issue #413: paper over harmless duplicate del_route()

Ideally it would only be called once, and in future maybe it can, but
right now we need to cope with these cases:

* Downstream parent notifies us of disconnection (DEL_ROUTE)
* We notify ourself of disconnection
* We notify ourself and so does downstream parent

It's case 3 that causes the error.

ansible_mitogen/services.py

@@ -303,12 +303,9 @@ class ContextService(mitogen.service.Service):
         longer reachable context.  This method runs in the Broker thread and
         must not to block.
         """
-        # TODO: there is a race between creation of a context and disconnection
-        # of its related stream. An error reply should be sent to any message
-        # in _latches_by_key below.
         self._lock.acquire()
         try:
-            LOG.info('Forgetting %r due to stream disconnect', context)
+            LOG.info('%r: Forgetting %r due to stream disconnect', self, context)
             self._forget_context_unlocked(context)
         finally:
             self._lock.release()

mitogen/core.py

@@ -2104,8 +2104,8 @@ class Router(object):
 
     def _on_del_route(self, msg):
         """
-        Stub DEL_ROUTE handler; fires 'disconnect' events on the corresponding
-        member of :attr:`_context_by_id`. This handler is replaced by
+        Stub :data:`DEL_ROUTE` handler; fires 'disconnect' events on the
+        corresponding :attr:`_context_by_id` member. This is replaced by
         :class:`mitogen.parent.RouteMonitor` in an upgraded context.
         """
         LOG.error('%r._on_del_route() %r', self, msg)

mitogen/parent.py

@@ -1558,6 +1558,9 @@ class RouteMonitor(object):
         #: stream; used to cleanup routes during disconnection.
         self._routes_by_stream = {}
 
+    def __repr__(self):
+        return 'RouteMonitor()'
+
     def _send_one(self, stream, handle, target_id, name):
         """
         Compose and send an update message on a stream.
@@ -1644,7 +1647,8 @@ class RouteMonitor(object):
         Respond to disconnection of a local stream by
         """
         routes = self._routes_by_stream.pop(stream)
-        LOG.debug('%r is gone; propagating DEL_ROUTE for %r', stream, routes)
+        LOG.debug('%r: %r is gone; propagating DEL_ROUTE for %r',
+                  self, stream, routes)
         for target_id in routes:
             self.router.del_route(target_id)
             self._propagate_up(mitogen.core.DEL_ROUTE, target_id)
@@ -1692,18 +1696,21 @@ class RouteMonitor(object):
 
         target_id = int(msg.data)
         registered_stream = self.router.stream_by_id(target_id)
+        if registered_stream is None:
+            return
+
         stream = self.router.stream_by_id(msg.auth_id)
         if registered_stream != stream:
-            LOG.error('Received DEL_ROUTE for %d from %r, expected %r',
-                      target_id, stream, registered_stream)
+            LOG.error('%r: received DEL_ROUTE for %d from %r, expected %r',
+                      self, target_id, stream, registered_stream)
             return
 
         context = self.router.context_by_id(target_id, create=False)
         if context:
-            LOG.debug('%r: Firing local disconnect for %r', self, context)
+            LOG.debug('%r: firing local disconnect for %r', self, context)
             mitogen.core.fire(context, 'disconnect')
 
-        LOG.debug('Deleting route to %d via %r', target_id, stream)
+        LOG.debug('%r: deleting route to %d via %r', self, target_id, stream)
         routes = self._routes_by_stream.get(stream)
         if routes:
             routes.discard(target_id)