Monitors stop themselves when the Topology is GC'ed.

pymongo/monitor.py

@@ -44,7 +44,12 @@ class Monitor(object):
         """
         super(Monitor, self).__init__()
         self._server_description = server_description
-        self._topology = weakref.proxy(topology)
+
+        # A weakref callback, takes ref to the dead topology as its parameter.
+        def close(dummy):
+            self.close()
+
+        self._topology = weakref.proxy(topology, close)
         self._pool = pool
         self._settings = topology_settings
         self._stopped = False

test/test_monitor.py

@@ -49,7 +49,6 @@ class TestMonitor(IntegrationTest):
         ref = wait_until(partial(find_monitor_ref, monitor),
                          'register monitor')
 
-        client.close()
         del monitor
         del client