From ab8786a76c6b0a3df19d6cc2eea505433e24065e Mon Sep 17 00:00:00 2001
From: Chris33871 <christian.harries15@gmail.com>
Date: Tue, 20 May 2025 15:06:32 +0100
Subject: [PATCH 01/12] gh-86802: Fix asyncio memory leak; shielded tasks where
 cancelled log once through the exception handler

---
 Lib/asyncio/tasks.py                | 30 ++++++++++++++++++++++-------
 Lib/test/test_asyncio/test_tasks.py | 28 +++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 7 deletions(-)

diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index 888615f8e5e1b3..39a5630d65176f 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -908,6 +908,19 @@ def _done_callback(fut, cur_task=cur_task):
     return outer
 
 
+def _log_on_cancel_callback(inner):
+    if not inner.cancelled():
+        exc = inner.exception()
+        context = {
+            'message':
+            f'{exc.__class__.__name__} exception in shielded future',
+            'exception': exc,
+            'future': inner,
+        }
+        if inner._source_traceback:
+            context['source_traceback'] = inner._source_traceback
+        inner._loop.call_exception_handler(context)
+
 def shield(arg):
     """Wait for a future, shielding it from cancellation.
 
@@ -953,14 +966,11 @@ 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 +982,16 @@ 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_cancel_callback)
+            inner.add_done_callback(_log_on_cancel_callback)
+
+    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..2c234d75813129 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -2116,6 +2116,34 @@ 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_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)

From b500a1f86f1ef1b8bb382e7fe4f6666545af7f55 Mon Sep 17 00:00:00 2001
From: Chris33871 <christian.harries15@gmail.com>
Date: Tue, 20 May 2025 15:14:00 +0100
Subject: [PATCH 02/12] Add blurb

---
 .../next/Library/2025-05-20-15-13-43.gh-issue-86802.trF7TM.rst | 3 +++
 1 file changed, 3 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2025-05-20-15-13-43.gh-issue-86802.trF7TM.rst

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.

From 37837edade2aa9d664a54e3378b06d010e938545 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C5=81ukasz=20Langa?= <lukasz@langa.pl>
Date: Tue, 20 May 2025 16:15:03 +0200
Subject: [PATCH 03/12] Fix formatting

---
 Lib/asyncio/tasks.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index 39a5630d65176f..dbe5e5f26d154d 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -921,6 +921,7 @@ def _log_on_cancel_callback(inner):
             context['source_traceback'] = inner._source_traceback
         inner._loop.call_exception_handler(context)
 
+
 def shield(arg):
     """Wait for a future, shielding it from cancellation.
 

From 0d595af36930374e21e534185059a18c3efc637a Mon Sep 17 00:00:00 2001
From: Chris33871 <christian.harries15@gmail.com>
Date: Tue, 20 May 2025 15:30:20 +0100
Subject: [PATCH 04/12] fix handle case with no exception

---
 Lib/asyncio/tasks.py                | 33 +++++++++++++++++------------
 Lib/test/test_asyncio/test_tasks.py | 12 +++++++++++
 2 files changed, 31 insertions(+), 14 deletions(-)

diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index dbe5e5f26d154d..fbd5c39a7c56ac 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -908,18 +908,23 @@ def _done_callback(fut, cur_task=cur_task):
     return outer
 
 
-def _log_on_cancel_callback(inner):
-    if not inner.cancelled():
-        exc = inner.exception()
-        context = {
-            'message':
-            f'{exc.__class__.__name__} exception in shielded future',
-            'exception': exc,
-            'future': inner,
-        }
-        if inner._source_traceback:
-            context['source_traceback'] = inner._source_traceback
-        inner._loop.call_exception_handler(context)
+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):
@@ -987,8 +992,8 @@ 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_cancel_callback)
-            inner.add_done_callback(_log_on_cancel_callback)
+            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)
diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py
index 2c234d75813129..f6f976f213ac02 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -2116,6 +2116,18 @@ 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)

From 17d39e9a5f5a23e9df5eb58e4fff1a9eb55e955a Mon Sep 17 00:00:00 2001
From: Chris33871 <christian.harries15@gmail.com>
Date: Tue, 20 May 2025 21:23:04 +0100
Subject: [PATCH 05/12] Fix offset with connection backlog - adapted the tests
 - created new tests for 0 and 1 connections

