如何在循环中使用UdpClient.BeginReceive

Question

我想做这个

for (int i = 0; i < 100; i++ )
{
    Byte[] receiveBytes = receivingUdpClient.Receive(ref RemoteIpEndPoint);
}

但UdpClient.Receive我不得不使用,而不是使用UdpClient.BeginReceive.问题是,我该怎么做？没有很多样本使用BeginReceive,MSDN示例根本没有帮助.我应该使用BeginReceive,还是只在一个单独的线程下创建它？

我一直都是ObjectDisposedException例外.我只收到第一个发送的数据.下一个数据将抛出异常.

public class UdpReceiver
{
    private UdpClient _client;
    public System.Net.Sockets.UdpClient Client
    {
        get { return _client; }
        set { _client = value; }
    }
    private IPEndPoint _endPoint;
    public System.Net.IPEndPoint EndPoint
    {
        get { return _endPoint; }
        set { _endPoint = value; }
    }
    private int _packetCount;
    public int PacketCount
    {
        get { return _packetCount; }
        set { _packetCount = value; }
    }
    private string _buffers;
    public string Buffers
    {
        get { return _buffers; }
        set { _buffers = value; }
    }
    private Int32 _counter;
    public System.Int32 Counter
    {
        get { return _counter; }
        set { _counter = value; }
    }
    private Int32 _maxTransmission;
    public System.Int32 MaxTransmission
    {
        get { return _maxTransmission; }
        set { _maxTransmission = value; }
    }

    public UdpReceiver(UdpClient udpClient, IPEndPoint ipEndPoint, string buffers, Int32 counter, Int32 maxTransmission)
    {
        _client = udpClient;
        _endPoint = ipEndPoint;
        _buffers = buffers;
        _counter = counter;
        _maxTransmission = maxTransmission;
    }
    public void StartReceive()
    {
        _packetCount = 0;
        _client.BeginReceive(new AsyncCallback(Callback), null);
    }

    private void Callback(IAsyncResult result)
    {
        try
        {
            byte[] buffer = _client.EndReceive(result, ref _endPoint);
            // Process buffer
            MainWindow.Log(Encoding.ASCII.GetString(buffer));
            _packetCount += 1;
            if (_packetCount < _maxTransmission)
            {
                _client.BeginReceive(new AsyncCallback(Callback), null);
            }
        }
        catch (ObjectDisposedException ex) 
        {
            MainWindow.Log(ex.ToString());
        }
        catch (SocketException ex) 
        { 
            MainWindow.Log(ex.ToString()); 
        }
        catch (System.Exception ex)
        {
            MainWindow.Log(ex.ToString()); 
        }
    }
}

是什么赋予了？

顺便说一下,一般的想法是:

1. 创建tcpclient管理器.
2. 使用udpclient开始发送/接收数据.
3. 当所有数据都已发送后,tcpclient manager将通知接收方已发送所有数据,并且应关闭udpclient连接.

Answer 1

它似乎UdpClient.BeginReceive()并UdpClient.EndReceive()没有得到很好的实施/理解.当然,与TcpListener的实现方式相比,使用起来要困难得多.

您可以采取一些措施来UdpClient.Receive()更好地利用这项工作.首先,在底层套接字客户端上设置超时将使控制能够通过(到异常),允许控制流继续或循环播放.其次,在一个新的线程(其中我还没有创建)创建UDP监听,你可避免的半阻挡作用UdpClient.Receive()的功能,如果你这样做是正确,你可以有效地中止该线程以后.

以下代码分为三部分.第一个和最后一个部分应分别位于入口和出口点的主循环中.第二部分应该在您创建的新线程中.

一个简单的例子:

// Define this globally, on your main thread
UdpClient listener = null;
// ...


