Technically, it could be implemented if the subreaper process were getting notified somehow of new processes being reparented to it. Alas, subreapers don't get

Technically, it could be implemented if the subreaper process were getting notified somehow of new processes being reparented to it. Alas, subreapers don't get such notifications. Also, you need some protection against children who do "kill(-getpid(), SIGKILL)" before the exit.