Diagonal Lines

Under the Food for thought category. I have come across this as well but since I was working on a communications program simply living with the slow down wasn't an option.
So I created a circular buffer (head/tail type) created some command codes (like draw line, update header) and had the worker thread write to it at full speed. Then the GUI thread would read the buffer and update the screen when it had time.

I also used a 'sloppy update' so I didn't need semaphores and such that meant my messages had a 0-1.5 second delay to getting the screen but none of the users every new that.

I have also used in the past something where I would group up a few updates in the worker thread and then post the entire group using the "PostMessage". But that method could make things look a bit choppy.

Another method I have used (and this one maybe over kill for your app) is to create to separate programs. A JKDeFragGUI and JKDefragCMD, where JKDefragCMD would be a command line version of the program that is capable of running without a window. JKDefragGUI would fork off JKDefragCMD and chat to it via Sockets. This method is the one that I use most currently. It has lots of advantages but it does have a few downsides. May not be good if you have LOTS of things to say and though communications logs make debugging between the apps a breeze, debugging the background task can be a little more challenging.

Anyway, I'm sure your working on much more important parts of V4.0 so performance may not be a big issue for the first kick at the re-write cat. Also, once V4.0 is up and running you may find that 98% of it's time is in the actual file moves so making the last 2% (the gui updates) twice as fast may not be of any real benifet.

So, like I said. Food for thought.