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gh-108951: document how to terminate an asyncio.TaskGroup #123837

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merged 3 commits into from
Sep 11, 2024
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gh-108951: document how to terminate an asyncio.TaskGroup #123837

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b4dc0bb
Document how to cancel an asynchronous task group.
picnixz Sep 8, 2024
4e1c6bc
Update Doc/library/asyncio-task.rst
picnixz Sep 10, 2024
cf21e18
address review
picnixz Sep 11, 2024
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47 changes: 47 additions & 0 deletions Doc/library/asyncio-task.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -414,6 +414,53 @@ reported by :meth:`asyncio.Task.cancelling`.
Improved handling of simultaneous internal and external cancellations
and correct preservation of cancellation counts.

Terminating a Task Group
------------------------

While terminating a task group is not natively supported by the standard
library, termination can be achieved by adding an exception-raising task
to the task group and ignoring the raised exception:

.. code-block:: python

import asyncio
from asyncio import TaskGroup

class TerminateTaskGroup(Exception):
"""Exception raised to terminate a task group."""

async def force_terminate_task_group():
"""Used to force termination of a task group."""
raise TerminateTaskGroup()

async def job(task_id, sleep_time):
print(f'Task {task_id}: start')
await asyncio.sleep(sleep_time)
print(f'Task {task_id}: done')

async def main():
try:
async with TaskGroup() as group:
# spawn some tasks
group.create_task(job(1, 0.5))
group.create_task(job(2, 1.5))
# sleep for 1 second
await asyncio.sleep(1)
# add an exception-raising task to force the group to terminate
group.create_task(force_terminate_task_group())
except* TerminateTaskGroup:
pass

asyncio.run(main())

Expected output:

.. code-block:: text

Task 1: start
Task 2: start
Task 1: done

Sleeping
========

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