asyncio.gather(..., return_exceptions=True) swallows cancellation

@bitdancer

BPO	32684
Nosy	@bitdancer, @asvetlov, @socketpair, @1st1
PRs	bpo-32684: Fix gather to propagate cancel of itself with return_exceptions #7209 [3.7] bpo-32684: Fix gather to propagate cancel of itself with return_exceptions (GH-7209) #7222 [3.6] bpo-32684: Fix gather to propagate cancel of itself with return_exceptions #7224 bpo-32684: Fix nits in tests #7225 [3.7] bpo-32684: Fix nits in tests (GH-7225) #7231

^{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 2018-05-30.00:59:24.287>
created_at = <Date 2018-01-27.05:38:11.141>
labels = ['3.8', 'type-bug', '3.7', 'expert-asyncio']
title = 'asyncio.gather(..., return_exceptions=True) swallows cancellation'
updated_at = <Date 2018-05-30.00:59:24.286>
user = 'https://github.com/socketpair'

bugs.python.org fields:

activity = <Date 2018-05-30.00:59:24.286>
actor = 'yselivanov'
assignee = 'none'
closed = True
closed_date = <Date 2018-05-30.00:59:24.287>
closer = 'yselivanov'
components = ['asyncio']
creation = <Date 2018-01-27.05:38:11.141>
creator = 'socketpair'
dependencies = []
files = []
hgrepos = []
issue_num = 32684
keywords = ['patch']
message_count = 8.0
messages = ['310843', '310846', '318059', '318093', '318127', '318138', '318139', '318142']
nosy_count = 4.0
nosy_names = ['r.david.murray', 'asvetlov', 'socketpair', 'yselivanov']
pr_nums = ['7209', '7222', '7224', '7225', '7231']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue32684'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

Proof:

================

import asyncio

async def test():
    while True:
        print('sleeping 1')
        await asyncio.gather(asyncio.sleep(1), return_exceptions=True)

async def amain():
    print('creating task')
    qwe = asyncio.Task(test())
    print('sleeping 2')
    await asyncio.sleep(2)
    print('cancelling task')
    qwe.cancel()
    print('waiting task for completion')
    try:
        await qwe
    except Exception as e:
        print('task complete: %r', e)

loop = asyncio.get_event_loop()
loop.run_until_complete(amain())

================

This program will never complete.

This case should be either fixed, or documented.

See also bpo-26923, but I think this problem is different.

Thanks for reporting this. Agree, this is a bug and makes it hard (if not impossible) to use gather. I've created a PR to address the issue.

New changeset 863b674 by Yury Selivanov in branch 'master':
bpo-32684: Fix gather to propagate cancel of itself with return_exceptions (GH-7209)
863b674

New changeset 0364342 by Yury Selivanov (Miss Islington (bot)) in branch '3.7':
bpo-32684: Fix gather to propagate cancel of itself with return_exceptions (GH-7209) (bpo-7222)
0364342

New changeset 3b263e6 by Yury Selivanov in branch '3.6':
bpo-32684: Fix gather to propagate cancel of itself with return_exceptions (GH-7224)
3b263e6

New changeset 6f75bae by Yury Selivanov in branch 'master':
bpo-32684: Fix nits in tests (GH-7225)
6f75bae

New changeset 3ddee64 by Yury Selivanov (Miss Islington (bot)) in branch '3.7':
bpo-32684: Fix nits in tests (GH-7225) (bpo-7231)
3ddee64

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asyncio.gather(..., return_exceptions=True) swallows cancellation #76865

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asyncio.gather(..., return_exceptions=True) swallows cancellation #76865

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socketpair commented on Jan 27, 2018

bitdancer commented on Jan 27, 2018

1st1 commented on May 29, 2018

1st1 commented on May 29, 2018

1st1 commented on May 29, 2018

1st1 commented on May 29, 2018

1st1 commented on May 29, 2018

1st1 commented on May 30, 2018

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