Method PullSource

cpp/src/arrow/util/async_generator.h:1180–1185

          final_error(Status::OK()) {}

    Future<AsyncGenerator<T>> PullSource() {
      // Need to guard access to source() so we don't pull sync-reentrantly which
      // is never valid.
      auto lock = mutex.Lock();
      return source();
    }

    void SignalErrorUnlocked(const util::Mutex::Guard& guard) {
      broken = true;