为什么使用异步
异步线程是由线程池负责管理，而多线程，我们可以自己控制，当然在多线程中我们也可以使用线程池。就拿网络扒虫而言，如果使用异步模式去实现，它使用线程池进行管理。异步操作执行时，会将操作丢给线程池中的某个工作线程来完成。当开始I/O操作的时候，异步会将工作线程还给线程池，这意味着获取网页的工作不会再占用任何CPU资源了。直到异步完成，即获取网页完毕，异步才会通过回调的方式通知线程池。可见，异步模式借助于线程池，极大地节约了CPU的资源。
注：DMA（Direct Memory Access）直接内存存取，顾名思义DMA功能就是让设备可以绕过处理器，直接由内存来读取资料。通过直接内存访问的数据交换几乎可以不损耗CPU的资源。在硬件中，硬盘、网卡、声卡、显卡等都有直接内存访问功能。异步编程模型就是让我们充分利用硬件的直接内存访问功能来释放CPU的压力。
两者的应用场景：
计算密集型工作，采用多线程。
IO密集型工作，采用异步机制。
C#中实现异步tcp通信
socket中仅仅需要将Blocking=false即可轻松实现异步，部分示例如下：
1 /// <summary> 2 /// 启动tcp监听 3 /// </summary> 4 public void Start() 5 { 6 if (!_isStarted) 7 { 8 _isStarted = true; 9 _server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); 10 11 #region socket配置 12 LingerOption lingerOption = new LingerOption(true, 30); 13 _server.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.Linger, lingerOption); 14 #endregion 15 16 _server.Blocking = false; 17 _server.ExclusiveAddressUse = false; 18 _server.Bind(new IPEndPoint(IPAddress.Any, this._port)); 19 _server.Listen(1000000); 20 Parallel.For(0, 1000000, i => 21 { 22 _server.BeginAccept(new AsyncCallback(ProcessAccept), _server); 23 }); 24 } 25 }
tcp异步中处理接io操作最关键的参数：IAsyncResult，使用一般用begin开始，end结束。
接收数据处理如下：
1 /// <summary> 2 /// 处理传入的连接请求 3 /// </summary> 4 private void ProcessAccept(IAsyncResult ar) 5 { 6 var s = (Socket)ar.AsyncState; 7 var remote = s.EndAccept(ar); 8 var user = new UserToken(this._maxBufferSize) { ID = remote.RemoteEndPoint.ToString(), Client = remote }; 9 remote.BeginReceive(user.ReceiveBuffer, 0, user.ReceiveBuffer.Length, SocketFlags.None, new AsyncCallback(ProcessReceive), 10 user); 11 s.BeginAccept(new AsyncCallback(ProcessAccept), s); 12 }
1 private void ProcessReceive(IAsyncResult ar) 2 { 3 var user = (UserToken)ar.AsyncState; 4 var remote = user.Client; 5 try 6 { 7 if (remote.Connected) 8 { 9 var ns = remote.EndReceive(ar); 10 11 if (ns > 0) 12 { 13 var buffer = new byte[ns]; 14 15 Buffer.BlockCopy(user.ReceiveBuffer, 0, buffer, 0, buffer.Length); 16 17 user.UnPackage(buffer, (p) => 18 { 19 Interlocked.Increment(ref this._receiveCount); 20 this.RaiseOnOnReceived(user, p); 21 }); 22 23 user.ClearReceiveBuffer(); 24 25 buffer = null; 26 27 remote.BeginReceive(user.ReceiveBuffer, 0, user.ReceiveBuffer.Length, SocketFlags.None, new AsyncCallback(ProcessReceive), user); 28 } 29 } 30 else 31 { 32 this.RaiseOnDisConnected(user, new Exception("客户端已断开连接")); 33 this.CloseClient(user); 34 } 35 } 36 catch (SocketException sex) 37 { 38 this.RaiseOnDisConnected(user, sex); 39 this.CloseClient(user); 40 } 41 catch (Exception ex) 42 { 43 this.RaiseOnError(user, ex); 44 this.CloseClient(user); 45 } 46 }
发送数据处理如下：
1 /// <summary> 2 /// 发送信息 3 /// </summary> 4 /// <param name="remote"></param> 5 /// <param name="data"></param> 6 /// <param name="type"></param> 7 /// <param name="auth"></param> 8 private void SendAsync(UserToken remote, byte[] data, TransportType type = TransportType.Heart) 9 { 10 try 11 { 12 using (var pakage = new TcpPackage(data, type, remote.Auth)) 13 { 14 remote.Client.BeginSend(pakage.Data, 0, pakage.Data.Length, SocketFlags.None, new AsyncCallback(EndSend), remote); 15 } 16 17 } 18 catch (SocketException sex) 19 { 20 this.RaiseOnDisConnected(remote, sex); 21 } 22 catch (Exception ex) 23 { 24 this.RaiseOnError(remote, ex); 25 } 26 }
1 private void EndSend(IAsyncResult ar) 2 { 3 var remote = (UserToken)ar.AsyncState; 4 remote.Client.EndSend(ar); 5 Interlocked.Increment(ref this._sendCount); 6 }
心跳、消息、文件等逻辑都可以基于发送逻辑来完成
1 /// <summary> 2 /// 回复心跳 3 /// </summary> 4 /// <param name="remote"></param> 5 /// <param name="package"></param> 6 private void ReplyHeart(UserToken remote, TcpPackage package) 7 { 8 this.SendAsync(remote, null, TransportType.Heart); 9 }
1 /// <summary> 2 /// 发送信息 3 /// </summary> 4 /// <param name="remote"></param> 5 /// <param name="msg"></param> 6 public void SendMsg(UserToken remote, byte[] msg) 7 { 8 this.SendAsync(remote, msg, TransportType.Message); 9 }
1 /// <summary> 2 /// 发送文件 3 /// </summary> 4 /// <param name="remote"></param> 5 /// <param name="filePath"></param> 6 public void SendFile(UserToken remote, string filePath) 7 { 8 using (var file = new TransferFileInfo() 9 { 10 ID = remote.ID, 11 FileBytes = File.ReadAllBytes(filePath), 12 Name = filePath.Substring(filePath.LastIndexOf("\\") + 1), 13 CreateTime = DateTime.Now.Ticks 14 }) 15 { 16 var buffer = TransferFileInfo.Serialize(file); 17 this.SendAsync(remote, buffer, TransportType.File); 18 buffer = null; 19 } 20 }
1 /// <summary> 2 /// 发送文件 3 /// </summary> 4 /// <param name="remote"></param> 5 /// <param name="fileName"></param> 6 /// <param name="file"></param> 7 public void SendFile(UserToken remote, string fileName, byte[] file) 8 { 9 using (var fileInfo = new TransferFileInfo() 10 { 11 ID = remote.ID, 12 FileBytes = file, 13 Name = fileName, 14 CreateTime = DateTime.Now.Ticks 15 }) 16 { 17 var buffer = TransferFileInfo.Serialize(fileInfo); 18 this.SendAsync(remote, buffer, TransportType.File); 19 buffer = null; 20 } 21 }
异步tcp通信——APM.Core 服务端概述
异步tcp通信——APM.Core 解包
异步tcp通信——APM.Server 消息推送服务的实现
异步tcp通信——APM.ConsoleDemo
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