Work around Python issue 18418 in RS client.

Author: A. Jesse Jiryu Davis

pymongo/mongo_replica_set_client.py

@@ -272,8 +272,15 @@ def __init__(self, rsc, event_class):
  self.rsc = weakref.proxy(rsc, self.shutdown)
  self.event = event_class()
  self.refreshed = event_class()
+ self.started_event = event_class()
  self.stopped = False
 
+ def start_sync(self):
+ """Start the Monitor and block until it's really started.
+ """
+ self.start() # Implemented in subclasses.
+ self.started_event.wait(5)
+
  def shutdown(self, dummy=None):
  """Signal the monitor to shutdown.
  """
@@ -299,6 +306,7 @@ def monitor(self):
  """Run until the RSC is collected or an
  unexpected error occurs.
  """
+ self.started_event.set()
  while True:
  self.event.wait(Monitor._refresh_interval)
  if self.stopped:
@@ -747,7 +755,11 @@ def __init__(self, hosts_or_uri=None, max_pool_size=10,
  register_monitor(self.__monitor)
 
  if _connect:
- self.__monitor.start()
+ # Wait for the monitor to really start. Otherwise if we return to
+ # caller and caller forks immediately, the monitor could think it's
+ # still alive in the child process when it really isn't.
+ # See http://bugs.python.org/issue18418.
+ self.__monitor.start_sync()
 
  def _cached(self, dbname, coll, index):
  """Test if `index` is cached.