Method Purge

cpp/src/arrow/util/async_generator.h:177–186

          finished(false) {}

    void Purge() {
      // This might be called by an original callback (if the source iterator fails or
      // ends) or by a mapped callback (if the map function fails or ends prematurely).
      // Either way it should only be called once and after finished is set so there is no
      // need to guard access to `waiting_jobs`.
      while (!waiting_jobs.empty()) {
        waiting_jobs.front().MarkFinished(IterationTraits<V>::End());
        waiting_jobs.pop_front();
      }
    }

    AsyncGenerator<T> source;
    std::function<Future<V>(const T&)> map;