public class AsyncUserToken

 {

     /// <summary>

     /// 客户端IP地址

     /// </summary>

     public IPAddress IPAddress { get; set; }

     /// <summary>

     /// 远程地址

     /// </summary>

     public EndPoint Remote { get; set; }

     /// <summary>

     /// 通信SOKET

     /// </summary>

     public Socket Socket { get; set; }

     /// <summary>

     /// 连接时间

     /// </summary>

     public DateTime ConnectTime { get; set; }

     /// <summary>

     /// 数据缓存区

     /// </summary>

     public List<byte> Buffer { get; set; }

     public AsyncUserToken()

     {

         this.Buffer = new List<byte>();

     }

 }

 public class SocketAsyncEventArgsPool

 {

     Stack<SocketAsyncEventArgs> m_pool;

     // Initializes the object pool to the specified size

     //

     // The "capacity" parameter is the maximum number of

     // SocketAsyncEventArgs objects the pool can hold

     public SocketAsyncEventArgsPool(int capacity)

     {

         m_pool = new Stack<SocketAsyncEventArgs>(capacity);

     }

     // Add a SocketAsyncEventArg instance to the pool

     //

     //The "item" parameter is the SocketAsyncEventArgs instance

     // to add to the pool

     public void Push(SocketAsyncEventArgs item)

     {

         if (item == null) { throw new ArgumentNullException("Items added to a SocketAsyncEventArgsPool cannot be null"); }

         lock (m_pool)

         {

             m_pool.Push(item);

         }

     }

     // Removes a SocketAsyncEventArgs instance from the pool

     // and returns the object removed from the pool

     public SocketAsyncEventArgs Pop()

     {

         lock (m_pool)

         {

             return m_pool.Pop();

         }

     }

     // The number of SocketAsyncEventArgs instances in the pool

     public int Count

     {

         get { return m_pool.Count; }

     }

 }

 public class BufferManager

 {

     int m_numBytes;                 // the total number of bytes controlled by the buffer pool

     byte[] m_buffer;                // the underlying byte array maintained by the Buffer Manager

     Stack<int> m_freeIndexPool;     //

     int m_currentIndex;

     int m_bufferSize;

     public BufferManager(int totalBytes, int bufferSize)

     {

         m_numBytes = totalBytes;

         m_currentIndex = ;

         m_bufferSize = bufferSize;

         m_freeIndexPool = new Stack<int>();

     }

     // Allocates buffer space used by the buffer pool

     public void InitBuffer()

     {

         // create one big large buffer and divide that

         // out to each SocketAsyncEventArg object

         m_buffer = new byte[m_numBytes];

     }

     // Assigns a buffer from the buffer pool to the

     // specified SocketAsyncEventArgs object

     //

     // <returns>true if the buffer was successfully set, else false</returns>

     public bool SetBuffer(SocketAsyncEventArgs args)

     {

         if (m_freeIndexPool.Count > )

         {

             args.SetBuffer(m_buffer, m_freeIndexPool.Pop(), m_bufferSize);

         }

         else

         {

             if ((m_numBytes - m_bufferSize) < m_currentIndex)

             {

                 return false;

             }

             args.SetBuffer(m_buffer, m_currentIndex, m_bufferSize);

             m_currentIndex += m_bufferSize;

         }

         return true;

     }

     // Removes the buffer from a SocketAsyncEventArg object.

     // This frees the buffer back to the buffer pool

     public void FreeBuffer(SocketAsyncEventArgs args)

     {

         m_freeIndexPool.Push(args.Offset);

         args.SetBuffer(null, , );

     }

 }

 public class Server

 {

     private int m_numConnections;   // the maximum number of connections the sample is designed to handle simultaneously

     private int m_receiveBufferSize;// buffer size to use for each socket I/O operation

     BufferManager m_bufferManager;  // represents a large reusable set of buffers for all socket operations

     const int opsToPreAlloc = ;    // read, write (don't alloc buffer space for accepts)

     Socket listenSocket;            // the socket used to listen for incoming connection requests

     // pool of reusable SocketAsyncEventArgs objects for write, read and accept socket operations

     SocketAsyncEventArgsPool m_readWritePool;

     int m_totalBytesRead;           // counter of the total # bytes received by the server

     int m_numConnectedSockets;      // the total number of clients connected to the server

     Semaphore m_maxNumberAcceptedClients;

     // Create an uninitialized server instance.

