Posix timers not behaving correctly

sean04 · 10-07-2007, 07:54 PM

Hi I don't understand how this isn't working correctly...I'm running Linux Kernel 2.6.9. What's happening is that as soon as I call the timer_settime function it immediately triggers the signal handler. No matter how big I set the time. Here's the code:

sigs.sa_handler = signal_handler_function;
sigemptyset(&sigs.sa_mask);
if (sigaction(SIGALRM, &sigs, (struct sigaction *) NULL) != 0)
{
exit(1);
}

if (timer_create(CLOCK_REALTIME,
(struct sigevent *) NULL, &timer_id ) != 0)
{
exit(1);
}

ItimerSpec.it_value.tv_sec = sec; //assume correct values
ItimerSpec.it_value.tv_nsec = nsec;//assume correct values
ItimerSpec.it_interval.tv_sec = 0;
ItimerSpec.it_interval.tv_nsec = 0;

if (timer_settime(timer_id,TIMER_ABSTIME,&ItimerSpec, NULL) != 0)
{
exit(1);
}

orgcandman · 10-07-2007, 11:34 PM

you might want to read the manpages.

The TIMER_ABSTIME flag is probably not what you want, unless you're getting seconds and nanoseconds in absolute time. In the above function, there's no indication that values you're getting _are_ correct, and the symptom you're seeing is characteristic of incorrect values.

I've got some timer code that works, and it looks like:

Code:

    timeout.it_value.tv_sec = 0;
    timeout.it_value.tv_nsec = 1000;

    timeout.it_interval.tv_sec = timeout.it_value.tv_sec;
    timeout.it_interval.tv_nsec = timeout.it_value.tv_nsec;

    status = timer_create(CLOCK_REALTIME, &evp, &m_nTimerIds[nTimerId]);

    sigaction(evp.sigev_signo, &sig_act, 0);

    if(status < 0)
    {
        fprintf(stderr, "ERROR: Cannot start timer for id: %d.\n", nTimerId);
        return status;
    }

    status = timer_settime(m_nTimerIds[nTimerId], 0, &timeout, NULL);
    if(status < 0)
    {
        perror("settimer failed");
        return -1;
    }

this is relative time based, rather than absolute time based (absolute time being prone to errors such as "The date is really tuesday, but you think its monday").