@Override
  public synchronized boolean checkForQuorum(long timeout) throws InterruptedException {
    if (quorumAchieved) {
      return true;
    }

    resume(); // make sure this quorum checker is the JGroups receiver

    if (isInfoEnabled) {
      logger.info("beginning quorum check with {}", this);
    }
    sendPingMessages();
    quorumAchieved = waitForResponses(lastView.getMembers().size(), timeout);
    // If we did not achieve full quorum, calculate if we achieved quorum
    if (!quorumAchieved) {
      quorumAchieved = calculateQuorum();
    }
    return quorumAchieved;
  }
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