How to stop a thread from running indefinitely in Swift?

Question

I run a function from a library which I can't see the implementation.

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    someClass.beginService();
});

This library class calls my class' delegate function.

class Mine: UIViewController, SomeClassDelegate {

    let someClass = SomeClass();

    override func viewDidLoad () {
        super.viewDidLoad();
        someClass.delegate = self;
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            self.someClass.beginService();
        });
    }

    func delegateCall () {
        print ("delegateCall is called!");
        // do some stuff
    }
}

The word delegateCall is called! is then printed periodically every 1 second in the log window, because I call the self.someClass.beginService();.

The problem is, how can I terminate this thread? I don't want to resort to:

class Mine: UIViewController, SomeClassDelegate {

    let someClass = SomeClass();
    var okToRun = false;

    override func viewDidLoad () {
        super.viewDidLoad();
        someClass.delegate = self;
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            self.someClass.beginService();
            okToRun = true;
        });
    }

    func delegateCall () {
        if okToRun {
            print ("delegateCall is called!");
            // do some stuff
        }
    }

    @IBAction func buttonStopTapped (sender: AnyObject) {
        okToRun = false;
    }
}

Because this means that the background routine is still working.

Answer 1

Try invalidate funtion. Like

var  thread = dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            self.someClass.beginService();

where do you want to stop

thread.invalidate()