Revert "gh-86802: Fix asyncio memory leak; shielded task exceptions log once through the exception handler (gh-134331)"

This reverts commit f695eca.

Author: ChristianHrs

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)

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)