Very occasionally, Emacs hangs on exit. For example, this happens
sometimes when bootstrapping Emacs (which involves starting emacs.exe
multiple times).

Here is a set of backtraces from attaching gdb to one of the stuck
processes:

Thread 3 (Thread 13168.0x19ec):
#0  0x00007ff80b6f8d61 in ntdll!DbgBreakPoint ()
   from C:\WINDOWS\SYSTEM32\ntdll.dll
#1  0x00007ff80b72536b in ntdll!DbgUiRemoteBreakin ()
   from C:\WINDOWS\SYSTEM32\ntdll.dll
#2  0x00007ff80ac72774 in KERNEL32!BaseThreadInitThunk ()
   from C:\WINDOWS\System32\kernel32.dll
#3  0x00007ff80b6c0d51 in ntdll!RtlUserThreadStart ()
   from C:\WINDOWS\SYSTEM32\ntdll.dll
#4  0x0000000000000000 in ?? ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

Thread 2 (Thread 13168.0x25a8):
#0  0x00007ff80b6f5424 in ntdll!ZwWaitForSingleObject ()
   from C:\WINDOWS\SYSTEM32\ntdll.dll
#1  0x00007ff80b6986ee in ntdll!RtlGetNtProductType ()
   from C:\WINDOWS\SYSTEM32\ntdll.dll
#2  0x00007ff80b6720ce in ntdll!LdrShutdownThread ()
   from C:\WINDOWS\SYSTEM32\ntdll.dll
#3  0x00007ff80b6c9bb9 in ntdll!LdrInitializeThunk ()
   from C:\WINDOWS\SYSTEM32\ntdll.dll
#4  0x00007ff80b6c9b1b in ntdll!LdrInitializeThunk ()
   from C:\WINDOWS\SYSTEM32\ntdll.dll
#5  0x00007ff80b6c9ace in ntdll!LdrInitializeThunk ()
   from C:\WINDOWS\SYSTEM32\ntdll.dll
#6  0x0000000000000000 in ?? ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

