@Override
  protected List<WAL> getWALs0() {
    if (wal != null) {
      return Lists.newArrayList(wal);
    }
    walCreateLock.readLock().lock();
    try {
      if (wal == null) {
        return Collections.emptyList();
      } else {
        return Lists.newArrayList(wal);
      }
    } finally {
      walCreateLock.readLock().unlock();
    }
  }
@param factory    factory that made us, identity used for FS layout. may not be null
@param conf       may not be null
@param providerId differentiate between providers from one factory, used for FS layout. may be
                  null
hbase-server/src/main/java/org/apache/hadoop/hbase/wal/AbstractFSWALProvider.java