def _start_all_backends(self):

        for backend in self.backends.values():
            worker = threading.Thread(
                name=backend._logger_name(),
                target=self._start_backend,
                args=(backend,))

            worker.daemon = True
            worker.start()

            # stash the worker thread in the backend, so we can check
            # whether it's still alive when _stop_all_backends is called
            backend.__thread = worker
Start all backends registed via Router.add_backend, by calling
dataset/ETHPy150Open rapidsms/rapidsms-core-dev/lib/rapidsms/router.py/Router._start_all_backends