gotAPulse()

In gotAPulse(), you can see how we've implemented the server's ability to time out a client. We walk down the list of clients, and since we know that the pulse is being triggered once per second, we simply decrement the number of seconds that the client has left before a timeout. If this value reaches zero, we reply to that client with a message saying, “Sorry, timed out” (the MT_TIMEDOUT message type).

You'll notice that we prepare this message ahead of time (outside the for loop), and then send it as needed. This is just a style/usage issue—if you expect to be doing a lot of replies, then it might make sense to incur the setup overhead once. If you don't expect to do a lot of replies, then it might make more sense to set it up as needed.

If the timeout value hasn't yet reached zero, we don't do anything about it—the client is still blocked, waiting for a message to show up.

/*
 *  gotAPulse
 *
 *  This routine is responsible for handling the fact that a
 *  timeout has occurred.  It runs through the list of clients
 *  to see which client has timed out, and replies to it with
 *  a timed-out response.
 */

void
gotAPulse (void)
{
    ClientMessageT  msg;
    int             i;

    if (debug) {
        time_t  now;

        time (&now);
        printf ("Got a Pulse at %s", ctime (&now));
    }

    // prepare a response message
    msg.messageType = MT_TIMEDOUT;

    // walk down list of clients
    for (i = 0; i < MAX_CLIENT; i++) {

        // is this entry in use?
        if (clients [i].in_use) {

            // is it about to time out?
            if (--clients [i].timeout == 0) {

                // send a reply
                MsgReply (clients [i].rcvid, EOK, &msg,
                          sizeof (msg));

                // entry no longer used
                clients [i].in_use = 0;
            }
        }
    }
}