22

我有这个代码...

internal static void Start()
{
    TcpListener listenerSocket = new TcpListener(IPAddress.Any, 32599);
    listenerSocket.Start();
    listenerSocket.BeginAcceptTcpClient(new AsyncCallback(AcceptClient), null);
}

然后我的回调函数看起来像这样......

private static void AcceptClient(IAsyncResult asyncResult)
{
    MessageHandler handler = new MessageHandler(listenerSocket.EndAcceptTcpClient(asyncResult));
    ThreadPool.QueueUserWorkItem((object state) => handler.Process());
    listenerSocket.BeginAcceptTcpClient(new AsyncCallback(AcceptClient), null);
}

现在，我调用 BeginAcceptTcpClient，然后一段时间后我想停止服务器。为此，我一直在调用 TcpListener.Stop() 或 TcpListener.Server.Close()。然而，这两个都执行我的 AcceptClient 函数。当我调用 EndAcceptTcpClient 时，这会引发异常。解决此问题的最佳做法是什么？一旦我调用了停止，我就可以放一个标志来停止 AcceptClient 的执行，但我想知道我是否遗漏了一些东西。

更新 1

目前我已经通过将代码更改为如下所示对其进行了修补。

private static void AcceptClient(IAsyncResult asyncResult)
{
     if (!shutdown)
     {
          MessageHandler handler = new MessageHandler(listenerSocket.EndAcceptTcpClient(asyncResult));
          ThreadPool.QueueUserWorkItem((object state) => handler.Process());
          listenerSocket.BeginAcceptTcpClient(new AsyncCallback(AcceptClient), null);
     }
}

private static bool shutdown = false;
internal static void Stop()
{
     shutdown = true;
     listenerSocket.Stop();
}

更新 2

我将其更改为暗示 Spencer Ruport 的答案。

private static void AcceptClient(IAsyncResult asyncResult)
{
    if (listenerSocket.Server.IsBound)
    {
            MessageHandler handler = new MessageHandler(listenerSocket.EndAcceptTcpClient(asyncResult));
            ThreadPool.QueueUserWorkItem((object state) => handler.Process());
            listenerSocket.BeginAcceptTcpClient(new AsyncCallback(AcceptClient), null);
    }
}
4

5 回答 5

17

我自己也遇到了这个问题，我相信您当前的解决方案不完整/不正确。不保证检查IsBound和后续调用之间的原子性EndAcceptTcpClient()。Stop()如果侦听器在这两个语句之间，您仍然可以获得异常。你没有说你得到了什么异常，但我认为它与我得到的相同，ObjectDisposedException（抱怨底层套接字已经被处理）。

您应该能够通过模拟线程调度来检查这一点：

  • IsBound在您的回调中签入后在行上设置断点
  • 冻结命中断点的线程（线程窗口->右键单击，“冻结”）
  • 运行/触发调用的代码TcpListener.Stop()
  • 打断电话并逐步完成EndAcceptTcpClient()通话。你应该看到ObjectDisposedException.

IMO 理想的解决方案是让微软在这种情况下抛出一个不同的异常EndAcceptTcpClient，例如ListenCanceledException或类似的东西。

事实上，我们必须从ObjectDisposedException. 只需捕获异常并采取相应的行为即可。在我的代码中，我默默地吃掉了异常，因为我在其他地方有代码在做真正的关闭工作（即TcpListener.Stop()首先调用的代码）。无论如何，您应该已经在该区域进行了异常处理，因为您可以获得各种SocketExceptions. 这只是将另一个 catch 处理程序附加到该 try 块上。

我承认我对这种方法感到不舒服，因为原则上捕获可能是误报，其中存在真正的“坏”对象访问。但另一方面，EndAcceptTcpClient()调用中没有太多对象访问可能会触发此异常。我希望。

这是我的代码。这是早期/原型的东西，忽略控制台调用。

    private void OnAccept(IAsyncResult iar)
    {
        TcpListener l = (TcpListener) iar.AsyncState;
        TcpClient c;
        try
        {
            c = l.EndAcceptTcpClient(iar);
            // keep listening
            l.BeginAcceptTcpClient(new AsyncCallback(OnAccept), l);
        }
        catch (SocketException ex)
        {
            Console.WriteLine("Error accepting TCP connection: {0}", ex.Message);

