checkElementsNotNull(contents, n);
    Arrays.sort(contents, 0, n, comparator);
    int uniques = 1;
    for (int i = 1; i < n; i++) {
      E cur = contents[i];
      E prev = contents[uniques - 1];
      if (comparator.compare(cur, prev) != 0) {
        contents[uniques++] = cur;
      }
    }
    Arrays.fill(contents, uniques, n, null);
    if (uniques < contents.length / 2) {

    while (true) {
      Waiter pred = null;
      Waiter curr = waiters;
      if (curr == Waiter.TOMBSTONE) {
        return; // give up if someone is calling complete
      }
      Waiter succ;
      while (curr != null) {
        succ = curr.next;
        if (curr.thread != null) { // we aren't unlinking this node, update pred.
          pred = curr;