code: public final Cache2kBuilder<K,V> loaderExecutor(Executor v) {
      config().setLoaderExecutor(new CustomizationReferenceSupplier<Executor>(v));
      return this;
    }
docs: Thread pool / executor service to use for asynchronous load operations. If no executor is specified
  the cache will create a thread pool, if needed.
  
  @see #loaderThreadCount(int)
  @see #prefetchExecutor(Executor)