private void ensureFDCapacity(int idx) {
    if (idx >= failureDetectionPorts.length) {
      int[] p = new int[idx + 10];
      if (failureDetectionPorts.length > 0) {
        System.arraycopy(failureDetectionPorts, 0, p, 0, failureDetectionPorts.length);
      }
      Arrays.fill(p, idx, idx + 9, -1);
      failureDetectionPorts = p;
    }
  }
ensures that there is a slot at idx to store an int
geode-membership/src/main/java/org/apache/geode/distributed/internal/membership/gms/GMSMembershipView.java