Implement weak persistent handles in the Dart API.

runtime/vm/handles.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_HANDLES_H_
 #define VM_HANDLES_H_
 
 #include "vm/allocation.h"
 
 namespace dart {
@@ skipping 40 matching lines @@
 //   NOHANDLESCOPE(isolate);
 //   ....
 //   ....
 // }
 
 
 // Forward declarations.
 class ObjectPointerVisitor;
 
 
+class HandleVisitor {
+ public:
+  virtual void Visit(uword* addr) = 0;
+
+  virtual ~HandleVisitor() {
+  }
+};
+
+
 template <int kHandleSizeInWords, int kHandlesPerChunk, int kOffsetOfRawPtr>
 class Handles {
  public:
   Handles()
       : zone_blocks_(NULL),
         first_scoped_block_(NULL),
         scoped_blocks_(&first_scoped_block_) {
   }
   ~Handles() {
     DeleteAll();
   }
 
   // Visit all object pointers stored in the various handles.
   void VisitObjectPointers(ObjectPointerVisitor* visitor);
 
+  // Visits all of the various handles.
+  void Visit(HandleVisitor* visitor);
+
   // Allocates a handle in the current handle scope. This handle is valid only
   // in the current handle scope and is destroyed when the current handle
   // scope ends.
   static uword AllocateHandle();
 
   // Allocates a handle in the current zone. This handle will be destroyed
   // when the current zone is destroyed.
   static uword AllocateZoneHandle();
 
   // Returns true if specified handle is a zone handle.
@@ skipping 49 matching lines @@
     uword AllocateHandle() {
       ASSERT(!IsFull());
       uword handle_address = reinterpret_cast<uword>(data_ + next_handle_slot_);
       next_handle_slot_ += kHandleSizeInWords;
       return handle_address;
     }
 
     // Visit all object pointers in the handle block.
     void VisitObjectPointers(ObjectPointerVisitor* visitor);
 
+    // Visit all of the handles in the handle block.
+    void Visit(HandleVisitor* visitor);
+
 #if defined(DEBUG)
     // Zaps the free handle area to an uninitialized value.
     void ZapFreeHandles();
 #endif
 
     // Returns number of active handles in the handle block.
     int HandleCount() const;
 
     // Accessors.
     intptr_t next_handle_slot() const { return next_handle_slot_; }
@@ skipping 145 matching lines @@
 };
 #endif  // defined(DEBUG)
 
 // Macro to start a no handles scope in the code.
 #define NOHANDLESCOPE(isolate)                                                \
     dart::NoHandleScope no_vm_internal_handles_scope_(isolate);
 
 }  // namespace dart
 
 #endif  // VM_HANDLES_H_