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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_SHAREDHEAP_HPP

 #define SHARE_VM_MEMORY_SHAREDHEAP_HPP

 #include "gc_interface/collectedHeap.hpp"

 #include "memory/generation.hpp"

 // A "SharedHeap" is an implementation of a java heap for HotSpot.  This

 // is an abstract class: there may be many different kinds of heaps.  This

 // class defines the functions that a heap must implement, and contains

 // infrastructure common to all heaps.

 class Generation;

 class BarrierSet;

 class GenRemSet;

 class Space;

 class SpaceClosure;

 class OopClosure;

 class OopsInGenClosure;

 class ObjectClosure;

 class SubTasksDone;

 class WorkGang;

 class FlexibleWorkGang;

 class CollectorPolicy;

 class KlassClosure;

 // Note on use of FlexibleWorkGang's for GC.

 // There are three places where task completion is determined.

 // In

 //    1) ParallelTaskTerminator::offer_termination() where _n_threads

 //    must be set to the correct value so that count of workers that

 //    have offered termination will exactly match the number

 //    working on the task.  Tasks such as those derived from GCTask

 //    use ParallelTaskTerminator's.  Tasks that want load balancing

 //    by work stealing use this method to gauge completion.

 //    2) SubTasksDone has a variable _n_threads that is used in

 //    all_tasks_completed() to determine completion.  all_tasks_complete()

 //    counts the number of tasks that have been done and then reset

 //    the SubTasksDone so that it can be used again.  When the number of

 //    tasks is set to the number of GC workers, then _n_threads must

 //    be set to the number of active GC workers. G1RootProcessor and

 //    GenCollectedHeap have SubTasksDone.

 //    3) SequentialSubTasksDone has an _n_threads that is used in

 //    a way similar to SubTasksDone and has the same dependency on the

 //    number of active GC workers.  CompactibleFreeListSpace and Space

 //    have SequentialSubTasksDone's.

 //

 // Examples of using SubTasksDone and SequentialSubTasksDone:

 //  G1RootProcessor and GenCollectedHeap::process_roots() use

 //  SubTasksDone* _process_strong_tasks to claim tasks for workers

 //

 //  GenCollectedHeap::gen_process_roots() calls

 //      rem_set()->younger_refs_iterate()

 //  to scan the card table and which eventually calls down into

 //  CardTableModRefBS::par_non_clean_card_iterate_work().  This method

 //  uses SequentialSubTasksDone* _pst to claim tasks.

 //  Both SubTasksDone and SequentialSubTasksDone call their method

 //  all_tasks_completed() to count the number of GC workers that have

 //  finished their work.  That logic is "when all the workers are

 //  finished the tasks are finished".

 //

 //  The pattern that appears  in the code is to set _n_threads

 //  to a value > 1 before a task that you would like executed in parallel

 //  and then to set it to 0 after that task has completed.  A value of

 //  0 is a "special" value in set_n_threads() which translates to

 //  setting _n_threads to 1.

 //

 //  Some code uses _n_terminiation to decide if work should be done in

 //  parallel.  The notorious possibly_parallel_oops_do() in threads.cpp

 //  is an example of such code.  Look for variable "is_par" for other

 //  examples.

 //

 //  The active_workers is not reset to 0 after a parallel phase.  It's

 //  value may be used in later phases and in one instance at least

 //  (the parallel remark) it has to be used (the parallel remark depends

 //  on the partitioning done in the previous parallel scavenge).

 class SharedHeap : public CollectedHeap {

   friend class VMStructs;

   friend class VM_GC_Operation;

   friend class VM_CGC_Operation;

 protected:

   // There should be only a single instance of "SharedHeap" in a program.

   // This is enforced with the protected constructor below, which will also

   // set the static pointer "_sh" to that instance.

   static SharedHeap* _sh;

   // and the Gen Remembered Set, at least one good enough to scan the perm

   // gen.

