private ListenableFuture<HDFSBlocksDistribution> asyncGetBlockDistribution(RegionInfo hri) {
    try {
      return loader.reload(hri, EMPTY_BLOCK_DISTRIBUTION);
    } catch (Exception e) {
      return Futures.immediateFuture(EMPTY_BLOCK_DISTRIBUTION);
    }
  }
Map hostname to ServerName, The output ServerName list will have the same order as input hosts.
@param hosts the list of hosts
@return ServerName list
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/RegionHDFSBlockLocationFinder.java