code: @Override
    public TransactionStateCache get() {
      if (instance == null) {
        synchronized (lock) {
          if (instance == null) {
            instance = new DefaultTransactionStateCache(namespace);
            instance.setConf(conf);
            instance.start();
          }
        }
      }
      return instance;
    }
docs: Returns a singleton instance of the transaction state cache, performing lazy initialization if necessary.
  @return A shared instance of the transaction state cache.