Method RestartTask

cpp/src/arrow/util/async_generator.h:1696–1715

    }

    Future<T> RestartTask(std::shared_ptr<State> state, util::Mutex::Guard guard,
                          Future<T> next) {
      if (TaskIsRunning()) {
        // If the task is still cleaning up we need to wait for it to finish before
        // restarting.  We also want to block the consumer until we've restarted the
        // reader to avoid multiple restarts
        return task_finished.Then([state, next]() {
          // This may appear dangerous (recursive mutex) but we should be guaranteed the
          // outer guard has been released by this point.  We know...
          // * task_finished is not already finished (it would be invalid in that case)
          // * task_finished will not be marked complete until we've given up the mutex
          auto guard_ = state->mutex.Lock();
          state->DoRestartTask(state, std::move(guard_));
          return next;
        });
      }
      // Otherwise we can restart immediately
      DoRestartTask(std::move(state), std::move(guard));
      return next;
    }

    internal::Executor* io_executor;
    const int max_q;