Reduce storage size of weak callbacks

src/global-handles.cc

 // Copyright 2009 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 65 matching lines @@
   ~Node() {
     // TODO(1428): if it's a weak handle we should have invoked its callback.
     // Zap the values for eager trapping.
     object_ = reinterpret_cast<Object*>(kGlobalHandleZapValue);
     class_id_ = v8::HeapProfiler::kPersistentHandleNoClassId;
     index_ = 0;
     set_independent(false);
     set_partially_dependent(false);
     set_in_new_space_list(false);
     parameter_or_next_free_.next_free = NULL;
-    weak_reference_callback_ = NULL;
     near_death_callback_ = NULL;
   }
 #endif
 
   void Initialize(int index, Node** first_free) {
     index_ = static_cast<uint8_t>(index);
     ASSERT(static_cast<int>(index_) == index);
     set_state(FREE);
     set_in_new_space_list(false);
     parameter_or_next_free_.next_free = *first_free;
     *first_free = this;
   }
 
   void Acquire(Object* object, GlobalHandles* global_handles) {
     ASSERT(state() == FREE);
     object_ = object;
     class_id_ = v8::HeapProfiler::kPersistentHandleNoClassId;
     set_independent(false);
     set_partially_dependent(false);
     set_state(NORMAL);
     parameter_or_next_free_.parameter = NULL;
-    weak_reference_callback_ = NULL;
     near_death_callback_ = NULL;
     IncreaseBlockUses(global_handles);
   }
 
   void Release(GlobalHandles* global_handles) {
     ASSERT(state() != FREE);
     set_state(FREE);
     // TODO(mstarzinger): Put behind debug flag once embedders are stabilized.
     object_ = reinterpret_cast<Object*>(kGlobalHandleZapValue);
 #ifdef DEBUG
     // Zap the values for eager trapping.
     class_id_ = v8::HeapProfiler::kPersistentHandleNoClassId;
     set_independent(false);
     set_partially_dependent(false);
-    weak_reference_callback_ = NULL;
     near_death_callback_ = NULL;
 #endif
     parameter_or_next_free_.next_free = global_handles->first_free_;
     global_handles->first_free_ = this;
     DecreaseBlockUses(global_handles);
   }
 
   // Object slot accessors.
   Object* object() const { return object_; }
   Object** location() { return &object_; }
@@ skipping 94 matching lines @@
     parameter_or_next_free_.next_free = value;
   }
 
   void MakeWeak(GlobalHandles* global_handles,
                 void* parameter,
                 WeakReferenceCallback weak_reference_callback,
                 NearDeathCallback near_death_callback) {
     ASSERT(state() != FREE);
     set_state(WEAK);
     set_parameter(parameter);
-    weak_reference_callback_ = weak_reference_callback;
-    near_death_callback_ = near_death_callback;
+    if (weak_reference_callback != NULL) {
+      flags_ = IsWeakCallback::update(flags_, true);
+      near_death_callback_ =
+          reinterpret_cast<NearDeathCallback>(weak_reference_callback);
+    } else {
+      flags_ = IsWeakCallback::update(flags_, false);
+      near_death_callback_ = near_death_callback;
+    }
   }
 
   void ClearWeakness(GlobalHandles* global_handles) {
     ASSERT(state() != FREE);
     set_state(NORMAL);
     set_parameter(NULL);
   }
 
   bool PostGarbageCollectionProcessing(Isolate* isolate,
                                        GlobalHandles* global_handles) {
     if (state() != Node::PENDING) return false;
-    if (weak_reference_callback_ == NULL &&
-        near_death_callback_ == NULL) {
+    if (near_death_callback_ == NULL) {
       Release(global_handles);
       return false;
     }
     void* par = parameter();
     set_state(NEAR_DEATH);
     set_parameter(NULL);
 
     v8::Persistent<v8::Object> object = ToApi<v8::Object>(handle());
     {
       // Check that we are not passing a finalized external string to
       // the callback.
       ASSERT(!object_->IsExternalAsciiString() ||
              ExternalAsciiString::cast(object_)->resource() != NULL);
       ASSERT(!object_->IsExternalTwoByteString() ||
              ExternalTwoByteString::cast(object_)->resource() != NULL);
       // Leaving V8.
       VMState state(isolate, EXTERNAL);
-      if (weak_reference_callback_ != NULL) {
-        weak_reference_callback_(object, par);
-      }
       if (near_death_callback_ != NULL) {
-        near_death_callback_(reinterpret_cast<v8::Isolate*>(isolate),
-                             object,
-                             par);
+        if (IsWeakCallback::decode(flags_)) {
+          WeakReferenceCallback callback =
+              reinterpret_cast<WeakReferenceCallback>(near_death_callback_);
+          callback(object, par);
+        } else {
+          near_death_callback_(reinterpret_cast<v8::Isolate*>(isolate),
+                               object,
+                               par);
+        }
       }
     }
     // Absence of explicit cleanup or revival of weak handle
     // in most of the cases would lead to memory leak.
     ASSERT(state() != NEAR_DEATH);
     return true;
   }
 
  private:
   inline NodeBlock* FindBlock();
@@ skipping 12 matching lines @@
 
   // Index in the containing handle block.
   uint8_t index_;
 
   // This stores three flags (independent, partially_dependent and
   // in_new_space_list) and a State.
   class NodeState:            public BitField<State, 0, 4> {};
   class IsIndependent:        public BitField<bool,  4, 1> {};
   class IsPartiallyDependent: public BitField<bool,  5, 1> {};
   class IsInNewSpaceList:     public BitField<bool,  6, 1> {};
+  class IsWeakCallback:       public BitField<bool,  7, 1> {};
 
   uint8_t flags_;
 
-  // Handle specific callback.
-  WeakReferenceCallback weak_reference_callback_;
+  // Handle specific callback - might be a weak reference in disguise.
   NearDeathCallback near_death_callback_;
 
   // Provided data for callback.  In FREE state, this is used for
   // the free list link.
   union {
     void* parameter;
     Node* next_free;
   } parameter_or_next_free_;
 
   DISALLOW_COPY_AND_ASSIGN(Node);
@@ skipping 150 matching lines @@
   number_of_global_handles_--;
   if (location == NULL) return;
   Node::FromLocation(location)->Release(this);
 }
 
 
 void GlobalHandles::MakeWeak(Object** location,
                              void* parameter,
                              WeakReferenceCallback weak_reference_callback,
                              NearDeathCallback near_death_callback) {
-  ASSERT((weak_reference_callback != NULL) !=
-         (near_death_callback != NULL));
+  ASSERT(near_death_callback != NULL);
   Node::FromLocation(location)->MakeWeak(this,
                                          parameter,
                                          weak_reference_callback,
                                          near_death_callback);
 }
 
 
 void GlobalHandles::ClearWeakness(Object** location) {
   Node::FromLocation(location)->ClearWeakness(this);
 }
@@ skipping 358 matching lines @@
   implicit_ref_groups_.Clear();
 }
 
 
 void GlobalHandles::TearDown() {
   // TODO(1428): invoke weak callbacks.
 }
 
 
 } }  // namespace v8::internal