#include <stdio.h>
#include <signal.h>
#include <unistd.h>

int cnt = 0;

void sigint_handler(int signo)
{
    if (cnt < 4) {
        printf("%d\n", cnt);
        fflush(stdout);
        ++cnt;
    } else {
        _exit(0);
    }
}

int main()
{
    sigset_t mask, oldmask;

    sigemptyset(&mask);
    sigaddset(&mask, SIGINT);

    sigprocmask(SIG_BLOCK, &mask, &oldmask);

    struct sigaction sa;

    sa.sa_handler = sigint_handler;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;
    sigaction(SIGINT, &sa, NULL);

    printf("%d\n", getpid());
    fflush(stdout);
    sigprocmask(SIG_UNBLOCK, &mask, &oldmask);

    while (1) {
    }

    return 0;
}