*
   * <p>It is imperative that the user manually synchronize on the returned deque when accessing any
   * of the deque's iterators:
   *
   * {@snippet :
   * Deque<E> deque = Queues.synchronizedDeque(Queues.newArrayDeque());
   * ...
   * deque.add(element);  // Needn't be in synchronized block
   * ...
   * synchronized (deque) {  // Must synchronize on deque!

   *
   * <p>It is imperative that the user manually synchronize on the returned deque when accessing any
   * of the deque's iterators:
   *
   * {@snippet :
   * Deque<E> deque = Queues.synchronizedDeque(Queues.newArrayDeque());
   * ...
   * deque.add(element);  // Needn't be in synchronized block
   * ...
   * synchronized (deque) {  // Must synchronize on deque!