GNU bug report logs - #24756
26.0.50; Emacs should not use pselect

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Philipp Stephani <p.stephani2 <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 26.0.50; Emacs should not use pselect
Date: Fri, 21 Oct 2016 17:41:21 +0200

Emacs uses pselect for IO multiplexing, limiting the number of available
file descriptors to FD_SETSIZE.  Rather, epoll/kqueue should be used, if
available.


In GNU Emacs 26.0.50.10 (x86_64-unknown-linux-gnu, GTK+ Version 3.10.8)
 of 2016-10-20 built on localhost
Repository revision: 56f8384bb3f20d55693a3a1db8aa2cf490e6d18e
Windowing system distributor 'The X.Org Foundation', version 11.0.11501000
System Description:	Ubuntu 14.04 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --with-modules --enable-checking
 --enable-check-lisp-object-type'

Configured features:
XPM JPEG TIFF GIF PNG SOUND GSETTINGS NOTIFY GNUTLS FREETYPE XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 MODULES

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message subr-x puny seq byte-opt gv
bytecomp byte-compile cl-extra help-mode cconv cl-loaddefs pcase cl-lib
dired dired-loaddefs format-spec rfc822 mml easymenu mml-sec
password-cache epa derived epg epg-config gnus-util rmail rmail-loaddefs
mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils
mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils time-date mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel term/x-win x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list newcomment elisp-mode lisp-mode prog-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev obarray minibuffer cl-preloaded nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote inotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 97880 7352)
 (symbols 48 20418 0)
 (miscs 40 331 119)
 (strings 32 18006 4996)
 (string-bytes 1 591250)
 (vectors 16 13824)
 (vector-slots 8 454325 6227)
 (floats 8 183 10)
 (intervals 56 215 0)
 (buffers 976 12)
 (heap 1024 22892 1161))

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Message #8 received at 24756 <at> debbugs.gnu.org (full text, mbox):

From: Philipp Stephani <p.stephani2 <at> gmail.com>
To: 24756 <at> debbugs.gnu.org
Subject: Re: bug#24756: 26.0.50; Emacs should not use pselect
Date: Tue, 25 Oct 2016 11:45:22 +0000

[Message part 1 (text/plain, inline)]

Philipp Stephani <p.stephani2 <at> gmail.com> schrieb am Fr., 21. Okt. 2016 um
17:42 Uhr:

>
> Emacs uses pselect for IO multiplexing, limiting the number of available
> file descriptors to FD_SETSIZE.  Rather, epoll/kqueue should be used, if
> available.
>
>
Some good counter-arguments were brought up:
- pselect is in the POSIX standard, whereas the possible replacements
(ppoll/epoll/kqueue) are not.
- The file descriptor limit should only be hit in pathological cases, e.g.
when leaking background processes, and is only a symptom of a bug somewhere
else. A higher FD limit would only hide the symptom, but not fix the
underlying root cause.

Given that, I'm no longer convinced that switching away from pselect would
be a good idea (but I'll leave this bug open for now to provide a space for
discussion).

[Message part 2 (text/html, inline)]

Message #13 received at 24756-done <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefan <at> marxist.se>
To: Philipp Stephani <p.stephani2 <at> gmail.com>
Cc: 24756-done <at> debbugs.gnu.org
Subject: Re: bug#24756: 26.0.50; Emacs should not use pselect
Date: Sun, 29 Sep 2019 06:02:56 +0200

Philipp Stephani <p.stephani2 <at> gmail.com> writes:

> Philipp Stephani <p.stephani2 <at> gmail.com> schrieb am Fr., 21. Okt. 2016 um 17:42 Uhr:
>
>  Emacs uses pselect for IO multiplexing, limiting the number of available
>  file descriptors to FD_SETSIZE.  Rather, epoll/kqueue should be used, if
>  available.
>
> Some good counter-arguments were brought up:
> - pselect is in the POSIX standard, whereas the possible replacements (ppoll/epoll/kqueue) are not.
> - The file descriptor limit should only be hit in pathological cases, e.g. when leaking background processes, and is only a symptom of a bug somewhere else. A higher FD limit would only hide the symptom, but not fix the underlying root cause.
>
> Given that, I'm no longer convinced that switching away from pselect would be a good idea (but I'll leave this bug open for now to provide a space for discussion).

That was three years ago, and no such discussion has taken place here.
If there is a continued need to discuss this, perhaps it's better to
take it to emacs-devel.  I'm therefore closing this bug report.

If anyone disagrees, they should feel free to reopen.

Best regards,
Stefan Kangas

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