   GenRemSet* _rem_set;

   // A gc policy, controls global gc resource issues

   CollectorPolicy *_collector_policy;

   // See the discussion below, in the specification of the reader function

   // for this variable.

   int _strong_roots_parity;

   // If we're doing parallel GC, use this gang of threads.

   FlexibleWorkGang* _workers;

   // Full initialization is done in a concrete subtype's "initialize"

   // function.

   SharedHeap(CollectorPolicy* policy_);

   // Returns true if the calling thread holds the heap lock,

   // or the calling thread is a par gc thread and the heap_lock is held

   // by the vm thread doing a gc operation.

   bool heap_lock_held_for_gc();

   // True if the heap_lock is held by the a non-gc thread invoking a gc

   // operation.

   bool _thread_holds_heap_lock_for_gc;

 public:

   static SharedHeap* heap() { return _sh; }

   void set_barrier_set(BarrierSet* bs);

   // Does operations required after initialization has been done.

   virtual void post_initialize();

   // Initialization of ("weak") reference processing support

   virtual void ref_processing_init();

   // This function returns the "GenRemSet" object that allows us to scan

   // generations in a fully generational heap.

   GenRemSet* rem_set() { return _rem_set; }

   // Iteration functions.

   void oop_iterate(ExtendedOopClosure* cl) = 0;

   // Iterate over all spaces in use in the heap, in an undefined order.

   virtual void space_iterate(SpaceClosure* cl) = 0;

   // A SharedHeap will contain some number of spaces.  This finds the

   // space whose reserved area contains the given address, or else returns

   // NULL.

   virtual Space* space_containing(const void* addr) const = 0;

   bool no_gc_in_progress() { return !is_gc_active(); }

   // Some collectors will perform "process_strong_roots" in parallel.

   // Such a call will involve claiming some fine-grained tasks, such as

   // scanning of threads.  To make this process simpler, we provide the

   // "strong_roots_parity()" method.  Collectors that start parallel tasks

   // whose threads invoke "process_strong_roots" must

   // call "change_strong_roots_parity" in sequential code starting such a

   // task.  (This also means that a parallel thread may only call

   // process_strong_roots once.)

   //

   // For calls to process_roots by sequential code, the parity is

   // updated automatically.

   //

   // The idea is that objects representing fine-grained tasks, such as

   // threads, will contain a "parity" field.  A task will is claimed in the

   // current "process_roots" call only if its parity field is the

   // same as the "strong_roots_parity"; task claiming is accomplished by

   // updating the parity field to the strong_roots_parity with a CAS.

   //

   // If the client meats this spec, then strong_roots_parity() will have

   // the following properties:

   //   a) to return a different value than was returned before the last

   //      call to change_strong_roots_parity, and

   //   c) to never return a distinguished value (zero) with which such

   //      task-claiming variables may be initialized, to indicate "never

   //      claimed".

  public:

   int strong_roots_parity() { return _strong_roots_parity; }

   // Call these in sequential code around process_roots.

   // strong_roots_prologue calls change_strong_roots_parity, if

   // parallel tasks are enabled.

   class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope {

     SharedHeap*   _sh;

    public:

     StrongRootsScope(SharedHeap* heap, bool activate = true);

   };

   friend class StrongRootsScope;

  private:

   void change_strong_roots_parity();

  public:

   FlexibleWorkGang* workers() const { return _workers; }

   // The functions below are helper functions that a subclass of

   // "SharedHeap" can use in the implementation of its virtual

   // functions.

 public:

   // Do anything common to GC's.

   virtual void gc_prologue(bool full) = 0;

   virtual void gc_epilogue(bool full) = 0;

   // Sets the number of parallel threads that will be doing tasks

   // (such as process roots) subsequently.

   virtual void set_par_threads(uint t);

   //

   // New methods from CollectedHeap

   //

   // Some utilities.

   void print_size_transition(outputStream* out,

                              size_t bytes_before,

                              size_t bytes_after,

                              size_t capacity);

 };

 #endif // SHARE_VM_MEMORY_SHAREDHEAP_HPP