[PR #10923/19643c9c backport][3.12] Fix weakref garbage collection race condition in DNS resolver manager (#10924)

Co-authored-by: J. Nick Koston <[email protected]>

Author: patchback[bot]

CHANGES/10923.feature.rst

@@ -0,0 +1 @@
+10847.feature.rst

aiohttp/resolver.py

@@ -257,11 +257,14 @@ def release_resolver(
             loop: The event loop the resolver was using.
         """
         # Remove client from its loop's tracking
+        if loop not in self._loop_data:
+            return
         resolver, client_set = self._loop_data[loop]
         client_set.discard(client)
         # If no more clients for this loop, cancel and remove its resolver
         if not client_set:
-            resolver.cancel()
+            if resolver is not None:
+                resolver.cancel()
             del self._loop_data[loop]
 
 

tests/test_resolver.py

@@ -628,3 +628,49 @@ async def test_dns_resolver_manager_multiple_event_loops(
         # Verify resolver cleanup
         resolver1.cancel.assert_called_once()
         resolver2.cancel.assert_called_once()
+
+
+@pytest.mark.skipif(not getaddrinfo, reason="aiodns >=3.2.0 required")
+async def test_dns_resolver_manager_weakref_garbage_collection() -> None:
+    """Test that release_resolver handles None resolver due to weakref garbage collection."""
+    manager = _DNSResolverManager()
+
+    # Create a mock resolver that will be None when accessed
+    mock_resolver = Mock()
+    mock_resolver.cancel = Mock()
+
+    with patch("aiodns.DNSResolver", return_value=mock_resolver):
+        # Create an AsyncResolver to get a resolver from the manager
+        resolver = AsyncResolver()
+        loop = asyncio.get_running_loop()
+
+        # Manually corrupt the data to simulate garbage collection
+        # by setting the resolver to None
+        manager._loop_data[loop] = (None, manager._loop_data[loop][1])  # type: ignore[assignment]
+
+        # This should not raise an AttributeError: 'NoneType' object has no attribute 'cancel'
+        await resolver.close()
+
+        # Verify no exception was raised and the loop data was cleaned up properly
+        # Since we set resolver to None and there was one client, the entry should be removed
+        assert loop not in manager._loop_data
+
+
+@pytest.mark.skipif(not getaddrinfo, reason="aiodns >=3.2.0 required")
+async def test_dns_resolver_manager_missing_loop_data() -> None:
+    """Test that release_resolver handles missing loop data gracefully."""
+    manager = _DNSResolverManager()
+
+    with patch("aiodns.DNSResolver"):
+        # Create an AsyncResolver
+        resolver = AsyncResolver()
+        loop = asyncio.get_running_loop()
+
+        # Manually remove the loop data to simulate race condition
+        manager._loop_data.clear()
+
+        # This should not raise a KeyError
+        await resolver.close()
+
+        # Verify no exception was raised
+        assert loop not in manager._loop_data