处理C#连接SQLServer总是连接不上

主要是三种情况：

1、sqlcommand执行超时；

2、sqlconnection执行超时；

3、数据库掉线TCP连接不上，针对第三种情况代码如下：

static void QuickOpen(this SqlConnection conn, int timeout)
        {
            // We'll use a Stopwatch here for simplicity. A comparison to a stored DateTime.Now value could also be used
            Stopwatch sw = new Stopwatch();
            bool connectSuccess = false;

            // Try to open the connection, if anything goes wrong, make sure we set connectSuccess = false
            Thread t = new Thread(delegate ()
            {
                try
                {
                    sw.Start();
                    conn.Open();
                    connectSuccess = true;
                }
                catch { }
            });

            // Make sure it's marked as a background thread so it'll get cleaned up automatically
            t.IsBackground = true;
            t.Start();

            // Keep trying to join the thread until we either succeed or the timeout value has been exceeded
            while (timeout > sw.ElapsedMilliseconds)
                if (t.Join(1))
                    break;

            // If we didn't connect successfully, throw an exception
            if (!connectSuccess)
                throw new Exception("Timed out while trying to connect.");
        }