     // To start the server listening for connection requests

     // call the Init method followed by Start method

     //

     // <param name="numConnections">the maximum number of connections the sample is designed to handle simultaneously</param>

     // <param name="receiveBufferSize">buffer size to use for each socket I/O operation</param>

     public Server(int numConnections, int receiveBufferSize)

     {

         m_totalBytesRead = ;

         m_numConnectedSockets = ;

         m_numConnections = numConnections;

         m_receiveBufferSize = receiveBufferSize;

         // allocate buffers such that the maximum number of sockets can have one outstanding read and

         //write posted to the socket simultaneously

         m_bufferManager = new BufferManager(receiveBufferSize * numConnections * opsToPreAlloc,

             receiveBufferSize);

         m_readWritePool = new SocketAsyncEventArgsPool(numConnections);

         m_maxNumberAcceptedClients = new Semaphore(numConnections, numConnections);

     }

     // Initializes the server by preallocating reusable buffers and

     // context objects.  These objects do not need to be preallocated

     // or reused, but it is done this way to illustrate how the API can

     // easily be used to create reusable objects to increase server performance.

     //

     public void Init()

     {

         // Allocates one large byte buffer which all I/O operations use a piece of.  This gaurds

         // against memory fragmentation

         m_bufferManager.InitBuffer();

         // preallocate pool of SocketAsyncEventArgs objects

         SocketAsyncEventArgs readWriteEventArg;

         for (int i = ; i < m_numConnections; i++)

         {

             //Pre-allocate a set of reusable SocketAsyncEventArgs

             readWriteEventArg = new SocketAsyncEventArgs();

             readWriteEventArg.Completed += new EventHandler<SocketAsyncEventArgs>(IO_Completed);

             readWriteEventArg.UserToken = new AsyncUserToken();

             // assign a byte buffer from the buffer pool to the SocketAsyncEventArg object

             m_bufferManager.SetBuffer(readWriteEventArg);

             // add SocketAsyncEventArg to the pool

             m_readWritePool.Push(readWriteEventArg);

         }

     }

     // Starts the server such that it is listening for

     // incoming connection requests.

     //

     // <param name="localEndPoint">The endpoint which the server will listening

     // for connection requests on</param>

     public void Start(IPEndPoint localEndPoint)

     {

         // create the socket which listens for incoming connections

         listenSocket = new Socket(localEndPoint.AddressFamily, SocketType.Stream, ProtocolType.Tcp);

         listenSocket.Bind(localEndPoint);

         // start the server with a listen backlog of 100 connections

         listenSocket.Listen();

         // post accepts on the listening socket

         StartAccept(null);

         //Console.WriteLine("{0} connected sockets with one outstanding receive posted to each....press any key", m_outstandingReadCount);

         Console.WriteLine("Press any key to terminate the server process....");

         Console.ReadKey();

     }

     // Begins an operation to accept a connection request from the client

     //

     // <param name="acceptEventArg">The context object to use when issuing

     // the accept operation on the server's listening socket</param>

     public void StartAccept(SocketAsyncEventArgs acceptEventArg)

     {

         if (acceptEventArg == null)

         {

             acceptEventArg = new SocketAsyncEventArgs();

             acceptEventArg.Completed += new EventHandler<SocketAsyncEventArgs>(AcceptEventArg_Completed);

         }

         else

         {

             // socket must be cleared since the context object is being reused

             acceptEventArg.AcceptSocket = null;

         }

         m_maxNumberAcceptedClients.WaitOne();

         bool willRaiseEvent = listenSocket.AcceptAsync(acceptEventArg);

         if (!willRaiseEvent)

         {

             ProcessAccept(acceptEventArg);

