Ex_23_2.c

/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2024.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU General Public License as published by the   *
* Free Software Foundation, either version 3 or (at your option) any      *
* later version. This program is distributed without any warranty.  See   *
* the file COPYING.gpl-v3 for details.                                    *
\*************************************************************************/

/* t_nanosleep.c

   Demonstrate the use of clock_nanosleep() to sleep for an interval
   specified in nanoseconds.

   See also t_clock_nanosleep.c.
*/
#define _POSIX_C_SOURCE 199309
#include <sys/time.h>
#include <time.h>
#include <signal.h>
#include "tlpi_hdr.h"

static void
sigintHandler(int sig)
{
    return;                     /* Just interrupt clock_nanosleep() */
}

int
main(int argc, char *argv[])
{
    struct timeval start, finish;
    struct timespec request, remain;
    struct sigaction sa;
    struct timespec tp;
    int s;

    if (argc != 3 || strcmp(argv[1], "--help") == 0)
        usageErr("%s secs nanosecs\n", argv[0]);
    
    if (clock_gettime(CLOCK_REALTIME, &tp) == -1)
        errExit("clock_gettime");

    request.tv_nsec = tp.tv_nsec + getLong(argv[2], 0, "nanosecs");
    request.tv_sec  = tp.tv_sec  + getLong(argv[1], 0, "secs") + 
                        request.tv_nsec/1000000000;
    request.tv_nsec %= 1000000000;

    /* Allow SIGINT handler to interrupt clock_nanosleep() */

    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sa.sa_handler = sigintHandler;
    if (sigaction(SIGINT, &sa, NULL) == -1)
        errExit("sigaction");

    if (gettimeofday(&start, NULL) == -1)
        errExit("gettimeofday");

    for (;;) {
        s = clock_nanosleep(CLOCK_REALTIME, TIMER_ABSTIME, &request, &remain);
        if (s == -1 && errno != EINTR)
            errExit("nanosleep");

        if (gettimeofday(&finish, NULL) == -1)
            errExit("gettimeofday");
        printf("Slept for: %9.6f secs\n", finish.tv_sec - start.tv_sec +
                        (finish.tv_usec - start.tv_usec) / 1000000.0);

        if (s == 0)
            break;                      /* clock_nanosleep() completed */

        printf("Remaining: %2ld.%09ld\n", (long) remain.tv_sec, remain.tv_nsec);
    }

    printf("Sleep complete\n");
    exit(EXIT_SUCCESS);
}