code: @Override
    public void setupLocal() {
      super.setupLocal();
      _res = new DeepWaterTask(_sharedmodel, _sync_fraction, (Job)_jobKey.get());
      addToPendingCount(1);
      _res.dfork(null, _fr, true /*run_local*/);
    }
docs: Do the local computation: Perform one DeepWaterTask (with run_local=true) iteration.
  Pass over all the data (will be replicated in dfork() here), and use _sync_fraction random rows.
  This calls DeepWaterTask's reduce() between worker threads that update the same local model_info via Hogwild!
  Once the computation is done, reduce() will be called