WF 多次提交问题

公司做了个审批的WF,现在遇到个问题,每当审批用户点击按钮两次那么工作流就被执行了两次,即使我们做了很多限制用户连续点击按钮,但是当多用户同时访问时,用户单击按钮N久后WF才提交,但是在等待的这个过程中,用户又一次打开当前这个链接,又单击了审批这个按钮,那么这种情况工作流就被重复执行了,网上看了好多资料都没提到这块,在此请教各位哪位大虾了.

下面是我工作流执行代码:

这段代码是写在Application里面的

protected static string connectionString = ConfigurationManager.ConnectionStrings["CHAS.REPAIR"].ConnectionString;
        protected void Application_Start(object sender, EventArgs e)
        {
            WorkflowRuntime workflowRuntime = new WorkflowRuntime();
            SqlTrackingService sqlTs = new SqlTrackingService(connectionString);

            SqlWorkflowPersistenceService persistService = new SqlWorkflowPersistenceService(connectionString);

            workflowRuntime.AddService(sqlTs);
            workflowRuntime.AddService(persistService);

            ExternalDataExchangeService dataServer = new ExternalDataExchangeService();
            workflowRuntime.AddService(dataServer);

            dataServer.AddService(new CHAS.REPAIR.BLL.InterFace.RepairHandler());

            workflowRuntime.StartRuntime();
            Application.Add("WorkflowRuntime", workflowRuntime);
        }

下面这段代码就是按钮单击所执行的代码了

private void RunWorkFlow(RepairFlows rf)
        {
           
            WorkflowRuntime wr = this.Application["WorkflowRuntime"] as WorkflowRuntime;

            //關聯workflw業務類
            ExternalDataExchangeService dataService = wr.GetService(typeof(ExternalDataExchangeService)) as ExternalDataExchangeService;
            RepairHandler wfRepair = dataService.GetService(typeof(RepairHandler)) as RepairHandler;
            wfRepair.UpRepair += new EventHandler<UpRepairEventArgs>(UpRepairEventArgs);
            WorkflowInstance instance = wr.GetWorkflow(rf.WorkFlowGuid);
            instance.Load();
            wfRepair.RepairEvent(rf.WorkFlowGuid, rf);
            if (rf.ApprovalResults == 1)
            {
                while (!instance.TryUnload())
                {
                    System.Threading.Thread.Sleep(500);
                }
            }
        }