How to know if a timer has ended in C - c

Question

I need to be able to start multiple timers simultaneously and know specifically if a timer has stopped or is still going.
#define RESEND_TIMEOUT 5
void timerCreate();
void timer_start(timer_t * timer, uint32 timeout);
bool timer_complete(timer_t * timer);
int main() {
timer_t resend_timer = timerCreate();
timer_start(&resend_timer, RESEND_TIMEOUT);
while(1) {
if (timer_complete(&resend_timer))
break;
}
}
void timer_start(timer_t * timer, uint32_t timeout)
{
printf("timer starting\n");
struct itimerspec it_val;
it_val.it_value.tv_sec = timeout;
it_val.it_value.tv_nsec = 0;
// timer expires once
it_val.it_interval.tv_sec = 0;
it_val.it_interval.tv_nsec = 0;
if (timer_settime(*timer, 0, &it_val, NULL) == -1) {
errExit("Could not set timeout");
}
}
// return true if timer ended
bool timer_complete(timer_t * timer)
{
if(timer_getoverrun(*timer) == 0)
return false;
else
return true;
}
I never break out of the loop. Why can't I get the overrun of the timer (it always returns 0, which means the timer has not passed its expiration)? Yet when I add a signal handler, I know that the timer expires.
I want to try timer_gettime(timer_t timerid, struct itimerspec *curr_value) inside of my timer_complete function to see if the remaining time is 0, but how can I pass the curr_value argument without having a global variable?
Last but not least, I have tried with the TIMER_ABSTIME flag when arming the timer with timer_settime. From the manpage of int timer_settime(timer_t timerid, int flags,
const struct itimerspec *new_value,
struct itimerspec * old_value):
By default, the initial expiration time specified in
new_value->it_value is interpreted relative to the current time on
the timer's clock at the time of the call. This can be modified by
specifying TIMER_ABSTIME in flags, in which case new_value->it_value
is interpreted as an absolute value as measured on the timer's clock;
that is, the timer will expire when the clock value reaches the value
specified by new_value->it_value. If the specified absolute time has
already passed, then the timer expires immediately, and the overrun
count (see timer_getoverrun(2)) will be set correctly.

Answer 1

I never break out of the loop. Why can't I get the overrun of the timer (it always returns 0, which means the timer has not passed its expiration)?
No, it means you had no overruns.
The OS is not going to queue timer signals even if you specify realtime signals. Overun tells you how many signals would have been queued if the wood chuck didn't chuck signals.
So consider you set a timer to go off once every second. But for some reason you didn't handle the signal. Say you had it blocked for 5 seconds. The overrun count is going to be 4 - the signal you will/are processing and the 4 you missed.
In your case you set a one-time timer to go off after "timeout" seconds. The signal was delivered. There will be no more signals hence overrun is always going to be 0, as it should be.