code: @SuppressWarnings("unchecked")
      public S parallel(ForkJoinPool fjp) {
          context = context.parallel(fjp);
          if (stream != null)
              stream = stream.parallel();
          return (S) this;
      }
docs: Returns an equivalent stream that is parallel and bound to the supplied
  {@link ForkJoinPool}.
  
  <p>
  This is an <a href="package-summary.html#StreamOps">intermediate</a>
  operation.
  
  <p>
  The terminal operation of this stream or any derived stream (except the
  streams created via {@link #parallel()} or {@link #sequential()} methods)
  will be executed inside the supplied {@code ForkJoinPool}. If current
  thread does not belong to that pool, it will wait till calculation
  finishes.
  
  @param fjp a {@code ForkJoinPool} to submit the stream operation to.
  @return a parallel stream bound to the supplied {@code ForkJoinPool}
  @since 0.2.0