function getusercount() {
            $.ajax({
                type: 'get',
                url: 'Ashx/GetUserCount.ashx',
                cache:false,
                success: function (result) {
                    $("#usercount").html(result);
                },
                error: function (XMLHttpRequest, textStatus, errorThrown) {
                    alert(XMLHttpRequest.status + "----" + XMLHttpRequest.readyState + "----" + textStatus);
                }
            });
        }

public void ProcessRequest(HttpContext context)
        {
            string result=string.Empty;
            context.Response.ContentType = "text/plain";
            lock(locker)
            {
                //声明一个xmlDocument对象，加载指定的XML文件
                XmlDocument doc = new XmlDocument();
                doc.Load(AppDomain.CurrentDomain.BaseDirectory + "usercount.xml");
                //得到根节点
                XmlNode xn = doc.SelectSingleNode("AllData");
                //得到根节点的所有子节点
                XmlNodeList xnl = xn.ChildNodes;
                XmlElement xe = (XmlElement)xnl.Item(0);
                if (xe.GetAttribute("Type").ToString() == "usercount")
                {
                    result = xe.GetAttribute("value").ToString();
                }
            }
            context