本地主机上高 UDP 数据包丢失的原因？

Question

在我的WPF 4.0 应用程序中，我实现了一个UDP 监听器，如下所示。在我的 Windows 7 PC 上，我在 localhost 上同时运行服务器和客户端。

每个接收到的数据报都是一个较大位图的扫描线，因此在接收到所有扫描线后，位图会显示在UI 线程上。这似乎有效。但是，有时会丢失一些 1-50% 的扫描线。我希望在网络连接较弱的情况下这样做，但在本地运行时不会。

以下代码可能导致UDP 包丢失？

IPEndPoint endPoint = new IPEndPoint(IPAddress.Any, PORT);
udpClient = new UdpClient(endPoint);
udpClient.Client.ReceiveBufferSize = 65535; // I've tried many different sizes...

var status = new UdpStatus()
{
    u = udpClient,
    e = endPoint
};

udpClient.BeginReceive(new AsyncCallback(UdpCallback), status);

private void UdpCallback(IAsyncResult ar)
{
    IPEndPoint endPoint = ((UdpStatus)(ar.AsyncState)).e;
    UdpClient client = ((UdpStatus)(ar.AsyncState)).u;

    byte[] datagram = client.EndReceive(ar, ref endPoint);

    // Immediately begin listening for next packet so as to not miss any.
    client.BeginReceive(new AsyncCallback(UdpCallback), ar.AsyncState);

    lock (bufferLock)
    {
        // Fast processing of datagram.
        // This merely involves copying the datagram (scanline) into a larger buffer.
        //
        // WHEN READY:
        // Here I can see that scanlines are missing in my larger buffer.
    }
}

如果我在回调中添加System.Diagnostics.Debug.WriteLine，则包裹丢失会急剧增加。似乎此回调中的小毫秒延迟会导致问题。不过，在我的发布版本中也出现了同样的问题。

更新

当我稍微强调一下 UI 时，错误变得更加频繁。 UdpClient 实例是否在主线程上执行？

Answer 1

为避免线程阻塞问题，请尝试使用较新的 IO Completion 端口接收方法的方法：

private void OnReceive(object sender, SocketAsyncEventArgs e)
{
TOP:
    if (e != null)
    {
        int length = e.BytesTransferred;
        if (length > 0)
        {
            FireBytesReceivedFrom(Datagram, length, (IPEndPoint)e.RemoteEndPoint);
        }
        e.Dispose(); // could possibly reuse the args?
    }
    Socket s = Socket;
    if (s != null && RemoteEndPoint != null)
    {
        e = new SocketAsyncEventArgs();
        try
        {
            e.RemoteEndPoint = RemoteEndPoint;
            e.SetBuffer(Datagram, 0, Datagram.Length); // don't allocate a new buffer every time
            e.Completed += OnReceive;
            // this uses the fast IO completion port stuff made available in .NET 3.5; it's supposedly better than the socket selector or the old Begin/End methods
            if (!s.ReceiveFromAsync(e)) // returns synchronously if data is already there
                goto TOP; // using GOTO to avoid overflowing the stack
        }
        catch (ObjectDisposedException)
        {
            // this is expected after a disconnect
            e.Dispose();
            Logger.Info("UDP Client Receive was disconnected.");
        }
        catch (Exception ex)
        {
            Logger.Error("Unexpected UDP Client Receive disconnect.", ex);
        }
    }
}