bug#34623: 25.3; infinite un-quittable loop somwhere under redisplay_window()

[Eli Zaretskii]

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> Date: Sat, 23 Feb 2019 11:59:58 -0800
> From: "Greg A. Woods" <woods@robohack.ca>
> 
> Huh, I've been using GNU Emacs exclusively for nearly 30 years, and
> debuggers in general as well as other kinds of Emacs for much longer,
> and I've encountered more than enough Emacs hangs over the years.
> 
> But somehow, as far as I can remember, I never knew about SIGUSR2.
> Probably because I get terribly bored trying to read documents written
> in the manner of the DEBUG document, and never get to the end of them.  :-)
> 
> Last time I read far enough to get to the 'xbacktrace' bit and I already
> knew about the source .gdbinit file, but without python in my gdb I
> didn't expect much.  This time I read to the bottom of the document.
> 
> Perhaps a TL/DR at the very top with the main points in short form would
> help some of us learn something new without having to retry as often.  :-)
> 
> So, I am able to reproduce the hang easily (by repeating the narrowing
> and doing a replace in the narrowed region, with the key bit being that
> it must be done in a Wanderlust draft message buffer, which is heavily
> fontified, though the narrowed region is not), and indeed SIGUSR2 pops
> up a debugger window exactly as hoped:
> 
> Debugger entered--entering a function:
> * put-text-property(2875 2876 fontified nil)
>   jit-lock-fontify-now(2850 3350)
>   jit-lock-function(2850)
>   redisplay_internal\ \(C\ function\)()

Is this still Emacs 25.3?

> And with all the frames expanded I see the reason C-g has no effect:

Not sure I understand that reason.  Can you spell it out for me?

> Debugger entered--entering a function:
> * put-text-property(2875 2876 fontified nil)
>     debugger-may-continue = nil
>     inhibit-redisplay = nil
>     inhibit-debugger = t
>     inhibit-changing-match-data = nil
>   jit-lock-fontify-now(2850 3350)
>     inhibit-point-motion-hooks = t
>     buffer-undo-list = t
>     inhibit-read-only = t
>     inhibit-modification-hooks = t
>   jit-lock-function(2850)
>     [no locals]
>   redisplay_internal\ \(C\ function\)()
>     inhibit-point-motion-hooks = t
>     fontification-functions = nil
>     inhibit-redisplay = t
> 
> 
> Is there anything more I could do to help further?

Can you tell why it is looping, or where in the code is it looping?

Thanks.