On Windows, the multiprocessing DupHandle.detach() method has race condition on DuplicateHandle(DUPLICATE_CLOSE_SOURCE).

Error on duplicate():

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  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

Example: bpo-34714


Error on detach():

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\multiprocessing\spawn.py", line 117, in spawn_main
    exitcode = _main(fd)
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\multiprocessing\spawn.py", line 127, in _main
    self = reduction.pickle.load(from_parent)
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\multiprocessing\connection.py", line 951, in rebuild_pipe_connection
    handle = dh.detach()
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\multiprocessing\reduction.py", line 133, in detach
    self._access, False, _winapi.DUPLICATE_CLOSE_SOURCE)
PermissionError: [WinError 5] Access is denied

Example: bpo-34513