检测服务器IP端口是否可用

private static double Scanner(string ip, int port)
        {
            try
            {
                System.Net.Sockets.TcpClient Tcp = new System.Net.Sockets.TcpClient();
                System.IAsyncResult ias = Tcp.BeginConnect(ip, port, null, null);//port为空=> 80
                DateTime tOut = DateTime.Now;
                while (ias.IsCompleted == false)
                {
                    //从tOut到目前为止的时间超过3秒，返回-1
                    if (DateTime.Now.Subtract(tOut).TotalMilliseconds >= 3000)
                    {
                        return -1;
                    }
                }
                Tcp.EndConnect(ias);
                Tcp.Close();
                Thread.Sleep(1);
                //获取从tOut到目前为止的毫秒数
                double tmp = DateTime.Now.Subtract(tOut).TotalMilliseconds / 1000;
                return tmp;
            }
            catch
            {
                return -1;
            }
        }