C# 线程池中取消线程的三种方式

三种方式都使用CancellationToken，只是使用方式不同，有类似于采用全局标志位的方式

第一种 检测IsCancellationRequested方式

        static void AsyncOperation1(CancellationToken token)
        {
            Console.WriteLine("starting the first task");
            for (int i = 0; i < 5; i++)
            {
                //取消任务信号
                if (token.IsCancellationRequested)
                {
                    Console.WriteLine("the first task has been canceled.");
                    return;
                }

                Thread.Sleep(TimeSpan.FromSeconds(1));
            }
            Console.WriteLine("the first task has completed successfully");
        }

第二种 抛出ThrowIfCancellationRequested方式

        static void AsyncOperation2(CancellationToken token)
        {
            try
            {
                Console.Write