Getting Started with QNX Neutrino - QNX Software Systems

© 2009, QNX Software Systems GmbH & Co. KG. Using timers
if (timer_create (CLOCK_REALTIME, &event, &timerid) == -1) {
fprintf (stderr, "%s: couldn’t create a timer, errno %d\n",
progname, errno);
perror (NULL);
exit (EXIT_FAILURE);
}
// setup the timer (1s delay, 1s reload)
timer.it_value.tv_sec = 1;
timer.it_value.tv_nsec = 0;
timer.it_interval.tv_sec = 1;
timer.it_interval.tv_nsec = 0;
}
// and start it!
timer_settime (timerid, 0, &timer, NULL);
gotAPulse()
In gotAPulse(), you can see how we’ve implemented the server’s ability to timeout 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 back 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
April 30, 2009 Chapter 3 • Clocks, Timers, and Getting a Kick Every So Often 153