docs: @AllowConcurrentEvents
      @Subscribe
      public void handleSubscriptionEvents(final BusInternalEvent event) {
          final List<CompletionUserRequestNotifier> runningWaiters = new ArrayList<CompletionUserRequestNotifier>();
          synchronized (activeWaiters) {
              runningWaiters.addAll(activeWaiters);
          }
          if (runningWaiters.size() == 0) {
              return;
          }
          for (final CompletionUserRequestNotifier cur : runningWaiters) {
              cur.onBusEvent(event);
          }
      }