code: def _on_trigger(self, task_spec):
          
          # Find a Task for this TaskSpec.
          my_task = self._find_my_task(task_spec)
          if my_task._has_state(Task.COMPLETED):
              state = Task.READY
          else:
              state = Task.FUTURE
          for output in self.outputs:
              new_task = my_task._add_child(output, state)
              new_task.triggered = True
              output._predict(new_task)
docs: May be called after execute() was already completed to create an
          additional outbound task.