supervise

It requires a bit of annoying machinery since you have to dedicate a process to being a subreaper. Still it's probably the best option, I made https://github.com/catern/supervise with it, see also https://catern.com/process.html

Excellent article! Thanks for posting it. It outlines all the problems and then offers a solution with this tool (by the author) https://github.com/catern/supervise

You might be interested in https://github.com/catern/supervise which does provide job-like behavior, using PR_SET_CHILD_SUBREPAER. I haven't written it down in that repo, but I believe that it exits in finite time even with an adversarial scheduler allowing arbitrary amounts of pid-wrap attacks. (and runs fairly efficiently in the absence of an adversary) Contrary to your article, I think systemd's logic also exits in guaranteed finite time even with adversarial scheduling. You didn't take into account the fact that systemd is (I assume) not reaping zombies when it's doing its kill-loop. Each zombie that is left unreaped occupies a pid. Eventually, pids will be exhausted and processes inside the cgroup will no longer be able to dodge kill() by forking off new processes.