code: def __send_ready_cb(self, last_send_failure_time):
          
          logger.debug('Readiness notification (last failed=%s)', last_send_failure_time)
          # It is possible for multiple timers to be scheduled (if multiple transport failures happen in a fairly short
          # amount of time. See logic for __send_retry_requests
          if last_send_failure_time is not None:
              self.__send_retry_requests_timer.cancel()
              # allow 10s for responses to come in before attempting to resend
              self.__send_retry_requests_timer = Timer(10, self.__send_retry_requests, args=(last_send_failure_time,))
              self.__send_retry_requests_timer.start()
docs: Callback from AmqpLink on send transport readiness. (Only ever comes from a single thread.)