C# 高效能 TCP 服務的多種實現

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本篇文章的主旨是使用 .NET/C# 實現 TCP 高效能服務的不同方式,包括但不限於如下內容:

  • APM 方式,即 Asynchronous Programming Model

  • TAP 方式,即 Task-based Asynchronous Pattern

  • SAEA 方式,即 SocketAsyncEventArgs

  • RIO 方式,即 Registered I/O

在 .NET/C# 中對於 Socket 的支援均是基於 Windows I/O Completion Ports 完成連接埠技術的封裝,通過不同的 Non-Blocking 封裝結構來滿足不同的編程需求。以上方式均已在 Cowboy.Sockets 中有完整實現,並且 APM 和 TAP 方式已經在實際項目中應用。Cowboy.Sockets 還在不斷的進化和完善中,如有任何問題請及時指正。

雖然有這麼多種實現方式,但抽象的看,它們是一樣一樣的,用兩個 Loop 即可描述:Accept LoopRead Loop,如所示。(這裡提及的 "Loop" 指的是一種迴圈方式,而非特指 while/for 等關鍵字。)

  • 在任何 TCP Server 的實現中,一定存在一個 Accept Socket Loop,用於接收 Client 端的 Connect 請求以建立 TCP Connection。

  • 在任何 TCP Server 的實現中,一定存在一個 Read Socket Loop,用於接收 Client 端 Write 過來的資料。

如果 Accept 迴圈阻塞,則會導致無法快速的建立串連,服務端 Pending Backlog 滿,進而導致 Client 端收到 Connect Timeout 的異常。如果 Read 迴圈阻塞,則顯然會導致無法及時收到 Client 端發過來的資料,進而導致 Client 端 Send Buffer 滿,無法再發送資料。

從實現細節的角度看,能夠導致服務阻塞的位置可能在:

  1. Accept 到新的 Socket,構建新的 Connection 需要分配各種資源,分配資源慢;

  2. Accept 到新的 Socket,沒有及時觸發下一次 Accept;

  3. Read 到新的 Buffer,判定 Payload 訊息長度,判定過程長;

  4. Read 到新的 Buffer,發現 Payload 還沒有收全,繼續 Read,則 "可能" 會導致一次 Buffer Copy;

  5. Payload 接收完畢,進行 De-Serialization 轉成可識別的 Protocol Message,還原序列化慢;

  6. 由 Business Module 來處理相應的 Protocol Message,處理過程慢;

1-2 涉及到 Accept 過程和 Connection 的建立過程,3-4 涉及到 ReceiveBuffer 的處理過程,5-6 涉及到應用邏輯側的實現。

Java 中著名的 Netty 網路程式庫從 4.0 版本開始對於 Buffer 部分做了全新的嘗試,採用了名叫 ByteBuf 的設計,實現 Buffer Zero Copy 以減少高並發條件下 Buffer 拷貝帶來的效能損失和 GC 壓力。DotNetty,Orleans ,Helios 等項目正在嘗試在 C# 中進行類似的 ByteBuf 的實現。

APM 方式:TcpSocketServer

TcpSocketServer 的實現是基於 .NET Framework 內建的 TcpListener 和 TcpClient 的更進一步的封裝,採用基於 APM 的 BeginXXX 和 EndXXX 介面實現。

TcpSocketServer 中的 Accept Loop 指的就是,

  • BeginAccept -> EndAccept-> BeginAccept -> EndAccept -> BeginAccept -> ...

每一個建立成功的 Connection 由 TcpSocketSession 來處理,所以 TcpSocketSession 中會包含 Read Loop,

  • BeginRead -> EndRead -> BeginRead -> EndRead -> BeginRead -> ...

