From 335bd1ee8be187b464ef797745d42f9a974bc970 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
<31488909+miss-islington@users.noreply.github.com>
Date: Sat, 10 Sep 2022 08:03:35 -0700
Subject: [PATCH] gh-94972: document that shield users need to keep a reference
to their task (GH-96724)
Co-authored-by: Thomas Grainger <tagrain@gmail.com>
Co-authored-by: Guido van Rossum <gvanrossum@gmail.com>
(cherry picked from commit 6281affee6423296893b509cd78dc563ca58b196)
Co-authored-by: Hendrik Makait <hendrik.makait@gmail.com>
---
Doc/library/asyncio-future.rst | 2 +-
Doc/library/asyncio-task.rst | 17 +++++++++++++----
Lib/asyncio/tasks.py | 11 +++++++++--
3 files changed, 23 insertions(+), 7 deletions(-)
diff --git a/Doc/library/asyncio-future.rst b/Doc/library/asyncio-future.rst
index f74f2e6f893..99a5d3a8287 100644
--- a/Doc/library/asyncio-future.rst
+++ b/Doc/library/asyncio-future.rst
@@ -55,7 +55,7 @@ Future Functions
preferred way for creating new Tasks.
Save a reference to the result of this function, to avoid
- a task disappearing mid execution.
+ a task disappearing mid-execution.
.. versionchanged:: 3.5.1
The function accepts any :term:`awaitable` object.
diff --git a/Doc/library/asyncio-task.rst b/Doc/library/asyncio-task.rst
index ffbf421bae5..221197ea40f 100644
--- a/Doc/library/asyncio-task.rst
+++ b/Doc/library/asyncio-task.rst
@@ -254,9 +254,9 @@ Creating Tasks
.. important::
Save a reference to the result of this function, to avoid
- a task disappearing mid execution. The event loop only keeps
+ 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.
+ may get garbage collected at any time, even before it's done.
For reliable "fire-and-forget" background tasks, gather them in
a collection::
@@ -520,7 +520,8 @@ Shielding From Cancellation
The statement::
- res = await shield(something())
+ task = asyncio.create_task(something())
+ res = await shield(task)
is equivalent to::
@@ -539,11 +540,19 @@ Shielding From Cancellation
the ``shield()`` function should be combined with a try/except
clause, as follows::
+ task = asyncio.create_task(something())
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.
+
.. versionchanged:: 3.10
Removed the *loop* parameter.
diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index 27fe58da151..56a355cbdc7 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -848,7 +848,8 @@ def shield(arg):
The statement
- res = await shield(something())
+ task = asyncio.create_task(something())
+ res = await shield(task)
is exactly equivalent to the statement
@@ -864,10 +865,16 @@ def shield(arg):
If you want to completely ignore cancellation (not recommended)
you can combine shield() with a try/except clause, as follows:
+ task = asyncio.create_task(something())
try:
- res = await shield(something())
+ res = await shield(task)
except CancelledError:
res = None
+
+ 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.
"""
inner = _ensure_future(arg)
if inner.done():
--
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