RegionLocations getRegionLocationInCache(TableName tableName, byte[] row) {
    TableCache tableCache = cache.get(tableName);
    if (tableCache == null) {
      return null;
    }
    return locateRowInCache(tableCache, row, RegionReplicaUtil.DEFAULT_REPLICA_ID);
  }
The asynchronous locator for regions other than meta.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncNonMetaRegionLocator.java