Send heartbeat packets, if necessary, and fail if none have been
        received recently.  This should be called frequently, on the order of
        once per second.

        :keyword rate: Ignored

def heartbeat_tick(self, rate=2):
        """Send heartbeat packets, if necessary, and fail if none have been
        received recently.  This should be called frequently, on the order of
        once per second.

        :keyword rate: Ignored
        """
        if not self.heartbeat:
            return

        # treat actual data exchange in either direction as a heartbeat
        sent_now = self.method_writer.bytes_sent
        recv_now = self.method_reader.bytes_recv
        if self.prev_sent is None or self.prev_sent != sent_now:
            self.last_heartbeat_sent = monotonic()
        if self.prev_recv is None or self.prev_recv != recv_now:
            self.last_heartbeat_received = monotonic()
        self.prev_sent, self.prev_recv = sent_now, recv_now

        # send a heartbeat if it's time to do so
        if monotonic() > self.last_heartbeat_sent + self.heartbeat:
            self.send_heartbeat()
            self.last_heartbeat_sent = monotonic()

        # if we've missed two intervals' heartbeats, fail; this gives the
        # server enough time to send heartbeats a little late
        if (self.last_heartbeat_received and
                self.last_heartbeat_received + 2 *
                self.heartbeat < monotonic()):
            raise ConnectionForced('Too many heartbeats missed')