最近在为公司的分布式服务框架做支持异步调用的开发，这种新特性的上线需要进行各种严格的测试。在并发性能测试时，性能一直非常差，而且非常的不稳定。经过不断的分析调优，发现Socket通信和多线程异步回调存在较为严重的性能问题。经过多方优化，性能终于达标。下面是原版本、支持异步最初版本和优化后版本的性能比较。差异还是非常巨大的。另外说明一下，总耗时是指10000次请求累计执行时间。
从上图可以看到，支持异步的版本，在单线程模式下，性能的表现与老版本差异并不明显，但是10线程下差异就非常巨大，而100线程的测试结果反而有所好转。通过分析，两个版本的性能差异如此巨大，主要是因为：
- 同步模式会阻塞客户端请求，说白了，在线程内就是串行请求的。但是在异步模式中，线程内的请求不再阻塞，网络流量、后台计算压力瞬间暴涨，峰值是同步模式的100倍。网络传输变成瓶颈点。
- 在压力暴涨的情况下，CPU资源占用也会突变， 并且ThreadPool、Task、异步调用的执行都将变慢。
在网络通信方面，把原先半异步的模式调整为了SocketAsyncEventArgs 模式。下面是Socket通信的几种模型的介绍和示例，总结一下，与大家分享。下次再与大家分享，并发下异步调用的性能优化方案。
APM方式： Asynchronous Programming Model
异步编程模型是一种模式，该模式允许用更少的线程去做更多的操作，.NET Framework很多类也实现了该模式，同时我们也可以自定义类来实现该模式。NET Framework中的APM也称为Begin/End模式。此种模式下，调用BeginXXX方法来启动异步操作，然后返回一个IAsyncResult 对象。当操作执行完成后，系统会触发IAsyncResult 对象的执行。 具体可参考： https://docs.microsoft.com/en-us/dotnet/standard/asynchronous-programming-patterns/asynchronous-programming-model-apm
.net中的Socket异步模式也支持APM，与同步模式或Blocking模式相比，可以更好的利用网络带宽和系统资源编写出具有更高性能的程序。参考具体代码如下：
服务端监听：Socket serverSocket =newSocket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);//本机预使用的IP和端口IPEndPoint serverIP =newIPEndPoint(IPAddress.Any, 9050);//绑定服务端设置的IPserverSocket.Bind(serverIP);//设置监听个数serverSocket.Listen(1);//异步接收连接请求serverSocket.BeginAccept(ar =>{base.communicateSocket = serverSocket.EndAccept(ar);AccessAciton();},null);
客户端连接：var communicateSocket =newSocket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);communicateSocket.Bind(newIPEndPoint(IPAddress.Any, 9051));//服务器的IP和端口IPEndPoint serverIP;try{serverIP =newIPEndPoint(IPAddress.Parse(IP), 9050);}catch{thrownewException(String.Format("{0}不是一个有效的IP地址!", IP));}//客户端只用来向指定的服务器发送信息,不需要绑定本机的IP和端口,不需要监听try{communicateSocket.BeginConnect(serverIP, ar =>{AccessAciton();},null);}catch{thrownewException(string.Format("尝试连接{0}不成功!", IP));}
客户端请求：if(communicateSocket.Connected ==false){thrownewException("还没有建立连接, 不能发送消息");}Byte[] msg = Encoding.UTF8.GetBytes(message);communicateSocket.BeginSend(msg,0, msg.Length, SocketFlags.None,ar => {},null);
服务端响应：Byte[] msg =newbyte[1024];//异步的接受消息communicateSocket.BeginReceive(msg, 0, msg.Length, SocketFlags.None,ar => {//对方断开连接时, 这里抛出Socket ExceptioncommunicateSocket.EndReceive(ar);ReceiveAction(Encoding.UTF8.GetString(msg).Trim(' ',' '));Receive(ReceiveAction);},null);
注意：异步模式虽好，但是如果进行大量异步套接字操作，是要付出很高代价的。针对每次操作，都必须创建一个IAsyncResult对象，而且该对象不能被重复使用。由于大量使用对象分配和垃圾收集，这会影响系统性能。如需要更好的理解APM模式，最了解EAP模式：Event-based Asynchronous Pattern：https://docs.microsoft.com/en-us/dotnet/standard/asynchronous-programming-patterns/event-based-asynchronous-pattern-eap 。
TAP 方式： Task-based Asynchronous Pattern
基于任务的异步模式，该模式主要使用System.Threading.Tasks.Task和Task<T>类来完成异步编程，相对于APM 模式来讲，TAP使异步编程模式更加简单(因为这里我们只需要关注Task这个类的使用)，同时TAP也是微软推荐使用的异步编程模式。APM与TAP的本质区别，请参考我的一篇历史博客：http://www.cnblogs.com/vveiliang/p/7943003.html
TAP模式与APM模式是两种异步模式的实现，从性能上看没有本质的差别。TAP的资料可参考：https://docs.microsoft.com/en-us/dotnet/standard/asynchronous-programming-patterns/task-based-asynchronous-pattern-tap 。参考具体代码如下：
服务端：
