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

pthread_once_t once, once0 = PTHREAD_ONCE_INIT;
int done = 0;

static void
init(void)
{

	done = 1;
}

static void *
thread(void *cookie)
{
	pthread_barrier_t *bar = cookie;

	(void)pthread_barrier_wait(bar);
	pthread_once(&once, &init);
	if (!done)
		errx(1, "fail");
}

int
main(int argc, char **argv)
{
	enum { N = 256 };
	unsigned n = argc == 2 ? atoi(argv[1]) : 16;

	if (n > N)
		errx(1, "too many");

	for (;;) {
		pthread_barrier_t bar;
		pthread_t t[N];
		unsigned i;
		int error;

		error = pthread_barrier_init(&bar, NULL, n + 1);
		if (error)
			errc(1, error, "pthread_barrier_init");
		for (i = 0; i < n; i++) {
			error = pthread_create(&t[i], NULL, &thread, &bar);
			if (error)
				errc(1, error, "pthread_create");
		}
		once = once0;
		done = 0;
		(void)pthread_barrier_wait(&bar);
		for (i = 0; i < n; i++) {
			error = pthread_join(t[i], NULL);
			if (error)
				errc(1, error, "pthread_join");
		}
		error = pthread_barrier_destroy(&bar);
		if (error)
			errc(1, error, "pthread_barrier_destroy");
	}
}