TcpSocketServer 通過暴露 Event 來實現 Connection 的建立與斷開和資料接收的通知。


  event EventHandler<TcpClientConnectedEventArgs> ClientConnected;  event EventHandler<TcpClientDisconnectedEventArgs> ClientDisconnected;  event EventHandler<TcpClientDataReceivedEventArgs> ClientDataReceived;

使用也是簡單直接,直接訂閱事件通知。


  private static void StartServer()  {      _server = new TcpSocketServer(22222);      _server.ClientConnected += server_ClientConnected;      _server.ClientDisconnected += server_ClientDisconnected;      _server.ClientDataReceived += server_ClientDataReceived;      _server.Listen();  }    static void server_ClientConnected(object sender, TcpClientConnectedEventArgs e)  {      Console.WriteLine(string.Format("TCP client {0} has connected {1}.", e.Session.RemoteEndPoint, e.Session));  }    static void server_ClientDisconnected(object sender, TcpClientDisconnectedEventArgs e)  {      Console.WriteLine(string.Format("TCP client {0} has disconnected.", e.Session));  }    static void server_ClientDataReceived(object sender, TcpClientDataReceivedEventArgs e)  {      var text = Encoding.UTF8.GetString(e.Data, e.DataOffset, e.DataLength);      Console.Write(string.Format("Client : {0} {1} --> ", e.Session.RemoteEndPoint, e.Session));      Console.WriteLine(string.Format("{0}", text));      _server.Broadcast(Encoding.UTF8.GetBytes(text));  }

TAP 方式:AsyncTcpSocketServer

AsyncTcpSocketServer 的實現是基於 .NET Framework 內建的 TcpListener 和 TcpClient 的更進一步的封裝,採用基於 TAP 的 async/await 的 XXXAsync 介面實現。

然而,實際上 XXXAsync 並沒有建立什麼神奇的效果,其內部實現只是將 APM 的方法轉換成了 TAP 的調用方式。


  //************* Task-based async public methods *************************  [HostProtection(ExternalThreading = true)]  public Task<Socket> AcceptSocketAsync()  {      return Task<Socket>.Factory.FromAsync(BeginAcceptSocket, EndAcceptSocket, null);  }    [HostProtection(ExternalThreading = true)]  public Task<TcpClient> AcceptTcpClientAsync()  {      return Task<TcpClient>.Factory.FromAsync(BeginAcceptTcpClient, EndAcceptTcpClient, null);  }

AsyncTcpSocketServer 中的 Accept Loop 指的就是,


  while (IsListening)  {      var tcpClient = await _listener.AcceptTcpClientAsync();  }

每一個建立成功的 Connection 由 AsyncTcpSocketSession 來處理,所以 AsyncTcpSocketSession 中會包含 Read Loop,


  while (State == TcpSocketConnectionState.Connected)  {      int receiveCount = await _stream.ReadAsync(_receiveBuffer, 0, _receiveBuffer.Length);  }

為了將 async/await 非同步到底,AsyncTcpSocketServer 所暴露的介面也同樣是 Awaitable 的。


  public interface IAsyncTcpSocketServerMessageDispatcher  {      Task OnSessionStarted(AsyncTcpSocketSession session);      Task OnSessionDataReceived(AsyncTcpSocketSession session, byte[] data, int offset, int count);      Task OnSessionClosed(AsyncTcpSocketSession session);  }

使用時僅需將一個實現了該介面的對象注入到 AsyncTcpSocketServer 的建構函式中即可。


  public class SimpleMessageDispatcher : IAsyncTcpSocketServerMessageDispatcher  {      public async Task OnSessionStarted(AsyncTcpSocketSession session)      {          Console.WriteLine(string.Format("TCP session {0} has connected {1}.", session.RemoteEndPoint, session));          await Task.CompletedTask;      }        public async Task OnSessionDataReceived(AsyncTcpSocketSession session, byte[] data, int offset, int count)      {          var text = Encoding.UTF8.GetString(data, offset, count);          Console.Write(string.Format("Client : {0} --> ", session.RemoteEndPoint));          Console.WriteLine(string.Format("{0}", text));            await session.SendAsync(Encoding.UTF8.GetBytes(text));      }        public async Task OnSessionClosed(AsyncTcpSocketSession session)      {          Console.WriteLine(string.Format("TCP session {0} has disconnected.", session));          await Task.CompletedTask;      }  }

當然,對於介面的實現也不是強制了,也可以在建構函式中直接注入方法的實現。


  public AsyncTcpSocketServer(      IPEndPoint listenedEndPoint,      Func<AsyncTcpSocketSession, byte[], int, int, Task> onSessionDataReceived = null,      Func<AsyncTcpSocketSession, Task> onSessionStarted = null,      Func<AsyncTcpSocketSession, Task> onSessionClosed = null,      AsyncTcpSocketServerConfiguration configuration = null)  {}

SAEA 方式:TcpSocketSaeaServer

SAEA 是 SocketAsyncEventArgs 的簡寫。SocketAsyncEventArgs 是 .NET Framework 3.5 開始支援的一種支援高效能 Socket 通訊的實現。SocketAsyncEventArgs 相比於 APM 方式的主要優點可以描述如下:

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.

