/* $begin waitforsignal */
#include "csapp.h"

volatile sig_atomic_t pid;

void sigchld_handler(int s)
{
    int olderrno = errno;
    pid = Waitpid(-1, NULL, 0);
    errno = olderrno;
}

void sigint_handler(int s)
{
}

#define N 10
int main(int argc, char **argv)
{
    struct sigaction sa;
    sigset_t mask, prev;
    int n = N; /* 10 */

    Sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;

    sa.sa_handler = sigchld_handler;
    Sigaction(SIGCHLD, &sa, 0);

    sa.sa_handler = sigint_handler;
    Sigaction(SIGINT, &sa, 0);

    Sigemptyset(&mask);
    Sigaddset(&mask, SIGCHLD);

    while (n--) {
        Sigprocmask(SIG_BLOCK, &mask, &prev); /* Block SIGCHLD */
        if (Fork() == 0) /* Child */
            exit(0);

        /* Parent */
        pid = 0;
        Sigprocmask(SIG_SETMASK, &prev, NULL); /* Unblock SIGCHLD */

        /* Wait for SIGCHLD to be received (wasteful) */
        while (!pid)
            ;

        /* Do some work after receiving SIGCHLD */
        printf(".");
    }
    printf("\n");
    exit(0);
}
/* $end waitforsignal */