Many thanks for your replies. I didn't like the idea of desensitizing the whole window as that is very big change to the display and possibly only for a short duration of time.

In the end I got the an event loop mechanism working that simply filtered out offending user input events, allowing for `stop' style buttons to be pressed. This module also handles context sensitive help, busy cursor handling and window recycling. I will probably put this on CPAN at some point. The event loop is only used when the app is busy, otherwise the default action takes place which avoids the unnecessary c to perl marshalling. It works really well now.

Many thanks for your help.

Tony.