利用 Jquery Deferred 异步你的程序

 public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "application/json";

            string action = context.Request.Form["Action"];
            //用Thread.Sleep()模拟请求Rest API时的网络延迟
            switch (action)
            {
                case "delay1Seconds":
                    Thread.Sleep(2000);
                    WriteSuccess(context, action, "2");
                    break;
                case "delay2Seconds":
                    Thread.Sleep(1000);
                    WriteSuccess(context, action, "1");
                    break;
                case "delay3Seconds":
                    Thread.Sleep(3000);
                    WriteSuccess(context, action, "3");
                    break;
                default:
                    break;
            }
        }

        public void WriteSuccess(HttpContext context, string action, string seconds)
        {
            //输出JSON结果
            string index = context.Request.Form["Index"];
            string json = "{\"flag\":0,\"msg\":" + seconds + ",\"Index\":" + index + "}";
            context.Response.Write(json);
        }

    <script src="Scripts/jquery-1.7.2.min.js" type="text/javascript"></script>
    <script type="text/javascript">
        $(function () {

            $("#btn_Request").click(
                function () {
                    $("#div_Content").html("");

                    //模拟请求Handler地址
                    var requestUrl = "JqueryHandler.ashx";

                    //ajax请求 action名称数组
                    var requestInfoArr =
                    [
                      { Action: "delay1Seconds" },
                     { Action: "delay2Seconds" },
                     { Action: "delay3Seconds" }
                    ];

                    //用于保存Jquery Defered对象
                    var deferredOBJ = [];

                    //创建3个 Jquery Deferred 对象
                    //与3个对 JqueryHandler.ashx 的异步请求一 一对应
                    for (var i = 0; i < requestInfoArr.length; i++) {
                        deferredOBJ[i] = $.Deferred();

                        var jsonData = requestInfoArr[i];

                        //记录当前ajax请求的索引,方便后面找到对应的Jquery Deferred对象
                        jsonData.Index = i;

                        //发出ajax请求
                        $.ajax({
                            type: "POST",
                            dataType: "json",
                            url: requestUrl,
                            data: jsonData,
                            success: function (data, statu) {
                                //flag为0时表示请求成功
                                if (data.flag == 0) {
                                    var result = requestInfoArr[data.Index].Action + " 请求成功,耗时:" + data.msg + "秒";
                                    $("#div_Content").append($("<p/>").text(result));

                                    //根据前面传过去的索引找到对应Deferred对象,将状态改成resolve(表示成功)
                                    deferredOBJ[data.Index].resolve();
                                } else {
                                    // 如果请求出错,将状态改成reject (表示失败)
                                    //这里调用reject()后,会立即执行下面的fail()函数
                                    deferredOBJ[data.Index].reject(data.msg);
                                }
                            },
                            error: function (data, statu) {
                                alert("ajax请求获取数据失败!");
                            }
                        });
                    }

                    //使用$.when() 来控制3个异步请求的流程,保证所有异步请求都完成后再执行done函数
                    $.when(deferredOBJ[0], deferredOBJ[1], deferredOBJ[2])
                     .done(function () {
                         var result = "所有请求完成...";
                         $("#div_Content").append($("<p/>").text(result));
                     })
                     .fail(function (error) {
                         alert("从JIRA获取度量项数据失败, 请重试");
                     });

                });

        });
    </script>