Remove HandleCell and use GlobalHandle and HandleScope::Escape instead.

src/handles.h

 // Copyright 2006-2008 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 75 matching lines @@
 
   // Closes the given scope, but lets this handle escape. See
   // implementation in api.h.
   inline Handle<T> EscapeFrom(v8::HandleScope* scope);
 
  private:
   T** location_;
 };
 
 
-// A handle-scope based variable. The value stored in the variable can change
-// over time. The value stored in the variable at any time is a root
-// for garbage collection.
-// The variable is backed by the current HandleScope.
-template <typename T>
-class HandleCell {
- public:
-  // Create a new HandleCell holding the given value.
-  explicit HandleCell(Handle<T> value);
-  explicit HandleCell(T* value);
-
-  // Create an alias of an existing HandleCell.
-  explicit HandleCell(const HandleCell<T>& value)
-      : location_(value.location_) { }
-
-  INLINE(T* operator->() const) { return operator*(); }
-  INLINE(T* operator*() const) {
-    return *location_;
-  }
-  INLINE(void operator=(T* value)) {
-    *location_ = value;
-  }
-  INLINE(void operator=(Handle<T> value)) {
-    *location_ = *value;
-  }
-  INLINE(void operator=(const HandleCell<T>& value)) {
-    *location_ = *value.location_;
-  }
-
-  // Extract the value of the variable and cast it to a give type.
-  // This is typically used for calling methods on a more specialized type.
-  template <typename S>
-  inline S* cast() {
-    S::cast(*location_);
-    return *reinterpret_cast<S**>(location_);
-  }
-
-  Handle<T> ToHandle() const {
-    return Handle<T>(*location_);
-  }
-
- private:
-  // Prevent implicit constructor from being created.
-  HandleCell();
-
-  T** location_;
-};
-
-
 // A stack-allocated class that governs a number of local handles.
 // After a handle scope has been created, all local handles will be
 // allocated within that handle scope until either the handle scope is
 // deleted or another handle scope is created.  If there is already a
 // handle scope and a new one is created, all allocations will take
 // place in the new handle scope until it is deleted.  After that,
 // new handles will again be allocated in the original handle scope.
 //
 // After the handle scope of a local handle has been deleted the
 // garbage collector will no longer track the object stored in the
 // handle and may deallocate it.  The behavior of accessing a handle
 // for which the handle scope has been deleted is undefined.
 class HandleScope {
  public:
   HandleScope() : prev_next_(current_.next), prev_limit_(current_.limit) {
     current_.level++;
   }
 
   ~HandleScope() {
-    current_.next = prev_next_;
-    current_.level--;
-    if (current_.limit != prev_limit_) {
-      current_.limit = prev_limit_;
-      DeleteExtensions();
-    }
-#ifdef DEBUG
-    ZapRange(prev_next_, prev_limit_);
-#endif
+    CloseScope();
   }
 
   // Counts the number of allocated handles.
   static int NumberOfHandles();
 
   // Creates a new handle with the given value.
   template <typename T>
   static inline T** CreateHandle(T* value) {
     internal::Object** cur = current_.next;
     if (cur == current_.limit) cur = Extend();
     // Update the current next field, set the value in the created
     // handle, and return the result.
     ASSERT(cur < current_.limit);
     current_.next = cur + 1;
 
     T** result = reinterpret_cast<T**>(cur);
     *result = value;
     return result;
   }
 
   // Deallocates any extensions used by the current scope.
   static void DeleteExtensions();
 
   static Address current_next_address();
   static Address current_limit_address();
   static Address current_level_address();
 
+  template <typename T>
+  Handle<T> Escape(Handle<T> handle_value) {

[Mads Ager (chromium), 2011/03/01 13:43:22]

I find the name Escape a little bit misleading since it also closes the scope.
Can we call it something like CloseAndEscape(handle)?

[Lasse Reichstein, 2011/03/01 14:02:32]

Done.

+    T* value = *handle_value;
+    // Throw away all handles in the current scope.
+    CloseScope();
+    // Allocate one handle in the parent scope.
+    ASSERT(current_.level > 0);
+    Handle<T> result(CreateHandle<T>(value));
+    // Reinitialize the current scope (so that it's ready
+    // to be used or closed again).
+    prev_next_ = current_.next;
+    prev_limit_ = current_.limit;
+    current_.level++;
+    return result;
+  }
+
  private:
   // Prevent heap allocation or illegal handle scopes.
   HandleScope(const HandleScope&);
   void operator=(const HandleScope&);
   void* operator new(size_t size);
   void operator delete(void* size_t);
 
+  inline void CloseScope() {
+    current_.next = prev_next_;
+    current_.level--;
+    if (current_.limit != prev_limit_) {
+      current_.limit = prev_limit_;
+      DeleteExtensions();
+    }
+#ifdef DEBUG
+    ZapRange(prev_next_, prev_limit_);
+#endif
+  }
+
   static v8::ImplementationUtilities::HandleScopeData current_;
-  Object** const prev_next_;
-  Object** const prev_limit_;
+  // Holds values on entry. The prev_next_ value is never NULL
+  // on_entry, but is set to NULL when this scope is closed.
+  Object** prev_next_;
+  Object** prev_limit_;
 
   // Extend the handle scope making room for more handles.
   static internal::Object** Extend();
 
   // Zaps the handles in the half-open interval [start, end).
   static void ZapRange(internal::Object** start, internal::Object** end);
 
   friend class v8::HandleScope;
   friend class v8::ImplementationUtilities;
 };
@@ skipping 215 matching lines @@
  private:
   bool has_been_transformed_;  // Tells whether the object has been transformed.
   int unused_property_fields_;  // Captures the unused number of field.
   Handle<JSObject> object_;    // The object being optimized.
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HANDLES_H_