code: public void lock() {
      locked = true;
      forAllObservables(new Consumer<ManagedObservable<?>>() {
        @Override
        public void accept(ManagedObservable<?> managedObservable) {
          managedObservable.lock();
        }
      });
    }
docs: Locks (prevents) Observables added to this group from emitting new events. Observables added
  via {@link #transform(Observer, String)} while the group is locked will
  **not** be subscribed until their respective group is unlocked. If it's never unlocked, then
  the Observable will never be subscribed to at all. This does not clear references to existing
  Observers. Please use {@link #dispose()} if you want to clear references to existing
  Observers.