code: public boolean offer(E e, long timeout, TimeUnit unit) {
          xfer(e, true, ASYNC, 0);
          return true;
      }
docs: Inserts the specified element at the tail of this queue.
  As the queue is unbounded, this method will never block or
  return {@code false}.
  
  @return {@code true} (as specified by
  {@link java.util.concurrent.BlockingQueue#offer(Object,long,TimeUnit)
  BlockingQueue.offer})
  @throws NullPointerException if the specified element is null