Remove asyncio.shield in _drain_helper to fix unhandled future warnings#12293
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joaquinhuigomez wants to merge 3 commits intoaio-libs:masterfrom
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Remove asyncio.shield in _drain_helper to fix unhandled future warnings#12293joaquinhuigomez wants to merge 3 commits intoaio-libs:masterfrom
joaquinhuigomez wants to merge 3 commits intoaio-libs:masterfrom
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…rnings Replace asyncio.shield(waiter) with direct await on waiter in _drain_helper. HTTP/1.1 has a single consumer per drain waiter, so shield is unnecessary and causes "Future exception was never retrieved" warnings on cancellation. Closes aio-libs#12281
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #12293 +/- ##
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- Coverage 99.11% 99.10% -0.01%
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Files 130 130
Lines 45446 45468 +22
Branches 2398 2398
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+ Hits 45044 45063 +19
- Misses 272 275 +3
Partials 130 130
Flags with carried forward coverage won't be shown. Click here to find out more. ☔ View full report in Codecov by Sentry. |
mypy flags the final assertion as unreachable after the suppress(CancelledError) context manager. The code IS reachable at runtime — the suppress catches the CancelledError from the cancelled task, and execution continues normally.
| assert pr._drain_waiter is None | ||
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| async def test_cancelled_drain_no_unhandled_future_warning() -> None: |
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Sorry, but I don't feel this test is validating aiohttp's behaviour. It may or may not match aiohttp's implementation at a given point in time.
As mentioned in the issue, I'd like to see a full functional test which shouldn't be too difficult given the reporter's reproducer and the example test I linked to.
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Replace
asyncio.shield(waiter)with directawait waiterin_drain_helper.HTTP/1.1 has a single consumer per drain waiter, so the shield is unnecessary. When a handler task is cancelled during write backpressure,
asyncio.shieldkeeps the original waiter alive and uncancelled.connection_lostthen callsset_exceptionon it, but nobody is awaiting it anymore, producing noisy "Future exception was never retrieved" warnings.Without the shield, cancellation propagates directly to the waiter.
connection_lostfindswaiter.done() == Trueand skipsset_exception.Includes a regression test that verifies the waiter is properly cancelled (not left with an unhandled exception) when the task is cancelled during backpressure and
connection_lostfires afterward.Closes #12281