public Set<ClientProxyMembershipID> getActiveClients() {
    Set<ClientProxyMembershipID> clients = new HashSet<>();
    for (CacheClientProxy proxy : getClientProxies()) {
      if (proxy.hasRegisteredInterested()) {
        ClientProxyMembershipID proxyID = proxy.getProxyID();
        clients.add(proxyID);
      }
    }
    return clients;
  }
Returns (possibly stale) set of memberIds for all clients being actively notified by this
server.

@return set of memberIds
geode-core/src/main/java/org/apache/geode/internal/cache/tier/sockets/CacheClientNotifier.java