code: @Nullable
    private MasterWorkerInfo registerWorkerInternal(long workerId) {
      for (IndexedSet<MasterWorkerInfo> workers: Arrays.asList(mTempWorkers, mLostWorkers)) {
        MasterWorkerInfo worker = workers.getFirstByField(ID_INDEX, workerId);
        if (worker == null) {
          continue;
        }
  
        synchronized (worker) {
          worker.updateLastUpdatedTimeMs();
          mWorkers.add(worker);
          workers.remove(worker);
          if (workers == mLostWorkers) {
            for (Consumer<Address> function : mLostWorkerFoundListeners) {
              function.accept(new Address(worker.getWorkerAddress().getHost(),
                    worker.getWorkerAddress().getRpcPort()));
            }
            LOG.warn("A lost worker {} has requested its old id {}.",
                worker.getWorkerAddress(), worker.getId());
          }
        }
  
        return worker;
      }
      return null;
    }
docs: Re-register a lost worker or complete registration after getting a worker id.
  
  @param workerId the worker id to register