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：
/// <summary>
/// 启动tcp监听
/// </summary>
public void Start()
{
if (!_isStarted)
{
_isStarted = true;
_server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); #region socket配置
LingerOption lingerOption = new LingerOption(true, );
_server.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.Linger, lingerOption);
#endregion _server.Blocking = false;
_server.ExclusiveAddressUse = false;
_server.Bind(new IPEndPoint(IPAddress.Any, this._port));
_server.Listen();
Parallel.For(, , i =>
{
_server.BeginAccept(new AsyncCallback(ProcessAccept), _server);
});
}
}
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：
/// <summary>
/// 处理传入的连接请求
/// </summary>
private void ProcessAccept(IAsyncResult ar)
{
var s = (Socket)ar.AsyncState;
var remote = s.EndAccept(ar);
var user = new UserToken(this._maxBufferSize) { ID = remote.RemoteEndPoint.ToString(), Client = remote };
remote.BeginReceive(user.ReceiveBuffer, , user.ReceiveBuffer.Length, SocketFlags.None, new AsyncCallback(ProcessReceive),
user);
s.BeginAccept(new AsyncCallback(ProcessAccept), s);
}
private void ProcessReceive(IAsyncResult ar)
{
var user = (UserToken)ar.AsyncState;
var remote = user.Client;
try
{
if (remote.Connected)
{
var ns = remote.EndReceive(ar); if (ns > )
{
var buffer = new byte[ns]; Buffer.BlockCopy(user.ReceiveBuffer, , buffer, , buffer.Length); user.UnPackage(buffer, (p) =>
{
Interlocked.Increment(ref this._receiveCount);
this.RaiseOnOnReceived(user, p);
}); user.ClearReceiveBuffer(); buffer = null; remote.BeginReceive(user.ReceiveBuffer, , user.ReceiveBuffer.Length, SocketFlags.None, new AsyncCallback(ProcessReceive), user);
}
}
else
{
this.RaiseOnDisConnected(user, new Exception("客户端已断开连接"));
this.CloseClient(user);
}
}
catch (SocketException sex)
{
this.RaiseOnDisConnected(user, sex);
this.CloseClient(user);
}
catch (Exception ex)
{
this.RaiseOnError(user, ex);
this.CloseClient(user);
}
}
发送数据处理如下：
/// <summary>
/// 发送信息
/// </summary>
/// <param name="remote"></param>
/// <param name="data"></param>
/// <param name="type"></param>
/// <param name="auth"></param>
private void SendAsync(UserToken remote, byte[] data, TransportType type = TransportType.Heart)
{
try
{
using (var pakage = new TcpPackage(data, type, remote.Auth))
{
remote.Client.BeginSend(pakage.Data, , pakage.Data.Length, SocketFlags.None, new AsyncCallback(EndSend), remote);
} }
catch (SocketException sex)
{
this.RaiseOnDisConnected(remote, sex);
}
catch (Exception ex)
{
this.RaiseOnError(remote, ex);
}
}
private void EndSend(IAsyncResult ar)
{
var remote = (UserToken)ar.AsyncState;
remote.Client.EndSend(ar);
Interlocked.Increment(ref this._sendCount);
}
心跳、消息、文件等逻辑都可以基于发送逻辑来完成
/// <summary>
/// 回复心跳
/// </summary>
/// <param name="remote"></param>
/// <param name="package"></param>
private void ReplyHeart(UserToken remote, TcpPackage package)
{
this.SendAsync(remote, null, TransportType.Heart);
}
/// <summary>
/// 发送信息
/// </summary>
/// <param name="remote"></param>
/// <param name="msg"></param>
public void SendMsg(UserToken remote, byte[] msg)
{
this.SendAsync(remote, msg, TransportType.Message);
}
/// <summary>
/// 发送文件
/// </summary>
/// <param name="remote"></param>
/// <param name="filePath"></param>
public void SendFile(UserToken remote, string filePath)
{
using (var file = new TransferFileInfo()
{
ID = remote.ID,
FileBytes = File.ReadAllBytes(filePath),
Name = filePath.Substring(filePath.LastIndexOf("\\") + ),
CreateTime = DateTime.Now.Ticks
})
{
var buffer = TransferFileInfo.Serialize(file);
this.SendAsync(remote, buffer, TransportType.File);
buffer = null;
}
}
/// <summary>
/// 发送文件
/// </summary>
/// <param name="remote"></param>
/// <param name="fileName"></param>
/// <param name="file"></param>
public void SendFile(UserToken remote, string fileName, byte[] file)
{
using (var fileInfo = new TransferFileInfo()
{
ID = remote.ID,
FileBytes = file,
Name = fileName,
CreateTime = DateTime.Now.Ticks
})
{
var buffer = TransferFileInfo.Serialize(fileInfo);
this.SendAsync(remote, buffer, TransportType.File);
buffer = null;
}
}
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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