def request_sensor_sampling_clear(self, req):
        """Set all sampling strategies for this client to none.

        Returns
        -------
        success : {'ok', 'fail'}
            Whether sending the list of devices succeeded.

        Examples
        --------
        ?sensor-sampling-clear
        !sensor-sampling-clear ok

        """
        f = Future()
        @gen.coroutine
        def _clear_strategies():
            self.clear_strategies(req.client_connection)
            raise gen.Return(('ok',))

        self.ioloop.add_callback(lambda: chain_future(_clear_strategies(), f))
        return f