publicclassStateContext{// Client socket.publicSocketWorkSocket =null;// Size of receive buffer.publicconstintBufferSize = 1024;// Receive buffer.publicbyte[] buffer =newbyte[BufferSize];// Received data string.publicStringBuildersb =newStringBuilder(100);}publicclassAsynchronousSocketListener{// Thread signal.publicstaticManualResetEventreSetEvent =newManualResetEvent(false);publicAsynchronousSocketListener(){}publicstaticvoidStartListening(){// Data buffer for incoming data.byte[] bytes =newByte[1024];// Establish the local endpoint for the socket.IPAddressipAddress =IPAddress.Parse("127.0.0.1");IPEndPointlocalEndPoint =newIPEndPoint(ipAddress, 11000);// Create a TCP/IP socket.Socketlistener =newSocket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);// Bind the socket to the localtry{listener.Bind(localEndPoint);listener.Listen(100);while(true){// Set the event to nonsignaled state.reSetEvent.Reset();// Start an asynchronous socket to listen for connections.Console.WriteLine("Waiting for a connection...");listener.BeginAccept(newAsyncCallback(AcceptCallback), listener);// Wait until a connection is made before continuing.reSetEvent.WaitOne();}}catch(Exceptione){Console.WriteLine(e.ToString());}Console.WriteLine(" Press ENTER to continue...");Console.Read();}publicstaticvoidAcceptCallback(IAsyncResultar){// Signal the main thread to continue.reSetEvent.Set();// Get the socket that handles the client request.Socketlistener = (Socket)ar.AsyncState;Sockethandler = listener.EndAccept(ar);// Create the state object.StateContextstate =newStateContext();state.WorkSocket = handler;handler.BeginReceive(state.buffer, 0,StateContext.BufferSize, 0,newAsyncCallback(ReadCallback), state);}publicstaticvoidReadCallback(IAsyncResultar){Stringcontent =String.Empty;StateContextstate = (StateContext)ar.AsyncState;Sockethandler = state.WorkSocket;// Read data from the client socket.intbytesRead = handler.EndReceive(ar);if(bytesRead > 0){// There might be more data, so store the data received so far.state.sb.Append(Encoding.ASCII.GetString(state.buffer, 0, bytesRead));// Check for end-of-file tag. If it is not there, read// more data.content = state.sb.ToString();if(content.IndexOf("<EOF>") > -1){Console.WriteLine("读取 {0} bytes. 数据: {1}", content.Length, content);Send(handler, content);}else{handler.BeginReceive(state.buffer, 0,StateContext.BufferSize, 0,newAsyncCallback(ReadCallback), state);}}}privatestaticvoidSend(Sockethandler,Stringdata){byte[] byteData =Encoding.ASCII.GetBytes(data);handler.BeginSend(byteData, 0, byteData.Length, 0,newAsyncCallback(SendCallback), handler);}privatestaticvoidSendCallback(IAsyncResultar){try{Sockethandler = (Socket)ar.AsyncState;intbytesSent = handler.EndSend(ar);Console.WriteLine("发送 {0} bytes.", bytesSent);handler.Shutdown(SocketShutdown.Both);handler.Close();}catch(Exceptione){Console.WriteLine(e.ToString());}}publicstaticintMain(String[] args){StartListening();return0;}
客户端：
