Closing async generator while it is running does not raise an exception #76707

achimnol · 2018-01-10T09:31:54Z

BPO	32526
Nosy	@njsmith, @asvetlov, @1st1, @achimnol
PRs	bpo-32526: Closing async generator while it is running does not raise an exception #5182

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-10-22.22:24:16.987>
created_at = <Date 2018-01-10.09:31:53.662>
labels = ['type-bug', '3.7', 'expert-asyncio']
title = 'Closing async generator while it is running does not raise an exception'
updated_at = <Date 2019-10-22.22:24:16.986>
user = 'https://github.com/achimnol'

bugs.python.org fields:

activity = <Date 2019-10-22.22:24:16.986>
actor = 'yselivanov'
assignee = 'none'
closed = True
closed_date = <Date 2019-10-22.22:24:16.987>
closer = 'yselivanov'
components = ['asyncio']
creation = <Date 2018-01-10.09:31:53.662>
creator = 'achimnol'
dependencies = []
files = []
hgrepos = []
issue_num = 32526
keywords = ['patch']
message_count = 3.0
messages = ['309760', '309783', '355162']
nosy_count = 4.0
nosy_names = ['njs', 'asvetlov', 'yselivanov', 'achimnol']
pr_nums = ['5182']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue32526'
versions = ['Python 3.6', 'Python 3.7']

achimnol · 2018-01-10T09:39:22Z

Here is the minimal example code:

https://gist.github.com/achimnol/965a6aecf7b1f96207abf11469b68965

Just run this code using "python -m pytest -s test.py" to see what happens.
(My setup uses Python 3.6.4 and pytest 3.3.2 on macOS High Sierra 10.13.2)

I tried the same logic using synchornous APIs such as threading.Thread / time.sleep instead of loop.create_task / asyncio.sleep, it raised "ValueError: generator already executing" when tried to close the generator.

njsmith · 2018-01-10T22:05:10Z

It looks like Python's tracking the "running" state of async generators wrong: we should have ag_running set to True when we enter asend/athrow/aclose and False when we exit, but instead it's being toggled back and forth on each *inner* send/throw on the individual coroutines.

Here's a minimal reproducer (using some random recent checkout of master):

>>> async def f():
...     await asyncio.sleep(1)
...     yield
... 
>>> ag = f()
>>> asend_coro = ag.asend(None)
>>> fut = asend_coro.send(None)
# Logically, ag.asend is still running, waiting for that sleep to
# finish, but we have lost track:
>>> ag.ag_running
False
# We can start another call to asend() going simultaneously
>>> fut.set_result(None)
>>> send_coro2 = ag.asend(None)
>>> send_coro2.send(None)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

It looks like async_generator did handle this case correctly, but didn't have a test case. I just added one: njsmith/async_generator@339fc63

1st1 · 2019-10-22T22:24:17Z

Was fixed as part of bpo-30773.

achimnol mannequin added topic-asyncio type-bug An unexpected behavior, bug, or error labels Jan 10, 2018

njsmith added the 3.7 (EOL) end of life label Jan 10, 2018

1st1 closed this as completed Oct 22, 2019

ezio-melotti transferred this issue from another repository Apr 10, 2022

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Closing async generator while it is running does not raise an exception #76707

Closing async generator while it is running does not raise an exception #76707

achimnol mannequin commented Jan 10, 2018

achimnol mannequin commented Jan 10, 2018

njsmith commented Jan 10, 2018

1st1 commented Oct 22, 2019

Closing async generator while it is running does not raise an exception #76707

Closing async generator while it is running does not raise an exception #76707

Comments

achimnol mannequin commented Jan 10, 2018

achimnol mannequin commented Jan 10, 2018

njsmith commented Jan 10, 2018

1st1 commented Oct 22, 2019