// ...
// Create a new thread and run this code:

IPEndPoint endPoint = new IPEndPoint(IPAddress.Any, 9999);
byte[] data = new byte[0];
string message = "";

listener.Client.SendTimeout = 5000;
listener.Client.ReceiveTimeout = 5000;

listener = new UdpClient(endPoint);
while(true)
{
    try
    {
        data = listener.Receive(ref endPoint);
        message = Encoding.ASCII.GetString(data);
    }
    catch(System.Net.Socket.SocketException ex)
    {
        if (ex.ErrorCode != 10060)
        {
            // Handle the error. 10060 is a timeout error, which is expected.
        }
    }

    // Do something else here.
    // ...
    //
    // If your process is eating CPU, you may want to sleep briefly
    // System.Threading.Thread.Sleep(10);
}
// ...


// ...
// Back on your main thread, when it's exiting, run this code
// in order to completely kill off the UDP thread you created above:
listener.Close();
thread.Close();
thread.Abort();
thread.Join(5000);
thread = null;

除此之外,您还可以检查UdpClient.Available > 0以确定在执行之前是否有任何UDP请求排队UdpClient.Receive()- 这完全消除了阻塞方面.我建议您谨慎尝试,因为此行为不会出现在Microsoft文档中,但似乎确实有效.

注意:

您在研究此问题时可能找到的MSDN exmaple代码需要一个额外的用户定义类 - UdpState.这不是.NET库类.在研究这个问题时,这似乎让很多人感到困惑.

该超时不必严格进行设置,以使您的应用程序完全退出,但他们会允许你做其他事情在这个循环,而不是永远阻塞.

该listener.Close()命令是非常重要的,因为它迫使UdpClient抛出一个异常,并退出循环,使Thread.Abort的()得到处理.如果没有这个,您可能无法正常终止侦听器线程,直到它超时或收到UDP数据包导致代码继续通过UdpClient.Receive()块.

只是为了补充这个无价的答案,这是一个经过实践检验的代码片段.(这里是Unity3D上下文,但当然对于任何c#.)

// minmal flawless UDP listener per PretorianNZ

using System.Collections;
using System;
using System.Net.Sockets;
using System.Net;
using System.Threading;

void Start()
   {
   listenThread = new Thread (new ThreadStart (SimplestReceiver));
   listenThread.Start();
   }

private Thread listenThread;
private UdpClient listenClient;
private void SimplestReceiver()
   {
   Debug.Log(",,,,,,,,,,,, Overall listener thread started.");

   IPEndPoint listenEndPoint = new IPEndPoint(IPAddress.Any, 1260);
   listenClient = new UdpClient(listenEndPoint);
   Debug.Log(",,,,,,,,,,,, listen client started.");

   while(true)
      {
      Debug.Log(",,,,, listen client listening");

      try
         {
         Byte[] data = listenClient.Receive(ref listenEndPoint);
         string message = Encoding.ASCII.GetString(data);
         Debug.Log("Listener heard: " +message);
         }
      catch( SocketException ex)
         {
         if (ex.ErrorCode != 10060)
            Debug.Log("a more serious error " +ex.ErrorCode);
         else
            Debug.Log("expected timeout error");
         }

      Thread.Sleep(10); // tune for your situation, can usually be omitted
      }
   }

void OnDestroy() { CleanUp(); }
void OnDisable() { CleanUp(); }
// be certain to catch ALL possibilities of exit in your environment,
// or else the thread will typically live on beyond the app quitting.

void CleanUp()
   {
   Debug.Log ("Cleanup for listener...");

   // note, consider carefully that it may not be running
   listenClient.Close();
   Debug.Log(",,,,, listen client correctly stopped");

   listenThread.Abort();
   listenThread.Join(5000);
   listenThread = null;
   Debug.Log(",,,,, listener thread correctly stopped");
   }

Answer 2

我认为您不应该在循环中使用它，而是每当调用 BeginReceive 回调时，您都会再次调用 BeginReceive ，并且如果您想将数量限制为 100，则保留一个公共变量用于计数。