Date: Wed, 14 Dec 2016 08:42:28 +0100 From: Goran =?utf-8?B?TWVracSH?= <meka@tilda.center> To: freebsd-hackers@freebsd.org Subject: How to use sem_timedwait? Message-ID: <20161214074228.zh6q5zya2gszw4g6@hal9000.meka.no-ip.org>
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Hello,
I'm trying to understand how sem_timedwait() works. For that I assambled a little program:
#include <stdio.h>
#include <sys/types.h>
#include <semaphore.h>
#include <errno.h>
#include <time.h>
int main() {
sem_t semaphore;
struct timespec ts;
clock_gettime(CLOCK_REALTIME, &ts);
ts.tv_sec += 3;
sem_init(&semaphore, 0, 0);
int result = sem_timedwait(&semaphore, &ts);
int error = errno;
printf("The sem_timedwait() should have ended at %lds and %ldns\n", ts.tv_sec, ts.tv_nsec);
clock_gettime(CLOCK_REALTIME, &ts);
printf("The sem_timedwait() exited at %lds and %ldns with %d status\n", ts.tv_sec, ts.tv_nsec, result);
clock_getres(CLOCK_REALTIME, &ts);
printf("Clock resolution is %lds and %ldns\n", ts.tv_sec, ts.tv_nsec);
if (result == -1) {
switch (error) {
case EINVAL:
printf("The semaphore does not refer to valid structure\n");
break;
case ETIMEDOUT:
printf("Timeout occured\n");
break;
case EINTR:
printf("Interupted\n");
break;
default:
printf("Unknown error\n");
break;
}
}
}
Running it I get the following output:
The sem_timedwait() should have ended at 1481700752s and 2050646ns
The sem_timedwait() exited at 1481700752s and 3813780ns with -1 status
Clock resolution is 0s and 1ns
Timeout occured
What I want to know is why the number of nanoseconds reported first and second time is not the same if the resolution reported on line 3 is 1ns? It doesn't change much if I use CLOCK_RELATIME_PRECISE. Thank you!
Regards,
meka
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