proof-of-concept of siglongjmp/ppoll-based signal handling in an event loop

sigevent.c

#define _GNU_SOURCE
#include <err.h>
#include <errno.h>
#include <poll.h>
#include <setjmp.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

static sigjmp_buf sig_buf;

static void sig_handler(int signo) {
    siglongjmp(sig_buf, signo);
}

int main(void) {
    sigset_t jesus, blocked; // none of you are free of sin
    sigemptyset(&blocked);
    sigaddset(&blocked, SIGINT);
    sigprocmask(SIG_BLOCK, &blocked, &jesus);

    int signo = sigsetjmp(sig_buf, 1);
    if (signo) {
        printf("caught signal %d\n", signo);
    } else if (sigaction(SIGINT, &(struct sigaction) { .sa_handler = sig_handler }, NULL)) {
        err(1, "signal");
    }

    struct pollfd pfd = {
        .fd = 0,
        .events = POLLIN
    };

    for (;;) {
        int ret = ppoll(&pfd, 1, NULL, signo ? NULL : &jesus);
        if (ret < 0) err(1, "ppoll");
        signo = 0;

        if (pfd.revents & (POLLIN | POLLERR)) {
            char buffer[32];
            int n;
            do { n = read(pfd.fd, buffer, sizeof buffer); }
            while (n < 0 && (errno == EAGAIN || errno == EINTR));
            if (n < 0) err(1, "read");
            write(1, buffer, n); // XXX: check the return value
        } else if (pfd.revents & POLLHUP) {
            break;
        }
    }

    return 0;
}