深入探析 socket

　　最近浏览了几篇有关Socket发送消息的文章，发现大家对Socket Send方法理解有所偏差，现将自己在开发过程中对Socket的领悟写出来，以供大家参考。

　　（一）架构

　　基于TCP协议的Socket通信，架构类似于B/S架构，一个Socket通信服务器，多个Socket通信客户端。Socket通信服务器启动时，会建立一个侦听Socket，侦听Socket将侦听到的Socket连接传给接受Socket，然后由接受Socket完成接受、发送消息，当Socket存在异常时，断开连接。在实际开发项目中，往往要求Socket通信服务器能提供高效、稳定的服务，一般会用到以下技术：双工通信、完成端口、SAEA、池、多线程、异步等。特别是池，用的比较多，池一般包括一下几种：

1）Buffer池，用于集中管控Socket缓冲区，防止内存碎片。

2）SAEA池，用于集中管控Socket，重复利用Socket。

3）SQL池，用于分离网络服务层与数据访问层（SQL的执行效率远远低于网络层执行效率）。

4）线程池，用于从线程池中调用空闲线程执行业务逻辑，进一步提高网络层运行效率。

 

　　（二）Send

　　主服务器接受Socket为一端口，客户端Socket为一端口，这两个端口通过TCP协议建立连接，通信基础系统负责管理此连接，它有两个功能：            

　　1）发送消息            

　　2）接受消息

　　Socket的Send方法，并非大家想象中的从一个端口发送消息到另一个端口，它仅仅是拷贝数据到基础系统的发送缓冲区，然后由基础系统将发送缓冲区的数据到连接的另一端口。值得一说的是，这里的拷贝数据与异步发送消息的拷贝是不一样的，同步发送的拷贝，是直接拷贝数据到基础系统缓冲区，拷贝完成后返回，在拷贝的过程中，执行线程会IO等待, 此种拷贝与Socket自带的Buffer空间无关，但异步发送消息的拷贝，是将Socket自带的Buffer空间内的所有数据，拷贝到基础系统发送缓冲区，并立即返回，执行线程无需IO等待，所以异步发送在发送前必须执行SetBuffer方法，拷贝完成后，会触发你自定义回调函数ProcessSend，在ProcessSend方法中，调用SetBuffer方法，重新初始化Buffer空间。

 

 

　　口说无凭，下面给个例子：

　　服务器端：

客户端：

解释：

 

客户端第一次发送数据：1234567890。

客户端第一个接受数据：1234567890，该数据由服务端用Send同步方法发送返回。

客户端第二个接受数据：1234567890，该数据由服务端用Send异步方法发送返回。

 

以上似乎没什么异常，好，接下来，我只发送abc。

客户端第一个接受数据：abc，理所当然，没什么问题。

客户端第二个接受数据：abc4567890！为什么呢？应该是abc才对呀！

 

好，现在为大家解释一下：

异步发送是将其Buffer空间中所有数据拷贝到基础系统发送缓冲区，第一次拷贝1234567890到发送缓冲区，所以收到1234567890，第二次拷贝abc到发送缓冲区，替换了先前的123，所以收到abc4567890，大家明白的？

 

源码：

 

 

using System.Collections.Generic;
using System.Net.Sockets;

// This class creates a single large buffer which can be divided up 
// and assigned to SocketAsyncEventArgs objects for use with each 
// socket I/O operation.  
// This enables bufffers to be easily reused and guards against 
// fragmenting heap memory.
// 
// The operations exposed on the BufferManager class are not thread safe.
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 =0;
        m_bufferSize = bufferSize;
        m_freeIndexPool =new Stack<int>();
    }

    // Allocates buffer space used by the buffer pool
publicvoid InitBuffer()
    {
        // create one big large buffer and divide that 
        // out to each SocketAsyncEventArg object
        m_buffer =newbyte[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>
publicbool SetBuffer(SocketAsyncEventArgs args)
    {

        if (m_freeIndexPool.Count >0)
        {
            args.SetBuffer(m_buffer, m_freeIndexPool.Pop(), m_bufferSize);
        }
        else
        {
            if ((m_numBytes - m_bufferSize) < m_currentIndex)
            {
                returnfalse;
            }
            args.SetBuffer(m_buffer, m_currentIndex, m_bufferSize);
            m_currentIndex += m_bufferSize;
        }
        returntrue;
    }

    // Removes the buffer from a SocketAsyncEventArg object.  
    // This frees the buffer back to the buffer pool
publicvoid FreeBuffer(SocketAsyncEventArgs args)
    {
        m_freeIndexPool.Push(args.Offset);
        args.SetBuffer(null, 0, 0);
    }

}

 

 

 

using System;
using System.Collections.Generic;
using System.Net.Sockets;

// Represents a collection of reusable SocketAsyncEventArgs objects.  
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
publicvoid Push(SocketAsyncEventArgs item)
    {
        if (item ==null) { thrownew 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
publicint Count
    {
        get { return m_pool.Count; }
    }

}

 

 

 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net.Sockets;

class AsyncUserToken
{
    public Socket Socket;
}

 

 

 

using System;
using System.Threading;
using System.Net.Sockets;
using System.Net;
using System.Text;

// Implements the connection logic for the socket server.  
// After accepting a connection, all data read from the client 
// is sent back to the client. The read and echo back to the client pattern 
// is continued until the client disconnects.
class Server
{
    privateint m_numConnections;   // the maximum number of connections the sample is designed to handle simultaneously 
privateint 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
constint opsToPreAlloc =2;    // 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 =0;
        m_numConnectedSockets =0;
        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.
    //
publicvoid 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 =0; 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>
publicvoid 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(100);

        // 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>
publicvoid 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);
    }

    privatevoid 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:
                thrownew 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.
    //
privatevoid ProcessReceive(SocketAsyncEventArgs e)
    {
        // check if the remote host closed the connection
        AsyncUserToken token = (AsyncUserToken)e.UserToken;
        if (e.BytesTransferred >0&& 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);


            Int32 BytesToProcess = e.BytesTransferred;
            Byte[] bt =new Byte[BytesToProcess];
            Buffer.BlockCopy(e.Buffer, e.Offset, bt, 0, BytesToProcess);
            string strReceive = Encoding.Default.GetString(bt);


            Send(token.Socket, bt, 0, bt.Length, 1000);


            Thread.Sleep(1000);

            //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);
        }
    }


    publicstaticvoid Send(Socket socket, byte[] buffer, int offset, int size, int timeout)
    {
        socket.SendTimeout =0;
        int startTickCount = Environment.TickCount;
        int sent =0;  // how many bytes is already sent
do
        {
            if (Environment.TickCount > startTickCount + timeout)
                //throw new Exception("Timeout.");
try
            {
                sent += socket.Send(buffer, offset + sent, size - sent, SocketFlags.None);
            }
            catch (SocketException ex)
            {
                if (ex.SocketErrorCode == SocketError.WouldBlock ||
                    ex.SocketErrorCode == SocketError.IOPending ||
                    ex.SocketErrorCode == SocketError.NoBufferSpaceAvailable)
                {
                    // socket buffer is probably full, wait and try again
                    Thread.Sleep(30);
                }
                else
                    throw ex;  // any serious error occurr
            }
        } while (sent < size);
    }



    // 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>
privatevoid ProcessSend(SocketAsyncEventArgs e)
    {
        if (e.SocketError == SocketError.Success)
        {
            //e.SetBuffer(e.Offset, 10);

            // 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);
        }
    }

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

        // Free the SocketAsyncEventArg so they can be reused by another client
        m_readWritePool.Push(e);
    }

}

 

 

 

 

using System;
using System.Net;
using System.Collections.Generic;
using System.IO;

class Program
{
    staticvoid Main(string[] args)
    {
        IPEndPoint iep =new IPEndPoint(IPAddress.Parse("10.1.20.6"), 1333);

        Server objServer =new Server(1000, 10);
        objServer.Init();
        objServer.Start(iep);
    }
}