private void startCleanupTimer() {
    cleanupTimer =
        LoggingExecutors.newScheduledThreadPool(1, "GMSMembership.cleanupTimer", false);

    cleanupTimer.scheduleAtFixedRate(this::cleanUpSurpriseMembers, surpriseMemberTimeout,
        surpriseMemberTimeout / 3, TimeUnit.MILLISECONDS);
  }
starts periodic task to perform cleanup chores such as expire surprise members
geode-membership/src/main/java/org/apache/geode/distributed/internal/membership/gms/GMSMembership.java