Add a new weak handle callback that passes an Isolate to an embedder

src/global-handles.cc

Index: src/global-handles.cc
diff --git a/src/global-handles.cc b/src/global-handles.cc
index 3f4e3bea59d5fb8d96e9435d3dbb0f6932ffd532..609dc6efa306ce6673443ba0f56e0eb90fc31cb2 100644
--- a/src/global-handles.cc
+++ b/src/global-handles.cc
@@ -78,8 +78,9 @@ class GlobalHandles::Node {
     set_independent(false);
     set_partially_dependent(false);
     set_in_new_space_list(false);
+    set_is_new_callback(false);
+    callback_.new_callback = NULL;
     parameter_or_next_free_.next_free = NULL;
-    callback_ = NULL;
   }
 #endif
 
@@ -100,7 +101,8 @@ class GlobalHandles::Node {
     set_partially_dependent(false);
     set_state(NORMAL);
     parameter_or_next_free_.parameter = NULL;
-    callback_ = NULL;
+    set_is_new_callback(false);
+    callback_.new_callback = NULL;
     IncreaseBlockUses(global_handles);
   }
 
@@ -161,6 +163,13 @@ class GlobalHandles::Node {
     flags_ = IsInNewSpaceList::update(flags_, v);
   }
 
+  bool is_new_callback() {
+    return IsNewCallback::decode(flags_);
+  }
+  void set_is_new_callback(bool v) {
+    flags_ = IsNewCallback::update(flags_, v);
+  }
+
   bool IsNearDeath() const {
     // Check for PENDING to ensure correct answer when processing callbacks.
     return state() == PENDING || state() == NEAR_DEATH;
@@ -195,8 +204,9 @@ class GlobalHandles::Node {
   }
   void clear_partially_dependent() { set_partially_dependent(false); }
 
-  // Callback accessor.
-  WeakReferenceCallback callback() { return callback_; }
+  // Callback accessors.
+  WeakReferenceCallback old_callback() { return callback_.old_callback; }
+  WeakenedReferenceCallback new_callback() { return callback_.new_callback; }
 
   // Callback parameter accessors.
   void set_parameter(void* parameter) {
@@ -230,7 +240,24 @@ class GlobalHandles::Node {
     }
     set_state(WEAK);
     set_parameter(parameter);
-    callback_ = callback;
+    set_is_new_callback(false);
+    callback_.old_callback = callback;
+  }
+
+  void MakeWeak(GlobalHandles* global_handles,
+                void* parameter,
+                WeakenedReferenceCallback callback) {
+    ASSERT(state() != FREE);
+    if (!IsWeakRetainer()) {
+      global_handles->number_of_weak_handles_++;
+      if (object_->IsJSGlobalObject()) {
+        global_handles->number_of_global_object_weak_handles_++;
+      }
+    }
+    set_state(WEAK);
+    set_parameter(parameter);
+    set_is_new_callback(true);
+    callback_.new_callback = callback;
   }
 
   void ClearWeakness(GlobalHandles* global_handles) {
@@ -248,8 +275,7 @@ class GlobalHandles::Node {
   bool PostGarbageCollectionProcessing(Isolate* isolate,
                                        GlobalHandles* global_handles) {
     if (state() != Node::PENDING) return false;
-    WeakReferenceCallback func = callback();
-    if (func == NULL) {
+    if (new_callback() == NULL) {

[Sven Panne, 2013/01/18 08:08:12]

This is a hack and works only because we don't actually check what is stored in
the union. Add an "callback_is_set()" predicate.

[haraken, 2013/01/22 00:27:37]

Done.

       Release(global_handles);
       return false;
     }
@@ -267,7 +293,13 @@ class GlobalHandles::Node {
              ExternalTwoByteString::cast(object_)->resource() != NULL);
       // Leaving V8.
       VMState state(isolate, EXTERNAL);
-      func(object, par);
+      if (is_new_callback()) {
+        WeakenedReferenceCallback callback = new_callback();
+        callback(reinterpret_cast<v8::Isolate*>(isolate), object, par);
+      } else {
+        WeakReferenceCallback callback = old_callback();
+        callback(object, par);
+      }
     }
     // Absence of explicit cleanup or revival of weak handle
     // in most of the cases would lead to memory leak.
@@ -299,11 +331,15 @@ class GlobalHandles::Node {
   class IsIndependent:        public BitField<bool,  4, 1> {};
   class IsPartiallyDependent: public BitField<bool,  5, 1> {};
   class IsInNewSpaceList:     public BitField<bool,  6, 1> {};
+  class IsNewCallback:        public BitField<bool,  7, 1> {};
 
   uint8_t flags_;
 
   // Handle specific callback.
-  WeakReferenceCallback callback_;
+  union {
+    WeakReferenceCallback old_callback;
+    WeakenedReferenceCallback new_callback;
+  } callback_;
 
   // Provided data for callback.  In FREE state, this is used for
   // the free list link.
@@ -478,6 +514,13 @@ void GlobalHandles::MakeWeak(Object** location, void* parameter,
 }
 
 
+void GlobalHandles::MakeWeak(Object** location, void* parameter,
+                             WeakenedReferenceCallback callback) {
+  ASSERT(callback != NULL);
+  Node::FromLocation(location)->MakeWeak(this, parameter, callback);
+}
+
+
 void GlobalHandles::ClearWeakness(Object** location) {
   Node::FromLocation(location)->ClearWeakness(this);
 }
@@ -523,16 +566,6 @@ void GlobalHandles::IterateWeakRoots(ObjectVisitor* v) {
 }
 
 
-void GlobalHandles::IterateWeakRoots(WeakReferenceGuest f,
-                                     WeakReferenceCallback callback) {
-  for (NodeIterator it(this); !it.done(); it.Advance()) {
-    if (it.node()->IsWeak() && it.node()->callback() == callback) {
-      f(it.node()->object(), it.node()->parameter());
-    }
-  }
-}
-
-
 void GlobalHandles::IdentifyWeakHandles(WeakSlotCallback f) {
   for (NodeIterator it(this); !it.done(); it.Advance()) {
     if (it.node()->IsWeak() && f(it.node()->location())) {