Method AddScanTasks

cpp/src/arrow/dataset/scan_node.cc:369–394

    }

    Future<> AddScanTasks(const std::shared_ptr<FragmentScanner>& fragment_scanner) {
      scan_state->fragment_scanner = fragment_scanner;
      ScanState* state_view = scan_state.get();
      Future<> list_and_scan_done = Future<>::Make();
      // Finish callback keeps the scan state alive until all scan tasks done
      struct StateHolder {
        Status operator()() {
          list_and_scan_done.MarkFinished();
          return Status::OK();
        }
        Future<> list_and_scan_done;
        std::unique_ptr<ScanState> scan_state;
      };

      std::unique_ptr<util::AsyncTaskGroup> scan_tasks = util::AsyncTaskGroup::Make(
          node->batches_throttle_.get(),
          StateHolder{list_and_scan_done, std::move(scan_state)});
      for (int i = 0; i < fragment_scanner->NumBatches(); i++) {
        node->num_batches_.fetch_add(1);
        scan_tasks->AddTask(std::make_unique<ScanBatchTask>(node, state_view, i));
      }
      return Status::OK();
      // The "list fragments" task doesn't actually end until the fragments are
      // all scanned.  This allows us to enforce fragment readahead.
      return list_and_scan_done;
    }

    // Take the dataset options, and the fragment evolution, and figure out exactly how
    // we should scan the fragment itself.