线程池：
线程池使用方式：ThreadPool.QueueUserWorkItem(WaitCallback callBack, object state)
WaitCallback的方法签名：public delegate void WaitCallback(object state) ; //传入一个object上下文Socket：
常用实例方法：Connect(), Bind(EndPoint localEP), Listen(int backlog), Accept(), Receive(byte[] buffer), Close()

示例：
// Server端

namespace SocketMultiThreadServer
{
    public partial class Form1 : Form
    {
        Socket socket;
        public Form1()
        {
            InitializeComponent();
            InitSocket();
        }private void InitSocket()
        {
            socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            IPHostEntry ipHostEntry = Dns.GetHostEntry(Dns.GetHostName());
            IPEndPoint ipEndPoint = new IPEndPoint(ipHostEntry.AddressList[0], 8091); // 这个AddressList属性返回的是一个IP列表，包括若干个IPv6、IPv4的值，我们要获取的IPv4值的下标会随着环境的变化改变，不知道有没有解决方法
            socket.Bind(ipEndPoint);
            socket.Listen(20); // 设置允许的挂起连接队列的长度最大值为20
        }private void btnBeginRec_Click(object sender, EventArgs e)
        {
            ThreadPool.QueueUserWorkItem((_) =>
            {
                while (true)
                {
                    Socket socketAccept = null;
                    if (socket.Poll(-1, SelectMode.SelectRead)) // 确定socket的状态
                    {
                        socketAccept = socket.Accept(); // 接收客户端发来的Socket连接，每个连接的客户端都会保持一个Socket实例
                    }
                    if (socketAccept != null)
                    {
                        ThreadPool.QueueUserWorkItem((o) =>
                        {
                            while (true)
                            {
                                byte[] byteArray = new byte[100];
                                socketAccept.Receive(byteArray); // 接收客户端发来的消息
                                string strRec = System.Text.Encoding.UTF8.GetString(byteArray);
                                if (this.txtMsg.InvokeRequired) // 判断当前线程(调用方)是否是主线程之外的线程，txtMsg是一个TextBox
                                {
                                    this.txtMsg.Invoke(new ChangeText(ShowMsg), strRec); // 返回给主线程去做UI呈现
                                }
                                System.Threading.Thread.Sleep(100);
                            }
                        });
                    }
                }
            });
            System.Threading.Thread.Sleep(100);
        }delegate void ChangeText(string obj);
        private void ShowMsg(string obj)
        {
            this.txtMsg.AppendText(obj + "  ");
        }
    }
}

namespace SocketMultiThreadClient
{
    class Program
    {
        static void Main(string[] args)
        {
            Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            IPHostEntry ipHostEntry = Dns.GetHostEntry(Dns.GetHostName());
            IPEndPoint ipEndPoint = new IPEndPoint(ipHostEntry.AddressList[0], 8091); //指定要连接的服务端的IP和端口
            socket.Connect(ipEndPoint);while (true)
            {
                string input = Console.ReadLine();
                try
                {
                    socket.Send(System.Text.Encoding.UTF8.GetBytes(input)); // 向服务端(指定的IP和端口)发送流消息
                }
                catch (Exception ex)
                {
                    if (socket != null)
                    {
                        socket.Close();
                        Console.WriteLine("Client Error: " + ex.Message);
                    }
                }
                System.Threading.Thread.Sleep(100);
            }
        }
    }
}