Use a tag bit for indicating prologue weak persistent handles, this avoids

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"
 #include "vm/flags.h"
 #include "vm/os.h"
@@ skipping 46 matching lines @@
 
 
 // Forward declarations.
 class ObjectPointerVisitor;
 
 DECLARE_FLAG(bool, verify_handles);
 DECLARE_DEBUG_FLAG(bool, trace_handles);
 
 class HandleVisitor {
  public:
-  virtual void VisitHandle(uword addr) = 0;
+  virtual void VisitHandle(uword addr, bool is_prologue_weak) = 0;
 
   virtual ~HandleVisitor() {
   }
 };
 
 
 template <int kHandleSizeInWords, int kHandlesPerChunk, int kOffsetOfRawPtr>
 class Handles {
  public:
   Handles()
@@ skipping 12 matching lines @@
   void VisitScopedHandles(ObjectPointerVisitor* visitor);
 
   // Visit all blocks that have been added since the last time
   // this method was called.
   // Be careful with this, since multiple users of this method could
   // interfere with eachother.
   // Currently only used by GC trace facility.
   void VisitUnvisitedScopedHandles(ObjectPointerVisitor* visitor);
 
   // Visit all of the various handles.
-  void Visit(HandleVisitor* visitor);
+  void Visit(HandleVisitor* visitor, bool is_prologue_weak);
 
   // Reset the handles so that we can reuse.
   void Reset();
 
   // 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(Isolate* isolate);
 
   // Allocates a handle in the current zone. This handle will be destroyed
@@ skipping 54 matching lines @@
       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);
+    void Visit(HandleVisitor* visitor, bool is_prologue_weak);
 
 #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.
@@ skipping 155 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_