def kill_running_tasks(self):
        """Stop running the specified task instance and downstream tasks.
        Obtain task_instance from session according to dag_id, run_id and task_id,
        If task_id is not empty, get task_instance with RUNNIN or NONE status from dag_run according to task_id,
          and set task_instance status to FAILED.
        If task_id is empty, get all task_instances whose status is RUNNIN or NONE from dag_run,
          and set the status of these task_instances to FAILED.

        args:
            dag_id: dag id
            run_id: the run id of dag run
            task_id: the task id of task instance of dag
        """
        logging.info("Executing custom 'kill_running_tasks' function")

        dagbag = self.get_dagbag()

        dag_id = self.get_argument(request, 'dag_id')
        run_id = self.get_argument(request, 'run_id')
        task_id = self.get_argument(request, 'task_id')

        session = settings.Session()
        query = session.query(DagRun)
        dag_run = query.filter(
            DagRun.dag_id == dag_id,
            DagRun.run_id == run_id
        ).first()

        if dag_run is None:
            return ApiResponse.not_found("dag run is not found")

        if dag_id not in dagbag.dags:
            return ApiResponse.bad_request("Dag id {} not found".format(dag_id))

        dag = dagbag.get_dag(dag_id)
        logging.info('dag: ' + str(dag))
        logging.info('dag_subdag: ' + str(dag.subdags))

        tis = []
        if task_id:
            task_instance = DagRun.get_task_instance(dag_run, task_id)
            if task_instance is None or task_instance.state not in [State.RUNNING, State.NONE]:
                return ApiResponse.not_found("task is not found or state is neither RUNNING nor NONE")
            else:
                tis.append(task_instance)
        else:
            tis = DagRun.get_task_instances(dag_run, [State.RUNNING, State.NONE])

        logging.info('tis: ' + str(tis))
        running_task_count = len(tis)

        if running_task_count > 0:
            for ti in tis:
                ti.state = State.FAILED
                ti.end_date = timezone.utcnow()
                session.merge(ti)
                session.commit()
        else:
            return ApiResponse.not_found("dagRun don't have running tasks")

        session.close()

        return ApiResponse.success()
    def restart_failed_task(self):
        """Restart the failed task in the specified dag run.
        According to dag_id, run_id get dag_run from session,
        query task_instances that status is FAILED in dag_run,
        restart them and clear status of all task_instance's downstream of them.

        args:
            dag_id: dag id
            run_id: the run id of dag run
        """
        logging.info("Executing custom 'restart_failed_task' function")

        dagbag = self.get_dagbag()

        dag_id = self.get_argument(request, 'dag_id')
        run_id = self.get_argument(request, 'run_id')

        session = settings.Session()
        query = session.query(DagRun)
        dag_run = query.filter(
            DagRun.dag_id == dag_id,
            DagRun.run_id == run_id
        ).first()

        if dag_run is None:
            return ApiResponse.not_found("dag run is not found")

        if dag_id not in dagbag.dags:
            return ApiResponse.bad_request("Dag id {} not found".format(dag_id))

        dag = dagbag.get_dag(dag_id)

        if dag is None:
            return ApiResponse.not_found("dag is not found")

        tis = DagRun.get_task_instances(dag_run, State.FAILED)
        logging.info('task_instances: ' + str(tis))

        failed_task_count = len(tis)
        if failed_task_count > 0:
            for ti in tis:
                dag = DAG.sub_dag(
                    self=dag,
                    task_regex=r"^{0}$".format(ti.task_id),
                    include_downstream=True,
                    include_upstream=False)

                count = DAG.clear(
                    self=dag,
                    start_date=dag_run.execution_date,
                    end_date=dag_run.execution_date,
                )
                logging.info('count:' + str(count))
        else:
            return ApiResponse.not_found("dagRun don't have failed tasks")

        session.close()

        return ApiResponse.success({
            'failed_task_count': failed_task_count,
            'clear_task_count': count
        })