*
   * <p>It is imperative that the user manually synchronize on the returned queue when accessing the
   * queue's iterator:
   *
   * <pre>{@code
   * Queue<E> queue = Queues.synchronizedQueue(MinMaxPriorityQueue.<E>create());
   * ...
   * queue.add(element);  // Needn't be in synchronized block
   * ...
   * synchronized (queue) {  // Must synchronize on queue!