GNU bug report logs - #61942
28.2; uninterruptible hang in vc-diff buffer

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

From: Tom Tromey <tom <at> tromey.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 28.2; uninterruptible hang in vc-diff buffer
Date: Fri, 03 Mar 2023 11:13:27 -0700

From *vc-outgoing*, I used '=' to see a diff.

The diff in question is pretty large.

Emacs showed this in the echo area:

Finding changes in ....

This was not interruptible -- I tried C-g, C-], and 'kill -USR1'

I don't know exactly what this is doing, but whatever it is should be
interruptible.

Tom




In GNU Emacs 28.2 (build 1, x86_64-redhat-linux-gnu, GTK+ Version 3.24.35, cairo version 1.17.6)
 of 2022-12-31 built on buildvm-x86-18.iad2.fedoraproject.org
Windowing system distributor 'The X.Org Foundation', version 11.0.12201007
System Description: Fedora Linux 36 (Workstation Edition)

Configured using:
 'configure --build=x86_64-redhat-linux-gnu
 --host=x86_64-redhat-linux-gnu --program-prefix=
 --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr
 --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc
 --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64
 --libexecdir=/usr/libexec --localstatedir=/var
 --sharedstatedir=/var/lib --mandir=/usr/share/man
 --infodir=/usr/share/info --with-dbus --with-gif --with-jpeg --with-png
 --with-rsvg --with-tiff --with-xpm --with-x-toolkit=gtk3 --with-gpm=no
 --with-xwidgets --with-modules --with-harfbuzz --with-cairo --with-json
 --with-native-compilation build_alias=x86_64-redhat-linux-gnu
 host_alias=x86_64-redhat-linux-gnu CC=gcc 'CFLAGS=-DMAIL_USE_LOCKF -O2
 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches
 -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
 -Wp,-D_GLIBCXX_ASSERTIONS
 -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong
 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic
 -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection'
 LDFLAGS=-Wl,-z,relro
 PKG_CONFIG_PATH=:/usr/lib64/pkgconfig:/usr/share/pkgconfig'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NATIVE_COMP NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS
X11 XDBE XIM XPM XWIDGETS GTK3 ZLIB

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

Major mode: Git-Log-View

Minor modes in effect:
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  bug-reference-mode: t
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  erc-hl-nicks-mode: t
  erc-button-mode: t
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  erc-noncommands-mode: t
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  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow emacsbug f90 descr-text reposition asm-mode gnus-draft rust-mode
arc-mode archive-mode js edmacro pcmpl-unix pcmpl-gnu conf-mode
compare-w gnus-icalendar org-capture org-refile icalendar webjump
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nxml-util nxml-enc xmltok term ehelp nroff-mode cmake-mode rst autoconf
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url-gw url-auth python tramp-sh pcase autoload lisp-mnt gud mule-util
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gnus-cite mail-extr gnus-bcklg gnus-async qp gnus-ml disp-table misearch
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rfn-eshadow isearch easymenu timer select scroll-bar mouse jit-lock
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make-network-process native-compile emacs)

Memory information:
((conses 16 5826176 675973)
 (symbols 48 118086 157)
 (strings 32 663988 63985)
 (string-bytes 1 24860746)
 (vectors 16 247905)
 (vector-slots 8 5951617 919156)
 (floats 8 621 871)
 (intervals 56 1006709 5268)
 (buffers 992 1662))

Message #8 received at 61942 <at> debbugs.gnu.org (full text, mbox):

From: Dmitry Gutov <dmitry <at> gutov.dev>
To: Tom Tromey <tom <at> tromey.com>, 61942 <at> debbugs.gnu.org,
 Juri Linkov <juri <at> linkov.net>
Subject: Re: bug#61942: 28.2; uninterruptible hang in vc-diff buffer
Date: Mon, 17 Jun 2024 04:15:00 +0300

Hi!

Late reply here.

On 03/03/2023 20:13, Tom Tromey wrote:
> From*vc-outgoing*, I used '=' to see a diff.
> 
> The diff in question is pretty large.
> 
> Emacs showed this in the echo area:
> 
> Finding changes in ....
> 
> This was not interruptible -- I tried C-g, C-], and 'kill -USR1'
> 
> I don't know exactly what this is doing, but whatever it is should be
> interruptible.

I've been doing some performance debugging for vc-diff, and the same 
thing has happened once when c-ts-mode was associated with *.c files.

That time I also turned off the cache for diff's revision syntax 
highlighting and repeated a 'vc-diff' for one revision several times.

Profiling this scenario gets me to

        7940  85%             - diff--get-revision-properties
        7940  85%              - let*
        5637  61%               - if
        5637  61%                - condition-case
        5637  61%                 - vc-find-revision-no-save
        5622  60%                  - decode-coding-inserted-region
           3   0%                   - set-auto-coding
           3   0%                    - find-auto-coding
           3   0%                     + set-auto-mode-1
          12   0%                  + set-auto-mode
           3   0%                  + vc-call-backend

and if we're talking about tree-sitter based modes, it might be due to 
memory usage (or not).

Anyway, if you're seeing this regularly

  (setq diff-font-lock-syntax 'hunk-only)

should help as a workaround.

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