protected final void closeClusterConnection() {
    if (asyncClusterConnection != null) {
      LOG.info("Close async cluster connection");
      try {
        this.asyncClusterConnection.close();
      } catch (IOException e) {
        // Although the {@link Closeable} interface throws an {@link
        // IOException}, in reality, the implementation would never do that.
        LOG.warn("Attempt to close server's AsyncClusterConnection failed.", e);
      }
    }
  }
Sets the abort state if not already set.
@return True if abortRequested set to True successfully, false if an abort is already in
        progress.
hbase-server/src/main/java/org/apache/hadoop/hbase/HBaseServerBase.java