bug#33194: 26.1; Auto-revert mode causes emacs to use 100% cpu whenever a file is being written to in the home directory

[Justin Van Winkle <justin.vanwinkle@gmail.com>]

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From: Justin Van Winkle
<jvanwink@ct.i-did-not-set--mail-host-address--so-tickle-me>
To: bug-gnu-emacs@gnu.org
Subject: 26.1; Auto-revert mode causes emacs to use 100% cpu whenever a
file is being written to in the home directory
--text follows this line--

I enable global-auto-revert-mode.  I noticed that when I was scp'ing a
large file to my home directory, every emacs process on my machine was
trying to use 100% cpu.  When I stopped the file transfer, emacs would
go back to idle cpu usage.  I ran the emacs profiler and narrowed it
down to revert-buffer.  Auto revert was apparently listening for changes
in my home directory, even for things like file creation or file
modified for files emacs did not have open.

I am running emacs from the MASTER branch from the github mirror.

Doing this little experiment again with the emacs25 build that is
distributed with Ubuntu, no extra cpu usage was seen, so the bug is
either specific to emacs>26 or something about my build (which should
have been basically generic: autogen.sh; ./configure; make -j8   or
something to that effect).


In GNU Emacs 26.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 of 2018-10-14 built on bt
Repository revision: 07f8f9bc5a51f5aa94eb099f3e15fbe0c20ea1ea
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 18.04.1 LTS

Recent messages:
Loading autorevert...done
Loading paren...done
Eshell virtualenv support initialized.
For information about GNU Emacs and the GNU system, type C-h C-a.
[2018-10-29 11:56:06] ‘*scratch*’ [1 259200]
[2018-10-29 11:56:06] ‘ *Minibuf-0*’ [1 259200]
[2018-10-29 11:56:06] ‘*Messages*’ [0 259200]
[2018-10-29 11:56:06] ‘ *code-conversion-work*’ [0 259200]
[2018-10-29 11:56:06] ‘ *Echo Area 0*’ [0 259200]
[2018-10-29 11:56:06] ‘ *Echo Area 1*’ [0 259200]

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 THREADS LIBSYSTEMD LCMS2

Important settings:
  value of $LC_ALL: en_US.UTF-8
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  global-flycheck-mode: t
  flycheck-mode: t
  show-paren-mode: t
  global-auto-revert-mode: t
  auto-insert-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-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
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml mml-sec epa epg 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 elec-pair justin-theme pcomplete esh-var esh-io esh-cmd
esh-opt esh-ext esh-proc esh-arg esh-groups eshell esh-module esh-mode
esh-util clang-format xml flycheck derived cl-extra json map find-func
help-mode rx subr-x pcase jka-compr compile let-alist virtualenvwrapper
advice gud easy-mmode comint ansi-color ring s dash cl diary-lib
diary-loaddefs cal-menu calendar cal-loaddefs midnight edmacro kmacro
paren autorevert filenotify autoinsert cus-start cus-load finder-inf
info package easymenu epg-config url-handlers url-parse auth-source
cl-seq eieio eieio-core cl-macs eieio-loaddefs password-cache url-vars
seq byte-opt gv bytecomp byte-compile cconv cl-loaddefs cl-lib 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 replace newcomment
text-mode elisp-mode lisp-mode prog-mode register page menu-bar
rfn-eshadow isearch 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 composite charscript charprop
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 dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting move-toolbar gtk
x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 228652 15199)
 (symbols 48 29258 1)
 (miscs 40 61 108)
 (strings 32 53756 2633)
 (string-bytes 1 1775330)
 (vectors 16 21499)
 (vector-slots 8 577491 8994)
 (floats 8 65 52)
 (intervals 56 244 59)
 (buffers 992 11))

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