asyncio overrides signal handlers

[franciscod]

BPO	44212
Nosy	@asvetlov, @1st1, @franciscod
PRs	bpo-44212: asyncio: store old signal handlers and call them #26306

^{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 = None
created_at = <Date 2021-05-22.03:09:03.053>
labels = ['type-bug', '3.8', '3.9', '3.10', '3.11', '3.7', 'expert-asyncio']
title = 'asyncio overrides signal handlers'
updated_at = <Date 2021-05-22.04:05:46.824>
user = 'https://github.com/franciscod'

bugs.python.org fields:

activity = <Date 2021-05-22.04:05:46.824>
actor = 'Francisco Demartino'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['asyncio']
creation = <Date 2021-05-22.03:09:03.053>
creator = 'Francisco Demartino'
dependencies = []
files = []
hgrepos = []
issue_num = 44212
keywords = ['patch']
message_count = 2.0
messages = ['394174', '394176']
nosy_count = 3.0
nosy_names = ['asvetlov', 'yselivanov', 'Francisco Demartino']
pr_nums = ['26306']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue44212'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10', 'Python 3.11']

[franciscod]

Hello,

It looks like when asyncio sets up a signal handler, it forgets about the previous one (if any).

Here's a patch (was about to create a PR but the default text brought me to bugs.python.org)
franciscod@bdac885

Tracked this down to the initial asyncio checkout, in commit 27b7c7e, a few commits before v3.4.0a4.

Not sure if this is a bug but it surprised me. I would have expected that it registered an "additional" signal handler, or at least that my previously installed signal handler would be called afterwards.

Also I'm not sure that it's a good idea to suddenly start running handlers that some current code might rely on not running, or have worked around this behaviour otherwise.

Thanks,
Francisco