publicclassAsynchronousClient{// The port number for the remote device.privateconstintport = 11000;// ManualResetEvent instances signal completion.privatestaticManualResetEventconnectResetEvent =newManualResetEvent(false);privatestaticManualResetEventsendResetEvent =newManualResetEvent(false);privatestaticManualResetEventreceiveResetEvent =newManualResetEvent(false);privatestaticStringresponse =String.Empty;privatestaticvoidStartClient(){try{IPAddressipAddress =IPAddress.Parse("127.0.0.1");IPEndPointremoteEP =newIPEndPoint(ipAddress, port);// Create a TCP/IP socket.Socketclient =newSocket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);// Connect to the remote endpoint.client.BeginConnect(remoteEP,newAsyncCallback(ConnectCallback), client);connectResetEvent.WaitOne();Send(client,"This is a test<EOF>");sendResetEvent.WaitOne();Receive(client);receiveResetEvent.WaitOne();Console.WriteLine("Response received : {0}", response);// Release the socket.client.Shutdown(SocketShutdown.Both);client.Close();Console.ReadLine();}catch(Exceptione){Console.WriteLine(e.ToString());}}privatestaticvoidConnectCallback(IAsyncResultar){try{Socketclient = (Socket)ar.AsyncState;client.EndConnect(ar);Console.WriteLine("Socket connected to {0}", client.RemoteEndPoint.ToString());connectResetEvent.Set();}catch(Exceptione){Console.WriteLine(e.ToString());}}privatestaticvoidReceive(Socketclient){try{StateContextstate =newStateContext();state.WorkSocket = client;client.BeginReceive(state.buffer, 0,StateContext.BufferSize, 0,newAsyncCallback(ReceiveCallback), state);}catch(Exceptione){Console.WriteLine(e.ToString());}}privatestaticvoidReceiveCallback(IAsyncResultar){try{StateContextstate = (StateContext)ar.AsyncState;Socketclient = state.WorkSocket;intbytesRead = client.EndReceive(ar);if(bytesRead > 0){state.sb.Append(Encoding.ASCII.GetString(state.buffer, 0, bytesRead));client.BeginReceive(state.buffer, 0,StateContext.BufferSize, 0,newAsyncCallback(ReceiveCallback), state);}else{if(state.sb.Length > 1){response = state.sb.ToString();}receiveResetEvent.Set();}}catch(Exceptione){Console.WriteLine(e.ToString());}}privatestaticvoidSend(Socketclient,Stringdata){byte[] byteData =Encoding.ASCII.GetBytes(data);client.BeginSend(byteData, 0, byteData.Length, 0,newAsyncCallback(SendCallback), client);}privatestaticvoidSendCallback(IAsyncResultar){try{Socketclient = (Socket)ar.AsyncState;intbytesSent = client.EndSend(ar);Console.WriteLine("Sent {0} bytes to server.", bytesSent);sendResetEvent.Set();}catch(Exceptione){Console.WriteLine(e.ToString());}}publicstaticintMain(String[] args){StartClient();return0;}}
SAEA方式： SocketAsyncEventArgs
APM模式、TAP模式虽然解决了Socket的并发问题，但是在大并发下还是有较大性能问题的。这主要是因为上述两种模式都会生产 IAsyncResult 等对象 ，而大量垃圾对象的回收会非常影响系统的性能。为此，微软推出了 SocketAsyncEventArgs 。SocketAsyncEventArgs 是 .NET Framework 3.5 开始支持的一种支持高性能 Socket 通信的实现。SocketAsyncEventArgs 相比于 APM 方式的主要优点可以描述如下，无需每次调用都生成 IAsyncResult 等对象，向原生 Socket 更靠近一些。这是官方的解释：
The main feature of these enhancements is the avoidance of the repeated allocation and synchronization of objects during high-volume asynchronous socket I/O. The Begin/End design pattern currently implemented by the Socket class for asynchronous socket I/O requires a System.IAsyncResult object be allocated for each asynchronous socket operation.
