Gatherers_B8.snippet

// Sort Parallel Gatherer
static <T> Gatherer<T, ?, T> sortWithComparator(Comparator<? super T> comparator) {

   return Gatherer.of(
      () -> new ArrayList<T>(),
      (list, element, _) -> {
         list.add(element);
         return true;
      },
      (list1, list2) -> {
         list1.sort(comparator);
         list2.sort(comparator);
         int initialCapacity = list1.size() + list2.size();
         var list3 = new ArrayList<T>(initialCapacity);
         for (int index1 = 0, index2 = 0, index3 = 0; index3 < initialCapacity; index3++) {
            if (index1 < list1.size() && index2 < list2.size()) {
               if (comparator.compare(list1.get(index1), list2.get(index2)) < 0) {
                  list3.add(list1.get(index1));
                  index1++;
               } else {
                  list3.add(list2.get(index2));
                  index2++;
               }
            } else if (index1 < list1.size()) {
               list3.add(list1.get(index1));
               index1++;
            } else if (index2 < list2.size()) {
               list3.add(list2.get(index2));
               index2++;
            }
         }
         return list3;
      },
      (list, downstream) -> {
         list.stream()
             .takeWhile(_ -> !downstream.isRejecting())
             .forEach(downstream::push);
      }
   );
}

static <T extends Comparable<? super T>> Gatherer<T, ?, T> sort() {
   return sortWithComparator(Comparator.naturalOrder());
}

var stream = Stream.of(3, 2, 4, 5, 3, 1, 2, 5, 4);
var result = stream.parallel().gather(sort()).toList();
System.out.println("result = " + result);