hotspot/src/share/vm/gc_implementation/parNew/parNewGeneration.hpp - platform/libcore - Git at Google

 /*
  * 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.
  *
  */

 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);)
 };
	/*
	* 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.
	*
	*/

	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);)
	};