---
 Lib/asyncio/selector_events.py                |  2 +-
 Lib/test/test_asyncio/test_selector_events.py | 17 +++++++++++++++--
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/Lib/asyncio/selector_events.py b/Lib/asyncio/selector_events.py
index 22147451fa7ebd..6ad84044adf146 100644
--- a/Lib/asyncio/selector_events.py
+++ b/Lib/asyncio/selector_events.py
@@ -173,7 +173,7 @@ def _accept_connection(
         # listening socket has triggered an EVENT_READ. There may be multiple
         # connections waiting for an .accept() so it is called in a loop.
         # See https://bugs.python.org/issue27906 for more details.
-        for _ in range(backlog):
+        for _ in range(backlog + 1):
             try:
                 conn, addr = sock.accept()
                 if self._debug:
diff --git a/Lib/test/test_asyncio/test_selector_events.py b/Lib/test/test_asyncio/test_selector_events.py
index de81936b7456f2..d03e2fb0c60e33 100644
--- a/Lib/test/test_asyncio/test_selector_events.py
+++ b/Lib/test/test_asyncio/test_selector_events.py
@@ -347,6 +347,19 @@ def test_process_events_write_cancelled(self):
               selectors.EVENT_WRITE)])
         self.loop._remove_writer.assert_called_with(1)
 
+    def test_accept_connection_zero_one(self):
+        for backlog in [0, 1]:
+            sock = mock.Mock()
+            sock.accept.return_value = (mock.Mock(), mock.Mock())
+            with self.subTest(backlog):
+                mock_obj = mock.patch.object
+                with mock_obj(self.loop, '_accept_connection2') as accept2_mock:
+                    self.loop._accept_connection(
+                        mock.Mock(), sock, backlog=backlog)
+                self.loop.run_until_complete(asyncio.sleep(0))
+                print("Accepted vs Backlog:", sock.accept.call_count, backlog)
+                self.assertEqual(sock.accept.call_count, backlog + 1)
+
     def test_accept_connection_multiple(self):
         sock = mock.Mock()
         sock.accept.return_value = (mock.Mock(), mock.Mock())
@@ -362,7 +375,7 @@ def test_accept_connection_multiple(self):
             self.loop._accept_connection(
                 mock.Mock(), sock, backlog=backlog)
         self.loop.run_until_complete(asyncio.sleep(0))
-        self.assertEqual(sock.accept.call_count, backlog)
+        self.assertEqual(sock.accept.call_count, backlog + 1)
 
     def test_accept_connection_skip_connectionabortederror(self):
         sock = mock.Mock()
@@ -388,7 +401,7 @@ def mock_sock_accept():
         # as in test_accept_connection_multiple avoid task pending
         # warnings by using asyncio.sleep(0)
         self.loop.run_until_complete(asyncio.sleep(0))
-        self.assertEqual(sock.accept.call_count, backlog)
+        self.assertEqual(sock.accept.call_count, backlog + 1)
 
 class SelectorTransportTests(test_utils.TestCase):
 

From d386169bfcddfdab230d1c1961aa4ea452360f2e Mon Sep 17 00:00:00 2001
From: Chris33871 <christian.harries15@gmail.com>
Date: Tue, 20 May 2025 21:26:05 +0100
Subject: [PATCH 06/12] Revert "Fix offset with connection backlog - adapted
 the tests - created new tests for 0 and 1 connections"

This reverts commit 17d39e9a5f5a23e9df5eb58e4fff1a9eb55e955a.
---
 Lib/asyncio/selector_events.py                |  2 +-
 Lib/test/test_asyncio/test_selector_events.py | 17 ++---------------
 2 files changed, 3 insertions(+), 16 deletions(-)

