bpo-45416: Fix use of asyncio.Condition() with explicit Lock objects

[achimnol]

Both asyncio.Lock and asyncio.Condition contacts the event loop in a deferred manner,
when they really need to make a future to wait on.

So the loop-match validation should be delegated to asyncio.mixins._LoopBoundMixin._get_loop()
and removed from the constructor of asyncio.Condition.

The above change requires updates on two test cases:

• test_explicit_loop() should not assert on the removed check in the constructor of
  asyncio.Condition, and it should be updated to simply test setting of the explicit lock
  instance. I also changed it to repeat the routines of test_context_manager() to expose
  the symptom reported in bpo-45416 when the change of asyncio.Condition constructor
  is not applied.
• test_ambiguous_loops() must be updated accordingly to trigger actual
  waiting on the lock to happen and _LoopBoundMixin._get_loop() to detect
  the wrong event loop attachment.

https://bugs.python.org/issue45416

[serhiy-storchaka]

I worked on this issue yesterday and I got similar code in general. I did not finish my work because I tried to only use the public API, and it was cumbersome.

[serhiy-storchaka]

The exception is raised in await cond.acquire(). I think it would be better to call it directly.

Suggested change

	async with cond:
	pass
	await cond.acquire()

It is raised because cond.acquire is the same as lock.acquire, and the latter fails because its loop is different.

But it would be nice to test less trivial case: cond.wait() which should raise RuntimeError in different code.

[serhiy-storchaka]

It would be nice to set it using only public API.

[achimnol]

I agree with it, but it says:

TypeError: As of 3.10, the *loop* parameter was removed from Lock() since it is no longer necessary

So I've added an explicit test for the TypeError and resorted back to lock._loop = loop.

[serhiy-storchaka]

I meant using the public API which implicitly sets _loop. But it would be not easy. We can leave it to following PRs.

[miss-islington]

Thanks @achimnol for the PR, and @serhiy-storchaka for merging it 🌮🎉.. I'm working now to backport this PR to: 3.10.
🐍🍒⛏🤖

[bedevere-bot]

GH-28856 is a backport of this pull request to the 3.10 branch.