bug#22814: 25.0.91; Emacs runs out of file descriptors on OS X

[Eli Zaretskii <eliz@gnu.org>]

> From: Michael Albinus <michael.albinus@gmx.de>
> Date: Sat, 27 Feb 2016 09:00:14 +0100
> Cc: 22814@debbugs.gnu.org
> 
> > One simple way to handle this is to define a variable with "max"
> > number of files the notification system can handle. We can set this
> > to, say, 200 on OS X and unlimited on other systems.
> 
> Would be possible, yes. I would prefer to set the limit to a system
> related value. Does there exist a portable way to detect, how many file
> descriptors / processes Emacs is able to consume?

Not portably, AFAIK.  Also, different implementations use different
resources for receiving file notifications.  For example, w32notify
uses one handle and one thread per watched file/directory.  The number
of handles a process can have on Windows is very large, and the
theoretical max number of threads is 32K, but both are limited by the
resources already consumed by the Emacs process.  So determining the
practical maximum at any given point will require a non-trivial
function.