也就是說,優點就是無需為每次調用都產生 IAsyncResult 等對象,向原生 Socket 更靠近一些。

使用 SocketAsyncEventArgs 的推薦步驟如下:

  1. Allocate a new SocketAsyncEventArgs context object, or get a free one from an application pool.

  2. Set properties on the context object to the operation about to be performed (the callback delegate method and data buffer, for example).

  3. Call the appropriate socket method (xxxAsync) to initiate the asynchronous operation.

  4. If the asynchronous socket method (xxxAsync) returns true in the callback, query the context properties for completion status.

  5. If the asynchronous socket method (xxxAsync) returns false in the callback, the operation completed synchronously. The context properties may be queried for the operation result.

  6. Reuse the context for another operation, put it back in the pool, or discard it.

重點在於池化(Pooling),池化的目的就是為了重用和減少運行時分配和記憶體回收的壓力。

TcpSocketSaeaServer 即是對 SocketAsyncEventArgs 的應用和封裝,並實現了 Pooling 技術。TcpSocketSaeaServer 中的重點是 SaeaAwaitable 類,SaeaAwaitable 中內建了一個 SocketAsyncEventArgs,並通過 GetAwaiter 返回 SaeaAwaiter 來支援 async/await 操作。同時,通過 SaeaExtensions 擴充方法對來擴充 SocketAsyncEventArgs 的 Awaitable 實現。


  public static SaeaAwaitable AcceptAsync(this Socket socket, SaeaAwaitable awaitable)  public static SaeaAwaitable ConnectAsync(this Socket socket, SaeaAwaitable awaitable)  public static SaeaAwaitable DisonnectAsync(this Socket socket, SaeaAwaitable awaitable)  public static SaeaAwaitable ReceiveAsync(this Socket socket, SaeaAwaitable awaitable)  public static SaeaAwaitable SendAsync(this Socket socket, SaeaAwaitable awaitable)

SaeaPool 則是一個 QueuedObjectPool<SaeaAwaitable> 的衍生實現,用於池化 SaeaAwaitable 執行個體。同時,為了減少 TcpSocketSaeaSession 的構建過程,也實現了 SessionPool 即 QueuedObjectPool<TcpSocketSaeaSession>。

TcpSocketSaeaServer 中的 Accept Loop 指的就是,


  while (IsListening)  {      var saea = _acceptSaeaPool.Take();        var socketError = await _listener.AcceptAsync(saea);      if (socketError == SocketError.Success)      {          var acceptedSocket = saea.Saea.AcceptSocket;      }        _acceptSaeaPool.Return(saea);  }

每一個建立成功的 Connection 由 TcpSocketSaeaSession 來處理,所以 TcpSocketSaeaSession 中會包含 Read Loop,


  var saea = _saeaPool.Take();  saea.Saea.SetBuffer(_receiveBuffer, 0, _receiveBuffer.Length);    while (State == TcpSocketConnectionState.Connected)  {      saea.Saea.SetBuffer(0, _receiveBuffer.Length);        var socketError = await _socket.ReceiveAsync(saea);      if (socketError != SocketError.Success)          break;        var receiveCount = saea.Saea.BytesTransferred;      if (receiveCount == 0)          break;  }

同樣,TcpSocketSaeaServer 對外所暴露的介面也同樣是 Awaitable 的。


  public interface ITcpSocketSaeaServerMessageDispatcher  {      Task OnSessionStarted(TcpSocketSaeaSession session);      Task OnSessionDataReceived(TcpSocketSaeaSession session, byte[] data, int offset, int count);      Task OnSessionClosed(TcpSocketSaeaSession session);  }

