> I don't know if it can be useful, but there is also the signal.pthread_sigmask() which can be used to "queue" pending signals. (...)

Oh, I didn't remember that I opened the issue #12060 to discuss "real time signals". The summary is that the wakeup fd should be used... Which is nice because it is the choice made by asyncio ;-)

FYI I also opened the issue #21998: "asyncio: a new self-pipe should be created in the child process after fork" which is somehow related to this issue.