bug#51110: Native-comp leaks fds open on /dev/ptmx

[Eli Zaretskii <eliz@gnu.org>]

> From: Andrea Corallo <akrl@sdf.org>
> Cc: Stephen Gildea <stepheng+emacs@gildea.com>, 51110@debbugs.gnu.org
> Date: Tue, 30 Nov 2021 20:13:07 +0000
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Stephen Gildea <stepheng+emacs@gildea.com>
> >> cc: Andrea Corallo <akrl@sdf.org>, 51110@debbugs.gnu.org
> >> Date: Sat, 09 Oct 2021 10:01:43 -0700
> >> 
> >> Apparently what's happening is that Emacs forks off a child Emacs to do
> >> the compile and allocates a pty to the child.  These ptys are not
> >> closed until the compile completes.  It seems Emacs needs to better
> >> manage the number of simultaneous open ptys.  Or at least be able to
> >> wait and retry if an open fails.
> >
> > Emacs limits the number of these background processes, see
> > native-comp-async-jobs-number.  (The value zero means use half of the
> > number of execution units available in the system's processor.)  So we
> > generally shouldn't have more than that number of open pipes at any
> > given time.  For the obvious reasons they cannot be closed until the
> > sub-process exits.
> 
> Is there any action we need/can take on this bug?

I don't think there's anything we _can_ do here, and I tried to
explain why.