[3.5] bpo-24484: Avoid race condition in multiprocessing cleanup (GH-2159) by pitrou · Pull Request #2167

[3.5] bpo-24484: Avoid race condition in multiprocessing cleanup (GH-2159) by pitrou · Pull Request #2167 · python/cpython

…honGH-2159)

* bpo-24484: Avoid race condition in multiprocessing cleanup

The finalizer registry can be mutated while inspected by multiprocessing
at process exit.

* Use test.support.start_threads()

* Add Misc/NEWS.
(cherry picked from commit 1eb6c00)