iOS:OSX: Timer Using GCD

gcd_timer.m

-(dispatch_source_t)createTimerWithQueue:(dispatch_queue_t)queue block:(dispatch_block_t)handler
{
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    
    if (timer) {
        uint64_t seconds = 30ull;
        uint64_t interval = seconds * NSEC_PER_SEC;
        uint64_t leeway = 1ull * NSEC_PER_SEC;
        
        dispatch_source_set_timer(timer, dispatch_walltime(NULL, 0), interval, leeway);
        dispatch_source_set_event_handler(timer, handler);
        
        dispatch_resume(timer);
    }
    
    return timer;
}