static <A extends Collection<? extends Collection>> L parallelMap(A l, fO f) ctex {

  ret parallelMap(iterator((Collection) l), f);

}

static L parallelMap(Iterator<? extends Collection> it, fO f) ctex {

  final new L<Pair<O, Int>> out;

  int poolSize = coresToUse(), queueSize = 10;

  NotifyingBlockingThreadPoolExecutor e = new(poolSize, queueSize, 15, TimeUnit.SECONDS);

  try {

    int i = 0;

    for (fO o : iterable(it)) {

      ++i;

      final int _i = i;

      e.execute(r { pcall {

        O x = callF(f, o);

        synchronized(out) {

          out.add(pair(x, _i));

        }

      }});

    }

    e.shutdown();

    e.awaitTermination(1, TimeUnit.DAYS);

  } finally {

    e.shutdown();

  }

  ret firstOfPairs(sortBySecondOfPairs_inPlace(out));

}