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[3.11] GH-95899: fix asyncio.Runner to call set_event_loop only once (GH-95900) #96003

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Merged
gvanrossum merged 1 commit into from
Aug 15, 2022
Merged

[3.11] GH-95899: fix asyncio.Runner to call set_event_loop only once (GH-95900) #96003

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GH-95899: fix asyncio.Runner to call set_event_loop only once (GH-95900) 
(cherry picked from commit 914f636)

Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>
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@kumaraditya303 @miss-islington
kumaraditya303 authored and miss-islington committed Aug 15, 2022
commit d500d1a66d321c821f5234fe4f47fdfef578cca8
8 changes: 5 additions & 3 deletions Lib/asyncio/runners.py
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Original file line number Diff line number Diff line change
Expand Up @@ -115,8 +115,6 @@ def run(self, coro, *, context=None):

self._interrupt_count = 0
try:
if self._set_event_loop:
events.set_event_loop(self._loop)
return self._loop.run_until_complete(task)
except exceptions.CancelledError:
if self._interrupt_count > 0:
Expand All @@ -137,7 +135,11 @@ def _lazy_init(self):
return
if self._loop_factory is None:
self._loop = events.new_event_loop()
self._set_event_loop = True
if not self._set_event_loop:
# Call set_event_loop only once to avoid calling
# attach_loop multiple times on child watchers
events.set_event_loop(self._loop)
self._set_event_loop = True
else:
self._loop = self._loop_factory()
if self._debug is not None:
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14 changes: 14 additions & 0 deletions Lib/test/test_asyncio/test_runners.py
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Expand Up @@ -456,6 +456,20 @@ async def coro():
):
runner.run(coro())

def test_set_event_loop_called_once(self):
# See https://github.com/python/cpython/issues/95736
async def coro():
pass

policy = asyncio.get_event_loop_policy()
policy.set_event_loop = mock.Mock()
runner = asyncio.Runner()
runner.run(coro())
runner.run(coro())

self.assertEqual(1, policy.set_event_loop.call_count)
runner.close()


if __name__ == '__main__':
unittest.main()
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2022-08-11-18-52-17.gh-issue-95899._Bi4uG.rst
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@@ -0,0 +1 @@
Fix :class:`asyncio.Runner` to call :func:`asyncio.set_event_loop` only once to avoid calling :meth:`~asyncio.AbstractChildWatcher.attach_loop` multiple times on child watchers. Patch by Kumar Aditya.