So you have: one thread that's handling the select-polling; and one or more threads which the work

Yes, but you're completely missing the point of the OPs question.

You set up you event loop in the primary process (main thread as you incorrectly term it), and then, to start your secondary, long-running, blocking processes, you use fork.

But, and here the rub, when you fork, you replicate everything that you had in the primary process...

Now re-read the OPs question starting from "But let's check this in deep..." and see how your reply, plus the conflation of the terms 'forking' and 'threading' mean that you did not even begin to answer the question asked.