code: public static RxEventLoopProvider useEventLoopProvider(RxEventLoopProvider provider) {
          RxEventLoopProvider oldProvider = rxEventLoopProvider;
          rxEventLoopProvider = provider;
          return oldProvider;
      }
docs: An implementation of {@link RxEventLoopProvider} to be used by all clients and servers created after this call.
  
  @param provider New provider to use.
  
  @return Existing provider.