SocketAsyncEventArgs主要为高性能网络服务器应用程序而设计，避免了在异步套接字 I/O 量非常大时，大量垃圾对象创建与回收。使用此类执行异步套接字操作的模式包含以下步骤，具体说明可参考：https://msdn.microsoft.com/en-us/library/system.net.sockets.socketasynceventargs(v=vs.110).aspx 。
- 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。
- 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）。
- 调用适当的套接字方法 (xxxAsync) 以启动异步操作。
- 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。
- 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。
- 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。
下面是封装的一个组件代码：
classBufferManager{intm_numBytes; // the total number of bytes controlled by the buffer poolbyte[] m_buffer; // the underlying byte array maintained by the Buffer ManagerStack<int> m_freeIndexPool; //intm_currentIndex;intm_bufferSize;publicBufferManager(inttotalBytes,intbufferSize){m_numBytes = totalBytes;m_currentIndex = 0;m_bufferSize = bufferSize;m_freeIndexPool =newStack<int>();}// Allocates buffer space used by the buffer poolpublicvoidInitBuffer(){// create one big large buffer and divide that// out to each SocketAsyncEventArg objectm_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>publicboolSetBuffer(SocketAsyncEventArgsargs){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 poolpublicvoidFreeBuffer(SocketAsyncEventArgsargs){m_freeIndexPool.Push(args.Offset);args.SetBuffer(null, 0, 0);}}///<summary>///This class is used to communicate with a remote application over TCP/IP protocol.///</summary>classTcpCommunicationChannel{#regionPrivate fields///<summary>///Size of the buffer that is used to receive bytes from TCP socket.///</summary>privateconstintReceiveBufferSize = 8 * 1024;//4KB///<summary>///This buffer is used to receive bytes///</summary>privatereadonlybyte[] _buffer;///<summary>///Socket object to send/reveice messages.///</summary>privatereadonlySocket_clientSocket;///<summary>///A flag to control thread's running///</summary>privatevolatilebool_running;///<summary>///This object is just used for thread synchronizing (locking).///</summary>privatereadonlyobject_syncLock;privateBufferManagerreceiveBufferManager;privateSocketAsyncEventArgsreceiveBuff =null;#endregion#regionConstructor///<summary>///Creates a new TcpCommunicationChannel object.///</summary>///<param name="clientSocket">A connected Socket object that is///used to communicate over network</param>publicTcpCommunicationChannel(SocketclientSocket){_clientSocket = clientSocket;_clientSocket.Blocking =false;_buffer =newbyte[ReceiveBufferSize];_syncLock =newobject();Init();}privatevoidInit(){//初始化接收Socket缓存数据receiveBufferManager =newBufferManager(ReceiveBufferSize*2, ReceiveBufferSize);receiveBufferManager.InitBuffer();receiveBuff =newSocketAsyncEventArgs();receiveBuff.Completed += ReceiveIO_Completed;receiveBufferManager.SetBuffer(receiveBuff);//初始化发送Socket缓存数据}#endregion#regionPublic methods///<summary>///Disconnects from remote application and closes channel.///</summary>publicvoidDisconnect(){_running =false;receiveBuff.Completed -= ReceiveIO_Completed;receiveBuff.Dispose();if(_clientSocket.Connected){_clientSocket.Close();}_clientSocket.Dispose();}#endregionpublicvoidStartReceive(){_running =true;boolresult = _clientSocket.ReceiveAsync(receiveBuff);}privatevoidReceiveIO_Completed(objectsender,SocketAsyncEventArgse){if(e.BytesTransferred > 0 && e.SocketError ==SocketError.Success && _clientSocket.Connected ==true&& e.LastOperation ==SocketAsyncOperation.Receive){if(!_running){return;}//Get received bytes countDateTimereceiveTime =DateTime.Now;//Copy received bytes to a new byte arrayvarreceivedBytes =newbyte[e.BytesTransferred];Array.Copy(e.Buffer, 0, receivedBytes, 0, e.BytesTransferred);//处理消息....if(_running){StartReceive();}}}///<summary>///Sends a message to the remote application.///</summary>///<param name="message">Message to be sent</param>publicvoidSendMessage(byte[] messageBytes){//Send messageif(_clientSocket.Connected){SocketAsyncEventArgsdata =newSocketAsyncEventArgs();data.SocketFlags =SocketFlags.None;data.Completed += (s, e) =>{e.Dispose();};data.SetBuffer(messageBytes, 0, messageBytes.Length);//Console.WriteLine("发送：" + messageBytes.LongLength);_clientSocket.SendAsync(data);}}}