Random random = new Random();
    int nKeys = keys.size();
    long blah = 0;
    for (int i = 0; i < reps; i++) {
      Integer key = keys.get(random.nextInt(nKeys));
      int delta = random.nextInt(5);
      blah += delta;
      multiset.add(key, delta);
    }
    return blah;
  }

  private long runAddRemoveSingleThread(int reps) {
    Random random = new Random();