PYTHON-525 Try to halt monitors before exiting.

pymongo/monitor.py

@@ -67,6 +67,7 @@ class Monitor(object):
             thread = threading.Thread(target=self.run)
             thread.daemon = True
             self._thread = weakref.proxy(thread)
+            register_monitor(self)
             thread.start()
 
     def close(self):
@@ -171,6 +172,11 @@ class Monitor(object):
         return IsMaster(result['data'][0]), time.time() - start
 
 
+# MONITORS has a weakref to each running Monitor. A Monitor is kept alive by
+# a strong reference from its Server and its Thread. Once both are destroyed
+# the Monitor is garbage-collected and removed from MONITORS. If, however,
+# any threads are still running when the interpreter begins to shut down,
+# we attempt to halt and join them to avoid spurious errors.
 MONITORS = set()
 
 
@@ -192,6 +198,6 @@ def shutdown_monitors():
         monitor = ref()
         if monitor:
             monitor.close()
-            monitor.join()
+            monitor.join(10)
 
 atexit.register(shutdown_monitors)

test/test_monitor.py

@@ -0,0 +1,42 @@
+# Copyright 2014 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 the monitor module."""
+
+import gc
+import sys
+
+sys.path[0:0] = [""]
+
+from pymongo.monitor import MONITORS
+from test import unittest, port, host, IntegrationTest
+from test.utils import get_client, wait_until
+
+
+class TestMonitor(IntegrationTest):
+    def test_atexit_hook(self):
+        n_monitors = len(MONITORS)
+        client = get_client(host, port)
+        wait_until(lambda: len(MONITORS) == n_monitors + 1,
+                   'register new monitor')
+
+        del client
+        gc.collect()
+
+        wait_until(lambda: len(MONITORS) == n_monitors,
+                   'unregister monitor')
+
+
+if __name__ == "__main__":
+    unittest.main()