code: def subtask(self, func, *args, **kw):
          
          self.started_task()
          try:
              func(*args, **kw)
          except Exception:
              self.log(ERROR, 'Subtask %s(*%s, **%s) failed!' % (func, args, kw))
          finally:
              self.finished_task()
docs: Helper function for tasks needing to run subthreads. Takes care of 
          remembering that the subtask is running, and of cleaning up after it.
          Example starting a simple.Task():
            backend.subtask(task.ignore, 1, 'a', verbose=False)
          
          *args and **kw will be propagated to `func`.