class ViewControllerBase: UIViewController {
    let timer:DispatchSourceTimer = DispatchSource.makeTimerSource(flags: [], queue:  DispatchQueue(label: "q.q"))
    
    deinit {
        NSLog("deinit of \(NSStringFromClass(type(of: self)))")
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        timer.scheduleRepeating(deadline: .now(), interval: .seconds(1))

        timer.setEventHandler {
            UIView.animate(withDuration: 0.2) { [weak self] in
                self?.view.backgroundColor = UIColor.green
            }
        }
}