code: private void sleepUntilAsyncSet() {
      LOG.info("Sleep a while until asynchronously set persistent timestamp");
      while (isAsyncSetPersistentTimestamp) {
        try {
          Thread.sleep(1);
        } catch (InterruptedException e) {
          LOG.fatal("Interrupt when sleep to set persistent timestamp, exit immediately");
          System.exit(0);
        }
      }
    }
docs: Sleep until asynchronously set persistent timestamp successfully.