public Set adviseBridgeServers() {
    Set/* <DistributedMember> */ result = cachedBridgeServerAdvise;
    if (result == null) {
      synchronized (cacheLock) {
        result = cachedBridgeServerAdvise;
        if (result == null) {
          result = Collections.unmodifiableSet(adviseFilter(BRIDGE_SERVER_FILTER));
          cachedBridgeServerAdvise = result;
        }
      }
    }
    return result;
  }
Return an unmodifiable Set<DistributedMember> of the cache servers in this system.
geode-core/src/main/java/org/apache/geode/internal/cache/GridAdvisor.java