void stop() {
      if (this.stopped) return;

      this.stopped = true;
      this.executor.shutdown();
    }
Gracefully shutdown the thread pool. An ongoing HRegion.flush() should not be interrupted
(see HBASE-13877)
hbase-server/src/main/java/org/apache/hadoop/hbase/procedure/flush/RegionServerFlushTableProcedureManager.java