最大在线人数统计

global.asax:
        protected void Session_Start(Object sender, EventArgs e)
        {    
            Application.Lock();
            DataSet objDataSet=new DataSet()
            objDataSet.ReadXml(Server.MapPath("database/count.xml"));
            if(Convert.ToInt32(objDataSet.Tables["MyCount"].Rows[0]["MaxCount"]) < (int)Application["user_sessions"])    //如果MaxCount标签里面的值小于当前在线人数的值，就存入，不小于则什么都不做。
                objDataSet.Tables["MyCount"].Rows[0]["MaxCount"] = (int)Application["user_sessions"];
            objDataSet.WriteXml(Server.MapPath("database/count.xml"));
            Application.UnLock();
        }