Allow overriding future-task compliance check in asyncio

[asvetlov]

BPO	47167
Nosy	@asvetlov, @1st1
PRs	bpo-47167: Allow overriding a future compliance check in asyncio.Task #32197

^{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 2022-03-30.15:34:50.023>
labels = ['3.11', 'expert-asyncio']
title = 'Allow overriding future-task compliance check in  asyncio'
updated_at = <Date 2022-04-01.02:14:55.054>
user = 'https://github.com/asvetlov'

bugs.python.org fields:

activity = <Date 2022-04-01.02:14:55.054>
actor = 'yselivanov'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['asyncio']
creation = <Date 2022-03-30.15:34:50.023>
creator = 'asvetlov'
dependencies = []
files = []
hgrepos = []
issue_num = 47167
keywords = ['patch']
message_count = 3.0
messages = ['416374', '416467', '416468']
nosy_count = 2.0
nosy_names = ['asvetlov', 'yselivanov']
pr_nums = ['32197']
priority = 'normal'
resolution = None
stage = 'resolved'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue47167'
versions = ['Python 3.11']

[asvetlov]

Now asyncio.Task has a strict hardcoded check for futures processes on task's step.
Sometimes third-party library [1] wants to replace it with custom logic.
Currently it is impossible without implementing the full asyncio.Task replacement from scratch.
asyncio.Task is a non-trivial highly optimized part of async, keeping a third-party version in sync with the reference implementation takes more time and effort than it should be.

This issue proposes adding Task._check_future(future) method that could be overridden in subclasses. The default C implementation uses a fast path that has no performance penalty.

1. https://github.com/aio-libs/aioloop-proxy implements nested loop proxies that are very useful for writing tests. A proxy can work in parallel with ancestors but checks all own acquired resources cleanup on
   the proxy closing.

[asvetlov]

New changeset d4bb38f by Andrew Svetlov in branch 'main':
bpo-47167: Allow overriding a future compliance check in asyncio.Task (GH-32197)
d4bb38f

[1st1]

Sorry, I don't like the committed change and I think it should be reverted.

Futures and Tasks have a documented get_loop() method which simply should be called by Task machinery, without the need to expose (and document) private methods.

[graingert]

This patch isn't needed to support the aioloop-proxy use case, you can use an interceptor coroutine to pass the check instead:

aio-libs/aioloop-proxy@a655652

this way aioloop proxy works with asyncio.Task CTask PyTask and in addition custom set_task_factory Tasks