docs: def _schedule_callbacks(self, clear_cb=False):
          """Recording the task_end_time and task_cost_time,
              and prevent super()._schedule_callbacks to clean self._callbacks."""
          self.task_end_time = time.time()
          self.task_cost_time = self.task_end_time - self.task_start_time
          callbacks = self._callbacks[:]
          if not callbacks:
              return
          if clear_cb:
              self._callbacks[:] = []
          for callback in callbacks:
              self._loop.call_soon(callback, self, *self.extra_args)