@Override
    public void run() {
      try {
        mapper.run(subcontext);
      } catch (Throwable ie) {
        LOG.error("Problem in running map.", ie);
      }
    }
Run the application's maps using a thread pool.
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapreduce/MultithreadedTableMapper.java