Implement prologue weak persistent handles.

runtime/vm/scavenger.h

Index: runtime/vm/scavenger.h
diff --git a/runtime/vm/scavenger.h b/runtime/vm/scavenger.h
index fc9b6e64d823e0e79525e14f61801d44d2ac9118..5975d2e2e3056c90b04e5a46b7944a31d5db9af8 100644
--- a/runtime/vm/scavenger.h
+++ b/runtime/vm/scavenger.h
@@ -59,7 +59,8 @@ class Scavenger {
   }
 
   // Collect the garbage in this scavenger.
-  void Scavenge();
+  void Scavenge() { Scavenge(false); }
+  void Scavenge(bool invoke_api_callbacks);

[siva, 2012/03/09 21:48:41]

Does it make sense to use a default argument here instead of two methods?

[cshapiro, 2012/03/13 23:06:43]

Sorry about this.  It was meant to be a placeholder for code that heuristically
determines when to invoke the API callbacks.  I have moved the code into the .cc
file and added a corresponding TODO.

 
   // Accessors to generate code for inlined allocation.
   uword* TopAddress() { return &top_; }
@@ -73,11 +74,15 @@ class Scavenger {
 
  private:
   uword FirstObjectStart() const { return to_->start() | object_alignment_; }
-  void Prologue();
-  void IterateRoots(Isolate* isolate, ObjectPointerVisitor* visitor);
-  void IterateWeakRoots(Isolate* isolate, HandleVisitor* visitor);
+  void Prologue(Isolate* isolate, bool invoke_api_callbacks);
+  void IterateRoots(Isolate* isolate,
+                    ObjectPointerVisitor* visitor,
+                    bool visit_prologue_weak_persistent_handles);
+  void IterateWeakRoots(Isolate* isolate,
+                        HandleVisitor* visitor,
+                        bool visit_prologue_weak_persistent_handles);
   void ProcessToSpace(ObjectPointerVisitor* visitor);
-  void Epilogue();
+  void Epilogue(Isolate* isolate, bool invoke_api_callbacks);
 
   // During a scavenge we need to remember the promoted objects.
   // This is implemented as a stack of objects at the end of the to space. As