gh-87063: Add closed attribute to multiprocessing.Process

[rruuaanng]

• Issue: Expose a way to determine if a process has been closed or not #87063

for example:

import multiprocessing


def f():
    print('hello')
    print('world')

if __name__ == "__main__":
    p = multiprocessing.Process(target=f)
    p.start()
    p.join()

    # In a more context, it's closed
    p.close()
    
    # Currnet context
    # It's thrown a ValueError
    if p.exitcode == 0:
        pass

    # Changed
    if not p.is_closed():
        print(p.exitcode)

[rruuaanng]

It seems that this NEWS error can be ignored.

[picnixz]

More generally, required CI checks must never be ignored except for NEWS missing / issue missing since normal users cannot apply the skip news/issue labels themselves.

[erlend-aasland]

@rruuaanng: I encourage you strongly to read the devguide. This change is a new feature, so it needs a What's New entry. Please take a look at existing What's New entries for inspiration!

[rruuaanng]

I'm not sure if the new changes are satisfactory, but I read what's under Doc/whatnews :). Please review it again!

[erlend-aasland]

No. I will repeat again: please read the devguide. If you don't, you will continue to waste review resources.

New features (and especially any new API, like this is) will need a What's New entry. I linked to the section in the devguide that talks about What's New entries, and I also asked you to look at existing entries for inspiration. Apparently, nothing of this was done.

I'll ask you again: please take a look at how we word NEWS and What's New entries for new APIs, and adapt your PR to follow our conventions. Please listen to advice.

[erlend-aasland]

PR author did not listen to feedback. Requesting changes to make this point clearer.

[bedevere-app]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.