This is xnu-11215.1.10. See this file in: 
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <stdint.h>
#include <errno.h>
#include <err.h>
#include <pthread.h>
#include <spawn.h>

extern char **environ;

char * const *newargv;

void usage(void);

void *work(void *);

int
main(int argc, char *argv[])
{
	int i, count, threadcount;
	int ret;
	pthread_t *threads;

	if (argc < 4) {
		usage();
	}

	threadcount = atoi(argv[1]);
	count = atoi(argv[2]);

	newargv = &argv[3];

	threads = (pthread_t *)calloc(threadcount, sizeof(pthread_t));
	for (i = 0; i < threadcount; i++) {
		ret = pthread_create(&threads[i], NULL, work, (void *)(intptr_t)count);
		if (ret) {
			err(1, "pthread_create");
		}
	}

	for (i = 0; i < threadcount; i++) {
		ret = pthread_join(threads[i], NULL);
		if (ret) {
			err(1, "pthread_join");
		}
	}

	return 0;
}

void
usage(void)
{
	fprintf(stderr, "Usage: %s <threadcount> <count> <program> [<arg1> [<arg2> ...]]\n",
	    getprogname());
	exit(1);
}

void *
work(void *arg)
{
	int count = (int)(intptr_t)arg;
	int i;
	int ret;
	pid_t pid;

	for (i = 0; i < count; i++) {
		ret = posix_spawn(&pid, newargv[0], NULL, NULL, newargv, environ);
		if (ret != 0) {
			errc(1, ret, "posix_spawn(%s)", newargv[0]);
		}

		while (-1 == waitpid(pid, &ret, 0)) {
			if (errno != EINTR) {
				err(1, "waitpid(%d)", pid);
			}
		}

		if (WIFSIGNALED(ret)) {
			errx(1, "process exited with signal %d", WTERMSIG(ret));
		} else if (WIFSTOPPED(ret)) {
			errx(1, "process stopped with signal %d", WSTOPSIG(ret));
		} else if (WIFEXITED(ret)) {
			if (WEXITSTATUS(ret) != 42) {
				errx(1, "process exited with unexpected exit code %d", WEXITSTATUS(ret));
			}
		} else {
			errx(1, "unknown exit condition %x", ret);
		}
	}

	return NULL;
}