_sleep.c

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/*      sleep() - Sleep for a number of seconds.        Author: Kees J. Bot
 *                                                              24 Apr 2000
 * (Inspired by the Minix-vmd version of same, except that
 * this implementation doesn't bother to check if all the signal
 * functions succeed.  Under Minix that is no problem.)
 */

#include <lib.h>
#define sleep _sleep
#include <signal.h>
#include <unistd.h>
#include <time.h>

static void handler(int sig)
{
        /* Dummy signal handler. */
}

unsigned sleep(unsigned sleep_seconds)
{
        sigset_t ss_full, ss_orig, ss_alarm;
        struct sigaction action_alarm, action_orig;
        unsigned alarm_seconds, nap_seconds;

        if (sleep_seconds == 0) return 0;       /* No rest for the wicked */

        /* Mask all signals. */
        sigfillset(&ss_full);
        sigprocmask(SIG_BLOCK, &ss_full, &ss_orig);

        /* Cancel currently running alarm. */
        alarm_seconds= alarm(0);

        /* How long can we nap without interruptions? */
        nap_seconds= sleep_seconds;
        if (alarm_seconds != 0 && alarm_seconds < sleep_seconds) {
                nap_seconds= alarm_seconds;
        }

        /* Now sleep. */
        action_alarm.sa_handler= handler;
        sigemptyset(&action_alarm.sa_mask);
        action_alarm.sa_flags= 0;
        sigaction(SIGALRM, &action_alarm, &action_orig);
        alarm(nap_seconds);

        /* Wait for a wakeup call, either our alarm, or some other signal. */
        ss_alarm= ss_orig;
        sigdelset(&ss_alarm, SIGALRM);
        sigsuspend(&ss_alarm);

        /* Cancel alarm, set mask and stuff back to normal. */
        nap_seconds -= alarm(0);
        sigaction(SIGALRM, &action_orig, NULL);
        sigprocmask(SIG_SETMASK, &ss_orig, NULL);

        /* Restore alarm counter to the time remaining. */
        if (alarm_seconds != 0 && alarm_seconds >= nap_seconds) {
                alarm_seconds -= nap_seconds;
                if (alarm_seconds == 0) {
                        raise(SIGALRM);         /* Alarm expires now! */
                } else {
                        alarm(alarm_seconds);   /* Count time remaining. */
                }
        }

        /* Return time not slept. */
        return sleep_seconds - nap_seconds;
}

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