bug#71289: 30.0.50; cmcheckmagic aborts when tty_write_glyphs writes "Garbage collecting..." in some cases

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 05 Jun 2024 18:06:49 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 71289@debbugs.gnu.org
> 
> > From: Daniel Clemente <n142857@gmail.com>
> > Date: Wed, 5 Jun 2024 13:50:48 +0000
> > Cc: 71289@debbugs.gnu.org
> > 
> > With it (running on 799f78a92c6c31f4d181390523b83d036020ede1 with no
> > other changes), I still see the same types of crash that I already
> > reported: in tty_write_glyphs (see BT1 below) and in
> > build_frame_matrix_from_leaf_window (see BT2 below).
> > However they don't mention GC now.
> 
> So it is not exactly the same type of crash.
> 
> In what scenario does this happen now?  IOW, what did you do to
> trigger those crashes?
> 
> I'd like to ask you to run that scenario with a watchpoint on the
> variable delayed_size_change, and the following two watchpoint
> commands:
> 
>   bt 5
>   continue
> 
> I hope the backtraces produced by this will explain who resets the
> delayed_size_change flag, seemingly prematurely(?), and might suggest
> ideas for a solution.  (I have an idea already, but would like to see
> some data to make sure the idea is solid.)

I decided to go with my idea anyway, so please update from Git before
trying next, and if the problem is still there, try answering my
questions above.

Thanks.