CancelableTimer.swift

class CancelableTimer: NSObject {
    private var queue = dispatch_queue_create("timer", nil)
    private var timer: dispatch_source_t!
    private var firstTime = true
    private var once: Bool
    private var handler: () -> ()
    
    init(once: Bool, handler: () -> ()) {
        self.once = once
        self.handler = handler
        super.init()
    }
    
    func startWithInterval(interval: Double) {
        firstTime = true
        cancel()
        timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue)
        dispatch_source_set_timer(timer, dispatch_walltime(nil, 0), UInt64(interval * Double(NSEC_PER_SEC)),
            UInt64(0.05 * Double(NSEC_PER_SEC)))
        dispatch_source_set_event_handler(timer) {
            if self.firstTime {
                self.firstTime = false
                return
            }
            self.handler()
            if self.once {
                self.cancel()
            }
        }
        dispatch_resume(timer)
    }
    
    func cancel() {
        if timer != nil {
            dispatch_source_cancel(timer)
        }
    }
}