using System;
using System.Data;
using System.Data.SqlClient;
using System.Threading;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        for (int i = 1; i <= 10; i++)
        {
            Response.Write("start:" + i.ToString());
            new Thread(new ThreadStart(MyThread)).Start();
        }

        for (int i = 1; i <= 10; i++)
        {
            Response.Write("start:" + i.ToString());
            new Thread(new ThreadStart(TestThread)).Start();
        }
    }

    private static string connectstring = @"Data Source=127.0.0.1;Initial Catalog=XXXXXX;Persist Security Info=True;User ID=sa;Password=sa";

    private static SqlConnection con;

    /// <summary>
    /// 取得连接
    /// </summary>
    public static SqlConnection Connection
    {
        get
        {

            if (con == null)
            {
                con = new SqlConnection(connectstring);
                con.Open();
            }
            else if (con.State == ConnectionState.Broken)
            {
                con.Close();
                con.Open();
            }
            else if (con.State == ConnectionState.Closed)
            {
                con.Open();
            }
            return con;
        }
    }



    static void MyThread()
    {
        try
        {
            var sql = "SELECT * FROM table1";

            SqlCommand cmd = new SqlCommand(sql, Connection);
            SqlDataReader reader = cmd.ExecuteReader();

            while (reader.Read())
            {
                Console.WriteLine(reader["mc"].ToString());
            }
            reader.Close();
        }
        catch (Exception ex)
        { 
        
        }
    }


    static void TestThread()
    {
        var sql = "SELECT * FROM table1";

        using (SqlConnection myconn = new SqlConnection(connectstring))
        {
            myconn.Open();
            SqlCommand cmd =new SqlCommand(sql,myconn);
            SqlDataReader reader = cmd.ExecuteReader();

            while (reader.Read())
            {
                Console.WriteLine(reader["mc"].ToString());
            }
            reader.Close();
        }
    }
}

------解决方案--------------------

缺点：
1.使用static，也就是全局能使用，如果有多线程，那么大家都来争这个资源，建议你可以在控制台中模拟多线程来测试一下，特别是两个线程几乎差不多时间进入此代码获取connection，你可以看看会怎样。
2.把connectstring放在代