How to implement a timed loop?

Question

I need to execute some code 1000 times per second. I would like to do something like:

set up interval timer
while (1)
{
   wait for timer
   do something
}

My attempt looks like

// Create timer
timer_t timerid;
struct sigevent sev;

sev.sigev_notify = SIGEV_SIGNAL;
sev.sigev_signo = SIGUSR1;

if (timer_create(CLOCK_REALTIME, &sev, &timerid))
{
perror("timer_create");
exit(1);
}

// Every one mSec (10^6 nsec)
struct itimerspec its;
its.it_value.tv_sec = 0;
its.it_value.tv_nsec = 1000000;
its.it_interval.tv_sec = 0;
its.it_interval.tv_nsec = 1000000;
if (timer_settime(timerid, 0, &its, NULL))
{
perror("timer_settime");
exit(1);
}

// Create mask to wait for SIGUSR1
sigset_t set;
sigemptyset(&set);
sigaddset(&set, SIGUSR1);

while (1)
{
int sig;

// Wait for the timer: Do this loop once per millisecond
sigwait(&set, &sig);

    (do something)
}

When I try this, I just get "User defined signal 1" at the console and my program exits. This is not surprising, as this is the default action for the signal. If I set the signal to SIG_IGN using sigaction(2), I never get to my (do something).

I presume I need to do something with sigaction(2), but I don't see an option for "deliver the signal". I don't want to ignore the signal, or do the default action, or call a function. What's the best way to accomplish my goal?

Or I can just give up and put my (do something) in a function :-)

Edit: I implemented the timerfd idea, and it seems to be working. On to the next bug...

Answer 1

Since you have tagged your question with embedded-linux I assume that portability is not an issue. In that case you might want to have a look at timerfd. It will allow you to use select(2)/poll(2) to receive your timer events. It will also make it easier to combine the interval timer with other event sources such as file descriptors.

Answer 2

I think you should set a true signal handler as suggested by n.m. Look at man sigaction for your version of Linux. You can either call your do_something in signal handler (and wait for something else for program termination) or have a return only handler and keep you sigwait logic.