Unconditionally shuts the TendrilManager down, killing all
        threads and closing all tendrils.

def shutdown(self):
        """
        Unconditionally shuts the TendrilManager down, killing all
        threads and closing all tendrils.
        """

        # Remove ourself from the dictionary of running managers
        try:
            del self._running_managers[self._manager_key]
        except KeyError:
            pass

        # Kill the listening thread
        self._listen_thread.kill()

        # Close all the connections
        for conn in self.tendrils.values():
            conn.close()

        # Ensure all data is appropriately reset
        self.tendrils = {}
        self.running = False
        self._local_addr = None
        self._local_addr_event.clear()
        self._listen_thread = None