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KQUEUE_CPONFORK example
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Authored by kib on Aug 20 2025, 10:56 AM.
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F126514721: KQUEUE_CPONFORK example
Aug 20 2025, 10:56 AM
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/* $Id: kqfork.c,v 1.4 2025/08/19 19:42:16 kostik Exp kostik $ */
#include <sys/param.h>
#include <sys/event.h>
#include <err.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#ifndef KQUEUE_CPONFORK
#define KQUEUE_CPONFORK 0x2
#endif
static pid_t pid_pipe_beat;
static pid_t pid_controller;
static void
sighup_handler(int sig __unused)
{
kill(pid_pipe_beat, SIGKILL);
_exit(1);
}
static void
pipe_beat(int wp)
{
static const char a[1] = { 'a' };
ssize_t s;
for (;;) {
sleep(1);
s = write(wp, a, 1);
if (s < 0)
err(1, "pipe write");
if (s == 0)
errx(1, "short pipe write");
}
}
static void
worker(int kq, int rp)
{
struct kevent ev[1];
char a[1];
ssize_t s;
int n;
for (;;) {
n = kevent(kq, NULL, 0, ev, nitems(ev), NULL);
if (n == -1) {
kill(pid_controller, SIGHUP);
err(1, "kqueue");
}
if (n == 0)
continue; // XXXKIB
switch (ev[0].filter) {
case EVFILT_TIMER:
printf("tick\n");
break;
case EVFILT_READ:
if (ev[0].ident != (uintptr_t)rp) {
kill(pid_controller, SIGHUP);
errx(1, "unknown read ident %d\n", ev[0].ident);
}
s = read(rp, a, sizeof(a));
if (s == -1) {
kill(pid_controller, SIGHUP);
err(1, "read");
}
if (s == 0) {
kill(pid_controller, SIGHUP);
errx(1, "EOF");
}
printf("%c\n", a[0]);
break;
default:
kill(pid_controller, SIGHUP);
errx(1, "unknown fiter %d\n", ev[0].filter);
break;
}
}
}
static void
usage(void)
{
fprintf(stderr, "Usage: kqfork [fork]\n");
exit(2);
}
int
main(int argc, char *argv[])
{
struct kevent ev[2];
struct sigaction sa;
int kq, n, pp[2];
pid_t pid_worker;
bool do_fork;
do_fork = false;
if (argc != 1 && argc != 2)
usage();
if (argc == 2) {
if (strcmp(argv[1], "fork") != 0)
usage();
do_fork = true;
}
memset(&sa, 0, sizeof(sa));
sa.sa_handler = sighup_handler;
if (sigaction(SIGHUP, &sa, NULL) == -1)
err(1, "sigaction(SIGHUP)");
memset(&sa, 0, sizeof(sa));
sa.sa_flags = SA_NOCLDWAIT | SA_NOCLDSTOP;
sa.sa_handler = SIG_IGN;
if (sigaction(SIGCHLD, &sa, NULL) == -1)
err(1, "sigaction(SIGCHLD)");
if (pipe(pp) == -1)
err(1, "pipe");
pid_pipe_beat = fork();
if (pid_pipe_beat == -1)
err(1, "fork");
if (pid_pipe_beat == 0) {
close(pp[0]);
pipe_beat(pp[1]);
}
kq = kqueuex(do_fork ? KQUEUE_CPONFORK : 0);
if (kq == -1)
err(1, "kqueuex");
EV_SET(&ev[0], 1, EVFILT_TIMER, EV_ADD, NOTE_SECONDS, 1, NULL);
EV_SET(&ev[1], pp[0], EVFILT_READ, EV_ADD, 0, 0, NULL);
n = kevent(kq, ev, nitems(ev), NULL, 0, NULL);
if (n == -1) {
kill(pid_pipe_beat, SIGKILL);
err(1, "kevent reg");
}
if (n != 0) {
kill(pid_pipe_beat, SIGKILL);
errx(1, "kevent reg %d", n);
}
pid_controller = getpid();
if (do_fork) {
pid_worker = fork();
if (pid_worker == -1) {
kill(pid_pipe_beat, SIGKILL);
err(1, "fork");
}
if (pid_worker == 0) {
close(pp[1]);
worker(kq, pp[0]);
}
for (;;)
pause();
} else {
worker(kq, pp[0]);
}
exit(0); // unreachable
}

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kib created this paste.Aug 20 2025, 10:56 AM
kib created this object in space S1 Global.