bug#10664: 24.0.93; JIT font-lock infloops in a C file

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 6 Feb 2012 11:09:57 +0000
> Cc: 10664@debbugs.gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> I got something similar for this socket.c.  I load it into emacs -Q, then
> start scrolling downwards, a page at a time.  The first five scrolls are
> fine.  Then it hangs on the sixth.
> 
> However, typing C-g (maybe twice) frees it up, and it does the scroll.
> Careful perusal reveals that the fontification is incomplete.  From now
> on, most key sequences must be followed by C-g to perform their commands.
> ;-(.
> 
> Did you actually try C-g when your session hung?

I'm quite sure I did.  But that was on Windows, where C-g is less
powerful than on Posix platforms (since keyboard input is not
interrupt driven).  So it could be that what you can interrupt on
GNU/Linux, I cannot on Windows.

> I was able to run elp on this, and I've a fairly good idea where it's got
> stuck, but not yet why.

Let me know if you need any further help.

> > > I still have that session in a debugger, so if someone wants me to
> > > look around and show some values, I can do that.
> 
> I'm not sure I'd be able to make much out of debugger results.  I'm not
> familiar enough with the internals of Emacs.  :-(

That's good, because I needed to kill that session in order to rebuild
Emacs.

> Can you restart this Emacs session?

No, but I can start another and do the same (i.e. wait for it to hang
in the same way).  The problem is reproducible in my configuration.
But I think it would be better to wait for you to fix that problem you
are zeroing in, and then see if it also fixes my hangs.

Thanks.