text: // Copyright 2007-2008 Google Inc. All Rights Reserved.
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
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  //       notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  //       copyright notice, this list of conditions and the following
  //       disclaimer in the documentation and/or other materials provided
  //       with the distribution.
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  //       contributors may be used to endorse or promote products derived
  //       from this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  #ifndef V8_GLOBAL_HANDLES_H_
  #define V8_GLOBAL_HANDLES_H_
  
  #include "list-inl.h"
  
  namespace v8 { namespace internal {
  
  // Structure for tracking global handles.
  // A single list keeps all the allocated global handles.
  // Destroyed handles stay in the list but is added to the free list.
  // At GC the destroyed global handles are removed from the free list
  // and deallocated.
  
  // Callback function on handling weak global handles.
  // typedef bool (*WeakSlotCallback)(Object** pointer);
  
  // An object group is indexed by an id. An object group is treated like
  // a single JS object: if one of object in the group is alive,
  // all objects in the same group are considered alive.
  // An object group is used to simulate object relationship in a DOM tree.
  class ObjectGroup : public Malloced {
   public:
    explicit ObjectGroup(void* id) : id_(id), objects_(4) {}
  
    void* id_;
    List<Object**> objects_;
  };
  
  
  class GlobalHandles : public AllStatic {
   public:
    // Creates a new global handle that is alive until Destroy is called.
    static Handle<Object> Create(Object* value);
  
    // Destroy a global handle.
    static void Destroy(Object** location);
  
    // Make the global handle weak and set the callback parameter for the
    // handle.  When the garbage collector recognizes that only weak global
    // handles point to an object the handles are cleared and the callback
    // function is invoked (for each handle) with the handle and corresponding
    // parameter as arguments.  Note: cleared means set to Smi::FromInt(0). The
    // reason is that Smi::FromInt(0) does not change during garage collection.
    static void MakeWeak(Object** location,
                         void* parameter,
                         WeakReferenceCallback callback);
  
    // Returns the current number of weak handles.
    static int NumberOfWeakHandles() { return number_of_weak_handles_; }
  
    // Returns the current number of weak handles to global objects.
    // These handles are also included in NumberOfWeakHandles().
    static int NumberOfGlobalObjectWeakHandles() {
      return number_of_global_object_weak_handles_;
    }
  
    // Clear the weakness of a global handle.
    static void ClearWeakness(Object** location);
  
    // Tells whether global handle is near death.
    static bool IsNearDeath(Object** location);
  
    // Tells whether global handle is weak.
    static bool IsWeak(Object** location);
  
    // Process pending weak handles.
    static void PostGarbageCollectionProcessing();
  
    // Iterates over all handles.
    static void IterateRoots(ObjectVisitor* v);
  
    // Iterates over all weak roots in heap.
    static void IterateWeakRoots(ObjectVisitor* v);
  
    // Mark the weak pointers based on the callback.
    static void MarkWeakRoots(WeakSlotCallback f);
  
    // Add an object to a group indexed by an id.
    // Should only used in GC callback function before a collection.
    // All groups are destroyed after a mark-compact collection.
    static void AddToGroup(void* id, Object** location);
  
    // Returns the object groups.
    static List<ObjectGroup*>& ObjectGroups() {
      return object_groups_;
    }
  
    // Remove bags, this should only happen after GC.
    static void RemoveObjectGroups();
  
    // Tear down the global handle structure.
    static void TearDown();
  
  #ifdef DEBUG
    static void PrintStats();
    static void Print();
  #endif
   private:
    // Internal node structure, one for each global handle.
    class Node;
  
    // Field always containing the number of weak and near-death handles.
    static int number_of_weak_handles_;
  
    // Field always containing the number of weak and near-death handles
    // to global objects.  These objects are also included in
    // number_of_weak_handles_.
    static int number_of_global_object_weak_handles_;
  
    // Global handles are kept in a single linked list pointed to by head_.
    static Node* head_;
    static Node* head() { return head_; }
    static void set_head(Node* value) { head_ = value; }
  
    // Free list for DESTROYED global handles not yet deallocated.
    static Node* first_free_;
    static Node* first_free() { return first_free_; }
    static void set_first_free(Node* value) { first_free_ = value; }
  
    // A list of object groups.
    static List<ObjectGroup*> object_groups_;
  };
  
  
  } }  // namespace v8::internal
  
  #endif  // V8_GLOBAL_HANDLES_H_
  