code: public static Function<Client<HttpRequest, HttpResponse>, ConcurrencyLimitingHttpClient> newDecorator(
              int maxConcurrency, long timeout, TimeUnit unit) {
          validateAll(maxConcurrency, timeout, unit);
          return delegate -> new ConcurrencyLimitingHttpClient(delegate, maxConcurrency, timeout, unit);
      }
docs: Creates a new {@link Client} decorator that limits the concurrent number of active HTTP requests.