Cogl.UserDataDestroyCallback
When associating private data with a Cogl.Object a callback can be given which will be called either if the object is destroyed or if Cogl.Object.set_user_data is called with NULL user_data for the same key.
When associating private data with a Cogl.Object a callback can be given which will be called either if the object is destroyed or if Cogl.Object.set_user_data is called with NULL user_data for the same key.