8000 gh-94972: document that shield users need to keep a reference to their task by hendrikmakait · Pull Request #96724 · python/cpython · GitHub
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gh-94972: document that shield users need to keep a reference to their task #96724

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Merged
merged 7 commits into from
Sep 10, 2022
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gh-94972: document that shield users need to keep a reference to their task #96724

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c0f34a6
gh-94972: document that shield users need to keep a reference to thei…
graingert Jul 18, 2022
b16416f
fix garbage-collected typo - the correct spelling is garbage collected
graingert Jul 19, 2022
951b85a
Merge branch 'main' into shield
graingert Jul 19, 2022
8ffb38c
correct mid execution typo, the correct spelling is mid-execution
graingert Jul 19, 2022
0868b77
Merge branch 'main' into shield
graingert Aug 24, 2022
2c2e396
Apply suggestions from code review
graingert Aug 24, 2022
9123abe
repeat changes in shield() docstring
hendrikmakait Sep 9, 2022
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gh-94972: document that shield users need to keep a reference to thei… 
…r task
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@graingert
graingert committed Jul 18, 2022
commit c0f34a6bd4784d54b1e9e5f9f68f6b60f42d9dfb
19 changes: 17 additions & 2 deletions Doc/library/asyncio-task.rst
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Expand Up @@ -520,7 +520,10 @@ Shielding From Cancellation

The statement::

res = await shield(something())
task = asyncio.create_task(something())
background_tasks.add(task)
task.add_done_callback(background_tasks.discard)
res = await shield(task)

is equivalent to::

Expand All @@ -539,11 +542,23 @@ Shielding From Cancellation
the ``shield()`` function should be combined with a try/except
clause, as follows::

task = asyncio.create_task(something())
background_tasks.add(task)
task.add_done_callback(background_tasks.discard)
try:
res = await shield(something())
res = await shield(task)
except CancelledError:
res = None

.. important::

Save a reference to tasks passed to this function, to avoid
a task disappearing mid execution. The event loop only keeps
weak references to tasks. A task that isn't referenced elsewhere
may get garbage-collected at any time, even before it's done.
For reliable "fire-and-forget" background tasks, gather them in
a collection.

.. versionchanged:: 3.10
Removed the *loop* parameter.

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