Well I was just looking at another one of your threads:
https://discourse.panda3d.org/t/asynchronous-screenshot-grabbing/29024
and could do the thing I wanted by counting the fragments through a ram image. I actually did this first but found it to also stall very heavily. I was using an FBO and a C extension I made to count the pixels from a buffer to see how many passed and could maybe consider using something like the post said where I can request an async ram FBO request where I wait till the ram data is available without stalling. Could this be done? From the post it only looks to be a screenshot at the moment.