bug#35204: 27.0.50; Crash on Cygwin

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 11 Apr 2019 11:31:11 +0900
> From: Katsumi Yamaoka <yamaoka@jpl.org>
> Cc: 35204@debbugs.gnu.org
> 
> >> configure --verbose --with-x-toolkit=gtk3
> 
> >> (I detached "CFLAGS=-O0")
> 
> > Does it mean you used "CFLAGS=-O0", or does it mean you did NOT use
> > it?  It is better to use it, together with -g3, as that makes
> > debugging easier.
> 
> At that time I didn't use CFLAGS=-O0 so as to exclude anything
> special, though I'm not sure it is worthwhile.  Today I tried
> building two types; one uses CFLAGS=-O0 and the other doesn't.
> The difference between them is that with the one built *with*
> CFLAGS=-O0 the gdb command `source .gdbinit' ends up with this
> error:
> 
> (gdb) source .gdbinit
> SIGINT is used by the debugger.
> Are you sure you want to change it? (y or n) [answered Y; input not from terminal]
> DISPLAY = :0.0
> TERM = xterm
> Breakpoint 1 at 0x10054a66a
> .gdbinit:1228: Error in sourced command file:
> No symbol "defined_HAVE_X_WINDOWS" in current context.

This is why I suggested to use CFLAGS='-O0 -g3', please try that next.

> > Is it normal to have so many threads?  What are they doing?
> 
> It's a result of I did many things to break Emacs since it can't
> seem to die soon.  But I got a good means to break Emacs at once,
> that is to eval: (x-display-monitor-attributes-list)

So please use this method from now on, to trigger the crash.  It is
important to have consistency in this.

> >> I don't konw what is the Lisp thread, sorry.
> 
> > That's usually the thread you get when you type "thread 1" at GDB
> > prompt.  But let's see what all those threads do, so please type this:
> 
> >   (gdb) thread apply all bt
> 
> > and post the results here.
> 
> Thanks.  Attached the one fetched with Emacs built without
> CFLAGS=-O0 (it has no notably difference from the one fetched
> with Emacs built with CFLAGS=-O0).  Note that gdb crashes when
> the `thread apply all bt' command is invoked.

This is still not the information we need.  Since "thread apply all"
crashes, please try this alternative:

  (gdb) thread 1
  (gdb) bt

And please separately do also this:

  (gdb) info threads

and post the results.

Thanks.

P.S. I see you are using Cygwin 3.0.6, could it be a bug in Cygwin
itself?  Is there a newer version of Cygwin?