[issue40221] Use new _at_fork_reinit() lock method in multiprocessing

[Dong-hee Na]

Change by Dong-hee Na <donghee.na92 at gmail.com>:


----------
pull_requests: +18864
pull_request: https://github.com/python/cpython/pull/19511

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40221>
_______________________________________