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      1 // Copyright 2014 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef EXTENSIONS_RENDERER_SCOPED_PERSISTENT_H_
      6 #define EXTENSIONS_RENDERER_SCOPED_PERSISTENT_H_
      7 
      8 #include "base/logging.h"
      9 #include "v8/include/v8.h"
     10 
     11 namespace extensions {
     12 
     13 // A v8::Persistent handle to a V8 value which destroys and clears the
     14 // underlying handle on destruction.
     15 template <typename T>
     16 class ScopedPersistent {
     17  public:
     18   ScopedPersistent() {}
     19 
     20   explicit ScopedPersistent(v8::Handle<T> handle) { reset(handle); }
     21 
     22   ~ScopedPersistent() { reset(); }
     23 
     24   void reset(v8::Handle<T> handle) {
     25     if (!handle.IsEmpty())
     26       handle_.Reset(GetIsolate(handle), handle);
     27     else
     28       reset();
     29   }
     30 
     31   void reset() { handle_.Reset(); }
     32 
     33   bool IsEmpty() const { return handle_.IsEmpty(); }
     34 
     35   v8::Handle<T> NewHandle() const {
     36     if (handle_.IsEmpty())
     37       return v8::Local<T>();
     38     return v8::Local<T>::New(GetIsolate(handle_), handle_);
     39   }
     40 
     41   v8::Handle<T> NewHandle(v8::Isolate* isolate) const {
     42     if (handle_.IsEmpty())
     43       return v8::Local<T>();
     44     return v8::Local<T>::New(isolate, handle_);
     45   }
     46 
     47   template <typename P>
     48   void SetWeak(P* parameters,
     49                typename v8::WeakCallbackData<T, P>::Callback callback) {
     50     handle_.SetWeak(parameters, callback);
     51   }
     52 
     53  private:
     54   template <typename U>
     55   static v8::Isolate* GetIsolate(v8::Handle<U> object_handle) {
     56     // Only works for v8::Object and its subclasses. Add specialisations for
     57     // anything else.
     58     if (!object_handle.IsEmpty())
     59       return GetIsolate(object_handle->CreationContext());
     60     return v8::Isolate::GetCurrent();
     61   }
     62   static v8::Isolate* GetIsolate(v8::Handle<v8::Context> context_handle) {
     63     if (!context_handle.IsEmpty())
     64       return context_handle->GetIsolate();
     65     return v8::Isolate::GetCurrent();
     66   }
     67   static v8::Isolate* GetIsolate(
     68       v8::Handle<v8::ObjectTemplate> template_handle) {
     69     return v8::Isolate::GetCurrent();
     70   }
     71 
     72   v8::Persistent<T> handle_;
     73 
     74   DISALLOW_COPY_AND_ASSIGN(ScopedPersistent);
     75 };
     76 
     77 }  // namespace extensions
     78 
     79 #endif  // EXTENSIONS_RENDERER_SCOPED_PERSISTENT_H_
     80