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Fix an outdated test in asyncio #24477

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merged 2 commits into from Dec 8, 2022
Merged

Fix an outdated test in asyncio #24477

merged 2 commits into from Dec 8, 2022

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fantix
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@fantix fantix commented Feb 7, 2021 •
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The test was added in f3e2e09 before _StopError was removed in 41f69f4, after which this test will not fail without the fix it covers. This PR fixes the test to resume its coverage.

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Refs: MagicStack/uvloop#337

@fantix
Fix an outdated test in asyncio
77ac8e7 
The test was added in f3e2e09 before `_StopError` was removed in
41f69f4, after which this test will not fail without the fix it covers.
This PR fixes the test to resume its coverage.
@bedevere-bot bedevere-bot added tests Tests in the Lib/test dir awaiting review labels Feb 7, 2021
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This PR is stale because it has been open for 30 days with no activity.

@github-actions github-actions bot added the stale Stale PR or inactive for long period of time. label Mar 10, 2021
MaxwellDupre
MaxwellDupre approved these changes Apr 2, 2022
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Ran 2287 tests in 83.131s
OK (skipped=18) All windows tests
Also hit base_events.
Looks good.

@github-actions github-actions bot removed the stale Stale PR or inactive for long period of time. label Aug 4, 2022
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netlify bot commented Dec 8, 2022 •
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@kumaraditya303 kumaraditya303 merged commit e8fff51 into python:main Dec 8, 2022
gvanrossum
gvanrossum reviewed Dec 8, 2022
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Lib/test/test_asyncio/test_base_events.py
self.loop.run_forever()
except KeyboardInterrupt:
pass
self.loop.call_later(0.01, func)
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A bit unfortunate that we had to add a 10 msec delay here -- in most cases that will waste 10 msec and occasionally it will not wait long enough and the test will flake-fail. Why won't call_soon work?

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Background: this test covers a bug that base exceptions like KeyboardInterrupt will cause the loop to be closed twice, leading to an early exit in the next loop run.

This test was added before _StopError was dropped, at that time the loop will stop as soon as _StopError is raised, even if the _ready queue still has a handle (which is the next run - the func() here), therefore this was a good test. But now the loop will exhaust the _ready queue before stopping, so this test couldn't cover the bug anymore without this PR. That's also why we cannot simply add func() into the _ready queue by call_soon().

You're right about the flakyness of using call_later() tho. Now I think a better fix would be to use chained call_soon() to skip the first iteration where the buggy stop occured:

Suggested change
self.loop.call_later(0.01, func)
# If the issue persists, the loop will exit early after the first iteration,
# in that case our func() in the second iteration won't be called.
self.loop.call_soon(self.loop.call_soon, func)

I verified and this error fails if the fix in f3e2e09 is reverted.

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Clever solution, go ahead and make it a PR, assign to me or @kumaraditya303 for review.

@fantix fantix mentioned this pull request Dec 9, 2022
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@MaxwellDupre MaxwellDupre MaxwellDupre approved these changes

@1st1 1st1 Awaiting requested review from 1st1 1st1 is a code owner

@asvetlov asvetlov Awaiting requested review from asvetlov asvetlov is a code owner

@kumaraditya303 kumaraditya303 Awaiting requested review from kumaraditya303 kumaraditya303 is a code owner

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