code: public static <E> Queue<E> synchronizedQueue(Queue<E> queue) {
      return Synchronized.queue(queue, null);
    }
docs: Returns a synchronized (thread-safe) queue backed by the specified queue. In order to guarantee
  serial access, it is critical that <b>all</b> access to the backing queue is accomplished
  through the returned queue.
  
  <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!
  Iterator<E> i = queue.iterator(); // Must be in synchronized block
  while (i.hasNext()) {
  foo(i.next());
  }
  }
  }</pre>
  
  <p>Failure to follow this advice may result in non-deterministic behavior.
  
  <p>The returned queue will be serializable if the specified queue is serializable.
  
  @param queue the queue to be wrapped in a synchronized view
  @return a synchronized view of the specified queue
  @since 14.0