@Override
  public void close() {
    if (channel != null && !channel.isClosed()) {
      channel.close();
    }
  }
GMSQuorumChecker is the implementation of QuorumChecker and can be used to determine
whether a quorum of membership is accessible.
geode-membership/src/main/java/org/apache/geode/distributed/internal/membership/gms/messenger/GMSQuorumChecker.java