Catching SIGVTALRM signal, cp - c++

Question

I am trying to catch a SIGVTALRM sent by setitimer, and I have no idea why it doesn't work. here's my code:
void time(int time) {
cout << "time" << endl;
exit(0);
}
int main(void) {
signal(SIGVTALRM, time);
itimerval tv;
tv.it_value.tv_sec = 5;
tv.it_value.tv_usec = 0;
tv.it_interval.tv_sec = 5;
tv.it_interval.tv_usec = 0;
setitimer(ITIMER_VIRTUAL, &tv, NULL);
while (true) {
cout << "waiting" << endl;
}
return 0;
}
For some reason it never invokes time() - is it because it doesn't catch the signal or because the signal wasn't sent in the first place I don't know.
It should be pretty simple. Any ideas? thanks

Answer 1

Are you sure it is not working?
Everything looks fine to me. May be you are not waiting enough. Since you are printing the string waiting inside the loop and you are using the virtual timer, as a result the clock ticks only when the process runs (IO time not included). So in reality your timer might expire after several (>5) seconds.
Try commenting out the printing part.

Answer 2

It is due to signal function. As mentioned in http://manpages.ubuntu.com/manpages//precise/en/man2/signal.2.html:
The behavior of signal() varies across UNIX versions, and has also varied historically across different versions of Linux. Avoid its use: use sigaction(2) instead.
So the main method should be:
int main(void) {
itimerval tv;
struct sigaction sa;
sigemptyset(&sa.sa_mask);
sa.sa_flags = 0;
sa.sa_handler = timer_handler;
if (sigaction(SIGVTALRM, &sa, NULL) == -1) {
printf("error with: sigaction\n");
exit(EXIT_FAILURE);
}
tv.it_value.tv_sec = 5;
tv.it_value.tv_usec = 0;
tv.it_interval.tv_sec = 5;
tv.it_interval.tv_usec = 0;
setitimer(ITIMER_VIRTUAL, &tv, NULL);
while (true) {
cout << "waiting" << endl;
}
return 0;
}