private AtomicBoolean addInternal(PacketRequest request) {
   AtomicBoolean firstRequest = new AtomicBoolean(false);
   requests.compute(
       request.selector(),
       (s, existingRequests) -> {
         if (existingRequests == null) {
           firstRequest.set(true);
           return ImmutableSet.of(request);
         } else if (!existingRequests.contains(request)) {
           return ImmutableSet.<PacketRequest>builder()
               .addAll(existingRequests)
               .add(request)
               .build();
         } else {
           return existingRequests;
         }
       });
   return firstRequest;
 }
 private AtomicBoolean removeInternal(PacketRequest request) {
   AtomicBoolean removedLast = new AtomicBoolean(false);
   requests.computeIfPresent(
       request.selector(),
       (s, existingRequests) -> {
         if (existingRequests.contains(request)) {
           Set<PacketRequest> newRequests = Sets.newHashSet(existingRequests);
           newRequests.remove(request);
           if (newRequests.size() > 0) {
             return ImmutableSet.copyOf(newRequests);
           } else {
             removedLast.set(true);
             return null;
           }
         } else {
           return existingRequests;
         }
       });
   return removedLast;
 }