C#: CancellationToken 不取消阻塞方法

Question

.NET 4.5.1:看来，我无法使用 CancellationTokenSource 内置超时取消在任务中运行的阻塞方法。

class Program
{
    static void Main(string[] args)
    {
        var cts = new System.Threading.CancellationTokenSource();

        System.Console.CancelKeyPress += (s, e) =>
        {
            e.Cancel = true;
            cts.Cancel();
        };

        MainAsync(args, cts.Token).Wait();
    }

    // MainAsync from http://stackoverflow.com/questions/9208921/async-on-main-method-of-console-app
    static async Task MainAsync(string[] args, System.Threading.CancellationToken token)
    {
        Console.WriteLine("Starting MainAsync");
        var cts = new System.Threading.CancellationTokenSource(3000);
        var task = Task.Factory.StartNew(() =>
        {
            Console.WriteLine("Starting task...");
            var t = new System.Net.Sockets.TcpClient();
            var buffer = new byte[t.ReceiveBufferSize];
            t.Connect(new System.Net.IPEndPoint(System.Net.IPAddress.Parse("127.0.0.1"), 1337));

            Console.WriteLine("Recieving...");
            t.Client.Receive(buffer);
            Console.WriteLine("Finished Recieving...");

            return true;
        }, cts.Token);

        var success = await task;

        Console.WriteLine("Did the task complete succesfuly?", success);
    }
}

上述简短、自包含、正确示例的输出(我希望它是正确的)是:

Starting MainAsync
Starting task...
Recieving...

为什么任务没有取消，没有抛出异常？

Answer 1

正如我在博客中所述，"You keep using that CancellationToken there. I do not think it means what you think it means."

特别是，传递给StartNew 的CancellationToken 只会取消委托(delegate)的开始。如果您希望委托(delegate)本身支持取消，则委托(delegate)本身必须观察 CancellationToken。