void start() {
    watcherFuture = watcherExecutorService.submit(watcherCallable);
    expirerFuture = expirerExecutorService.submit(expirerCallable);
  }
Invoke when a pathIdentifier has been found, or is no longer of interest
@param pathIdentifier
llap-server/src/java/org/apache/hadoop/hive/llap/shufflehandler/DirWatcher.java