'Update task state.
Arguments:
task_id (str): Id of the task to update.
Defaults to the id of the current task.
state (str): New state.
meta (Dict): State meta-data.'

def update_state(self, task_id=None, state=None, meta=None):

    if (task_id is None):
        task_id = self.request.id
    self.backend.store_result(task_id, meta, state)
