init() {
    loop.startLoop();
    return new Promise((resolve, reject) => {
      // assign the ffi callback to 'this' so we retain a reference
      // after this.init() finishes. If we don't do this Node
      // will garbage collect it and we will get a segmentation
      // fault when C calls into it.
      this.onActivate = ffi.Callback('void', [type.GtkWidgetPtr], (windowPtr) => {
        this.window = new Window({ pointer: windowPtr });
        resolve(this.window);
      });
      app.register_on_activate(this.onActivate);

      // If we call app.init() then it blocks the main loop
      // forever and out program halts.
      // If we call app.init.async() then FFI will call the
      // foreign function in another thread (https://github.com/node-ffi/node-ffi/wiki/Node-FFI-Tutorial#async-library-calls)
      // My guess is that it will be scheduled on one of the
      // threads that LibUV controls for IO tasks.
      // This means we avoid blocking the event loop but this
      // results in a segmentation fault after some time and
      // I can't figure out why. My only guess is that it's a
      // multi-thread issue with GTK???
      app.init.async(this.pointer, () => null);
    });
  }