Use your own main loop on OSX. Related blog post: http://daurnimator.com/post/147024385399/using-your-own-main-loop-on-osx

4CF.c

#include <mach/port.h> /* mach_port_t */
#include <mach/mach.h> /* mach_port_allocate(), mach_task_self(), mach_port_insert_member(), MACH_PORT_RIGHT_PORT_SET */
#include <sys/event.h> /* kqueue(), kevent64(), struct kevent64_s, EVFILT_MACHPORT, EV_SET64, EV_ADD */
#include <sys/time.h> /* struct timespec */

//#include <dispatch/private.h>
extern mach_port_t _dispatch_get_main_queue_port_4CF(void);
extern void _dispatch_main_queue_callback_4CF(void);

#include <stdio.h>
#include <errno.h>
#include <unistd.h> /* close() */
#include <dispatch/dispatch.h>

int main() {
	int fd;
	struct kevent64_s event;
	int n;

	if (-1 == (fd = kqueue()))
		return (perror("kqueue"), 1);
	/* TODO: set cloexec */

	mach_port_t x = _dispatch_get_main_queue_port_4CF();
	printf("PORT 4CF=%d\n", x);

	/* EVFILT_MACHPORT does not allow ports; only portsets */
	mach_port_t y;
	if (KERN_SUCCESS != mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_PORT_SET, &y))
		return 1;
	printf("PORT SET=%d\n", y);
	EV_SET64(&event, y, EVFILT_MACHPORT, EV_ADD|EV_CLEAR, MACH_RCV_MSG, 0, 0, 0, 0);
	if (0 != kevent64(fd, &event, 1, NULL, 0, 0, &(struct timespec){0,0}))
		return (perror("kevent"), 1);

	/* XXX: a port can only belong to one portset at once. this needs additional hackery when in a CF-using application */
	if (KERN_SUCCESS != mach_port_insert_member(mach_task_self(), x, y))
		return 1;

	/* say hello */
	dispatch_async(
		dispatch_get_main_queue(),
		^{
			printf("hello\n");
		}
	);

	/* in 2 seconds say hello again. */
	dispatch_after(
		dispatch_time(DISPATCH_TIME_NOW, 2LL*NSEC_PER_SEC),
		dispatch_get_main_queue(),
		^{
			printf("hello from timer\n");
		}
	);

	while (1) {
		/* You could poll/select on `fd` now. instead, I'm just going to use a blocking kevent call. */
		if (-1 == (n = kevent64(fd, NULL, 0, &event, 1, 0, NULL)))
			return (perror("kevent"), 1);

		if (n) {
			printf("GOT EVENT. ident=%llu filter=%d\n",
				event.ident, event.filter);
			_dispatch_main_queue_callback_4CF();
		} else
			return 2;
	}

	close(fd);

	return 0;
}

From https://opensource.apple.com/source/xnu/xnu-1456.1.26/bsd/sys/event.h

Only portsets are support at this time.

From http://web.mit.edu/darwin/src/modules/xnu/osfmk/man/mach_msg.html

A port may not be- long to more than one port set, and if a port is a member of a port set, the holder of the receive right can't receive directly from the port.