diff --git a/Lib/asyncio/selector_events.py b/Lib/asyncio/selector_events.py
index 6ad84044adf146..22147451fa7ebd 100644
--- a/Lib/asyncio/selector_events.py
+++ b/Lib/asyncio/selector_events.py
@@ -173,7 +173,7 @@ def _accept_connection(
         # listening socket has triggered an EVENT_READ. There may be multiple
         # connections waiting for an .accept() so it is called in a loop.
         # See https://bugs.python.org/issue27906 for more details.
-        for _ in range(backlog + 1):
+        for _ in range(backlog):
             try:
                 conn, addr = sock.accept()
                 if self._debug:
diff --git a/Lib/test/test_asyncio/test_selector_events.py b/Lib/test/test_asyncio/test_selector_events.py
index d03e2fb0c60e33..de81936b7456f2 100644
--- a/Lib/test/test_asyncio/test_selector_events.py
+++ b/Lib/test/test_asyncio/test_selector_events.py
@@ -347,19 +347,6 @@ def test_process_events_write_cancelled(self):
               selectors.EVENT_WRITE)])
         self.loop._remove_writer.assert_called_with(1)
 
-    def test_accept_connection_zero_one(self):
-        for backlog in [0, 1]:
-            sock = mock.Mock()
-            sock.accept.return_value = (mock.Mock(), mock.Mock())
-            with self.subTest(backlog):
-                mock_obj = mock.patch.object
-                with mock_obj(self.loop, '_accept_connection2') as accept2_mock:
-                    self.loop._accept_connection(
-                        mock.Mock(), sock, backlog=backlog)
-                self.loop.run_until_complete(asyncio.sleep(0))
-                print("Accepted vs Backlog:", sock.accept.call_count, backlog)
-                self.assertEqual(sock.accept.call_count, backlog + 1)
-
     def test_accept_connection_multiple(self):
         sock = mock.Mock()
         sock.accept.return_value = (mock.Mock(), mock.Mock())
@@ -375,7 +362,7 @@ def test_accept_connection_multiple(self):
             self.loop._accept_connection(
                 mock.Mock(), sock, backlog=backlog)
         self.loop.run_until_complete(asyncio.sleep(0))
-        self.assertEqual(sock.accept.call_count, backlog + 1)
+        self.assertEqual(sock.accept.call_count, backlog)
 
     def test_accept_connection_skip_connectionabortederror(self):
         sock = mock.Mock()
@@ -401,7 +388,7 @@ def mock_sock_accept():
         # as in test_accept_connection_multiple avoid task pending
         # warnings by using asyncio.sleep(0)
         self.loop.run_until_complete(asyncio.sleep(0))
-        self.assertEqual(sock.accept.call_count, backlog + 1)
+        self.assertEqual(sock.accept.call_count, backlog)
 
 class SelectorTransportTests(test_utils.TestCase):
 

From 2c603b9c3640efdd2e6c90c786ed8334c7f2fc3e Mon Sep 17 00:00:00 2001
From: Chris33871 <christian.harries15@gmail.com>
Date: Tue, 20 May 2025 21:28:56 +0100
Subject: [PATCH 07/12] fix connection backlog offset - updated tests - added
 tests for 0 and 1

---
 Lib/asyncio/selector_events.py                |  2 +-
 Lib/test/test_asyncio/test_selector_events.py | 16 ++++++++++++++--
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/Lib/asyncio/selector_events.py b/Lib/asyncio/selector_events.py
index 22147451fa7ebd..6ad84044adf146 100644
--- a/Lib/asyncio/selector_events.py
+++ b/Lib/asyncio/selector_events.py
@@ -173,7 +173,7 @@ def _accept_connection(
         # listening socket has triggered an EVENT_READ. There may be multiple
         # connections waiting for an .accept() so it is called in a loop.
         # See https://bugs.python.org/issue27906 for more details.
-        for _ in range(backlog):
+        for _ in range(backlog + 1):
             try:
                 conn, addr = sock.accept()
                 if self._debug:
diff --git a/Lib/test/test_asyncio/test_selector_events.py b/Lib/test/test_asyncio/test_selector_events.py
index de81936b7456f2..aab6a779170eb9 100644
--- a/Lib/test/test_asyncio/test_selector_events.py
+++ b/Lib/test/test_asyncio/test_selector_events.py
@@ -347,6 +347,18 @@ def test_process_events_write_cancelled(self):
               selectors.EVENT_WRITE)])
         self.loop._remove_writer.assert_called_with(1)
 
