int getSizeOfCleaners() {
    return oldWALsCleaner.size();
  }
@param period    the period of time to sleep between each run
@param stopper   the stopper
@param conf      configuration to use
@param fs        handle to the FS
@param oldLogDir the path to the archived logs
@param pool      the thread pool used to scan directories
hbase-server/src/main/java/org/apache/hadoop/hbase/master/cleaner/LogCleaner.java