private void reenableDisabledNode(NodeInfo nodeInfo) {
    writeLock.lock();
    try {
      LOG.info("Attempting to re-enable node: " + nodeInfo.toShortString());
      if (activeInstances.getInstance(nodeInfo.getNodeIdentity()) != null) {
        nodeInfo.enableNode();
        if (metrics != null) {
          metrics.setDisabledNodeCount(disabledNodesQueue.size());
        }
      } else {
        LOG.info("Not re-enabling node: {}, since it is not present in the RegistryActiveNodeList",
            nodeInfo.toShortString());
      }
    } finally {
      writeLock.unlock();
    }
  }
@param request the list of preferred hosts. null implies any host
@return
llap-tez/src/java/org/apache/hadoop/hive/llap/tezplugins/LlapTaskSchedulerService.java