bug#12196: 24.1.50; setting cache-long-line-scans to non-nil freezes Emacs

[Eli Zaretskii <eliz@gnu.org>]

> From: Michael Heerdegen <michael_heerdegen@web.de>
> Cc: 12196@debbugs.gnu.org
> Date: Fri, 24 Aug 2012 14:19:34 +0200
> 
> Thanks, Eli.  However, I still see the freezing.  I have 
> 
>    GNU Emacs 24.2.50.1 (i486-pc-linux-gnu, GTK+ Version 3.4.2)
>    of 2012-08-23 on dex, modified by Debian
> 
> now, so your fix should be included.

Do you see a reference to bug#12196 in src/ChangeLog of that
distribution?  If not, then my fix is not included.

> In emacs -Q, I did C-x d ~ RET and set `cache-long-line-scans' to t.
> Then I moved around in that buffer with the arrow keys and prior/ next.
> After a few seconds, Emacs was frozen.
> 
> In another test, I started emacs -Q and evaluated
> 
>   (setq-default cache-long-line-scans t)
> 
> Then I did some trivial things like changing current buffer and moving
> around.  In some cases, CPU consumption went to 100% while I did
> nothing, and Emacs didn't respond anymore.  Another time, Emacs aborted.

I cannot reproduce any of this on my system.  Emacs never freezes on
me.

Does Emacs really freeze, or does it just do some prolonged operation?
(And is your CPU really an i486?)  If you wait for a long time, does
Emacs eventually recover and become responsive again?

If Emacs really freezes, attach a debugger to it when it does, type
"bt" at the debugger's prompt, and post here everything the debugger
displays in response.  Then try to follow the advice in etc/DEBUG,
under "If the symptom of the bug is that Emacs fails to respond", to
establish which Emacs function, if any, is looping.