using System;
using System.Collections.Generic;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.Threading;
namespace AsyncServer
{
 public class UdpState
 {
  public UdpClient udpClient;
  public IPEndPoint ipEndPoint;
  public const int BufferSize = 1024;
  public byte[] buffer = new byte[BufferSize];
  public int counter = 0;
 }
 public class AsyncUdpSever
 {
  private IPEndPoint ipEndPoint = null;
  private IPEndPoint remoteEP = null;
  private UdpClient udpReceive = null;
  private UdpClient udpSend = null;
  private const int listenPort = 1100;
  private const int remotePort = 1101;
  UdpState udpReceiveState = null;
  UdpState udpSendState = null;
  private ManualResetEvent sendDone = new ManualResetEvent(false);
  private ManualResetEvent receiveDone = new ManualResetEvent(false);
  public AsyncUdpSever()
  {
   ipEndPoint = new IPEndPoint(IPAddress.Any, listenPort);
   remoteEP = new IPEndPoint(Dns.GetHostAddresses(Dns.GetHostName())[0], remotePort);
   udpReceive = new UdpClient(ipEndPoint);
   udpSend = new UdpClient();
   udpReceiveState = new UdpState();   
   udpReceiveState.udpClient = udpReceive;
   udpReceiveState.ipEndPoint = ipEndPoint;
   udpSendState = new UdpState();
   udpSendState.udpClient = udpSend;
   udpSendState.ipEndPoint = remoteEP;
  }
  public void ReceiveMsg()
  {
   Console.WriteLine("listening for messages");
   while(true)
   {
    lock (this)
    { 
     IAsyncResult iar = udpReceive.BeginReceive(new AsyncCallback(ReceiveCallback), udpReceiveState);
     receiveDone.WaitOne();
     Thread.Sleep(100);
    }
   }
  }
  private void ReceiveCallback(IAsyncResult iar)
  {
   UdpState udpReceiveState = iar.AsyncState as UdpState;
   if (iar.IsCompleted)
   {
    Byte[] receiveBytes = udpReceiveState.udpClient.EndReceive(iar, ref udpReceiveState.ipEndPoint);
    string receiveString = Encoding.ASCII.GetString(receiveBytes);
    Console.WriteLine("Received: {0}", receiveString);
    //Thread.Sleep(100);
    receiveDone.Set();
    SendMsg();
   }
  }
  private void SendMsg()
  {
   udpSend.Connect(udpSendState.ipEndPoint);
   udpSendState.udpClient = udpSend;
   udpSendState.counter ++;
   string message = string.Format("第{0}個UDP請求處理完成！",udpSendState.counter);
   Byte[] sendBytes = Encoding.Unicode.GetBytes(message);
   udpSend.BeginSend(sendBytes, sendBytes.Length, new AsyncCallback(SendCallback), udpSendState);
   sendDone.WaitOne();
  }
  private void SendCallback(IAsyncResult iar)
  {
   UdpState udpState = iar.AsyncState as UdpState;
   Console.WriteLine("第{0}個請求處理完畢！", udpState.counter);
   Console.WriteLine("number of bytes sent: {0}", udpState.udpClient.EndSend(iar));
   sendDone.Set();
  }
  public static void Main()
  {
   AsyncUdpSever aus = new AsyncUdpSever();
   Thread t = new Thread(new ThreadStart(aus.ReceiveMsg));
   t.Start();
   Console.Read();
  }
 }
}

using System;
using System.Collections.Generic;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.Threading;
namespace AsyncClient
{
 public class UdpState
 {
  public UdpClient udpClient = null;
  public IPEndPoint ipEndPoint = null;
  public const int BufferSize = 1024;
  public byte[] buffer = new byte[BufferSize];
  public int counter = 0;
 }
 public class AsyncUdpClient
 {
  public static bool messageSent = false;
  // Receive a message and write it to the console.
  private const int listenPort = 1101;
  private const int remotePort = 1100;
  private IPEndPoint localEP = null;
  private IPEndPoint remoteEP = null;
  private UdpClient udpReceive = null;
  private UdpClient udpSend = null;
  private UdpState udpSendState = null;
  private UdpState udpReceiveState = null;
  private int counter = 0;
  private ManualResetEvent sendDone = new ManualResetEvent(false);
  private ManualResetEvent receiveDone = new ManualResetEvent(false);
  private Socket receiveSocket;
  private Socket sendSocket;
  public AsyncUdpClient()
  {
   localEP = new IPEndPoint(IPAddress.Any, listenPort);
   remoteEP = new IPEndPoint(Dns.GetHostAddresses(Dns.GetHostName())[0],remotePort);
   udpReceive = new UdpClient(localEP);   
   udpSend = new UdpClient();
   udpSendState = new UdpState();
   udpSendState.ipEndPoint = remoteEP;
   udpSendState.udpClient = udpSend;
   udpReceiveState = new UdpState();
   udpReceiveState.ipEndPoint = remoteEP;
   udpReceiveState.udpClient = udpReceive;
   receiveSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
   receiveSocket.Bind(localEP);
   sendSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
   sendSocket.Bind(remoteEP);
  }
  public void SendMsg()
  { 
   udpSend.Connect(remoteEP);
   //Thread t = new Thread(new ThreadStart(ReceiveMessages));
   //t.Start();
   Byte[] sendBytes;
   string message;   
   while (true)
   { 
    message = "Client" + (counter++).ToString();
    lock (this)
    {
     sendBytes = Encoding.ASCII.GetBytes(message);
     udpSendState.counter = counter;
     udpSend.BeginSend(sendBytes, sendBytes.Length, new AsyncCallback(SendCallback), udpSendState);
     sendDone.WaitOne();
     Thread.Sleep(200);
     ReceiveMessages();
    }
   }    
  }
  public void SendCallback(IAsyncResult iar)
  {
   UdpState udpState = iar.AsyncState as UdpState;
   if (iar.IsCompleted)
   {
    Console.WriteLine("第{0}個發(fā)送完畢！", udpState.counter);
    Console.WriteLine("number of bytes sent: {0}", udpState.udpClient.EndSend(iar));
    //if (udpState.counter == 10)
    //{
    // udpState.udpClient.Close();
    //}
    sendDone.Set();
   }   
  }
  public void ReceiveMessages()
  {
   lock (this)
   {
    udpReceive.BeginReceive(new AsyncCallback(ReceiveCallback), udpReceiveState);
    receiveDone.WaitOne();
    Thread.Sleep(100);
   } 
  }
  public void ReceiveCallback(IAsyncResult iar)
  {
   UdpState udpState = iar.AsyncState as UdpState;
   if (iar.IsCompleted)
   {
    Byte[] receiveBytes = udpState.udpClient.EndReceive(iar, ref udpReceiveState.ipEndPoint);
    string receiveString = Encoding.Unicode.GetString(receiveBytes);
    Console.WriteLine("Received: {0}", receiveString);
    receiveDone.Set();
   }   
  }
  public static void Main()
  {
   AsyncUdpClient auc = new AsyncUdpClient();
   auc.SendMsg();
   Console.Read();
  }
 }
}