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>

diff --git a/Doc/library/asyncio-future.rst b/Doc/library/asyncio-future.rst
index 7426e8291e1424a3142fdbd15f2a15893df36d53..412304ab6148889981b4c1a0ddf0759ec3833c38 100644 (file)
--- 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 e535a5bf0425428f1a254435a2c0eb7026cd1613..8f9cef727463a2da3ac11685034a228b3374a6e7 100644 (file)
--- a/Doc/library/asyncio-task.rst
+++ b/Doc/library/asyncio-task.rst
@@ -262,9 +262,9 @@ 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::
 
@@ -441,7 +441,8 @@ Shielding From Cancellation
 
    The statement::
 
-       res = await shield(something())
+       task = asyncio.create_task(something())
+       res = await shield(task)
 
    is equivalent to::
 
@@ -460,11 +461,19 @@ 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 c4bedb5c72b0ef80905152c6f136942fa2b802fb..f391586d128730328c424541420db6a02fcf39c7 100644 (file)
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -809,7 +809,8 @@ def shield(arg):
 
     The statement
 
-        res = await shield(something())
+        task = asyncio.create_task(something())
+        res = await shield(task)
 
     is exactly equivalent to the statement
 
@@ -825,10 +826,16 @@ 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():