+    def test_accept_connection_zero_one(self):
+        for backlog in [0, 1]:
+            sock = mock.Mock()
+            sock.accept.return_value = (mock.Mock(), mock.Mock())
+            with self.subTest(backlog):
+                mock_obj = mock.patch.object
+                with mock_obj(self.loop, '_accept_connection2') as accept2_mock:
+                    self.loop._accept_connection(
+                        mock.Mock(), sock, backlog=backlog)
+                self.loop.run_until_complete(asyncio.sleep(0))
+                self.assertEqual(sock.accept.call_count, backlog + 1)
+
     def test_accept_connection_multiple(self):
         sock = mock.Mock()
         sock.accept.return_value = (mock.Mock(), mock.Mock())
@@ -362,7 +374,7 @@ def test_accept_connection_multiple(self):
             self.loop._accept_connection(
                 mock.Mock(), sock, backlog=backlog)
         self.loop.run_until_complete(asyncio.sleep(0))
-        self.assertEqual(sock.accept.call_count, backlog)
+        self.assertEqual(sock.accept.call_count, backlog + 1)
 
     def test_accept_connection_skip_connectionabortederror(self):
         sock = mock.Mock()
@@ -388,7 +400,7 @@ def mock_sock_accept():
         # as in test_accept_connection_multiple avoid task pending
         # warnings by using asyncio.sleep(0)
         self.loop.run_until_complete(asyncio.sleep(0))
-        self.assertEqual(sock.accept.call_count, backlog)
+        self.assertEqual(sock.accept.call_count, backlog + 1)
 
 class SelectorTransportTests(test_utils.TestCase):
 

From 39f4654b1cec2d317d6c019ec89cf69fffd8e0b0 Mon Sep 17 00:00:00 2001
From: Chris33871 <christian.harries15@gmail.com>
Date: Tue, 20 May 2025 21:30:30 +0100
Subject: [PATCH 08/12] Revert "fix connection backlog offset - updated tests -
 added tests for 0 and 1"

This reverts commit 2c603b9c3640efdd2e6c90c786ed8334c7f2fc3e.
---
 Lib/asyncio/selector_events.py                |  2 +-
 Lib/test/test_asyncio/test_selector_events.py | 16 ++--------------
 2 files changed, 3 insertions(+), 15 deletions(-)

diff --git a/Lib/asyncio/selector_events.py b/Lib/asyncio/selector_events.py
index 6ad84044adf146..22147451fa7ebd 100644
--- a/Lib/asyncio/selector_events.py
+++ b/Lib/asyncio/selector_events.py
@@ -173,7 +173,7 @@ def _accept_connection(
         # listening socket has triggered an EVENT_READ. There may be multiple
         # connections waiting for an .accept() so it is called in a loop.
         # See https://bugs.python.org/issue27906 for more details.
-        for _ in range(backlog + 1):
+        for _ in range(backlog):
             try:
                 conn, addr = sock.accept()
                 if self._debug:
diff --git a/Lib/test/test_asyncio/test_selector_events.py b/Lib/test/test_asyncio/test_selector_events.py
index aab6a779170eb9..de81936b7456f2 100644
--- a/Lib/test/test_asyncio/test_selector_events.py
+++ b/Lib/test/test_asyncio/test_selector_events.py
@@ -347,18 +347,6 @@ def test_process_events_write_cancelled(self):
               selectors.EVENT_WRITE)])
         self.loop._remove_writer.assert_called_with(1)
 
-    def test_accept_connection_zero_one(self):
-        for backlog in [0, 1]:
-            sock = mock.Mock()
-            sock.accept.return_value = (mock.Mock(), mock.Mock())
-            with self.subTest(backlog):
-                mock_obj = mock.patch.object
-                with mock_obj(self.loop, '_accept_connection2') as accept2_mock:
-                    self.loop._accept_connection(
-                        mock.Mock(), sock, backlog=backlog)
-                self.loop.run_until_complete(asyncio.sleep(0))
-                self.assertEqual(sock.accept.call_count, backlog + 1)
-
     def test_accept_connection_multiple(self):
         sock = mock.Mock()
         sock.accept.return_value = (mock.Mock(), mock.Mock())
@@ -374,7 +362,7 @@ def test_accept_connection_multiple(self):
             self.loop._accept_connection(
                 mock.Mock(), sock, backlog=backlog)
         self.loop.run_until_complete(asyncio.sleep(0))
-        self.assertEqual(sock.accept.call_count, backlog + 1)
+        self.assertEqual(sock.accept.call_count, backlog)
 
