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Fix an outdated test in asyncio #24477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Fix an outdated test in asyncio #24477

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77ac8e7
Fix an outdated test in asyncio
fantix Feb 7, 2021
c793590
Merge branch 'main' into fix-outdated-test
kumaraditya303 Dec 8, 2022
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11 changes: 3 additions & 8 deletions Lib/test/test_asyncio/test_base_events.py
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Original file line number Diff line number Diff line change
Expand Up @@ -856,20 +856,15 @@ async def raise_keyboard_interrupt():

self.loop._process_events = mock.Mock()

try:
with self.assertRaises(KeyboardInterrupt):
self.loop.run_until_complete(raise_keyboard_interrupt())
except KeyboardInterrupt:
pass

def func():
self.loop.stop()
func.called = True
func.called = False
try:
self.loop.call_soon(func)
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.

self.loop.run_forever()
self.assertTrue(func.called)

def test_single_selecter_event_callback_after_stopping(self):
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