Fix RemoteFunction._last_export_session (#4243)

python/ray/remote_function.py

@@ -59,9 +59,9 @@ class RemoteFunction(object):
 
         # Export the function.
         worker = ray.worker.get_global_worker()
-        worker.function_actor_manager.export(self)
         # In which session this function was exported last time.
         self._last_export_session = worker._session_index
+        worker.function_actor_manager.export(self)
 
     def __call__(self, *args, **kwargs):
         raise Exception("Remote functions cannot be called directly. Instead "