How to invalidate frames after they're rendered?

Hi there!

I am writing an effect plugin that does work on a thread in the background, and while working, outputs the input with a progress bar on top, just like in Warp Stabilizer and 3D Camera Tracker.

However, I cannot figure out how to invalidate the progress bar frames once the background work is done so AE will re-render them rather than continuing to use the cached frames.

I've tried a number of things - I know that changing a hidden paramter using AEGP Stream Suites could do it, but those suites throw an error when I try to access them from an IdleHook function, and UserChangedParam and UpdateParamUI don't get called often enough.

I have also tried using GuidMixInPtr() as in the SmartyPants SDK example, but cannot get it to work - whether I point it at a bool in global_dataP (that changes frequently) or all of global_dataP (which includes a float that changes frequently), no frames ever seem to get invalidated. I'm not sure if it's supposed to work with global data or not - if so, it seems like the ideal solution, but I unfortunately can't get it to work as intended.

Somehow Warp Stabilizer and 3D Camera Tracker manage to do it, so I remain optimistic that it is possible. If anyone has any insight, it would be greatly appreciated.

Thank you!