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

为了将 async/await 异步到底，AsyncTcpSocketServer 所暴露的接口也同样是 Awaitable 的。

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

使用时仅需将一个实现了该接口的对象注入到 AsyncTcpSocketServer 的构造函数中即可。

public class SimpleMessageDispatcher : IAsyncTcpSocketServerMessageDispatcher { public async Task OnSessionStarted(AsyncTcpSocketSession session) { Console.WriteLine(, 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(, session.RemoteEndPoint)); Console.WriteLine(, text)); await session.SendAsync(Encoding.UTF8.GetBytes(text)); } public async Task OnSessionClosed(AsyncTcpSocketSession session) { Console.WriteLine(, session)); await Task.CompletedTask; } }

当然，对于接口的实现也不是强制了，也可以在构造函数中直接注入方法的实现。

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 是 SocketAsyncEventArgs 的简写。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：

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.

也就是说，优点就是无需为每次调用都生成 IAsyncResult 等对象，向原生 Socket 更靠近一些。

使用 SocketAsyncEventArgs 的推荐步骤如下：

重点在于池化（Pooling），池化的目的就是为了重用和减少运行时分配和垃圾回收的压力。

TcpSocketSaeaServer 即是对 SocketAsyncEventArgs 的应用和封装，并实现了 Pooling 技术。TcpSocketSaeaServer 中的重点是 SaeaAwaitable 类，SaeaAwaitable 中内置了一个 SocketAsyncEventArgs，并通过 GetAwaiter 返回 SaeaAwaiter 来支持 async/await 操作。同时，通过 SaeaExtensions 扩展方法对来扩展 SocketAsyncEventArgs 的 Awaitable 实现。

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 则是一个 QueuedObjectPool<SaeaAwaitable> 的衍生实现，用于池化 SaeaAwaitable 实例。同时，为了减少 TcpSocketSaeaSession 的构建过程，也实现了 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); }

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; }

同样，TcpSocketSaeaServer 对外所暴露的接口也同样是 Awaitable 的。