@Override
    public void run() {
      try {
        runReader();
      } finally {
        closeTable();
        numThreadsWorking.decrementAndGet();
      }
    }
@param readerId only the keys with this remainder from division by {@link #numThreads} will
                be read by this thread
hbase-diagnostics/src/main/java/org/apache/hadoop/hbase/util/MultiThreadedReader.java