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// 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 PermGen;

class Generation;

class BarrierSet;

class GenRemSet;

class Space;

class SpaceClosure;

class OopClosure;

class OopsInGenClosure;

class ObjectClosure;

class SubTasksDone;

class WorkGang;

class CollectorPolicy;

class KlassHandle;

class SharedHeap : public CollectedHeap {

  friend class VMStructs;

  friend class VM_GC_Operation;

  friend class VM_CGC_Operation;

private:

  // For claiming strong_roots tasks.

  SubTasksDone* _process_strong_tasks;

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;

  // All heaps contain a "permanent generation."  This is some ways

  // similar to a generation in a generational system, in other ways not.

  // See the "PermGen" class.

  PermGen* _perm_gen;

  // 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.

  // Number of parallel threads currently working on GC tasks.

  // O indicates use sequential code; 1 means use parallel code even with

  // only one thread, for performance testing purposes.

  int _n_par_threads;

  // 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; }

  CollectorPolicy *collector_policy() const { return _collector_policy; }

  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();

  void set_perm(PermGen* perm_gen) { _perm_gen = perm_gen; }

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

  // generations; at least the perm gen, possibly more in a fully

  // generational heap.

  GenRemSet* rem_set() { return _rem_set; }

  // These function return the "permanent" generation, in which

  // reflective objects are allocated and stored.  Two versions, the second

  // of which returns the view of the perm gen as a generation.

  PermGen* perm() const { return _perm_gen; }

  Generation* perm_gen() const { return _perm_gen->as_gen(); }

  // Iteration functions.

  void oop_iterate(OopClosure* cl) = 0;

  // Same as above, restricted to a memory region.

  virtual void oop_iterate(MemRegion mr, OopClosure* cl) = 0;

  // Iterate over all objects allocated since the last collection, calling

  // "cl->do_object" on each.  The heap must have been initialized properly

  // to support this function, or else this call will fail.

  virtual void object_iterate_since_last_GC(ObjectClosure* 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_strong_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_strong_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".

 private:

  void change_strong_roots_parity();

 public:

  int strong_roots_parity() { return _strong_roots_parity; }

  // Call these in sequential code around process_strong_roots.

  // strong_roots_prologue calls change_strong_roots_parity, if

  // parallel tasks are enabled.

  class StrongRootsScope : public MarkingCodeBlobClosure::MarkScope {

  public:

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

    ~StrongRootsScope();

  };

  friend class StrongRootsScope;

  enum ScanningOption {

    SO_None                = 0x0,

    SO_AllClasses          = 0x1,

    SO_SystemClasses       = 0x2,

    SO_Symbols             = 0x4,

    SO_Strings             = 0x8,

    SO_CodeCache           = 0x10

  };

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

  // (such as process strong roots) subsequently.

  virtual void set_par_threads(int t);

  // Number of threads currently working on GC tasks.

  int n_par_threads() { return _n_par_threads; }

  // Invoke the "do_oop" method the closure "roots" on all root locations.

  // If "collecting_perm_gen" is false, then roots that may only contain

  // references to permGen objects are not scanned.  If true, the

  // "perm_gen" closure is applied to all older-to-younger refs in the

  // permanent generation.  The "so" argument determines which of roots

  // the closure is applied to:

  // "SO_None" does none;

  // "SO_AllClasses" applies the closure to all entries in the SystemDictionary;

  // "SO_SystemClasses" to all the "system" classes and loaders;

  // "SO_Symbols" applies the closure to all entries in SymbolsTable;

  // "SO_Strings" applies the closure to all entries in StringTable;

  // "SO_CodeCache" applies the closure to all elements of the CodeCache.

  void process_strong_roots(bool activate_scope,

                            bool collecting_perm_gen,

                            ScanningOption so,

                            OopClosure* roots,

                            CodeBlobClosure* code_roots,

                            OopsInGenClosure* perm_blk);

  // Apply "blk" to all the weak roots of the system.  These include

  // JNI weak roots, the code cache, system dictionary, symbol table,

  // string table.

  void process_weak_roots(OopClosure* root_closure,

                          CodeBlobClosure* code_roots,

                          OopClosure* non_root_closure);

  // 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;

  //

  // New methods from CollectedHeap

  //

  size_t permanent_capacity() const {

    assert(perm_gen(), "NULL perm gen");

    return perm_gen()->capacity();

  }

  size_t permanent_used() const {

    assert(perm_gen(), "NULL perm gen");

    return perm_gen()->used();

  }

  bool is_in_permanent(const void *p) const {

    assert(perm_gen(), "NULL perm gen");

    return perm_gen()->is_in_reserved(p);

  }

  // Different from is_in_permanent in that is_in_permanent

  // only checks if p is in the reserved area of the heap

  // and this checks to see if it in the commited area.

  // This is typically used by things like the forte stackwalker

  // during verification of suspicious frame values.

  bool is_permanent(const void *p) const {

    assert(perm_gen(), "NULL perm gen");

    return perm_gen()->is_in(p);

  }

  HeapWord* permanent_mem_allocate(size_t size) {

    assert(perm_gen(), "NULL perm gen");

    return _perm_gen->mem_allocate(size);

  }

  void permanent_oop_iterate(OopClosure* cl) {

    assert(perm_gen(), "NULL perm gen");

    _perm_gen->oop_iterate(cl);

  }

  void permanent_object_iterate(ObjectClosure* cl) {

    assert(perm_gen(), "NULL perm gen");

    _perm_gen->object_iterate(cl);

  }

  // Some utilities.

  void print_size_transition(outputStream* out,

                             size_t bytes_before,

                             size_t bytes_after,

                             size_t capacity);

};