cancel asynch postback with lengthy server process

I'm having a bit of trouble cancelling an asynch postback. I have an update panel with an update progress which contains a cancel button so that the user can cancel the postback. When the user clicks a button to generate a report the update progress is shown. The report can take a bit of time as it has to loop through a thousand or so times creating an excel spreadsheet. If the user decides to cancel run开发者_JS百科ning the report for any reason then they can click the cancel button which I then call abortPostBack() in javascript which stops the update progress and the page is shown again. However, the user can't do anything else like navigate to another page as the server is still processing the loop. How would I stop the loop on the server processing when the user has clicked the cancel button? Any help appreciated!

Are you saying that a simple HTTP link is not accessible on the client side until the async postback is complete? If so, that sounds like a conundrum, since you either have to optimize your server side process, or set a smaller server-side request timeout. Either that or redesign your user-interaction to make the server side Excel generation process an asynchronous one, rather than synchronous, so that the user doesn't have to wait until the Excel generation is complete. You could fancy this up on the client side to then set a JavaScript timer to periodically query the server to see if the file was ready, and if so, indicate that to the user with and give them a download file link option, or something.

Otherwise, if you could invoke another AJAX request while waiting on that to return (which you may not to from the sound of it), you could simply perform a new HTTP request that "cancels" the long running process. But that seems like it would not work since the server is still handling the long running HTTP request. So I'd opt to investigate the options in my first paragraph.

If cancelling did allow an async HTTP request to be performed on the client side, then you could set a session state value to indicate that cancel was requested. Personally I wouldn't approach it this way. But if you did, then your long-running server-side process could periodically look for the existence of a session value. Say:

if (Session["cancel-me"] != null) 
{
    Session["cancel-me"] = null;
    abortThisLongProcess();
}

Yep, even if you navigate away from the page using the browser back button, as soon as you click anything else that needs to post back to the server the page hangs until the long process has completed. Looks like there's no way of canceling so I will have to look at redesigning the Excel generation.

I haven't found a way to cancel the request that's running, but there's no real reason that you can't start a new one.

By default ASP.Net tries (it can't always) to apply an exclusive lock on the session object - as soon as one page reads it every other page request that passes the same session ID (by cookie or on the URL) has to wait for the first page to release the session.

It doesn't matter that the client has cancelled the request - the server will continue to lock the session until the original page finishes executing.

I think the solution is to do away with the ASP session entirely. Then when the user requests another page it begins immediately, even though the server is still processing the old request on another thread.