协作式取消和超时

    internal static class CancellationDemo
    {
        public static void Go()
        {
            //向应该被取消的CancellationToken发送信号
            CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();

            ThreadPool.QueueUserWorkItem(o => Count(cancellationTokenSource.Token, 100));

            //指定毫秒（2000）后取消操作
            //cancellationTokenSource.CancelAfter(2000);

            Console.WriteLine("Press <Enter> to cancel the operation.");

            Console.ReadLine();

            //如果Count方法已返回，Cancel无任何效果
            cancellationTokenSource.Cancel();
            //Cancel立即返回，方法从这里继续执行

            Console.ReadLine();
        }

        private static void Count(CancellationToken cancellationToken, int countTo)
        {
            for (int i = 0; i < countTo; i++)
            {
                if (cancellationToken.IsCancellationRequested)
                {
                    Console.WriteLine("Count is cancelled.");
                    break;
                }
                Console.WriteLine(i);
                Thread.Sleep(200);
            }
            Console.WriteLine("Count is done.");
        }
    }