Task created by StreamReaderProtocol gets garbage collected.

@asvetlov

BPO	46309
Nosy	@asvetlov, @1st1, @kumaraditya303, @simwr872
PRs	bpo-46309: Added reference to task created by StreamReaderProtocol #30505
Files	example.py

^{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 2022-01-08.23:35:55.417>
labels = ['3.11', 'type-bug', '3.9', '3.10', 'expert-asyncio']
title = 'Task created by StreamReaderProtocol gets garbage collected.'
updated_at = <Date 2022-01-11.15:54:38.380>
user = 'https://github.com/simwr872'

bugs.python.org fields:

activity = <Date 2022-01-11.15:54:38.380>
actor = 'AlexWaygood'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['asyncio']
creation = <Date 2022-01-08.23:35:55.417>
creator = 'simwr872'
dependencies = []
files = ['50552']
hgrepos = []
issue_num = 46309
keywords = ['patch']
message_count = 3.0
messages = ['410124', '410134', '410310']
nosy_count = 4.0
nosy_names = ['asvetlov', 'yselivanov', 'kumaraditya', 'simwr872']
pr_nums = ['30505']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue46309'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

Documentation states that a reference must be kept when creating a task, https://docs.python.org/3/library/asyncio-task.html#asyncio.create_task.

This is not done in StreamReaderProtocol, https://github.com/python/cpython/blob/main/Lib/asyncio/streams.py#L244.

I've provided a simple example to force garbage collection of this task which results in Task was destroyed but it is pending!. Uncommenting the commented code of the example shows that the task is not destroyed when a reference is kept.

Am I missing something or using the library incorrectly? I've followed the examples at https://docs.python.org/3/library/asyncio-stream.html#tcp-echo-server-using-streams.

Thanks for the bug report.

Seems like your analysis is correct.

Could you make a pull request which adds a task reference?

As a workaround, it's possible to keep the reference in a global variable

background_tasks = set()
def create_connection_task(*args, **kwargs):
    task = asyncio.create_task(handle_connection(*args, **kwargs))
    background_tasks.add(task)
    task.add_done_callback(background_tasks.discard)

# asyncio.start_server(create_connection_task, ..)

pythongh-90467: StreamReaderProtocol - add strong reference to create…

gh-90467: StreamReaderProtocol - add strong reference to created task (…

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Task created by StreamReaderProtocol gets garbage collected. #90467

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Task created by StreamReaderProtocol gets garbage collected. #90467

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simwr872 commented on Jan 8, 2022

asvetlov commented on Jan 9, 2022

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python273 commented on Aug 26, 2022

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