sleep.c

来自「unix环境高级编程的源代码」· C语言 代码 · 共 46 行

#include    <signal.h>
#include    <stddef.h>
#include    "ourhdr.h"

static void 
sig_alrm(int signo)    /* th */
{
    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 */

                    /* reset signal mask, which unblocks SIGALRM */
    sigprocmask(SIG_SETMASK, &oldmask, NULL);

    return(unslept);
}