Semaphore example in Objective C

semaphore.m

dispatch_semaphore_t sema = dispatch_semaphore_create(0);

[object runSomeLongOperationAndDo:^{
    // hack hack hack...

    dispatch_semaphore_signal(sema);
}];

dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER);
dispatch_release(sema);