#include <sys/wait.h>

#include <err.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>

pthread_once_t once;
int x;
long long ntrials;

static void
ofunc_silent(void)
{
	x++;
}

static void *
fork_and_once(void *cookie)
{
	pthread_barrier_t *bar = cookie;
	pid_t pid, child;
	int status;

	(void)pthread_barrier_wait(bar);
	if ((pid = fork()) == -1)
		err(1, "fork");
	if (pid == 0) {
		(void)alarm(1);
		(void)pthread_once(&once, &ofunc_silent);
		_exit(x - 1);
	}
	if ((child = waitpid(pid, &status, 0)) == -1)
		err(1, "waitpid");
	if (child != pid) {
		errx(1, "[%llu trials] child=%lld pid=%lld", ntrials,
		    (long long)child, (long long)pid);
	}
	if (WIFSIGNALED(status)) {
		errx(1, "[%llu trials] child exited on signal %d (%s)",
		    ntrials,
		    WTERMSIG(status),
		    strsignal(WTERMSIG(status)));
	}
	if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
		errx(1, "[%llu trials] child exited 0x%x", ntrials, status);
	return NULL;
}

int
main(void)
{
	static pthread_once_t once0 = PTHREAD_ONCE_INIT;
	pthread_barrier_t bar;
	int error;

	error = pthread_barrier_init(&bar, NULL, 2);
	if (error)
		err(1, "pthread_barrier_init");

	for (ntrials = 1;; ntrials++) {
		pthread_t t;

		once = once0;
		x = 0;

		error = pthread_create(&t, NULL, &fork_and_once, &bar);
		if (error)
			errc(1, error, "pthread_create");
		(void)alarm(1);
		(void)pthread_barrier_wait(&bar);
		(void)pthread_once(&once, &ofunc_silent);
		(void)alarm(0);
		error = pthread_join(t, NULL);
		if (error)
			errc(1, error, "pthread_join");

		if (x != 1)
			errx(1, "[%llu trials] x=%d\n", ntrials, x);
	}
	return 0;
}