Handling Unhandled errors that happen in a secondary threaded process.

Question

I have a asp.net 2.0 web app which calls a long running stored proc (about 3 minutes). The sp actually performs many tasks on the backend.

My page uses threading and ajax (update panel) and a timer control to dispaly a progess bar to the user. This all works great unless there is an error in the sp which just freezes the screen.

I have tried useing a SafeThread class which I found on codeProject which wraps the thread process and creates an event which can be handled in the case of an exception.

In the event handler I just want to redirect the user to an error page and display an error. When testing I can break in the event handler. Calling either Server.Transfer or Response.Redirect however, has no effect at all.

I am not sure why this happenning. I will post my code below. Any ideas or alternative suggestions appreciated.

    protected void btnSave_OnClick(object sender, EventArgs e)
    {
        DAC dac = new DAC();
        Session["RerunStatus"] = 0;
        SafeThread thrd = new SafeThread(new ParameterizedThreadStart(dac.RerunTest));
        thrd.IsBackground = true;

        //tell the SafeThread to report 
        //ThreadAbort exceptions
        thrd.ShouldReportThreadAbort = true;
        //attach a ThreadException handler for 
        //reporting SafeThread exceptions
        thrd.ThreadException += new
        ThreadThrewExceptionHandler(thrd_ThreadException);

        thrd.Start(ddlRundate.SelectedItem.Text);
        Session["RerunThread"] = thrd;
        btnSave.Enabled = false;
        Timer1.Enabled = true;
    }

    void thrd_ThreadException(SafeThread thrd, Exception ex)
    {
        //thrd.Abort();
        Timer1.Enabled = false;
        //Response.Redirect("ErrorPage.aspx");
        Server.Transfer("ErrorPage.aspx?ErrorMsg=" + ex.Message);
        //thrd.Abort();
    }

Answer 1

You can only use Server.Transfer()/Response.Redirect() when handling a request - that is not the case when your thrd_ThreadException() get's called.

Try to set a flag in your thrd_ThreadException and do the redirect in the Timer1 Tick event.