求教一个socket连接问题 为什么下面这段代码 客户端请求连接一次 服务端会多产生5个多线程啊？急求解啊

 /// <summary>
        /// 开始监听客户端的Socket请求
        /// </summary>
        private void StartListening()
        {
            try
            {
                if (this.listener != null)
                {
                    //if (this.listener.Blocking)
                    //{
                    //    this.listener.Blocking = false;
                    //}
                    this.listener.Dispose();
                    this.listener.Close();
                    logger.Info("关闭SocketServer成功(开始)！");
                }
                //byte[] bytes = new Byte[1024];
                DataTable dt = new DataTable("ipTable");
                dt.ReadXml(Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().GetName().CodeBase)+@"\IpSetting.xml");
                IPAddress ipAddress = IPAddress.Parse(dt.Rows[1][1].ToString());//dt.Rows[1][1].ToString());   // 127.0.0.1  
                IPEndPoint localEndPoint = new IPEndPoint(ipAddress, Convert.ToInt32(ClientContext.Instance.SocketPort));
                this.listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);  // Create a TCP/IP socket.   
                //this.listener.
                this.listener.Bind(localEndPoint);   //绑定
                this.listener.Listen(Convert.ToInt32(ClientContext.Instance.SocketPort));   //监听
                while (this.isRun)
                {
                    allDone.Reset();  //                  
                    logger.Info("Waiting for a connection...");  // Start an asynchronous socket to listen for connections.
                    //using (Socket clientSocket = this.listener.Accept())
                    //{  
                        Socket clientSocket = this.listener.Accept();//创建一个新的Socket连接                    
                        td = new Thread(new ParameterizedThreadStart(this.AcceptCallback));
                        //接受客户端请求并进行验票操作
                        td.Name = "Socket" + SocketCount.ToString();
                        SocketCount++;
                        td.IsBackground = true;
                        logger.Info("线程ID号"+td.ManagedThreadId );
                        list.Add(td);
                        td.Start(clientSocket);
                        allDone.WaitOne();
                        
                    //}  // 等待线程-这将引起等待线程无限期的阻塞并等待类来通知。 
                }
                if (this.listener != null)    //终止“Socket服务器端”
                {
                    this.listener.Dispose();
                    this.listener.Close();
                    logger.Info("关闭SocketServer成功(结束)！");
                }            }
            catch (Exception ex)
            {
                logger.Info(" 开始监听客户端的Socket请求时发生异常，原因是：" + ex.ToString());
            }
        }