How do I create a NSTimer on a background thread?

Question

I have a task that needs to be performed every 1 second. Currently I have an NSTimer firing repeatedly every 1 sec. How do I have the timer fire in a background thread (no

Answer 1

If you want to go pure GCD and use a dispatch source, Apple has some sample code for this in their Concurrency Programming Guide:

dispatch_source_t CreateDispatchTimer(uint64_t interval, uint64_t leeway, dispatch_queue_t queue, dispatch_block_t block)
{
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    if (timer)
    {
        dispatch_source_set_timer(timer, dispatch_walltime(NULL, 0), interval, leeway);
        dispatch_source_set_event_handler(timer, block);
        dispatch_resume(timer);
    }
    return timer;
}

Swift 3:

func createDispatchTimer(interval: DispatchTimeInterval,
                         leeway: DispatchTimeInterval,
                         queue: DispatchQueue,
                         block: @escaping ()->()) -> DispatchSourceTimer {
    let timer = DispatchSource.makeTimerSource(flags: DispatchSource.TimerFlags(rawValue: 0),
                                               queue: queue)
    timer.scheduleRepeating(deadline: DispatchTime.now(),
                            interval: interval,
                            leeway: leeway)

    // Use DispatchWorkItem for compatibility with iOS 9. Since iOS 10 you can use DispatchSourceHandler
    let workItem = DispatchWorkItem(block: block)
    timer.setEventHandler(handler: workItem)
    timer.resume()
    return timer
}

You could then set up your one-second timer event using code like the following:

dispatch_source_t newTimer = CreateDispatchTimer(1ull * NSEC_PER_SEC, (1ull * NSEC_PER_SEC) / 10, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // Repeating task
});

making sure to store and release your timer when done, of course. The above gives you a 1/10th second leeway on the firing of these events, which you could tighten up if you desired.