* @cancellable: (allow-none): optional #GCancellable object
* @callback: (scope async): a #GAsyncReadyCallback
* @user_data: (closure): a #gpointer
* @cancellable: (allow-none): optional #GCancellable object
* @callback: (scope async): a #GAsyncReadyCallback
* @user_data: (closure): a #gpointer