@Override
        public Void call() throws IOException {
          task.editRegion(hri);
          return null;
        }
Execute the task on the specified set of regions.
@param exec    Thread Pool Executor
@param regions {@link RegionInfo} that describes the regions to edit
@param task    {@link RegionFillTask} custom code to edit the region
hbase-server/src/main/java/org/apache/hadoop/hbase/util/ModifyRegionUtils.java