Introduce one way dependencies into object grouping.

src/global-handles.h

 // Copyright 2007-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       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
@@ skipping 21 matching lines @@
 
 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 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:
   ObjectGroup() : objects_(4) {}
   ObjectGroup(size_t capacity, v8::RetainedObjectInfo* info)
       : objects_(static_cast<int>(capacity)),
         info_(info) { }
   ~ObjectGroup() { if (info_ != NULL) info_->Dispose(); }
 
   List<Object**> objects_;
   v8::RetainedObjectInfo* info_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ObjectGroup);
 };
 
 
+// An implicit references group consists of two parts: a parent object and
+// a list of children objects.  If the parent is alive, all the children
+// are alive too.
+class ImplicitRefGroup : public Malloced {
+ public:
+  ImplicitRefGroup() : children_(4) {}
+  ImplicitRefGroup(HeapObject* parent, size_t capacity)
+      : parent_(parent),
+        children_(static_cast<int>(capacity)) { }
+
+  HeapObject* parent_;
+  List<Object**> children_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ImplicitRefGroup);
+};
+
+
 typedef void (*WeakReferenceGuest)(Object* object, void* parameter);
 
 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);
 
@@ skipping 47 matching lines @@
 
   // Iterates over weak roots that are bound to a given callback.
   static void IterateWeakRoots(WeakReferenceGuest f,
                                WeakReferenceCallback callback);
 
   // Find all weak handles satisfying the callback predicate, mark
   // them as pending.
   static void IdentifyWeakHandles(WeakSlotCallback f);
 
   // Add an object group.
-  // Should only used in GC callback function before a collection.
+  // Should be only used in GC callback function before a collection.
   // All groups are destroyed after a mark-compact collection.
-  static void AddGroup(Object*** handles,
-                       size_t length,
-                       v8::RetainedObjectInfo* info);
+  static void AddObjectGroup(Object*** handles,
+                             size_t length,
+                             v8::RetainedObjectInfo* info);
+
+  // Add an implicit references' group.
+  // Should be only used in GC callback function before a collection.
+  // All groups are destroyed after a mark-compact collection.
+  static void AddImplicitRefGroup(HeapObject* parent,
+                                  Object*** children,
+                                  size_t length);
 
   // Returns the object groups.
   static List<ObjectGroup*>* ObjectGroups();
 
+  // Returns the implicit references' groups.
+  static List<ImplicitRefGroup*>* ImplicitRefGroups();
+
   // Remove bags, this should only happen after GC.
   static void RemoveObjectGroups();
+  static void RemoveImplicitRefGroups();
 
   // Tear down the global handle structure.
   static void TearDown();
 
 #ifdef DEBUG
   static void PrintStats();
   static void Print();
 #endif
   class Pool;
  private:
@@ skipping 33 matching lines @@
   static Node* first_deallocated() { return first_deallocated_; }
   static void set_first_deallocated(Node* value) {
     first_deallocated_ = value;
   }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_GLOBAL_HANDLES_H_