private void sendPingMessages() {
    // send a ping message to each member in the last view seen
    List<ID> members = lastView.getMembers();
    for (ID addr : members) {
      if (!receivedAcks.contains(addr)) {
        JGAddress dest = new JGAddress(addr);
        if (isInfoEnabled) {
          logger.info("quorum check: sending request to {}", addr);
        }
        try {
          pingPonger.sendPingMessage(channel, myAddress, dest);
        } catch (Exception e) {
          logger.info("Failed sending Ping message to " + dest);
        }
      }
    }
  }
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