private void initThreadPool() {
    this.executorService =
        Executors.newSingleThreadScheduledExecutor(
            r -> {
              Thread t =
                  new Thread(
                      Thread.currentThread().getThreadGroup(), r, "PeriodicalUpdateDNList", 0);
              if (!t.isDaemon()) {
                t.setDaemon(true);
              }
              if (t.getPriority() != Thread.NORM_PRIORITY) {
                t.setPriority(Thread.NORM_PRIORITY);
              }
              return t;
            });
  }
Multiple nodeUrl,If one node down, connect to the next one

@param nodeUrls List<String> Multiple ip:rpcPort eg.127.0.0.1:9001
iotdb-client/session/src/main/java/org/apache/iotdb/session/Session.java