@Override
  public synchronized void stopThreads() {
    if (LOGGER.isDebugEnabled()) {
      LOGGER.debug("Stopping expired delegation token remover thread");
    }
    running = false;
    if (tokenRemoverThread != null) {
      tokenRemoverThread.interrupt();
    }
  }
Synchronize master key updates / sequence generation for multiple nodes.
NOTE: {@link AbstractDelegationTokenSecretManager} keeps currentKey private, so we need
to utilize this "hook" to manipulate the key through the object reference.
This .20S workaround should cease to exist when Hadoop supports token store.
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/security/TokenStoreDelegationTokenSecretManager.java