#include "csapp.h"

static volatile long num_jobs;

void initjobs(void)
{
    num_jobs = 0;
}

void addjob(int pid)
{
    num_jobs ++;
    printf("Add: %ld jobs\n", num_jobs);
}

void deletejob(int pid)
{
    num_jobs --;
    sio_puts("Delete: ");
    sio_putl(num_jobs);
    sio_puts(" jobs\n");
}

/* $begin procmask2 */
void handler(int sig)
{
    int olderrno = errno;
    sigset_t mask_all, prev_all;
    pid_t pid;

    Sigfillset(&mask_all);
    while ((pid = waitpid(-1, NULL, 0)) > 0) { /* Reap a zombie child */
        Sigprocmask(SIG_BLOCK, &mask_all, &prev_all);
        deletejob(pid); /* Delete the child from the job list */
        Sigprocmask(SIG_SETMASK, &prev_all, NULL);
    }
    if (errno != ECHILD)
        Sio_error("waitpid error");
    errno = olderrno;
}

#define N 5
int main(int argc, char **argv)
{
    int pid;
    int n = N;
    sigset_t mask_all, mask_one, prev_one;
    struct sigaction sa;

    Sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;
    sa.sa_handler = handler;
    Sigaction(SIGCHLD, &sa, NULL);

    Sigfillset(&mask_all);
    Sigemptyset(&mask_one);
    Sigaddset(&mask_one, SIGCHLD);
    initjobs(); /* Initialize the job list */

    while (n--) {
        Sigprocmask(SIG_BLOCK, &mask_one, &prev_one); /* Block SIGCHLD */
        if ((pid = Fork()) == 0) { /* Child process */
            Sigprocmask(SIG_SETMASK, &prev_one, NULL); /* Unblock SIGCHLD */
            Execve("/bin/date", argv, NULL);
        }
        Sigprocmask(SIG_BLOCK, &mask_all, NULL); /* Parent process */
        addjob(pid);  /* Add the child to the job list */
        Sigprocmask(SIG_SETMASK, &prev_one, NULL);  /* Unblock SIGCHLD */
    }
    exit(0);
}
/* $end procmask2 */