node/src/object_wrap.h

#ifndef object_wrap_h
#define object_wrap_h

#include <v8.h>
#include <assert.h>

namespace node {

class ObjectWrap {
 public:
  ObjectWrap ( ) {
    attached_ = 0;
  }

  virtual ~ObjectWrap ( ) {
    if (!handle_.IsEmpty()) {
      assert(handle_.IsNearDeath());
      handle_->SetInternalField(0, v8::Undefined());
      handle_.Dispose();
      handle_.Clear(); 
    }
  }

 protected:
  template <class T>
  static inline T* Unwrap (v8::Handle<v8::Object> handle)
  {
    assert(!handle.IsEmpty());
    assert(handle->InternalFieldCount() > 0);
    return static_cast<T*>(v8::Handle<v8::External>::Cast(
        handle->GetInternalField(0))->Value());
  }

  inline void Wrap (v8::Handle<v8::Object> handle)
  {
    assert(handle_.IsEmpty());
    assert(handle->InternalFieldCount() > 0);
    handle_ = v8::Persistent<v8::Object>::New(handle);
    handle_->SetInternalField(0, v8::External::New(this));
    handle_->Set(v8::String::NewSymbol("nodeId"), v8::Integer::New((int32_t)this));
    MakeWeak();
  }

  inline void MakeWeak (void)
  {
    handle_.MakeWeak(this, WeakCallback);
  }

  /* Attach() marks the object as being attached to an event loop.
   * Attached objects will not be garbage collected, even if
   * all references are lost.
   */
  void Attach() {
    assert(!handle_.IsEmpty());
    assert(handle_.IsWeak());
    attached_++;
  }
  
  /* Detach() marks an object as detached from the event loop.  This is its
   * default state.  When an object with a "weak" reference changes from
   * attached to detached state it will be freed. Be careful not to access
   * the object after making this call as it might be gone!
   * (A "weak reference" is v8 terminology for an object that only has a
   * persistant handle.)
   *
   * DO NOT CALL THIS FROM DESTRUCTOR
   */
  void Detach() {
    assert(!handle_.IsEmpty());
    assert(handle_.IsWeak());
    assert(attached_ > 0);
    attached_--;
    if (attached_ == 0 && handle_.IsNearDeath()) delete this;
  }

  v8::Persistent<v8::Object> handle_; // ro
  int attached_; // ro

 private:
  static void WeakCallback (v8::Persistent<v8::Value> value, void *data)
  {
    ObjectWrap *obj = static_cast<ObjectWrap*>(data);
    assert(value == obj->handle_);
    if (obj->attached_ == 0) {
      delete obj;
    } else {
      obj->MakeWeak();
    }
  }
};

} // namespace node
#endif // object_wrap_h