// from https://dl.dropboxusercontent.com/u/3820193/VbierClientUnderTheHood.pdf

class PingThread : NSThread {
    var pingTaskIsRunning = false
    var semaphore = dispatch_semaphore_create(0)
    override func main() {
        while !self.cancelled {
            pingTaskIsRunning = true
            dispatch_async(dispatch_get_main_queue()) {
                self.pingTaskIsRunning = false
                dispatch_semaphore_signal(self.semaphore)
            }
            NSThread.sleepForTimeInterval(0.4)
            if pingTaskIsRunning {
                // warning here
            }
            dispatch_semaphore_wait(semaphore,
                DISPATCH_TIME_FOREVER)
        }
    }
}