@Override
    public synchronized Void call() throws Exception {
      try {
        checkRegionConsistency(key, hbi);
      } catch (Exception e) {
        // If the region is non-META region, skip this region and send warning/error message; if
        // the region is META region, we should not continue.
        LOG.warn(
          "Unable to complete check or repair the region '" + hbi.getRegionNameAsString() + "'.",
          e);
        if (hbi.getHdfsHRI().isMetaRegion()) {
          throw e;
        }
        LOG.warn("Skip region '" + hbi.getRegionNameAsString() + "'");
        addSkippedRegion(hbi);
      }
      return null;
    }
Check consistency of all regions using multiple threads concurrently.
hbase-server/src/main/java/org/apache/hadoop/hbase/util/HBaseFsck.java