bpo-35125: remove inner callback on outer cancellation in asyncio shield (GH-10340)

When the future returned by shield is cancelled, its completion callback of the
inner future is not removed. This makes the callback list of inner inner future
grow each time a shield is created and cancelled.

This change unregisters the callback from the inner future when the outer
future is cancelled.



https://bugs.python.org/issue35125

1 files changed, 10 insertions, 1 deletions

diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py
index c4f6d70..fa9783f 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -1777,7 +1777,7 @@ class BaseTaskTests:
         test_utils.run_briefly(self.loop)
         self.assertIs(outer.exception(), exc)
 
-    def test_shield_cancel(self):
+    def test_shield_cancel_inner(self):
         inner = self.new_future(self.loop)
         outer = asyncio.shield(inner)
         test_utils.run_briefly(self.loop)
@@ -1785,6 +1785,15 @@ class BaseTaskTests:
         test_utils.run_briefly(self.loop)
         self.assertTrue(outer.cancelled())
 
+    def test_shield_cancel_outer(self):
+        inner = self.new_future(self.loop)
+        outer = asyncio.shield(inner)
+        test_utils.run_briefly(self.loop)
+        outer.cancel()
+        test_utils.run_briefly(self.loop)
+        self.assertTrue(outer.cancelled())
+        self.assertEqual(0, 0 if outer._callbacks is None else len(outer._callbacks))
+
     def test_shield_shortcut(self):
         fut = self.new_future(self.loop)
         fut.set_result(42)