Expose a way to determine if a process has been closed or not

[petervansickel]

BPO	42897
Nosy	@petervansickel

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-01-11.19:55:45.985>
labels = ['type-feature', '3.10']
title = 'Expose a way to determine if a process has been closed or not'
updated_at = <Date 2021-01-11.19:55:45.985>
user = 'https://github.com/petervansickel'

bugs.python.org fields:

activity = <Date 2021-01-11.19:55:45.985>
actor = 'petervansickel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2021-01-11.19:55:45.985>
creator = 'petervansickel'
dependencies = []
files = []
hgrepos = []
issue_num = 42897
keywords = []
message_count = 1.0
messages = ['384860']
nosy_count = 1.0
nosy_names = ['petervansickel']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue42897'
versions = ['Python 3.10']

Linked PRs

• gh-87063: Add closed attribute to multiprocessing.Process #125838

[petervansickel]

I have been using the multiprocessing Process class a good bit lately. I have a class that is managing the a given list of processes from launch to completion.
Recently I started using Process close(). I found myself wanting to determine if a given process instance was closed or not before I did anything like check its exitcode or invoke any of the other methods that raise a ValueError if done so on a closed process.
As far as I can tell there is no exposed way to check if the process is closed. The Process class has a _closed instance variable and a _check_closed() method, but those are not intended for direct use.
I created a simple wrapper class that has its own closed instance variable and wraps the close() method of Process so that the closed instance variable can be set to True when close() is called and then call super().close() to allow the normal close operation to complete.
It would be convenient if the Process class itself supported an is_closed() method or exposed a Boolean closed attribute to easily determine if a process instance has been closed.

[erlend-aasland]

FTR, close was added by @pitrou in #74781 (PR #2010). There was no discussion regarding a closed attribute at that time.

[erlend-aasland]

I'm not sure convenience is a good enough reason to add this API; the workaround in the OP is straight-forward.