main.m

#import <Foundation/Foundation.h>

int main(int argc, char *argv[]) {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^(void) {
        sleep(1);
        dispatch_semaphore_signal(semaphore);
    });

    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
    NSLog(@"Start");
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
    NSLog(@"1");

    dispatch_release(semaphore);
    NSLog(@"Done");
    [pool release];
    return 0;
}