def __send_retry_requests(self, last_send_failure_time):
        """Called via Timer from __send_ready to resend requests which might not have been sent due to transport
           failure. This can happen since the current transport implementation does not received acknowledgements
           for sent messages."""
        # make sure multiple failures having set multiple times do not run concurrently
        with self.__send_retry_requests_lock:
            with self.__requests:
                # produce list instead of generator as requests mapping can change during subsequent loop
                retry_reqs = [req for req in self.__requests.values()
                              if req._sent_without_response(last_send_failure_time)]

            retry_req_count = 0
            # don't continue if another network failure has occured (which will trigger this function again)
            while retry_reqs and self.__amqplink.last_send_exc_time <= last_send_failure_time:
                req = retry_reqs.pop()
                # lock individuallly so incoming request handling does not 'pause' for too long
                with self.__requests:
                    # might have received a response (or finished since)
                    if not (req.id_ in self.__requests and req._sent_without_response(last_send_failure_time)):
                        logger.debug('Not resending request %s (finished or has received response)', req.id_)
                        continue
                logger.debug('Resending request %s', req.id_)
                if not self.__retry_enqueue(PreparedMessage(req._inner_msg_out, req.id_)):
                    # client shutdown
                    break
                retry_req_count += 1

        if retry_req_count:
            logger.debug('Resending of %d request(s) complete (before %s)', retry_req_count, last_send_failure_time)