Used thread-safe dict.copy().keys() for MP consumer partitions

kafka/consumer/multiprocess.py

@@ -123,7 +123,10 @@ class MultiProcessConsumer(Consumer):
         self.pause = Event()        # Requests the consumers to pause fetch
         self.size = Value('i', 0)   # Indicator of number of messages to fetch
 
-        partitions = list(self.offsets.keys())
+        # dict.keys() returns a view in py3 + it's not a thread-safe operation
+        # http://blog.labix.org/2008/06/27/watch-out-for-listdictkeys-in-python-3
+        # It's safer to copy dict as it only runs during the init.
+        partitions = list(self.offsets.copy().keys())
 
         # By default, start one consumer process for all partitions
         # The logic below ensures that