单线程服务器只能通过一种方式来做，就是Socket.Select，这种方式的性能也很好，服务端和客户端同在我的笔记本上，可以并发60000+连接，连接速度和IOCP差不多，接收处理速度比IOCP慢三倍左右。虽然是三倍，但因为IOCP在60000个连接时接收处理也是毫秒级的，所以这个三倍从绝对数字上并不算慢。
传输文件时可能分包是比较直觉的方法，但windows提供了TransmitPackets（.net中为SendPacketsAsync），这个的优势google一下可以了解，除了性能优势之外，这种方式传输整个文件夹是非常方便的。带来的问题就是如果不单独建立接收文件的套接字，在文件包没有自定协议的情况下如何与带有自定协议的正常数据进行区分，所以需要接收时有自适应的处理过程。在IOCP模式中处理这个比较复杂，但在单线程服务器中就是通过套接字的一些标识进行简单的判断（示例中仅有一个定义文件的数据包，数据类型和流程比较简单，所以该标识实际上就是DataSock类的FileStream是否为null）。
下面的示例如果要作大量并发的测试，请将用于接受连接的套接字单独Poll，这个示例是把它和建立了连接的套接字一起Select了。示例很简单，有很多在性能上需要优化的地方。
服务端
class Program
{
public static void Main(string[] arg)
{
IPAddress ip = IPAddress.Parse("192.168.0.103");
int port = 5555;
List<Socket> ReadSock = new List<Socket>();
List<Socket> ErrorSock = new List<Socket>();
Socket server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
ReadSock.Add(server);
Dictionary<Socket, SockData> ClientRecvFile = new Dictionary<Socket, SockData>();
server.Bind(new IPEndPoint(ip, port));
server.Listen(10);
while (true)
{
List<Socket> rs = new List<Socket>(ReadSock);
List<Socket> es = new List<Socket>(ErrorSock);
Socket.Select(rs, null, es, -1);
foreach (Socket sk in rs)
{
if (sk == server)
{
AcceptSock(ReadSock, ErrorSock, sk, ClientRecvFile);
continue;
}
if (sk.Available == 0)
{
CloseSock(ReadSock, ErrorSock, sk, ClientRecvFile);
continue;
}
ReceiveFile(sk, ClientRecvFile);
}
foreach (Socket sk in es)
CloseSock(ReadSock, ErrorSock, sk, ClientRecvFile);
}
}
static void AcceptSock(List<Socket> readsock, List<Socket> errorsock,
Socket server, Dictionary<Socket,SockData> clientfs)
{
Socket client = server.Accept();
readsock.Add(client);
errorsock.Add(client);
SockData sd = new SockData();
sd.DataRecvLen = 4;
sd.Buffer = new byte[4096];
clientfs.Add(client, sd);
Console.WriteLine("{0}建立连接", client.RemoteEndPoint);
}
static void ReceiveFile(Socket client, Dictionary<Socket,SockData> clientfs)
{
SockData sd = clientfs[client];
if (sd.SockFile == null)
{
ReceiveData(client, sd);
return;
}
int len = client.Receive(sd.Buffer);
sd.SockFile.Write(sd.Buffer, 0, len);
sd.FileRecvLen += len;
Console.SetCursorPosition(0, Console.CursorTop);
Console.Write("{0:P}", (double)sd.FileRecvLen / sd.FileLen);
if (sd.FileRecvLen < sd.FileLen)
return;
sd.Clear();
Console.WriteLine();
}
static void ReceiveData(Socket client, SockData sd)
{
int len2 = client.Receive(sd.Buffer, sd.OffSet, sd.DataRecvLen, SocketFlags.None);
if (len2 != sd.DataRecvLen)
{
sd.SetBuffer(sd.OffSet + len2, sd.DataRecvLen - len2);
return;
}
if (sd.OffSet < 4)
{
int datalen = BitConverter.ToInt32(sd.Buffer, 0);
if (datalen <= 4)
{
sd.SetBuffer(0, 4);
return;
}
sd.SetBuffer(4, datalen - 4);
return;
}
DoSomething(client, sd);
}
static void DoSomething(Socket client, SockData sd)
{
string filename = sd.SetFileInfo();
Console.WriteLine("开始接收文件{0}", filename);
}
static void CloseSock(List<Socket> readsock, List<Socket> errorsock,
Socket client, Dictionary<Socket, SockData> clientfs)
{
Console.WriteLine("{0}断开连接", client.RemoteEndPoint);
client.Shutdown(SocketShutdown.Both);
client.Close();
readsock.Remove(client);
errorsock.Remove(client);
clientfs[client].Dispose();
clientfs.Remove(client);
}
}
class SockData : IDisposable
{
public int OffSet { get; set; }
public int DataRecvLen { get; set; }
public int FileLen { get; set; }
public int FileRecvLen { get; set; }
public FileStream SockFile { get; set; }
public byte[] Buffer { get; set; }
public void SetBuffer(int offset, int len)
{
OffSet = offset;
DataRecvLen = len;
}
public string SetFileInfo()
{
FileLen = BitConverter.ToInt32(Buffer, 4);
int filenamelen = BitConverter.ToInt32(Buffer, 8);
string filename = Encoding.Unicode.GetString(Buffer, 12, filenamelen);
SockFile = new FileStream(filename, FileMode.Create, FileAccess.Write);
return filename;
}
public void Clear()
{
OffSet = 0;
DataRecvLen = 4;
FileLen = 0;
FileRecvLen = 0;
if (SockFile == null)
return;
SockFile.Close();
SockFile = null;
}
public void Dispose()
{
if (SockFile != null)
SockFile.Close();
GC.SuppressFinalize(this);
}
~SockData()
{
if (SockFile != null)
SockFile.Close();
}
}
