gistfile1.m

int main (int argc, const char * argv[]) {
	dispatch_queue_t waitingChairs = dispatch_queue_create("com.madebysofa.waitingChairs", 0);
	dispatch_semaphore_t semaphore = dispatch_semaphore_create((long)3);
	NSInteger index = -1;
	
	while (YES) {
		index++;
		long success = dispatch_semaphore_wait(semaphore, DISPATCH_TIME_NOW);
		if (success != 0) {
			NSLog(@"Customer turned away %i", index);
			continue;
		}
		dispatch_async(waitingChairs, ^{
			dispatch_semaphore_signal(semaphore);
			NSLog(@"Shave and a haircut %i", index);
		});		
	}
	
	dispatch_release(waitingChairs);
	dispatch_release(semaphore);
    return 0;
}