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Failing ensure_future still creates a Task #70739
Description
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GitHub fields:
assignee = None
closed_at = <Date 2022-01-28.22:26:00.502>
created_at = <Date 2016-03-13.11:46:10.277>
labels = ['easy', 'type-bug', '3.9', '3.10', '3.11', 'expert-asyncio']
title = 'Failing ensure_future still creates a Task'
updated_at = <Date 2022-01-29.06:57:25.632>
user = 'https://bugs.python.org/gordon'bugs.python.org fields:
activity = <Date 2022-01-29.06:57:25.632>
actor = 'gvanrossum'
assignee = 'none'
closed = True
closed_date = <Date 2022-01-28.22:26:00.502>
closer = 'gvanrossum'
components = ['asyncio']
creation = <Date 2016-03-13.11:46:10.277>
creator = 'gordon'
dependencies = []
files = []
hgrepos = []
issue_num = 26552
keywords = ['patch', 'easy']
message_count = 7.0
messages = ['261696', '261701', '407294', '412036', '412038', '412039', '412057']
nosy_count = 6.0
nosy_names = ['gvanrossum', 'yselivanov', 'gordon', 'dmzz', 'iritkatriel', 'kumaraditya']
pr_nums = ['30287', '30288', '31003']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue26552'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']
Activity
gordon commentedon Mar 13, 2016
When calling asyncio.ensure_future() on a coroutine, and if the loop is closed, ensure_future() will raise a RuntimeError.
However, it still creates a Task, which will generate a RuntimeWarning that we can’t fix since there is no way to cancel the Task.
Here is the code to reproduce the bug:
try:
# Since the exception raises here, fut is never set
# so we can't call fut.cancel()
fut = asyncio.ensure_future(foo())
except RuntimeError:
pass
# stderr:
# aio.py:12: RuntimeWarning: coroutine 'foo' was never awaited
# pass
gvanrossum commentedon Mar 13, 2016
Sounds like an easy fix. Could you submit a patch?
iritkatriel commentedon Nov 29, 2021
Reproduced on 3.11.
gvanrossum commentedon Jan 28, 2022
So I just realized that the OP's description is slightly misleading. (Their code is spot on though!)
The code does not create an unwaited-for *task*, assuming that "task" refers to the asyncio.Task class.
What is created is a *coroutine* object that's never awaited (as the quoted RuntimeWarning message says: "coroutine 'foo' was never awaited").
So the thing that needs to be closed in the bowels of _ensure_future() is indeed the argument (coro_or_future), in case it is a coroutine object.
gvanrossum commentedon Jan 28, 2022
New changeset 24cc641 by Kumar Aditya in branch 'main':
bpo-26552: Fixed case where failing
asyncio.ensure_futuredid not close the coroutine (bpo-30288)24cc641
gvanrossum commentedon Jan 28, 2022
Thanks Kumar for the fix!
gvanrossum commentedon Jan 29, 2022
New changeset a5451c9 by Kumar Aditya in branch '3.10':
bpo-26552: Fixed case where failing
asyncio.ensure_futuredid not close the coroutine (bpo-30288) (bpo-31003)a5451c9