Github user ilooner commented on the issue:
https://github.com/apache/drill/pull/1105
@sachouche I traced through the code. The updateAggregateStats method is
called, which then calls the getOutgoingBatches method of the code generated
Partitioners. That method is just a simple getter. So no one is acquiring the
same lock. But even if someone else was, the code in the close method is single
threaded, and synchronize blocks are reentrant. ---
