code: public static AlluxioProperties defaults() {
      if (sDefaultProperties == null) {
        synchronized (DEFAULT_PROPERTIES_LOCK) { // We don't want multiple threads to reload
          // properties at the same time.
          // Check if properties are still null so we don't reload a second time.
          if (sDefaultProperties == null) {
            reloadProperties();
          }
        }
      }
      return sDefaultProperties.copy();
    }
docs: Returns an instance of {@link AlluxioConfiguration} with the defaults and values from
  alluxio-site properties.
  
  @return the set of Alluxio properties loaded from the site-properties file