@Override
  public synchronized MetricsMasterSource create(MetricsMasterWrapper masterWrapper) {
    if (FactoryStorage.INSTANCE.masterSource == null) {
      FactoryStorage.INSTANCE.masterSource = new MetricsMasterSourceImpl(masterWrapper);
    }
    return FactoryStorage.INSTANCE.masterSource;
  }
Factory to create MetricsMasterSource when given a MetricsMasterWrapper
hbase-hadoop-compat/src/main/java/org/apache/hadoop/hbase/master/MetricsMasterSourceFactoryImpl.java