Keep app responsive during long task

Question

A certain form in our application displays a graphical view of a model. The user can, amongst loads of other stuff, initiate a transformation of the model that can take quit

Answer 1

I'd certainly go with threads. Working out how a thread will interact with the user is often difficult, but the solution that has worked well for me is to not have the thread interact with the user, but have the user side GUI interact with the thread. This solves the problem of updating the GUI using synchronize, and gives the user more responsive activity.

So, to do this, I use various variables in the thread, accessed by Get/Set routines that use critical sections, to contain status information. For starters, I'd have a "Cancelled" property for the GUI to set to ask the thread to stop please. Then a "Status"property that indicates if the thread is waiting, busy or complete. You might have a "human readable" status to indicate what is happening, or a percentage complete.

To read all this information, just use a timer on the form and update. I tend to have a "statusChanged" property too, which is set if one of the other items needs refreshing, which stops too much reading going on.

This has worked well for me in various apps, including one which displays the status of up to 8 threads in a list box with progress bars.