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bpo-37658: Actually return result in race condition #29202

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Merged
asvetlov merged 6 commits into from
Nov 29, 2021
Merged

bpo-37658: Actually return result in race condition #29202

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019ed9d
Actually fix issue37658
Dreamsorcerer Oct 24, 2021
ffe5106
Correct test
Dreamsorcerer Oct 24, 2021
722fe3a
Update test_tasks.py
Dreamsorcerer Oct 24, 2021
54d0118
Remove redundant else condition.
Dreamsorcerer Oct 24, 2021
169294e
Avoid timing issues with test.
Dreamsorcerer Oct 25, 2021
5cfc8b7
Create 2021-11-28-15-30-34.bpo-37658.8Hno7d.rst
Dreamsorcerer Nov 28, 2021
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4 changes: 2 additions & 2 deletions Lib/asyncio/tasks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -415,7 +415,7 @@ async def wait_for(fut, timeout):

await _cancel_and_wait(fut, loop=loop)
try:
fut.result()
return fut.result()
except exceptions.CancelledError as exc:
raise exceptions.TimeoutError() from exc
else:
Expand Down Expand Up @@ -455,7 +455,7 @@ async def wait_for(fut, timeout):
# exception, we should re-raise it
# See https://bugs.python.org/issue40607
try:
fut.result()
return fut.result()
except exceptions.CancelledError as exc:
raise exceptions.TimeoutError() from exc
else:
Expand Down
37 changes: 7 additions & 30 deletions Lib/test/test_asyncio/test_tasks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1009,20 +1009,15 @@ def gen():
self.assertEqual(res, "ok")

def test_wait_for_cancellation_race_condition(self):
def gen():
yield 0.1
yield 0.1
yield 0.1
yield 0.1
async def inner():
await asyncio.wait_for(asyncio.sleep(1), timeout=2)
return 1

loop = self.new_test_loop(gen)
async def main():
result = await asyncio.wait_for(inner(), timeout=1)
assert result == 1

fut = self.new_future(loop)
loop.call_later(0.1, fut.set_result, "ok")
task = loop.create_task(asyncio.wait_for(fut, timeout=1))
loop.call_later(0.1, task.cancel)
res = loop.run_until_complete(task)
self.assertEqual(res, "ok")
asyncio.run(main())

def test_wait_for_waits_for_task_cancellation(self):
loop = asyncio.new_event_loop()
Expand Down Expand Up @@ -1101,24 +1096,6 @@ async def inner():
with self.assertRaises(FooException):
loop.run_until_complete(foo())

def test_wait_for_raises_timeout_error_if_returned_during_cancellation(self):
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@Dreamsorcerer Dreamsorcerer Oct 24, 2021

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This test literally tests that we don't return a value when it has completed successfully...

I can't see any reason for this test, the issue linked to the PR does not mention anything that warrants this test existing: https://bugs.python.org/issue40607

So, as far as I can tell, this test should be binned and the behaviour should be as defined in the above changes.

loop = asyncio.new_event_loop()
self.addCleanup(loop.close)

async def foo():
async def inner():
try:
await asyncio.sleep(0.2)
except asyncio.CancelledError:
return 42

inner_task = self.new_task(loop, inner())

await asyncio.wait_for(inner_task, timeout=_EPSILON)

with self.assertRaises(asyncio.TimeoutError):
loop.run_until_complete(foo())

def test_wait_for_self_cancellation(self):
loop = asyncio.new_event_loop()
self.addCleanup(loop.close)
Expand Down