在引擎盖下的阻塞任务中取消令牌

Question

我有两个按钮可以启动和停止 TcpListener。

private void buttonStartServer_Click(object sender, EventArgs e)
{
    ThreadPool.SetMinThreads(50, 50);
    IPAddress ipAddress = IPAddress.Parse("127.0.0.1");
    _listener = new TcpListener(ipAddress, 5000);
    cancelSource = new CancellationTokenSource();
    CancellationToken token = cancelSource.Token;
    var taskListener = Task.Factory.StartNew(
                        (t) => Listener(token),token,TaskCreationOptions.LongRunning);
}

void Listener(CancellationToken token)
{
    _listener.Start();
    while (!token.IsCancellationRequested)
    {
        TcpClient c;
        try
        {
            c = _listener.AcceptTcpClient();
        }
        catch
        {
            break;
        }
        Task t = Task.Factory.StartNew(() => Accept(c))
            .ContinueWith(ant => richTextBoxMessage.AppendText(ant.Result), _uiScheduler);
    }
}

private void buttonStopServer_Click(object sender, EventArgs e)
{
    cancelSource.Cancel();
    _listener.Stop();
    richTextBoxMessage.AppendText("Server shutdown");
}

Accept 是一些从 TcpClient 读取的方法。我的问题是，在我通过单击按钮停止服务器之前，我的服务器被阻止在

try {c = _listener.AcceptTcpClient();}

那么单击取消按钮如何杀死 taskListener？没有 ManualResetEvent 或 ManualResetEventSlim？我可以在服务器关闭和服务器重启之间切换。幕后发生了什么？我的目标是 .NET 4.0

Answer 1

So how does clicking the cancel button kill the taskListener?

当您在取消事件处理程序中调用 TcpListener.Stop 时，它会在内部关闭基础 Socket，并引发 SocketException。这个异常被你的 catch all 块吞没了，它只是打破了循环。

文档明确说明了这一点（强调我的）：

Stop closes the listener. Any unaccepted connection requests in the queue will be lost. Remote hosts waiting for a connection to be accepted will throw a SocketException. You are responsible for closing your accepted connections separately.

您可以通过在 catch 块中打印出异常来看到这一点：

TcpClient c;
try
{
    c = _listener.AcceptTcpClient();
}
catch (SocketException e)
{
    Debug.WriteLine("Socket exception was raised: {0}", e);
    if (e.SocketErrorCode == SocketError.Interrupted)
        Debug.WriteLine("Blocking listen was interrupted");
}

在引擎盖下的阻塞任务中取消令牌

Cancel Token within Blocking Task under the hood

.net

c#

multithreading

task-parallel-library