code: def _wait(self):
          
          val = self.wait_change.get()
  
          if isinstance(val, Exception):
              # Don't other uncharging, because execution is going to stop
              raise val
          else:
              # Uncharge for resources.
              self.member_burden -= len(val)
              self.concurrency_burden -= 1
docs: Block until an upload finishes
  
          Raise an exception if that tar volume failed with an error.