code: public final Cache2kBuilder<K,V> asyncListenerExecutor(Executor v) {
      config().setAsyncListenerExecutor(new CustomizationReferenceSupplier<Executor>(v));
      return this;
    }
docs: Executor for asynchronous listeners. If no executor is specified, an internal
  executor is used that has unbounded thread capacity.
  
  @see #addAsyncListener(CacheEntryOperationListener)