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

[Daniel Clemente <n142857@gmail.com>]

> > I also saw a new type of TTY+GC error (not sure if it's the same issue
> > as this bug):
> >
> > alloc.c:7517: Emacs fatal error: assertion failed: t->name != NULL
> >
> > Breakpoint 1, terminate_due_to_signal (sig=6,
> > backtrace_limit=2147483647) at emacs.c:443
> > 443      signal (sig, SIG_DFL);
> > (gdb) bt
> > #0  terminate_due_to_signal (sig=6, backtrace_limit=2147483647) at emacs.c:443
> > #1  0x000055555573591a in die (msg=0x55555586f838 "t->name != NULL",
> > file=0x55555586e97e "alloc.c", line=7517) at alloc.c:8082
> > #2  0x00005555557346e8 in mark_terminals () at alloc.c:7517
>
> If this was while you only resized the terminal, how come a terminal
> was deleted?  Any idea what would cause this?

I assume that it's t->name == NULL what tells you that a terminal was deleted.
But apparently this terminal wasn't fully deleted, because it's in the
terminal_list.  If delete_terminal had run, shouldn't it have removed
it from the list?
So I don't know what happened. reference_count is still 1.

I might have actually tried to close an X window while I testing; I
can't remember. I'm collecting many backtraces and I wasn't very
careful in this one.
This backtrace may be a different bug; if you want I file it
separately. But since it happened during GC, it could also be due to
the same problems as this one (71289).
I don't know how to reproduce it.
Unless it clearly shows a defect, we can ignore this backtrace until
it happens again.