code: public double sum(DoubleStream stream) {
          Callable<Double> callable = () -> stream.sum();
          return ThreadMethods.forkJoinExecution(callable, concurrencyConfiguration, stream.isParallel());
      }
docs: Executes sum on the provided DoubleStream using the provided collector.
  If the Stream is parallel, it is executed using the custom pool, else it
  is executed directly from the main thread.
  
  @param stream
  @return