bug#20927: 24.5; Cygwin Emacs completely blocks for 5+ seconds

[Sebastien Vauban]

Hello,

When:

1. Starting Cygwin Emacs,
2. Opening whichever local file (`org-mode/lisp/org.el', in my case),
   and
3. Keeping constantly our index on the Down arrow key to make the buffer
   scroll indefinitely,

Emacs blocks (after 30 seconds scroll or so) for 5 entire seconds, and
then revives...

I've tracked down this problem in Cygwin Emacs, and it's due to this
line:

--8<---------------cut here---------------start------------->8---
  (global-auto-revert-mode 1)           ; Auto refresh buffers.
--8<---------------cut here---------------end--------------->8---

When it's commented, Cygwin Emacs behaves normally.

Note the above line does NOT cause any trouble in Windows Emacs...

PS- The above recipe is an easy way to reproduce the blocking
    problem. But that problem occurs everywhere (in Gnus, etc.) at any
    time: Emacs becomes unresponsive for a much too long time (from an
    interactive point of view).

In GNU Emacs 24.5.1 (x86_64-unknown-cygwin)
 of 2015-04-10 on desktop-new
Windowing system distributor `Microsoft Corp.', version 6.3.9600
Configured using:
 `configure 
--srcdir=/home/kbrown/src/cygemacs/emacs-24.5-1.x86_64/src/emacs-24.5 
--prefix=/usr --exec-prefix=/usr --localstatedir=/var --sysconfdir=/etc 
--docdir=/usr/share/doc/emacs --htmldir=/usr/share/doc/emacs/html -C --with-w32
 'CFLAGS=-ggdb -O2 -pipe -Wimplicit-function-declaration 
-fdebug-prefix-map=/home/kbrown/src/cygemacs/emacs-24.5-1.x86_64/build=/usr/src/debug/emacs-24.5-1
 
-fdebug-prefix-map=/home/kbrown/src/cygemacs/emacs-24.5-1.x86_64/src/emacs-24.5=/usr/src/debug/emacs-24.5-1'
 CPPFLAGS= LDFLAGS='