Question

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

每个接收到的数据报都是较大位图的扫描线，因此在收到所有扫描线后，位图显示在UI线程上。这似乎有效。但是，偶尔会丢失一些1-50％的扫描线。我希望这在弱网络连接上，但在本地运行时不会。

使用以下代码可能会导致UDP包裹丢失？

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，则包裹损失会急剧增加。似乎这个回调中的一个小毫秒延迟会导致问题。不过，在我的发布版本中也可以看到同样的问题。

更新

当我稍微强调一下UI时，错误变得更加频繁。主线程上是否执行了UdpClient实例？

Answer 1

要避免线程阻塞问题，请尝试使用较新的IO完成端口接收方法的此方法：

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);
        }
    }
}

localhost上UDP包丢失的原因？

更新

1 个答案: