code: def shutdown(self):
          
          # Remove reference to inputQueue (raises exception if inputQueue is used after method call)
          inputQueue = self.inputQueue
          self.inputQueue = None
          for i in range(self.numWorkers):
              inputQueue.put(None)
          for thread in self.workerThreads:
              thread.join()
          BatchSystemSupport.workerCleanup(self.workerCleanupInfo)
docs: Cleanly terminate worker threads. Add sentinels to inputQueue equal to maxThreads. Join
          all worker threads.