如何在循环中使用UdpClient.BeginReceive

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");
   }