            // unrecoverable
            _doneEvent.Set();
            return;
        }
        catch (ObjectDisposedException)
        {
            // The listener was Stop()'d, disposing the underlying socket and
            // triggering the completion of the callback. We're already exiting,
            // so just return.
            Console.WriteLine("Listen canceled.");
            return;
        }

        // meanwhile...
        SslStream s = new SslStream(c.GetStream());
        Console.WriteLine("Authenticating...");
        s.BeginAuthenticateAsServer(_cert, new AsyncCallback(OnAuthenticate), s);
    }
于 2009-08-04T22:40:53.190 回答
8

不，你没有错过任何东西。您可以检查 Socket 对象的 IsBound 属性。至少对于 TCP 连接，当套接字正在侦听时，这将设置为 true，并且在您调用 close 之后，它的值将是 false。不过，您自己的实现也可以正常工作。

于 2009-07-23T19:39:21.553 回答
1

试试这个。它对我来说很好，不会捕获异常。

private void OnAccept(IAsyncResult pAsyncResult)
{
    TcpListener listener = (TcpListener) pAsyncResult.AsyncState;
    if(listener.Server == null)
    {
        //stop method was called
        return;
    }
    ...
}
于 2010-11-18T12:56:54.767 回答
0

我认为所有树的东西都是需要的，BeginAcceptTcpClient 的重启应该放在 EndAcceptTcpClient 的 tryctach 之外。

    private void AcceptTcpClientCallback(IAsyncResult ar)
    {
        var listener = (TcpListener)ar.AsyncState;

        //Sometimes the socket is null and somethimes the socket was set
        if (listener.Server == null || !listener.Server.IsBound)
            return;

        TcpClient client = null;

        try
        {
            client = listener.EndAcceptTcpClient(ar);
        }
        catch (SocketException ex)
        {
            //the client is corrupt
            OnError(ex);
        }
        catch (ObjectDisposedException)
        {
            //Listener canceled
            return;
        }

        //Get the next Client
        listener.BeginAcceptTcpClient(new AsyncCallback(AcceptTcpClientCallback), listener);

        if (client == null)
            return; //Abort if there was an error with the client

        MyConnection connection = null;
        try
        {
            //Client-Protocoll init
            connection = Connect(client.GetStream()); 
        }
        catch (Exception ex)
        {
            //The client is corrupt/invalid
            OnError(ex);

            client.Close();
        }            
    }
于 2011-09-15T12:54:05.483 回答
0

这是一个简单的例子，如何开始监听，如何异步处理请求，如何停止监听。

完整的例子在这里。

public class TcpServer
{
    #region Public.     
    // Create new instance of TcpServer.
    public TcpServer(string ip, int port)
    {
        _listener = new TcpListener(IPAddress.Parse(ip), port);
    }

    // Starts receiving incoming requests.      
    public void Start()
    {
        _listener.Start();
        _ct = _cts.Token;
        _listener.BeginAcceptTcpClient(ProcessRequest, _listener);
    }

    // Stops receiving incoming requests.
    public void Stop()
    { 
        // If listening has been cancelled, simply go out from method.
        if(_ct.IsCancellationRequested)
        {
            return;
        }

        // Cancels listening.
        _cts.Cancel();

        // Waits a little, to guarantee 
        // that all operation receive information about cancellation.
        Thread.Sleep(100);
        _listener.Stop();
    }
    #endregion

    #region Private.
    // Process single request.
    private void ProcessRequest(IAsyncResult ar)
    { 
        //Stop if operation was cancelled.
        if(_ct.IsCancellationRequested)
        {
            return;
        }

        var listener = ar.AsyncState as TcpListener;
        if(listener == null)
        {
            return;
        }

        // Check cancellation again. Stop if operation was cancelled.
        if(_ct.IsCancellationRequested)
        {
            return;
        }

        // Starts waiting for the next request.
        listener.BeginAcceptTcpClient(ProcessRequest, listener);

        // Gets client and starts processing received request.
        using(TcpClient client = listener.EndAcceptTcpClient(ar))
        {
            var rp = new RequestProcessor();
            rp.Proccess(client);
        }
    }
    #endregion

    #region Fields.
    private CancellationToken _ct;
    private CancellationTokenSource _cts = new CancellationTokenSource();
    private TcpListener _listener;
    #endregion
}
于 2015-10-01T14:52:52.267 回答