Threads the task, then runs a callback on success or an error callback
        on fail.
        
        cb       -- The function to be called with a successful result.
        error_cb -- The function to be called when an error occurs.
        
        For information on `task`, *args, and **kw, see work().

def callback(self, task, cb, error_cb, *args, **kw):
        """
        Threads the task, then runs a callback on success or an error callback
        on fail.
        
        cb       -- The function to be called with a successful result.
        error_cb -- The function to be called when an error occurs.
        
        For information on `task`, *args, and **kw, see work().
        """
        threaded(self._do_cb, (task, cb, error_cb) + args, kw)