font-lock latency

[Simon Josefsson <jas@extundo.com>]

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In GNU Emacs 21.2.1 (i386-debian-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2002-03-22 on raven, modified by Debian
configured using `configure  i386-debian-linux-gnu --prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/lib --localstatedir=/var/lib --infodir=/usr/share/info --mandir=/usr/share/man --with-pop=yes --with-x=yes --with-x-toolkit=athena --without-gif'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: nil
  locale-coding-system: nil
  default-enable-multibyte-characters: t

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

This has really started to annoy me, and isn't fixed in CVS, so I'm
reporting it.  I did not investigate the causes so this may be known,
but I didn't find anything in PROBLEMS.  It doesn't happen in Emacs 20
or Emacs 19.

$ emacs -q --no-site-file foo.c
M-x font-lock-mode RET

change the line

#include "foo.h"

into

#include "foo.

and wait a couple of seconds.  Then add the " back.  Font locking in
the buffer is now messed up and the only way to restore it is to wait
a couple of seconds again.

I find myself wasting many seconds each day staring at the screen
waiting for it to redisplay. ;-)

Is there a workaround?  Ideally I think this should not be present at
all by default.  IMHO, highlighting of unterminated strings should be
disabled if this can't be fixed properly.

foo.c looks like:

#include "foo.h"

int
main()
{
  int i;
  for (i=0;i<42;i++)
    puts("foo");
  return i;
}


Recent input:
<down-mouse-5> <mouse-5> <double-down-mouse-5> <double-mouse-5> 
<down-mouse-5> <mouse-5> <down-mouse-1> <mouse-1> <down-mouse-5> 
<mouse-5> <double-down-mouse-5> <double-mouse-5> <triple-down-mouse-5> 
<triple-mouse-5> <triple-down-mouse-5> <triple-mouse-5> 
<down-mouse-1> <mouse-1> M-x f o n t - o c <backspace> 
<backspace> l o c k - m o d e <return> <down-mouse-1> 
<mouse-1> <backspace> SPC f o o " C-_ C-_ M-x r e p 
o r <tab> e <backspace> <return>

Recent messages:
Loading image...done
Loading tooltip...done
For information about the GNU Project and its goals, type C-h C-p.
Loading cc-mode...done
Loading font-lock...
Loading regexp-opt...done
Loading font-lock...done
Font-Lock mode enabled
Undo! [2 times]
Loading emacsbug...done