         }

     }

     // This method is the callback method associated with Socket.AcceptAsync

     // operations and is invoked when an accept operation is complete

     //

     void AcceptEventArg_Completed(object sender, SocketAsyncEventArgs e)

     {

         ProcessAccept(e);

     }

     private void ProcessAccept(SocketAsyncEventArgs e)

     {

         Interlocked.Increment(ref m_numConnectedSockets);

         Console.WriteLine("Client connection accepted. There are {0} clients connected to the server",

             m_numConnectedSockets);

         // Get the socket for the accepted client connection and put it into the

         //ReadEventArg object user token

         SocketAsyncEventArgs readEventArgs = m_readWritePool.Pop();

         ((AsyncUserToken)readEventArgs.UserToken).Socket = e.AcceptSocket;

         // As soon as the client is connected, post a receive to the connection

         bool willRaiseEvent = e.AcceptSocket.ReceiveAsync(readEventArgs);

         if (!willRaiseEvent)

         {

             ProcessReceive(readEventArgs);

         }

         // Accept the next connection request

         StartAccept(e);

     }

     // This method is called whenever a receive or send operation is completed on a socket

     //

     // <param name="e">SocketAsyncEventArg associated with the completed receive operation</param>

     void IO_Completed(object sender, SocketAsyncEventArgs e)

     {

         // determine which type of operation just completed and call the associated handler

         switch (e.LastOperation)

         {

             case SocketAsyncOperation.Receive:

                 ProcessReceive(e);

                 break;

             case SocketAsyncOperation.Send:

                 ProcessSend(e);

                 break;

             default:

                 throw new ArgumentException("The last operation completed on the socket was not a receive or send");

         }

     }

     // This method is invoked when an asynchronous receive operation completes.

     // If the remote host closed the connection, then the socket is closed.

     // If data was received then the data is echoed back to the client.

     //

     private void ProcessReceive(SocketAsyncEventArgs e)

     {

         // check if the remote host closed the connection

         AsyncUserToken token = (AsyncUserToken)e.UserToken;

         if (e.BytesTransferred >  && e.SocketError == SocketError.Success)

         {

             //increment the count of the total bytes receive by the server

             Interlocked.Add(ref m_totalBytesRead, e.BytesTransferred);

             Console.WriteLine("The server has read a total of {0} bytes", m_totalBytesRead);

             //echo the data received back to the client

             e.SetBuffer(e.Offset, e.BytesTransferred);

             bool willRaiseEvent = token.Socket.SendAsync(e);

             if (!willRaiseEvent)

             {

                 ProcessSend(e);

             }

         }

         else

         {

             CloseClientSocket(e);

         }

     }

     // This method is invoked when an asynchronous send operation completes.

     // The method issues another receive on the socket to read any additional

     // data sent from the client

     //

     // <param name="e"></param>

     private void ProcessSend(SocketAsyncEventArgs e)

     {

         if (e.SocketError == SocketError.Success)

         {

             // done echoing data back to the client

             AsyncUserToken token = (AsyncUserToken)e.UserToken;

             // read the next block of data send from the client

             bool willRaiseEvent = token.Socket.ReceiveAsync(e);

             if (!willRaiseEvent)

             {

                 ProcessReceive(e);

             }

         }

         else

         {

             CloseClientSocket(e);

         }

     }

     private void CloseClientSocket(SocketAsyncEventArgs e)

     {

         AsyncUserToken token = e.UserToken as AsyncUserToken;

         // close the socket associated with the client

         try

         {

             token.Socket.Shutdown(SocketShutdown.Send);

         }

         // throws if client process has already closed

         catch (Exception) { }

         token.Socket.Close();

         // decrement the counter keeping track of the total number of clients connected to the server

         Interlocked.Decrement(ref m_numConnectedSockets);

         // Free the SocketAsyncEventArg so they can be reused by another client

         m_readWritePool.Push(e);

         m_maxNumberAcceptedClients.Release();

         Console.WriteLine("A client has been disconnected from the server. There are {0} clients connected to the server", m_numConnectedSockets);

     }

 }