PYTHON-4147: Silence noisy thread.start() RuntimeError at shutdown

pymongo/periodic_executor.py

@@ -23,6 +23,8 @@
 
 from pymongo.lock import _create_lock
 
+_THREAD_START_ON_SHUTDOWN_ERR = "can't create new thread at interpreter shutdown"
+
 
 class PeriodicExecutor:
     def __init__(
@@ -91,7 +93,15 @@ def open(self) -> None:
             thread.daemon = True
             self._thread = weakref.proxy(thread)
             _register_executor(self)
-            thread.start()
+            # Mitigation to RuntimeError firing when thread starts on shutdown
+            # https://github.com/python/cpython/issues/114570
+            try:
+                thread.start()
+            except RuntimeError as e:
+                if str(e) == _THREAD_START_ON_SHUTDOWN_ERR:
+                    self._thread = None
+                    return
+                raise
 
     def close(self, dummy: Any = None) -> None:
         """Stop. To restart, call open().

test/test_monitor.py

@@ -16,6 +16,7 @@
 from __future__ import annotations
 
 import gc
+import subprocess
 import sys
 from functools import partial
 
@@ -79,6 +80,17 @@ def test_cleanup_executors_on_client_close(self):
         for executor in executors:
             wait_until(lambda: executor._stopped, f"closed executor: {executor._name}", timeout=5)
 
+    @unittest.skipIf(sys.version_info[:2] >= (3, 12), reason="Python version must be (>=3.12)")
+    def test_no_thread_start_runtime_err_on_shutdown(self):
+        """Test we silence noisy runtime errors fired when the MongoClient spawns a new thread
+        on process shutdown."""
+        command = ["python", "-c", "'from pymongo import MongoClient; c = MongoClient()'"]
+        completed_process: subprocess.CompletedProcess = subprocess.run(
+            " ".join(command), shell=True, capture_output=True
+        )
+
+        assert not completed_process.stderr
+
 
 if __name__ == "__main__":
     unittest.main()