On AppVeyor CI, test_multiprocessing_spawn was running for longer than 50 min, whereas usually it only takes around 2 minutes

https://ci.appveyor.com/project/python/cpython/builds/19594644

...
running: test_multiprocessing_spawn (50 min 33 sec)
running: test_multiprocessing_spawn (51 min 3 sec)

Related PR:

https://github.com/python/cpython/pull/9936

Question: why faulthandler didn't kill the test after 15 min? .github/appveyor.yml runs the test suite using --timeout=1200. Extract of logs:
---
PCbuild\rt.bat -q -uall -u-cpu -u-largefile -rwW --slowest --timeout=1200 --fail-env-changed -j0
C:\projects\cpython>"C:\projects\cpython\PCbuild\win32\python.exe"  -u -Wd -E -bb -m test  -uall -u-cpu -u-largefile -rwW --slowest --timeout 1200 --fail-env-changed -j0 
== CPython 3.7.1rc2+ (a4ccd9402d:a4ccd9402d, Oct 17 2018, 23:09:59) [MSC v.1915 32 bit (Intel)]
== Windows-10-10.0.14393-SP0 little-endian
== cwd: C:\projects\cpython\build\test_python_4988
== CPU count: 2
== encodings: locale=cp1252, FS=utf-8
Using random seed 7230291
Run tests in parallel using 4 child processes
0:00:00 [  1/416] test_wait4 skipped
test_wait4 skipped -- object <module 'os' from 'C:\\projects\\cpython\\lib\\os.py'> has no attribute 'fork'
0:00:00 [  2/416] test_augassign passed
(...)
---

See also bpo-34714 and "timeout in test_multiprocessing_spawn x86 Windows7 3.x buildbot" and bpo-34513: "test_multiprocessing_spawn fails on x86 Windows7 3.7 buildbot".

I identified a race condition:

https://bugs.python.org/issue33966
https://github.com/python/cpython/pull/7966

Extract of bpo-34714:

  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\multiprocessing\spawn.py", line 107, in spawn_main
    new_handle = reduction.duplicate(pipe_handle,
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\multiprocessing\reduction.py", line 79, in duplicate
    return _winapi.DuplicateHandle(
PermissionError: [WinError 5] Access is denied

That's why I'm asking if this issue can be related to bpo-33966.

I haven't seen this bug for 2 months, I'm unable to reproduce the bug and I don't know how to fix it. I close the bug as out of date. Reopen it if it comes back.