_closure() { return _evacuate_followers; }
  DefNewGeneration::IsAliveClosure& is_alive_closure() { return _is_alive_closure; }
  ParScanWeakRefClosure&            scan_weak_ref_closure() { return _scan_weak_ref_closure; }
  ParKeepAliveClosure&              keep_alive_closure() { return _keep_alive_closure; }
  ParScanClosure&                   older_gen_closure() { return _older_gen_closure; }
  ParRootScanWithoutBarrierClosure& to_space_root_closure() { return _to_space_root_closure; };

  // Decrease queue size below "max_size".
  void trim_queues(int max_size);

  // Is new_obj a candidate for scan_partial_array_and_push_remainder method.
  inline bool should_be_partially_scanned(oop new_obj, oop old_obj) const;

  int* hash_seed()  { return &_hash_seed; }
  int  thread_num() { return _thread_num; }

  // Allocate a to-space block of size "sz", or else return NULL.
  HeapWord* alloc_in_to_space_slow(size_t word_sz);

  HeapWord* alloc_in_to_space(size_t word_sz) {
    HeapWord* obj = to_space_alloc_buffer()->allocate(word_sz);
    if (obj != NULL) return obj;
    else return alloc_in_to_space_slow(word_sz);
  }

  HeapWord* young_old_boundary() { return _young_old_boundary; }

  void set_young_old_boundary(HeapWord *boundary) {
    _young_old_boundary = boundary;
  }

  // Undo the most recent allocation ("obj", of "word_sz").
  void undo_alloc_in_to_space(HeapWord* obj, size_t word_sz);

  int pushes() { return _pushes; }
  int pops()   { return _pops; }
  int steals() { return _steals; }
  int steal_attempts() { return _steal_attempts; }
  int term_attempts()  { return _term_attempts; }
  int overflow_pushes() { return _overflow_pushes; }
  int overflow_refills() { return _overflow_refills; }
  int overflow_refill_objs() { return _overflow_refill_objs; }

  void note_push()  { if (PAR_STATS_ENABLED) _pushes++; }
  void note_pop()   { if (PAR_STATS_ENABLED) _pops++; }
  void note_steal() { if (PAR_STATS_ENABLED) _steals++; }
  void note_steal_attempt() { if (PAR_STATS_ENABLED) _steal_attempts++; }
  void note_term_attempt()  { if (PAR_STATS_ENABLED) _term_attempts++; }
  void note_overflow_push() { if (PAR_STATS_ENABLED) _overflow_pushes++; }
  void note_overflow_refill(int objs) {
    if (PAR_STATS_ENABLED) {
      _overflow_refills++;
      _overflow_refill_objs += objs;
    }
  }

  void start_strong_roots() {
    _start_strong_roots = os::elapsedTime();
  }
  void end_strong_roots() {
    _strong_roots_time += (os::elapsedTime() - _start_strong_roots);
  }
  double strong_roots_time() { return _strong_roots_time; }
  void start_term_time() {
    note_term_attempt();
    _start_term = os::elapsedTime();
  }
  void end_term_time() {
    _term_time += (os::elapsedTime() - _start_term);
  }
  double term_time() { return _term_time; }

  double elapsed() {
    return os::elapsedTime() - _start;
  }

};

class ParNewGenTask: public AbstractGangTask {
  ParNewGeneration* _gen;
  Generation* _next_gen;
  HeapWord* _young_old_boundary;
  class ParScanThreadStateSet* _state_set;

public:
  ParNewGenTask(ParNewGeneration*      gen,
                Generation*            next_gen,
                HeapWord*              young_old_boundary,
                ParScanThreadStateSet* state_set);

  HeapWord* young_old_boundary() { return _young_old_boundary; }

  void work(int i);
};

class KeepAliveClosure: public DefNewGeneration::KeepAliveClosure {
 public:
  KeepAliveClosure(ScanWeakRefClosure* cl);
  void do_oop(oop* p);
};

class EvacuateFollowersClosureGeneral: public VoidClosure {
    GenCollectedHeap* _gch;
    int _level;
    OopsInGenClosure* _scan_cur_or_nonheap;
    OopsInGenClosure* _scan_older;
  public:
    EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, int level,
                                    OopsInGenClosure* cur,
                                    OopsInGenClosure* older);
    void do_void();
};

// Closure for scanning ParNewGeneration.
// Same as ScanClosure, except does parallel GC barrier.
class ScanClosureWithParBarrier: public ScanClosure {
public:
  ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier);
  void do_oop(oop* p);
};

// Implements AbstractRefProcTaskExecutor for ParNew.
class ParNewRefProcTaskExecutor: public AbstractRefProcTaskExecutor {
public:

  ParNewRefProcTaskExecutor(ParNewGeneration& generation,
                            ParScanThreadStateSet& state_set)
    : _generation(generation), _state_set(state_set)
  { }

  // Executes a task using worker threads.
  virtual void execute(ProcessTask& task);
  virtual void execute(EnqueueTask& task);
  // Switch to single threaded mode.
  virtual void set_single_threaded_mode();
private:
  ParNewGeneration&      _generation;
  ParScanThreadStateSet& _state_set;
};


// A Generation that does parallel young-gen collection.

class ParNewGeneration: public DefNewGeneration {
  friend class ParNewGenTask;
  friend class ParNewRefProcTask;
  friend class ParNewRefProcTaskExecutor;
  friend class ParScanThreadStateSet;

  // XXX use a global constant instead of 64!
  struct ObjToScanQueuePadded {
        ObjToScanQueue work_queue;
        char pad[64 - sizeof(ObjToScanQueue)];  // prevent false sharing
  };

  // The per-thread work queues, available here for stealing.
  ObjToScanQueueSet* _task_queues;

  // Desired size of survivor space plab's
  PLABStats _plab_stats;

  // A list of from-space images of to-be-scanned objects, threaded through
  // klass-pointers (klass information already copied to the forwarded
  // image.)  Manipulated with CAS.
  oop _overflow_list;

  // If true, older generation does not support promotion undo, so avoid.
  static bool _avoid_promotion_undo;

  // This closure is used by the reference processor to filter out
  // references to live referent.
  DefNewGeneration::IsAliveClosure _is_alive_closure;

  static oop real_forwardee_slow(oop obj);
  static void waste_some_time();

  // Preserve the mark of "obj", if necessary, in preparation for its mark
  // word being overwritten with a self-forwarding-pointer.
  void preserve_mark_if_necessary(oop obj, markOop m);

 protected:

  bool _survivor_overflow;

  bool avoid_promotion_undo() { return _avoid_promotion_undo; }
  void set_avoid_promotion_undo(bool v) { _avoid_promotion_undo = v; }

  bool survivor_overflow() { return _survivor_overflow; }
  void set_survivor_overflow(bool v) { _survivor_overflow = v; }

  // Adjust the tenuring threshold.  See the implementation for
  // the details of the policy.
  virtual void adjust_desired_tenuring_threshold();

public:
  ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level);

  ~ParNewGeneration() {
    for (uint i = 0; i < ParallelGCThreads; i++)
        delete _task_queues->queue(i);

    delete _task_queues;
  }

  virtual void ref_processor_init();
  virtual Generation::Name kind()        { return Generation::ParNew; }
  virtual const char* name() const;
  virtual const char* short_name() const { return "ParNew"; }

  // override
  virtual bool refs_discovery_is_mt()     const {
    assert(UseParNewGC, "ParNewGeneration only when UseParNewGC");
    return ParallelGCThreads > 1;
  }

  // Make the collection virtual.
  virtual void collect(bool   full,
                       bool   clear_all_soft_refs,
                       size_t size,
                       bool   is_tlab);

  // This needs to be visible to the closure function.
  // "obj" is the object to be copied, "m" is a recent value of its mark
  // that must not contain a forwarding pointer (though one might be
  // inserted in "obj"s mark word by a parallel thread).
  inline oop copy_to_survivor_space(ParScanThreadState* par_scan_state,
                             oop obj, size_t obj_sz, markOop m) {
    if (_avoid_promotion_undo) {
       return copy_to_survivor_space_avoiding_promotion_undo(par_scan_state,
                                                             obj, obj_sz, m);
    }

    return copy_to_survivor_space_with_undo(par_scan_state, obj, obj_sz, m);
  }

  oop copy_to_survivor_space_avoiding_promotion_undo(ParScanThreadState* par_scan_state,
                             oop obj, size_t obj_sz, markOop m);

  oop copy_to_survivor_space_with_undo(ParScanThreadState* par_scan_state,
                             oop obj, size_t obj_sz, markOop m);

  // Push the given (from-space) object on the global overflow list.
  void push_on_overflow_list(oop from_space_obj);

  // If the global overflow list is non-empty, move some tasks from it
  // onto "work_q" (which must be empty).  No more than 1/4 of the
  // max_elems of "work_q" are moved.
  bool take_from_overflow_list(ParScanThreadState* par_scan_state);

  // The task queues to be used by parallel GC threads.
  ObjToScanQueueSet* task_queues() {
    return _task_queues;
  }

  PLABStats* plab_stats() {
    return &_plab_stats;
  }

  size_t desired_plab_sz() {
    return _plab_stats.desired_plab_sz();
  }

  static oop real_forwardee(oop obj);

  DEBUG_ONLY(static bool is_legal_forward_ptr(oop p);)
};