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

[Michael Albinus]

Justin Van Winkle <justin.vanwinkle@gmail.com> writes:

Hi Justin,

> I mean it is certainly a bug to use 100% of a cpu just because a file
> that is in the same directory to a file you are editing is being
> written to, but it may not be unintentional behavior.

I could reproduce the problem. I have a running Emacs for some days, and
I've enabled `global-auto-revert-mode'. Starting scp copy of a large
file outside Emacs, brought Emacs up to 100% cpu usage.

The variable `file-notify-descriptors' contains

#s(hash-table size 97 test equal rehash-size 1.5 rehash-threshold 0.8125 data 
((1 . 0) #s(file-notify--watch /home/albinus .emacs auto-revert-notify-handler) 
(1 . 1) #s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 
. 2) #s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 
3) #s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 4) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 5) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 6) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (2 . 0) 
#s(file-notify--watch /usr/local/src/emacs/src nil auto-revert-notify-handler) 
(1 . 7) #s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 
. 8) #s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 
9) #s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 10) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 11) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 12) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (3 . 0) 
#s(file-notify--watch /usr/local/src/elpa/packages/debbugs nil 
auto-revert-notify-handler) (3 . 1) #s(file-notify--watch 
/usr/local/src/elpa/packages/debbugs nil auto-revert-notify-handler) (3 . 2) 
#s(file-notify--watch /usr/local/src/elpa/packages/debbugs nil 
auto-revert-notify-handler) (3 . 3) #s(file-notify--watch 
/usr/local/src/elpa/packages/debbugs nil auto-revert-notify-handler) (3 . 4) 
#s(file-notify--watch /usr/local/src/elpa/packages/debbugs nil 
auto-revert-notify-handler) (3 . 5) #s(file-notify--watch 
/usr/local/src/elpa/packages/debbugs nil auto-revert-notify-handler) (1 . 13) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (3 . 6) 
#s(file-notify--watch /home/albinus/src/elpa/packages/debbugs nil 
auto-revert-notify-handler) (3 . 7) #s(file-notify--watch 
/usr/local/src/elpa/packages/debbugs nil auto-revert-notify-handler) (3 . 8) 
#s(file-notify--watch /usr/local/src/elpa/packages/debbugs nil 
auto-revert-notify-handler) (3 . 9) #s(file-notify--watch 
/usr/local/src/elpa/packages/debbugs nil auto-revert-notify-handler) (3 . 10) 
#s(file-notify--watch /usr/local/src/elpa/packages/debbugs nil 
auto-revert-notify-handler) (4 . 0) #s(file-notify--watch /usr/local/src/elpa 
nil auto-revert-notify-handler) (3 . 11) #s(file-notify--watch 
/usr/local/src/elpa/packages/debbugs nil auto-revert-notify-handler) (5 . 0) 
#s(file-notify--watch /usr/local/src/emacs-25/doc/misc nil 
auto-revert-notify-handler) (3 . 12) #s(file-notify--watch 
/home/albinus/src/elpa/packages/debbugs nil auto-revert-notify-handler) (6 . 0) 
#s(file-notify--watch /home/albinus/src/tramp/texi nil 
auto-revert-notify-handler) (6 . 1) #s(file-notify--watch 
/home/albinus/src/tramp/texi nil auto-revert-notify-handler) (6 . 2) 
#s(file-notify--watch /home/albinus/src/tramp/texi nil 
auto-revert-notify-handler) (4 . 1) #s(file-notify--watch /usr/local/src/elpa 
nil auto-revert-notify-handler) (7 . 0) #s(file-notify--watch /usr/share/info 
nil auto-revert-notify-handler) (8 . 0) #s(file-notify--watch 
/home/albinus/src/tramp/lisp nil auto-revert-notify-handler) (8 . 1) 
#s(file-notify--watch /home/albinus/src/tramp/lisp nil 
auto-revert-notify-handler) (8 . 2) #s(file-notify--watch 
/home/albinus/src/tramp/lisp nil auto-revert-notify-handler) (9 . 0) 
#s(file-notify--watch /home/albinus/src/tramp nil auto-revert-notify-handler) 
(1 . 14) #s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 
. 15) #s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 
16) #s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (4 . 2) 
#s(file-notify--watch /usr/local/src/elpa nil auto-revert-notify-handler) (4 . 
3) #s(file-notify--watch /usr/local/src/elpa nil auto-revert-notify-handler) (3 
. 13) #s(file-notify--watch /usr/local/src/elpa/packages/debbugs nil 
auto-revert-notify-handler) (3 . 14) #s(file-notify--watch 
/usr/local/src/elpa/packages/debbugs nil auto-revert-notify-handler) (3 . 15) 
#s(file-notify--watch /usr/local/src/elpa/packages/debbugs nil 
auto-revert-notify-handler) (3 . 16) #s(file-notify--watch 
/usr/local/src/elpa/packages/debbugs nil auto-revert-notify-handler) (4 . 4) 
#s(file-notify--watch /usr/local/src/elpa nil auto-revert-notify-handler) (4 . 
5) #s(file-notify--watch /usr/local/src/elpa nil auto-revert-notify-handler) (3 
. 17) #s(file-notify--watch /home/albinus/src/elpa/packages/debbugs nil 
auto-revert-notify-handler) (3 . 18) #s(file-notify--watch 
/usr/local/src/elpa/packages/debbugs nil auto-revert-notify-handler) (1 . 17) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 18) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 19) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 20) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 21) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 22) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 23) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 24) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 25) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 26) 
#s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 27) 
#s(file-notify--watch /home/albinus .newsrc-dribble auto-revert-notify-handler) 
(1 . 28) #s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 
. 29) #s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (1 . 
30) #s(file-notify--watch /home/albinus nil auto-revert-notify-handler) (10 . 
0) #s(file-notify--watch /usr/local/share/emacs/27.0.50/lisp filenotify.el.gz 
auto-revert-notify-handler) (10 . 1) #s(file-notify--watch 
/usr/local/share/emacs/27.0.50/lisp nil auto-revert-notify-handler)))

As we can see, many identical entries #s(file-notify--watch /home/albinus nil 
auto-revert-notify-handler).
Every incoming event for "/home/albinus" triggers the many calls of
`auto-revert-notify-handler', although one entry would be sufficient. I
will check, where all these entries come from.

Best regards, Michael.