     def test_accept_connection_skip_connectionabortederror(self):
         sock = mock.Mock()
@@ -400,7 +388,7 @@ def mock_sock_accept():
         # as in test_accept_connection_multiple avoid task pending
         # warnings by using asyncio.sleep(0)
         self.loop.run_until_complete(asyncio.sleep(0))
-        self.assertEqual(sock.accept.call_count, backlog + 1)
+        self.assertEqual(sock.accept.call_count, backlog)
 
 class SelectorTransportTests(test_utils.TestCase):
 

From 5893d43d8482777bf9c4adbe0f67c410cc0891ef Mon Sep 17 00:00:00 2001
From: Chris33871 <christian.harries15@gmail.com>
Date: Tue, 20 May 2025 21:31:28 +0100
Subject: [PATCH 09/12] Revert "gh-86802: Fix asyncio memory leak; shielded
 task exceptions log once through the exception handler (gh-134331)"

This reverts commit f695eca60cfc53cf3322323082652037d6d0cfef.
---
 Lib/asyncio/tasks.py                          | 36 ++++-------------
 Lib/test/test_asyncio/test_tasks.py           | 40 -------------------
 ...5-05-20-15-13-43.gh-issue-86802.trF7TM.rst |  3 --
 3 files changed, 7 insertions(+), 72 deletions(-)
 delete mode 100644 Misc/NEWS.d/next/Library/2025-05-20-15-13-43.gh-issue-86802.trF7TM.rst

diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index fbd5c39a7c56ac..888615f8e5e1b3 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -908,25 +908,6 @@ 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.
 
@@ -972,11 +953,14 @@ def shield(arg):
     else:
         cur_task = None
 
-    def _clear_awaited_by_callback(inner):
-        futures.future_discard_from_awaited_by(inner, cur_task)
+    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 _inner_done_callback(inner):
         if outer.cancelled():
+            if not inner.cancelled():
+                # Mark inner's result as retrieved.
+                inner.exception()
             return
 
         if inner.cancelled():
@@ -988,16 +972,10 @@ def _inner_done_callback(inner):
             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 f6f976f213ac02..44498ef790e450 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -2116,46 +2116,6 @@ 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
deleted file mode 100644
index d3117b16f04436..00000000000000
--- a/Misc/NEWS.d/next/Library/2025-05-20-15-13-43.gh-issue-86802.trF7TM.rst
+++ /dev/null
@@ -1,3 +0,0 @@
-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.

From a78bde0607df475e3ac009485ec22afba8d05e59 Mon Sep 17 00:00:00 2001
From: Chris33871 <christian.harries15@gmail.com>
Date: Tue, 20 May 2025 21:33:34 +0100
Subject: [PATCH 10/12] Fix connection backlog offset + updated tests + added
 test for backlog=0 and backlog=1

---
 Lib/asyncio/selector_events.py                |  2 +-
 Lib/test/test_asyncio/test_selector_events.py | 16 ++++++++++++++--
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/Lib/asyncio/selector_events.py b/Lib/asyncio/selector_events.py
index 22147451fa7ebd..6ad84044adf146 100644
--- a/Lib/asyncio/selector_events.py
+++ b/Lib/asyncio/selector_events.py
@@ -173,7 +173,7 @@ def _accept_connection(
         # listening socket has triggered an EVENT_READ. There may be multiple
         # connections waiting for an .accept() so it is called in a loop.
         # See https://bugs.python.org/issue27906 for more details.
-        for _ in range(backlog):
+        for _ in range(backlog + 1):
             try:
                 conn, addr = sock.accept()
                 if self._debug:
diff --git a/Lib/test/test_asyncio/test_selector_events.py b/Lib/test/test_asyncio/test_selector_events.py
index de81936b7456f2..aab6a779170eb9 100644
--- a/Lib/test/test_asyncio/test_selector_events.py
+++ b/Lib/test/test_asyncio/test_selector_events.py
@@ -347,6 +347,18 @@ def test_process_events_write_cancelled(self):
               selectors.EVENT_WRITE)])
         self.loop._remove_writer.assert_called_with(1)
 
