sleep.c

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#include <sys/types.h>
#include <stddef.h>
#include <signal.h>
#include <unistd.h>

static void sig_alrm (int signo)
{
    return; /* nothing to do, just returning wakes up sigsuspend() */
}

unsigned int sleep (unsigned int nsecs)
{
    struct sigaction        newact, oldact;
    sigset_t                newmask, oldmask, suspmask;
    unsigned int            unslept;

    newact.sa_handler = sig_alrm;
    sigemptyset (&newact.sa_mask);
    newact.sa_flags = 0;
    sigaction (SIGALRM, &newact, &oldact);
                             /* set our handler, save previous information */
    sigemptyset (&newmask);
    sigaddset (&newmask, SIGALRM);
                             /* block SIGALRM and save current signal mask */
    sigprocmask (SIG_BLOCK, &newmask, &oldmask);

    alarm (nsecs);

    suspmask = oldmask;
    sigdelset (&suspmask, SIGALRM);      /* make sure SIGALRM isn't blocked */
    
    sigsuspend (&suspmask);              /* wait for any signal to be caught */

    /* some signal has been caught, SIGALRM is now blocked */

    unslept = alarm (0);
    sigaction (SIGALRM, &oldact, NULL);  /* reset previous action */

    sigprocmask (SIG_SETMASK, &oldmask, NULL);

    return (unslept);
}