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Question

I have a function which is taking a lot of time in a web application. So i decided to create a thread for it.

Thread t = new Thread(getEventErrors);
            t.Start();

The function calculates a value and applies it in a label.

This is an issue because in asp.net the page loads once and the label is not updated till then.

how do i implement this using the AJAX?

Is there a way in which the page is loaded and after the value is calculated the label gets updated?

Any sample code will be highly appreciated.

Thanks

 private void getEventErrors()
    {         
        EventLog eventLog = new EventLog("Application", ".");

        getEvents(eventLog.Entries);
    }

 private void getEvents(EventLogEntryCollection eventLogEntryCollection)
    {
        int errorEvents = 0;

        foreach (EventLogEntry logEntry in eventLogEntryCollection)
        {
            if (logEntry.Source.Equals("Application Name"))
            {
                DateTime variable = Convert.ToDateTime(logEntry.TimeWritten);
                long eventTimeTicks = (variable.Ticks);
                long eventTimeUTC = (eventTimeTicks - 621355968000000000) / 10000000;

                long presentDayTicks = DateTime.Now.Ticks;
                long daysBackSeconds = ((presentDayTicks - 864000000000) - 621355968000000000) / 10000000;


                if (eventTimeUTC > daysBackSeconds)
                {
                    if (logEntry.EntryType.ToString() == "Error")
                    {
                        errorEvents = errorEvents + 1;
                    }                        
                }
            }
        }
        btn_Link_Event_Errors_Val.Text = errorEvents.ToString(GUIUtility.TWO_DECIMAL_PT_FORMAT);            
        if (errorEvents == 0)
        {
            lbl_EventErrorColor.Attributes.Clear();
            lbl_EventErrorColor.Attributes.Add("class", "green");
        }
        else
        {
            lbl_EventErrorColor.Attributes.Clear();
            lbl_EventErrorColor.Attributes.Add("class", "red");
        }            
    }

this is the code.. but i want to handle all the long time consuming code using ajax.

For example the page should load fast and the long function should keep loading in the thread with a wait cursor, when the value is got it gets displayed in the label or any other control.

Answer 1

There is no way for the server to send some data after the response has been sent with an "update". A spontaneity request sent by the server to a client is just going to be ignored.

Your client will need to send a request to the server after the page is loaded (meaning JavaScript code) to request additional data that you can then update the page with.

The best method that I can think of would be to make a web service/web method with the data in the form, or to make an ICallbackEventHandler (I rather like working with these) which allows you to request the data from some JavaScript method. Now at this point you can either setup these web method to calculate just this piece of data when asked, or you can spin up the thread like you're doing and use the session. This would mean having the other thread calculate the data and store it in session on page load, and then have the JavaScript method get the value of out of the session. The latter method is a bit more fragile. (If they hit the page several times in different browsers/tabs at the same time, for example.) On top of that, if the session value hasn't been populated yet you'll either need to block the thread (bad idea) or have the JavaScript method poll repeatedly until the session value is populated.