Some multiprocessing APIs should be possible to import or use even when multiprocessing itself isn't available

Bug report

Bug description:

Android doesn't support multiprocessing because it doesn't support the System V IPC API, and iOS doesn't support subprocesses at all. However, there are a couple of things that should still work on these platforms, but currently don't:

• multiprocessing.dummy.Pool (aka multiprocessing.pool.ThreadPool) currently depends on the multiprocessing synchronization primitives, when it could use the threading equivalents instead.

• multiprocessing.synchronize throws an exception on import if the synchronization primitives are unavailable. But this breaks some packages like joblib, which imports the primitives but doesn't always use them (joblib/joblib#825).

Chaquopy has some monkey patches to work around these issues, but it would be better if they were fixed upstream.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Other

Linked PRs

• gh-148050

Commencez par examiner les points d’entrée multiprocessing.dummy.Pool et multiprocessing.pool.ThreadPool, puis inspectez multiprocessing.synchronize et son échec lors de l’importation sur les plateformes dépourvues de primitives de synchronisation. Comparez le comportement requis avec les équivalents de threading et examinez la PR liée gh-148050 ; le travail est considéré comme terminé lorsque les API prises en charge peuvent être importées ou utilisées sans fonctionnalités multiprocessing indisponibles.