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Switch to ThreadedChildWatcher and test #5877

Merged
merged 9 commits into from
Jul 28, 2021
Merged

Switch to ThreadedChildWatcher and test #5877

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dc361c4
Switch to ThreadedChildWatcher and test
Jul 14, 2021
95b0e5d
Add to changes
Jul 14, 2021
6b2d5af
Fix mypy
Jul 14, 2021
3072ae0
Tear down test loop in thread
Jul 14, 2021
8af64ab
Fix mypy
Jul 14, 2021
3b51df0
Fix changelog
Jul 27, 2021
0d624ca
Create subprocess in test loop
Jul 27, 2021
b56b139
Fail test on python 3.7
Jul 27, 2021
b99f35c
Update tests/test_loop.py
sweatybridge Jul 28, 2021
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1 change: 1 addition & 0 deletions CHANGES/5877.bugfix
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@@ -0,0 +1 @@
Uses `ThreadedChildWatcher` under POSIX to allow setting up test loop in non-main thread.
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2 changes: 1 addition & 1 deletion aiohttp/test_utils.py
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Expand Up @@ -497,7 +497,7 @@ def setup_test_loop(
# * https://stackoverflow.com/a/58614689/595220
# * https://bugs.python.org/issue35621
# * https://github.com/python/cpython/pull/14344
watcher = asyncio.MultiLoopChildWatcher()
watcher = asyncio.ThreadedChildWatcher()
except AttributeError: # Python < 3.8
watcher = asyncio.SafeChildWatcher()
watcher.attach_loop(loop)
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13 changes: 12 additions & 1 deletion tests/test_loop.py
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Expand Up @@ -6,7 +6,7 @@
import pytest

from aiohttp import web
from aiohttp.test_utils import AioHTTPTestCase
from aiohttp.test_utils import AioHTTPTestCase, loop_context


@pytest.mark.skipif(
Expand Down Expand Up @@ -43,3 +43,14 @@ def test_default_loop(self) -> None:

def test_default_loop(loop: Any) -> None:
assert asyncio.get_event_loop() is loop


def test_setup_loop_non_main_thread() -> None:
def target() -> None:
with loop_context():
pass
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Could we run something in this loop and maybe process some signal? This is what may go wrong potentially.

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Setting up the loop context in python 3.7 still uses SafeChildWatcher, which in turn registers signals. I've updated the test to expect failure on python 3.7 and success in 3.8+. This way we have both code paths covered.

Subsequently after merging pytest-xdist, we might see occasional failures on python 3.7 tests in CI for the same reason. This could happen with any tests that use the asyncio event loop, not specific to this test alone. This will be ok once we deprecate 3.7.

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I'd rather vendor a backport and use it under Python 3.7. Also, it's not yet time to drop it anyway. aiohttp 3.8 still supports Python 3.6 even. It'll be EOL in 5 months but for CPython 3.7 there are 2 years to go.
Being a framework/library forces us to support a wider range of versions, unlike projects that are just apps bound to a single env.

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Yup, agree that backporting is better.

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here's the backport with manually resolved merge conflicts #5919


# Ensures setup_test_loop can be called by pytest-xdist in non-main thread.
t = threading.Thread(target=target)
t.start()
t.join()