https://github.com/python/cpython/commit/efdaae5b356a158cf6028844d08b0efd1c5313cb
commit: efdaae5b356a158cf6028844d08b0efd1c5313cb
branch: 3.14
author: Miss Islington (bot) <31488909+miss-isling...@users.noreply.github.com>
committer: ambv <luk...@langa.pl>
date: 2025-05-20T19:43:09+02:00
summary:
[3.14] gh-86802: Fix asyncio memory leak; shielded task exceptions log once
through the exception handler (gh-134331) (gh-134343)
(cherry picked from commit f695eca60cfc53cf3322323082652037d6d0cfef)
Co-authored-by: Christian Harries
<68507104+christian...@users.noreply.github.com>
Co-authored-by: Łukasz Langa <luk...@langa.pl>
files:
A Misc/NEWS.d/next/Library/2025-05-20-15-13-43.gh-issue-86802.trF7TM.rst
M Lib/asyncio/tasks.py
M Lib/test/test_asyncio/test_tasks.py
diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index 888615f8e5e1b3..fbd5c39a7c56ac 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -908,6 +908,25 @@ def _done_callback(fut, cur_task=cur_task):
return outer
+def _log_on_exception(fut):
+ if fut.cancelled():
+ return
+
+ exc = fut.exception()
+ if exc is None:
+ return
+
+ context = {
+ 'message':
+ f'{exc.__class__.__name__} exception in shielded future',
+ 'exception': exc,
+ 'future': fut,
+ }
+ if fut._source_traceback:
+ context['source_traceback'] = fut._source_traceback
+ fut._loop.call_exception_handler(context)
+
+
def shield(arg):
"""Wait for a future, shielding it from cancellation.
@@ -953,14 +972,11 @@ def shield(arg):
else:
cur_task = None
- def _inner_done_callback(inner, cur_task=cur_task):
- if cur_task is not None:
- futures.future_discard_from_awaited_by(inner, cur_task)
+ def _clear_awaited_by_callback(inner):
+ futures.future_discard_from_awaited_by(inner, cur_task)
+ def _inner_done_callback(inner):
if outer.cancelled():
- if not inner.cancelled():
- # Mark inner's result as retrieved.
- inner.exception()
return
if inner.cancelled():
@@ -972,10 +988,16 @@ def _inner_done_callback(inner, cur_task=cur_task):
else:
outer.set_result(inner.result())
-
def _outer_done_callback(outer):
if not inner.done():
inner.remove_done_callback(_inner_done_callback)
+ # Keep only one callback to log on cancel
+ inner.remove_done_callback(_log_on_exception)
+ inner.add_done_callback(_log_on_exception)
+
+ if cur_task is not None:
+ inner.add_done_callback(_clear_awaited_by_callback)
+
inner.add_done_callback(_inner_done_callback)
outer.add_done_callback(_outer_done_callback)
diff --git a/Lib/test/test_asyncio/test_tasks.py
b/Lib/test/test_asyncio/test_tasks.py
index 44498ef790e450..f6f976f213ac02 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -2116,6 +2116,46 @@ def test_shield_cancel_outer(self):
self.assertTrue(outer.cancelled())
self.assertEqual(0, 0 if outer._callbacks is None else
len(outer._callbacks))
+ def test_shield_cancel_outer_result(self):
+ mock_handler = mock.Mock()
+ self.loop.set_exception_handler(mock_handler)
+ inner = self.new_future(self.loop)
+ outer = asyncio.shield(inner)
+ test_utils.run_briefly(self.loop)
+ outer.cancel()
+ test_utils.run_briefly(self.loop)
+ inner.set_result(1)
+ test_utils.run_briefly(self.loop)
+ mock_handler.assert_not_called()
+
+ def test_shield_cancel_outer_exception(self):
+ mock_handler = mock.Mock()
+ self.loop.set_exception_handler(mock_handler)
+ inner = self.new_future(self.loop)
+ outer = asyncio.shield(inner)
+ test_utils.run_briefly(self.loop)
+ outer.cancel()
+ test_utils.run_briefly(self.loop)
+ inner.set_exception(Exception('foo'))
+ test_utils.run_briefly(self.loop)
+ mock_handler.assert_called_once()
+
+ def test_shield_duplicate_log_once(self):
+ mock_handler = mock.Mock()
+ self.loop.set_exception_handler(mock_handler)
+ inner = self.new_future(self.loop)
+ outer = asyncio.shield(inner)
+ test_utils.run_briefly(self.loop)
+ outer.cancel()
+ test_utils.run_briefly(self.loop)
+ outer = asyncio.shield(inner)
+ test_utils.run_briefly(self.loop)
+ outer.cancel()
+ test_utils.run_briefly(self.loop)
+ inner.set_exception(Exception('foo'))
+ test_utils.run_briefly(self.loop)
+ mock_handler.assert_called_once()
+
def test_shield_shortcut(self):
fut = self.new_future(self.loop)
fut.set_result(42)
diff --git
a/Misc/NEWS.d/next/Library/2025-05-20-15-13-43.gh-issue-86802.trF7TM.rst
b/Misc/NEWS.d/next/Library/2025-05-20-15-13-43.gh-issue-86802.trF7TM.rst
new file mode 100644
index 00000000000000..d3117b16f04436
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-05-20-15-13-43.gh-issue-86802.trF7TM.rst
@@ -0,0 +1,3 @@
+Fixed asyncio memory leak in cancelled shield tasks. For shielded tasks
+where the shield was cancelled, log potential exceptions through the
+exception handler. Contributed by Christian Harries.
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