> Regarding pidfd and kqueue -- I love to see pull requests with proposals. Now nothing exists. The pidfd is available starting from the latest released Linux 5.3;  we need to wait for a decade before all Linux distros adopt it and we can drop all other implementations.

I hope that it will take less time to expose pidfd_open() in Python! It is *already* available in the Linux kernel 5.3. My laptop is already running Linux 5.3! (Thanks Fedora 30.)

I would prefer to keep an API to choose the child watcher since it seems like even in 2019, there are still new APIs (pidfd) to wait for a process completion. I expect that each implementation will have advantages and drawbacks.