protected void processActiveMembers(Set activeMembers) {
    for (final InternalDistributedMember member : members) {
      if (member != null) {
        if (!activeMembers.contains(member)) {
          memberDeparted(getDistributionManager(), member, false);
        }
      }
    }
  }
perform initial membership processing while under synchronization of this.members

@param activeMembers the DM's current membership set
geode-core/src/main/java/org/apache/geode/distributed/internal/ReplyProcessor21.java