Function MakeReadaheadIterator

cpp/src/arrow/util/async_generator.h:1927–1940

/// MakeGeneratorIterator.
template <typename T>
Result<Iterator<T>> MakeReadaheadIterator(Iterator<T> it, int readahead_queue_size) {
  ARROW_ASSIGN_OR_RAISE(auto io_executor, internal::ThreadPool::Make(1));
  auto max_q = readahead_queue_size;
  auto q_restart = std::max(1, max_q / 2);
  ARROW_ASSIGN_OR_RAISE(
      auto background_generator,
      MakeBackgroundGenerator(std::move(it), io_executor.get(), max_q, q_restart));
  // Capture io_executor to keep it alive as long as owned_bg_generator is still
  // referenced
  AsyncGenerator<T> owned_bg_generator = [io_executor, background_generator]() {
    return background_generator();
  };
  return MakeGeneratorIterator(std::move(owned_bg_generator));
}

/// \brief Make a generator that returns a single pre-generated future
///