update ui while processing in carbon

my app will sometimes process large files and during such processing, i'm throwing up a modal window with a progress bar control to inform the user of the um... progress.

naturally, the progress bar never gets updated because of the heavy processing, so i'm wondering if carbon provides any simple way to achieve this besides resorting to some elaborate threading system. or alternatively, if there's another clever way to show progres without too much effort.

and btw, i did try setting up pthreads, but just crashed my app when it tried to redraw views.