def _retry_deliveries(self):
        """
        Handle [MQTT-4.4.0-1] by resending PUBLISH and PUBREL messages for pending out messages
        :return:
        """
        self.logger.debug("Begin messages delivery retries")
        tasks = []
        for message in itertools.chain(self.session.inflight_in.values(), self.session.inflight_out.values()):
            tasks.append(asyncio.wait_for(self._handle_message_flow(message), 10, loop=self._loop))
        if tasks:
            done, pending = yield from asyncio.wait(tasks, loop=self._loop)
            self.logger.debug("%d messages redelivered" % len(done))
            self.logger.debug("%d messages not redelivered due to timeout" % len(pending))
        self.logger.debug("End messages delivery retries")
Handle [MQTT-4.4.0-1] by resending PUBLISH and PUBREL messages for pending out messages
        :return: