C#高性能大容量SOCKET并发（二）：SocketAsyncEventArgs封装

1、SocketAsyncEventArgs介绍

SocketAsyncEventArgs是微软提供的高性能异步Socket实现类，主要为高性能网络服务器应用程序而设计，主要是为了避免在在异步套接字 I/O 量非常大时发生重复的对象分配和同步。使用此类执行异步套接字操作的模式包含以下步骤：
1.分配一个新的 SocketAsyncEventArgs 上下文对象，或者从应用程序池中获取一个空闲的此类对象。
2.将该上下文对象的属性设置为要执行的操作（例如，完成回调方法、数据缓冲区、缓冲区偏移量以及要传输的最大数据量）。
3.调用适当的套接字方法 (xxxAsync) 以启动异步操作。
4.如果异步套接字方法 (xxxAsync) 返回 true，则在回调中查询上下文属性来获取完成状态。
5.如果异步套接字方法 (xxxAsync) 返回 false，则说明操作是同步完成的。 可以查询上下文属性来获取操作结果。
6.将该上下文重用于另一个操作，将它放回到应用程序池中，或者将它丢弃。

2、SocketAsyncEventArgs封装

使用SocketAsyncEventArgs之前需要先建立一个Socket监听对象，使用如下代码：

        public void Start(IPEndPoint localEndPoint)
        {
            listenSocket = new Socket(localEndPoint.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
            listenSocket.Bind(localEndPoint);
            listenSocket.Listen(m_numConnections);
            Program.Logger.InfoFormat("Start listen socket {0} success", localEndPoint.ToString());
            //for (int i = 0; i < 64; i++) //不能循环投递多次AcceptAsync，会造成只接收8000连接后不接收连接了
            StartAccept(null);
            m_daemonThread = new DaemonThread(this);
        }

然后开始接受连接，SocketAsyncEventArgs有连接时会通过Completed事件通知外面，所以接受连接的代码如下：

        public void StartAccept(SocketAsyncEventArgs acceptEventArgs)
        {
            if (acceptEventArgs == null)
            {
                acceptEventArgs = new SocketAsyncEventArgs();
                acceptEventArgs.Completed += new EventHandler(AcceptEventArg_Completed);
            }
            else
            {
                acceptEventArgs.AcceptSocket = null; //释放上次绑定的Socket，等待下一个Socket连接
            }

            m_maxNumberAcceptedClients.WaitOne(); //获取信号量
            bool willRaiseEvent = listenSocket.AcceptAsync(acceptEventArgs);
            if (!willRaiseEvent)
            {
                ProcessAccept(acceptEventArgs);
            }
        }

接受连接响应事件代码：

        void AcceptEventArg_Completed(object sender, SocketAsyncEventArgs acceptEventArgs)
        {
            try
            {
                ProcessAccept(acceptEventArgs);
            }
            catch (Exception E)
            {
                Program.Logger.ErrorFormat("Accept client {0} error, message: {1}", acceptEventArgs.AcceptSocket, E.Message);
                Program.Logger.Error(E.StackTrace);  
            }            
        }

        private void ProcessAccept(SocketAsyncEventArgs acceptEventArgs)
        {
            Program.Logger.InfoFormat("Client connection accepted. Local Address: {0}, Remote Address: {1}",
                acceptEventArgs.AcceptSocket.LocalEndPoint, acceptEventArgs.AcceptSocket.RemoteEndPoint);

            AsyncSocketUserToken userToken = m_asyncSocketUserTokenPool.Pop();
            m_asyncSocketUserTokenList.Add(userToken); //添加到正在连接列表
            userToken.ConnectSocket = acceptEventArgs.AcceptSocket;
            userToken.ConnectDateTime = DateTime.Now;

            try
            {
                bool willRaiseEvent = userToken.ConnectSocket.ReceiveAsync(userToken.ReceiveEventArgs); //投递接收请求
                if (!willRaiseEvent)
                {
                    lock (userToken)
                    {
                        ProcessReceive(userToken.ReceiveEventArgs);
                    }
                }                    
            }
            catch (Exception E)
            {
                Program.Logger.ErrorFormat("Accept client {0} error, message: {1}", userToken.ConnectSocket, E.Message);
                Program.Logger.Error(E.StackTrace);                
            }            

            StartAccept(acceptEventArgs); //把当前异步事件释放，等待下次连接
        }

接受连接后，从当前Socket缓冲池AsyncSocketUserTokenPool中获取一个用户对象AsyncSocketUserToken，AsyncSocketUserToken包含一个接收异步事件m_receiveEventArgs，一个发送异步事件m_sendEventArgs，接收数据缓冲区m_receiveBuffer，发送数据缓冲区m_sendBuffer，协议逻辑调用对象m_asyncSocketInvokeElement，建立服务对象后，需要实现接收和发送的事件响应函数：

        void IO_Completed(object sender, SocketAsyncEventArgs asyncEventArgs)
        {
            AsyncSocketUserToken userToken = asyncEventArgs.UserToken as AsyncSocketUserToken;
            userToken.ActiveDateTime = DateTime.Now;
            try
            {                
                lock (userToken)
                {
                    if (asyncEventArgs.LastOperation == SocketAsyncOperation.Receive)
                        ProcessReceive(asyncEventArgs);
                    else if (asyncEventArgs.LastOperation == SocketAsyncOperation.Send)
                        ProcessSend(asyncEventArgs);
                    else
                        throw new ArgumentException("The last operation completed on the socket was not a receive or send");
                }   
            }
            catch (Exception E)
            {
                Program.Logger.ErrorFormat("IO_Completed {0} error, message: {1}", userToken.ConnectSocket, E.Message);
                Program.Logger.Error(E.StackTrace);
            }                     
        }

在Completed事件中需要处理发送和接收的具体逻辑代码，其中接收的逻辑实现如下：

        private void ProcessReceive(SocketAsyncEventArgs receiveEventArgs)
        {
            AsyncSocketUserToken userToken = receiveEventArgs.UserToken as AsyncSocketUserToken;
            if (userToken.ConnectSocket == null)
                return;
            userToken.ActiveDateTime = DateTime.Now;
            if (userToken.ReceiveEventArgs.BytesTransferred > 0 && userToken.ReceiveEventArgs.SocketError == SocketError.Success)
            {
                int offset = userToken.ReceiveEventArgs.Offset;
                int count = userToken.ReceiveEventArgs.BytesTransferred;
                if ((userToken.AsyncSocketInvokeElement == null) & (userToken.ConnectSocket != null)) //存在Socket对象，并且没有绑定协议对象，则进行协议对象绑定
                {
                    BuildingSocketInvokeElement(userToken);
                    offset = offset + 1;
                    count = count - 1;
                }
                if (userToken.AsyncSocketInvokeElement == null) //如果没有解析对象，提示非法连接并关闭连接
                {
                    Program.Logger.WarnFormat("Illegal client connection. Local Address: {0}, Remote Address: {1}", userToken.ConnectSocket.LocalEndPoint, 
                        userToken.ConnectSocket.RemoteEndPoint);
                    CloseClientSocket(userToken);
                }
                else
                {
                    if (count > 0) //处理接收数据
                    {
                        if (!userToken.AsyncSocketInvokeElement.ProcessReceive(userToken.ReceiveEventArgs.Buffer, offset, count))
                        { //如果处理数据返回失败，则断开连接
                            CloseClientSocket(userToken);
                        }
                        else //否则投递下次介绍数据请求
                        {
                            bool willRaiseEvent = userToken.ConnectSocket.ReceiveAsync(userToken.ReceiveEventArgs); //投递接收请求
                            if (!willRaiseEvent)
                                ProcessReceive(userToken.ReceiveEventArgs);
                        }
                    }
                    else
                    {
                        bool willRaiseEvent = userToken.ConnectSocket.ReceiveAsync(userToken.ReceiveEventArgs); //投递接收请求
                        if (!willRaiseEvent)
                            ProcessReceive(userToken.ReceiveEventArgs);
                    }
                }
            }
            else
            {
                CloseClientSocket(userToken);
            }
        }

由于我们制定的协议第一个字节是协议标识，因此在接收到第一个字节的时候需要绑定协议解析对象，具体代码实现如下：

        private void BuildingSocketInvokeElement(AsyncSocketUserToken userToken)
        {
            byte flag = userToken.ReceiveEventArgs.Buffer[userToken.ReceiveEventArgs.Offset];
            if (flag == (byte)SocketFlag.Upload)
                userToken.AsyncSocketInvokeElement = new UploadSocketProtocol(this, userToken);
            else if (flag == (byte)SocketFlag.Download)
                userToken.AsyncSocketInvokeElement = new DownloadSocketProtocol(this, userToken);
            else if (flag == (byte)SocketFlag.RemoteStream)
                userToken.AsyncSocketInvokeElement = new RemoteStreamSocketProtocol(this, userToken);
            else if (flag == (byte)SocketFlag.Throughput)
                userToken.AsyncSocketInvokeElement = new ThroughputSocketProtocol(this, userToken);
            else if (flag == (byte)SocketFlag.Control)
                userToken.AsyncSocketInvokeElement = new ControlSocketProtocol(this, userToken);
            else if (flag == (byte)SocketFlag.LogOutput)
                userToken.AsyncSocketInvokeElement = new LogOutputSocketProtocol(this, userToken);
            if (userToken.AsyncSocketInvokeElement != null)
            {
                Program.Logger.InfoFormat("Building socket invoke element {0}.Local Address: {1}, Remote Address: {2}",
                    userToken.AsyncSocketInvokeElement, userToken.ConnectSocket.LocalEndPoint, userToken.ConnectSocket.RemoteEndPoint);
            } 
        }

发送响应函数实现需要注意，我们是把发送数据放到一个列表中，当上一个发送事件完成响应Completed事件，这时我们需要检测发送队列中是否存在未发送的数据，如果存在则继续发送。

        private bool ProcessSend(SocketAsyncEventArgs sendEventArgs)
        {
            AsyncSocketUserToken userToken = sendEventArgs.UserToken as AsyncSocketUserToken;
            if (userToken.AsyncSocketInvokeElement == null)
                return false;
            userToken.ActiveDateTime = DateTime.Now;
            if (sendEventArgs.SocketError == SocketError.Success)
                return userToken.AsyncSocketInvokeElement.SendCompleted(); //调用子类回调函数
            else
            {
                CloseClientSocket(userToken);
                return false;
            }
        }

SendCompleted用于回调下次需要发送的数据，具体实现过程如下：

        public virtual bool SendCompleted()
        {
            m_activeDT = DateTime.UtcNow;
            m_sendAsync = false;
            AsyncSendBufferManager asyncSendBufferManager = m_asyncSocketUserToken.SendBuffer;
            asyncSendBufferManager.ClearFirstPacket(); //清除已发送的包
            int offset = 0;
            int count = 0;
            if (asyncSendBufferManager.GetFirstPacket(ref offset, ref count))
            {
                m_sendAsync = true;
                return m_asyncSocketServer.SendAsyncEvent(m_asyncSocketUserToken.ConnectSocket, m_asyncSocketUserToken.SendEventArgs,
                    asyncSendBufferManager.DynamicBufferManager.Buffer, offset, count);
            }
            else
                return SendCallback();
        }

        //发送回调函数，用于连续下发数据
        public virtual bool SendCallback()
        {
            return true;
        }

当一个SocketAsyncEventArgs断开后，我们需要断开对应的Socket连接，并释放对应资源，具体实现函数如下：

        public void CloseClientSocket(AsyncSocketUserToken userToken)
        {
            if (userToken.ConnectSocket == null)
                return;
            string socketInfo = string.Format("Local Address: {0} Remote Address: {1}", userToken.ConnectSocket.LocalEndPoint,
                userToken.ConnectSocket.RemoteEndPoint);
            Program.Logger.InfoFormat("Client connection disconnected. {0}", socketInfo);
            try
            {
                userToken.ConnectSocket.Shutdown(SocketShutdown.Both);
            }
            catch (Exception E) 
            {
                Program.Logger.ErrorFormat("CloseClientSocket Disconnect client {0} error, message: {1}", socketInfo, E.Message);
            }
            userToken.ConnectSocket.Close();
            userToken.ConnectSocket = null; //释放引用，并清理缓存，包括释放协议对象等资源

            m_maxNumberAcceptedClients.Release();
            m_asyncSocketUserTokenPool.Push(userToken);
            m_asyncSocketUserTokenList.Remove(userToken);
        }

3、SocketAsyncEventArgs封装和MSDN的不同点

MSDN在http://msdn.microsoft.com/zh-cn/library/system.net.sockets.socketasynceventargs(v=vs.110).aspx实现了示例代码，并实现了初步的池化处理，我们是在它的基础上扩展实现了接收数据缓冲，发送数据队列，并把发送SocketAsyncEventArgs和接收SocketAsyncEventArgs分开，并实现了协议解析单元，这样做的好处是方便后续逻辑实现文件的上传，下载和日志输出。

DEMO下载地址：http://download.csdn.net/detail/sqldebug_fan/7467745
免责声明：此代码只是为了演示C#完成端口编程，仅用于学习和研究，切勿用于商业用途。水平有限，C#也属于初学，错误在所难免，欢迎指正和指导。邮箱地址：[email protected]。