[ruby-core:111790] Re: [Ruby master Feature#19322] Support spawning "private" child processes

"Eregon (Benoit Daloze) via ruby-core" <[e-mail]> wrote:
> IMHO this sounds like some code is doing bad stuff and not
> properly caring about its own resources.
> 
> In the example you shown, I believe it's none of Unicorn's
> business to reap arbitrary processes, it doesn't compose (I
> could be wrong, but this seems a general rule when it come to
> resources of a program: don't mess with what you don't own).
> Unicorn should keep a list of pid subprocesses it created, and
> only do something on the `Signal.trap(:CHLD) do` if it's one
> of these pids.

There'd be lots of zombies if unicorn did what you propose
(at least for non-MJIT-Rubies).

KJ: do you need to care about the exit status?
Or just whether or not a process has exited?

If it's only the latter, turning FD_CLOEXEC off on the write
end of a pipe would let you IO.select/poll/epoll_wait on the
read end to detect when the child+descendents are all dead:

  r, w = IO.pipe
  Process.spawn ..., w => w # share `w' with all descendents
  w.close
  IO.select([r, ...], ...)

I've started using the above pattern in tests for setsid daemons
lately.
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