This is part of the threaded client interface. Call this once to
        start a new thread to process network traffic. This provides an
        alternative to repeatedly calling loop() yourself.

def loop_start(self):
        """This is part of the threaded client interface. Call this once to
        start a new thread to process network traffic. This provides an
        alternative to repeatedly calling loop() yourself.
        """
        if self._thread is not None:
            return MQTT_ERR_INVAL

        self._thread_terminate = False
        self._thread = threading.Thread(target=self._thread_main)
        self._thread.daemon = True
        self._thread.start()