使用起來也是簡單直接:


  public class SimpleMessageDispatcher : ITcpSocketSaeaServerMessageDispatcher  {      public async Task OnSessionStarted(TcpSocketSaeaSession session)      {          Console.WriteLine(string.Format("TCP session {0} has connected {1}.", session.RemoteEndPoint, session));          await Task.CompletedTask;      }        public async Task OnSessionDataReceived(TcpSocketSaeaSession session, byte[] data, int offset, int count)      {          var text = Encoding.UTF8.GetString(data, offset, count);          Console.Write(string.Format("Client : {0} --> ", session.RemoteEndPoint));          Console.WriteLine(string.Format("{0}", text));            await session.SendAsync(Encoding.UTF8.GetBytes(text));      }        public async Task OnSessionClosed(TcpSocketSaeaSession session)      {          Console.WriteLine(string.Format("TCP session {0} has disconnected.", session));          await Task.CompletedTask;      }  }

RIO 方式:TcpSocketRioServer

從 Windows 8.1 / Windows Server 2012 R2 開始,微軟推出了 Registered I/O Networking Extensions 來支援高效能 Socket 服務的實現,簡稱 RIO。

The following functions are supported for Windows Store apps on Windows 8.1, Windows Server 2012 R2, and later. Microsoft Visual Studio 2013 Update 3 or later is required for Windows Store apps.

  • RIOCloseCompletionQueue

  • RIOCreateCompletionQueue

  • RIOCreateRequestQueue

  • RIODequeueCompletion

  • RIODeregisterBuffer

  • RIONotify

  • RIOReceive

  • RIOReceiveEx

  • RIORegisterBuffer

  • RIOResizeCompletionQueue

  • RIOResizeRequestQueue

  • RIOSend

  • RIOSendEx

到目前為止,.NET Framework 還沒有推出對 RIO 的支援,所以若想在 C# 中實現 RIO 則只能通過 P/Invoke 方式,RioSharp 是開源項目中的一個比較完整的實現。

Cowboy.Sockets 直接引用了 RioSharp 的原始碼,放置在 Cowboy.Sockets.Experimental 名空間下,以供實驗和測試使用。

同樣,通過 TcpSocketRioServer 來實現 Accept Loop,


_listener.OnAccepted = (acceptedSocket) =>{    Task.Run(async () =>    {        await Process(acceptedSocket);    })    .Forget();};

通過 TcpSocketRioSession 來處理 Read Loop,


  while (State == TcpSocketConnectionState.Connected)  {      int receiveCount = await _stream.ReadAsync(_receiveBuffer, 0, _receiveBuffer.Length);      if (receiveCount == 0)          break;  }

測試代碼一如既往的類似:


  public class SimpleMessageDispatcher : ITcpSocketRioServerMessageDispatcher  {      public async Task OnSessionStarted(TcpSocketRioSession session)      {          //Console.WriteLine(string.Format("TCP session {0} has connected {1}.", session.RemoteEndPoint, session));          Console.WriteLine(string.Format("TCP session has connected {0}.", session));          await Task.CompletedTask;      }        public async Task OnSessionDataReceived(TcpSocketRioSession session, byte[] data, int offset, int count)      {          var text = Encoding.UTF8.GetString(data, offset, count);          //Console.Write(string.Format("Client : {0} --> ", session.RemoteEndPoint));          Console.Write(string.Format("Client : --> "));          Console.WriteLine(string.Format("{0}", text));            await session.SendAsync(Encoding.UTF8.GetBytes(text));      }        public async Task OnSessionClosed(TcpSocketRioSession session)      {          Console.WriteLine(string.Format("TCP session {0} has disconnected.", session));          await Task.CompletedTask;      }  }

參考資料

  • Asynchronous Programming Model (APM)

  • Task-based Asynchronous Pattern (TAP)

  • Event-based Asynchronous Pattern (EAP)

  • SocketAsyncEventArgs

  • Registered I/O

  • Netty: Reference counted objects

  • Socket Performance Enhancements in Version 3.5

  • What's New for Windows Sockets for Windows 8.1 and Windows Server 2012 R2

  • RIO_EXTENSION_FUNCTION_TABLE structure

  • Windows 8 Registered I/O Networking Extensions

本篇文章《C#高效能TCP服務的多種實現方式》由 Dennis Gao 發表自部落格園個人部落格,未經作者本人同意禁止以任何的形式轉載,任何自動的或人為的爬蟲轉載行為均為耍流氓。

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