bug#18894: 24.4.51; Erratic freezing on Cygwin

[aidalgol]

On Thu, 30 Oct 2014 05:41:49 +0200, Eli Zaretskii wrote:
> > Date: Thu, 30 Oct 2014 11:27:36 +1300
> > From: aidalgol@amuri.net
> >
> > Emacs freezes occasionally in such a way that sending it a 
> > DebugBreak
> > (see <https://cygwin.com/ml/cygwin/2006-06/msg00321.html>) has no
> > effect, and I have to kill it from the Task Manager (so I can not 
> > get a
> > backtrace).  When Emacs is in this state, it does not redraw its 
> > frames
> > when brought in focus.
>
> Does it consume any CPU?

Not when I last checked, but I did not check last time it occurred, so 
I will check next time.

> Can you attach GDB to Emacs when it is in such a state?  If not, can
> you observe any activity of its threads via Process Explorer?

I have been always running Emacs under GDB, so yes.  I forgot to attach 
the GDB output in my original report; it is at the end of this 
paragraph.  When Emacs freezes, nothing is printed in the terminal 
(either by GDB or Emacs).  I also forgot to mention the version of Emacs 
I am using: from git branch emacs-24, commit 1500355.

GNU gdb (GDB) 7.8
This GDB was configured as "x86_64-pc-cygwin".
Reading symbols from ./emacs.exe...done.
SIGINT is used by the debugger.
Are you sure you want to change it? (y or n) [answered Y; input not 
from terminal]
Environment variable "DISPLAY" not defined.
TERM = xterm
Breakpoint 1 at 0x1005215c1: file emacs.c, line 351.
Temporary breakpoint 2 at 0x10054dd3c: file sysdep.c, line 854.
(gdb) run
Starting program: /home/agauland/src/emacs/src/emacs.exe
[New Thread 6204.0xeb0]
[New Thread 6204.0xc84]
[New Thread 6204.0x1588]
[New Thread 6204.0x13c0]
[New Thread 6204.0x2e8]
[New Thread 6204.0x140c]
[New Thread 6204.0x1450]
[New Thread 6204.0xd64]
[New Thread 6204.0x18b8]
[New Thread 6204.0x12e0]
[New Thread 6204.0x16f0]
[New Thread 6204.0x15a4]
[New Thread 6204.0x13c4]
[Thread 6204.0x15a4 exited with code 0]
[Thread 6204.0x13c0 exited with code 0]
[New Thread 6204.0x1bc]
[New Thread 6204.0x428]
[Thread 6204.0x140c exited with code 0]
[New Thread 6204.0x860]
[New Thread 6204.0x16a0]