+    def test_accept_connection_zero_one(self):
+        for backlog in [0, 1]:
+            sock = mock.Mock()
+            sock.accept.return_value = (mock.Mock(), mock.Mock())
+            with self.subTest(backlog):
+                mock_obj = mock.patch.object
+                with mock_obj(self.loop, '_accept_connection2') as accept2_mock:
+                    self.loop._accept_connection(
+                        mock.Mock(), sock, backlog=backlog)
+                self.loop.run_until_complete(asyncio.sleep(0))
+                self.assertEqual(sock.accept.call_count, backlog + 1)
+
     def test_accept_connection_multiple(self):
         sock = mock.Mock()
         sock.accept.return_value = (mock.Mock(), mock.Mock())
@@ -362,7 +374,7 @@ def test_accept_connection_multiple(self):
             self.loop._accept_connection(
                 mock.Mock(), sock, backlog=backlog)
         self.loop.run_until_complete(asyncio.sleep(0))
-        self.assertEqual(sock.accept.call_count, backlog)
+        self.assertEqual(sock.accept.call_count, backlog + 1)
 
     def test_accept_connection_skip_connectionabortederror(self):
         sock = mock.Mock()
@@ -388,7 +400,7 @@ def mock_sock_accept():
         # as in test_accept_connection_multiple avoid task pending
         # warnings by using asyncio.sleep(0)
         self.loop.run_until_complete(asyncio.sleep(0))
-        self.assertEqual(sock.accept.call_count, backlog)
+        self.assertEqual(sock.accept.call_count, backlog + 1)
 
 class SelectorTransportTests(test_utils.TestCase):
 

From f710535b4ac047027b9fb96d92b90700fb5cf925 Mon Sep 17 00:00:00 2001
From: Chris33871 <christian.harries15@gmail.com>
Date: Tue, 20 May 2025 21:46:26 +0100
Subject: [PATCH 11/12] added blurb

---
 .../next/Library/2025-05-20-21-45-58.gh-issue-90871.Gkvtp6.rst  | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2025-05-20-21-45-58.gh-issue-90871.Gkvtp6.rst

diff --git a/Misc/NEWS.d/next/Library/2025-05-20-21-45-58.gh-issue-90871.Gkvtp6.rst b/Misc/NEWS.d/next/Library/2025-05-20-21-45-58.gh-issue-90871.Gkvtp6.rst
new file mode 100644
index 00000000000000..12026535720ff4
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-05-20-21-45-58.gh-issue-90871.Gkvtp6.rst
@@ -0,0 +1,2 @@
+Fixed an off by one error concerning the backlog parameter in
+asyncio.create_unix_server. Contributed by Christian Harries.

From 0f28986c47bfcd1822d8ff24f3551ab7bc725af2 Mon Sep 17 00:00:00 2001
From: Kumar Aditya <kumaraditya@python.org>
Date: Wed, 21 May 2025 17:28:34 +0530
Subject: [PATCH 12/12] Update
 Misc/NEWS.d/next/Library/2025-05-20-21-45-58.gh-issue-90871.Gkvtp6.rst

---
 .../next/Library/2025-05-20-21-45-58.gh-issue-90871.Gkvtp6.rst  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Library/2025-05-20-21-45-58.gh-issue-90871.Gkvtp6.rst b/Misc/NEWS.d/next/Library/2025-05-20-21-45-58.gh-issue-90871.Gkvtp6.rst
index 12026535720ff4..49397c9705ecfe 100644
--- a/Misc/NEWS.d/next/Library/2025-05-20-21-45-58.gh-issue-90871.Gkvtp6.rst
+++ b/Misc/NEWS.d/next/Library/2025-05-20-21-45-58.gh-issue-90871.Gkvtp6.rst
@@ -1,2 +1,2 @@
 Fixed an off by one error concerning the backlog parameter in
-asyncio.create_unix_server. Contributed by Christian Harries.
+:meth:`~asyncio.loop.create_unix_server`. Contributed by Christian Harries.