def scheduleExpire(self, msgs, ack_key):
            # Forget about this message, eventually.
            if self.expire_dcall:
                self.expire_dcall.reset(180.0)
                return

            def cb():
                self.expire_dcall = None
                self.cancelAllSends()
                del msgs[ack_key]

            self.expire_dcall = reactor.callLater(180.0, cb)