truesleep.c

#include <time.h>
#include <stdio.h>

/**
 * Sleep for `sec' seconds, without relying on the wall clock of time(2)
 * or gettimeofday(2).
 *
 * Under ideal conditions is accurate to one microsecond. To get nanosecond
 * accuracy, replace sleep()/usleep() with something with higher resolution
 * like nanosleep() or ppoll().
 */
void true_sleep(int sec) {
    struct timespec ts_start;
    struct timespec ts_end;

    clock_gettime(CLOCK_MONOTONIC, &ts_start);

    ts_end = ts_start;
    ts_end.tv_sec += sec;

    for (;;) {
        struct timespec ts_current;
        struct timespec ts_remaining;

        clock_gettime(CLOCK_MONOTONIC, &ts_current);

        ts_remaining.tv_sec = ts_end.tv_sec - ts_current.tv_sec;
        ts_remaining.tv_nsec = ts_end.tv_nsec - ts_current.tv_nsec;

        while (ts_remaining.tv_nsec > 1000000000) {
            ts_remaining.tv_sec++;
            ts_remaining.tv_nsec -= 1000000000;
        }
        while (ts_remaining.tv_nsec < 0) {
            ts_remaining.tv_sec--;
            ts_remaining.tv_nsec += 1000000000;
        }

        if (ts_remaining.tv_sec < 0) {
            break;
        }

        if (ts_remaining.tv_sec > 0) {
            sleep(ts_remaining.tv_sec);
        } else {
            usleep(ts_remaining.tv_nsec / 1000);
        }
    }
}

int main() {
    true_sleep(10); // Sleep for 10 seconds
    return 0;
}