Method DoRestartTask

cpp/src/arrow/util/async_generator.h:1672–1694

    }

    void DoRestartTask(std::shared_ptr<State> state, util::Mutex::Guard guard) {
      // If we get here we are actually going to start a new task so let's create a
      // task_finished future for it
      state->task_finished = Future<>::Make();
      state->reading = true;
      auto spawn_status = io_executor->Spawn(
          [state]() { BackgroundGenerator::WorkerTask(std::move(state)); });
      if (!spawn_status.ok()) {
        // If we can't spawn a new task then send an error to the consumer (either via a
        // waiting future or the queue) and mark ourselves finished
        state->finished = true;
        state->task_finished = Future<>();
        if (waiting_future.has_value()) {
          auto to_deliver = std::move(waiting_future.value());
          waiting_future.reset();
          guard.Unlock();
          to_deliver.MarkFinished(spawn_status);
        } else {
          ClearQueue();
          queue.push(spawn_status);
        }
      }
    }

    Future<T> RestartTask(std::shared_ptr<State> state, util::Mutex::Guard guard,
                          Future<T> next) {