Detect when a session times out and execute a function

[eluser]funkmyer[/eluser]
Is this possible? If so, has anyone had any experience with this? Basically, I have a shopping cart that decrements stock counts as items are entered into their basket. I have a function that fires when someone "empties" their basket that will free those stock levels back up.

If someone puts items in a cart and then goes out for the day, the session will expire and lose the cart contents, thus stock levels will now be incorrect. Can anyone think of an intelligent way to handle this situation without running an interval'd cron job.

Thanks a bunch, and long live CI!