private void shutdownExecutorService() {
    if (executor != null) {
      executor.shutdown();
      executor = null;
    }
  }
A procedure for migrating replication queue data from zookeeper to hbase:replication table.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/replication/MigrateReplicationQueueFromZkToTableProcedure.java