PYTHON-5406 - AsyncPeriodicExecutor must reset CSOT contextvars befor… (#2360)

Author: NoahStapp

pymongo/_csot.py

@@ -32,6 +32,12 @@
 DEADLINE: ContextVar[float] = ContextVar("DEADLINE", default=float("inf"))
 
 
+def reset_all() -> None:
+    TIMEOUT.set(None)
+    RTT.set(0.0)
+    DEADLINE.set(float("inf"))
+
+
 def get_timeout() -> Optional[float]:
     return TIMEOUT.get(None)
 

pymongo/periodic_executor.py

@@ -23,6 +23,7 @@
 import weakref
 from typing import Any, Optional
 
+from pymongo import _csot
 from pymongo._asyncio_task import create_task
 from pymongo.lock import _create_lock
 
@@ -93,6 +94,8 @@ def skip_sleep(self) -> None:
         self._skip_sleep = True
 
     async def _run(self) -> None:
+        # The CSOT contextvars must be cleared inside the executor task before execution begins
+        _csot.reset_all()
         while not self._stopped:
             if self._task and self._task.cancelling():  # type: ignore[unused-ignore, attr-defined]
                 raise asyncio.CancelledError

test/asynchronous/test_async_contextvars_reset.py

@@ -0,0 +1,43 @@
+# Copyright 2025-present MongoDB, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Test that AsyncPeriodicExecutors do not copy ContextVars from their parents."""
+from __future__ import annotations
+
+import asyncio
+import sys
+from test.asynchronous.utils import async_get_pool
+from test.utils_shared import delay, one
+
+sys.path[0:0] = [""]
+
+from test.asynchronous import AsyncIntegrationTest
+
+
+class TestAsyncContextVarsReset(AsyncIntegrationTest):
+    async def test_context_vars_are_reset_in_executor(self):
+        if sys.version_info < (3, 11):
+            self.skipTest("Test requires asyncio.Task.get_context (added in Python 3.11)")
+
+        client = self.simple_client()
+
+        await client.db.test.insert_one({"x": 1})
+        for server in client._topology._servers.values():
+            for context in [
+                c
+                for c in server._monitor._executor._task.get_context()
+                if c.name in ["TIMEOUT", "RTT", "DEADLINE"]
+            ]:
+                self.assertIn(context.get(), [None, float("inf"), 0.0])
+        await client.db.test.delete_many({})

tools/synchro.py

@@ -185,6 +185,7 @@ def async_only_test(f: str) -> bool:
         "test_concurrency.py",
         "test_async_cancellation.py",
         "test_async_loop_safety.py",
+        "test_async_contextvars_reset.py",
     ]