Thread 1 (Thread 13168.0x310):
#0  0x00007ff80b6f5424 in ntdll!ZwWaitForSingleObject ()
   from C:\WINDOWS\SYSTEM32\ntdll.dll
#1  0x00007ff80b6986ee in ntdll!RtlGetNtProductType ()
   from C:\WINDOWS\SYSTEM32\ntdll.dll
#2  0x00007ff80b69d26f in ntdll!RtlExitUserProcess ()
   from C:\WINDOWS\SYSTEM32\ntdll.dll
#3  0x00007ff80ac7c0da in KERNEL32!FatalExit ()
   from C:\WINDOWS\System32\kernel32.dll
#4  0x00007ff80adca045 in msvcrt!_exit () from C:\WINDOWS\System32\msvcrt.dll
#5  0x00007ff80adca68d in msvcrt!_initterm_e ()
   from C:\WINDOWS\System32\msvcrt.dll
#6  0x00000004000de21c in Fkill_emacs (arg=...) at emacs.c:2045
#7  0x000000040017a6d6 in funcall_subr (subr=0x400281110 <Skill_emacs>,
    numargs=numargs@entry=1, args=args@entry=0xbfdb20) at eval.c:2841
#8  0x0000000400178cf1 in Ffuncall (nargs=nargs@entry=2,
    args=args@entry=0xbfdb18) at eval.c:2766
#9  0x00000004001c6095 in exec_byte_code (bytestr=..., vector=...,
    maxdepth=..., args_template=..., args_template@entry=...,
    nargs=<optimized out>, nargs@entry=0, args=<optimized out>,
    args@entry=0xbfdf18) at bytecode.c:629
#10 0x0000000400178503 in funcall_lambda (fun=..., fun@entry=...,
    nargs=nargs@entry=0, arg_vector=arg_vector@entry=0xbfdf18) at eval.c:2967
#11 0x0000000400178c20 in Ffuncall (nargs=nargs@entry=1,
    args=args@entry=0xbfdf10) at eval.c:2780
#12 0x00000004001c6095 in exec_byte_code (bytestr=..., vector=...,
    maxdepth=..., args_template=..., args_template@entry=...,
    nargs=<optimized out>, nargs@entry=1, args=<optimized out>,
    args@entry=0xbfe690) at bytecode.c:629
#13 0x0000000400178503 in funcall_lambda (fun=..., fun@entry=...,
    nargs=nargs@entry=1, arg_vector=arg_vector@entry=0xbfe690) at eval.c:2967
#14 0x0000000400178c20 in Ffuncall (nargs=nargs@entry=2,
    args=args@entry=0xbfe688) at eval.c:2780
#15 0x00000004001c6095 in exec_byte_code (bytestr=..., vector=...,
    maxdepth=..., args_template=..., args_template@entry=...,
    nargs=<optimized out>, nargs@entry=0, args=<optimized out>,
    args@entry=0xbff0b8) at bytecode.c:629
#16 0x0000000400178503 in funcall_lambda (fun=..., fun@entry=...,
    nargs=nargs@entry=0, arg_vector=arg_vector@entry=0xbff0b8) at eval.c:2967
#17 0x0000000400178c20 in Ffuncall (nargs=nargs@entry=1,
    args=args@entry=0xbff0b0) at eval.c:2780
#18 0x00000004001c6095 in exec_byte_code (bytestr=..., vector=...,
    maxdepth=..., args_template=..., args_template@entry=...,
    nargs=<optimized out>, nargs@entry=0, args=<optimized out>,
    args@entry=0xbff4c0) at bytecode.c:629
#19 0x0000000400178503 in funcall_lambda (fun=..., fun@entry=...,
    nargs=nargs@entry=0, arg_vector=arg_vector@entry=0xbff4c0) at eval.c:2967
#20 0x000000040017b7dc in apply_lambda (fun=fun@entry=..., args=..., count=4,
    count@entry=3) at eval.c:2903
#21 0x0000000400177aa3 in eval_sub (form=form@entry=...) at eval.c:2306
#22 0x000000040017bc9f in Feval (form=..., lexical=...) at eval.c:2051
#23 0x00000004001768d6 in internal_condition_case (
    bfun=0x4005c0000 <tzbuf_format+752>,
    bfun@entry=0x4000de980 <top_level_2>, handlers=..., handlers@entry=...,
    hfun=0xf490, hfun@entry=0x4000e1600 <cmd_error>) at eval.c:1332
#24 0x00000004000de93d in top_level_1 (ignore=...) at keyboard.c:1131
#25 0x000000040017676a in internal_catch (tag=..., tag@entry=..., func=0x0,
    func@entry=0x4000de8e0 <top_level_1>, arg=..., arg@entry=...)
    at eval.c:1097
#26 0x00000004000de845 in command_loop () at keyboard.c:1092
#27 0x0000000000000000 in ?? ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)



In GNU Emacs 26.0.50 (build 1, x86_64-w64-mingw32)
 of 2017-09-14 built on MACHINE
Repository revision: 0d5f0a8d56bb7e15607c77a7d5d6e36776eff94d
Windowing system distributor 'Microsoft Corp.', version 10.0.15063
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
mwheel-scroll: Beginning of buffer

Configured using:
 'configure --with-modules --without-pop 'CFLAGS=-O3 -ggdb3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS MODULES LCMS2

Important settings:
  value of $EMACSLOADPATH: c:\emacs-lisp;
  value of $LANG: ENG
  locale-coding-system: cp1252

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message subr-x puny seq byte-opt gv
bytecomp byte-compile cconv cl-loaddefs cl-lib dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils elec-pair time-date
mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel dos-w32 ls-lisp disp-table term/w32-win w32-win
w32-vars term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow isearch timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese composite charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote w32notify w32 lcms2 multi-tty make-network-process emacs)

Memory information:
((conses 16 97046 10925)
 (symbols 56 20144 1)
 (miscs 48 39 87)
 (strings 32 29581 1047)
 (string-bytes 1 746755)
 (vectors 16 13998)
 (vector-slots 8 482061 7969)
 (floats 8 50 79)
 (intervals 56 232 0)
 (buffers 992 11))