@Override
  public void close() {
    root.lock.lock();
    try {
      root.datas = null;
      root.children = null;
    } finally {
      root.lock.unlock();
    }
  }
shared lock manager for dedicated hive server. all locks are managed in memory
ql/src/java/org/apache/hadoop/hive/ql/lockmgr/EmbeddedLockManager.java