asyncio: is it time to make ProactorEventLoop as the default event loop?

[vstinner]

BPO	34687
Nosy	@vstinner, @asvetlov, @1st1, @miss-islington, @carltongibson
PRs	bpo-34687: asynico uses ProactorEventLoop by default #9538 bpo-34687: Update asyncio doc for ProactorEventLoop #9623

^{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 2018-09-25.15:31:18.247>
created_at = <Date 2018-09-14.19:35:17.919>
labels = ['3.8', 'expert-asyncio']
title = 'asyncio: is it time to make ProactorEventLoop as the default event loop?'
updated_at = <Date 2019-10-23.12:14:41.970>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2019-10-23.12:14:41.970>
actor = 'carltongibson'
assignee = 'none'
closed = True
closed_date = <Date 2018-09-25.15:31:18.247>
closer = 'vstinner'
components = ['asyncio']
creation = <Date 2018-09-14.19:35:17.919>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 34687
keywords = ['patch']
message_count = 9.0
messages = ['325391', '325394', '326361', '326363', '326424', '326641', '355210', '355211', '355215']
nosy_count = 5.0
nosy_names = ['vstinner', 'asvetlov', 'yselivanov', 'miss-islington', 'carltongibson']
pr_nums = ['9538', '9623']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue34687'
versions = ['Python 3.8']

[vstinner]

Is it time to make ProactorEventLoop as the default event loop?

Since 2014, many features have been added to ProactorEventLoop (ex: SSL support) and the implementation is way more today than it was 4 years ago.

Comparison of SelectorEventLoop and ProactorEventLoop on Windows:
https://docs.python.org/dev/library/asyncio-platforms.html#windows

[1st1]

I'm not sure that ProactorEventLoop is stable enough TBH :( And I wouldn't be able to be on call for Windows users to fix all bugs in ProactieEventLoop.

Andrew, your thoughts on this?

[1st1]

New changeset 6ea29c5 by Yury Selivanov (Victor Stinner) in branch 'master':
bpo-34687: Make asynico use ProactorEventLoop by default (GH-9538)
6ea29c5

[vstinner]

Thank you for the review Yury ;-)

[asvetlov]

I think the only way to make sure that proactor event loop is stable -- starting to use it everywhere on Windows.

Let's do it.

[miss-islington]

New changeset 37aae9d by Miss Islington (bot) (Victor Stinner) in branch 'master':
bpo-34687: Update asyncio doc for ProactorEventLoop (GH-9623)
37aae9d

[carltongibson]

This change causes an issue in asgiref (and so Django) for Windows and Python 3.8.

django/asgiref#132
https://code.djangoproject.com/ticket/30900

It looks as if ProactorEventLoop needs to check the current thread before triggering the signal...

File "C:\Jenkins\workspace\django-windows\database\sqlite3\label\windows\python\Python38\.env\lib\site-packages\asgiref\sync.py", line 130, in _run_event_loop
File "C:\Python38\lib\asyncio\proactor_events.py", line 679, in close
    signal.set_wakeup_fd(-1)
ValueError: set_wakeup_fd only works in main thread

... but I'm not familiar with the internals here as yet.

(I'm guessing I need to create a new issue?)

[vstinner]

(I'm guessing I need to create a new issue?)

Please open a new issue.

[carltongibson]

Created: https://bugs.python.org/issue38563

Thanks!