code: public boolean offer(E e) {
          final ReentrantLock lock = this.lock;
          lock.lock();
          try {
              q.offer(e);
              if (q.peek() == e) {
                  leader = null;
                  available.signal();
              }
              return true;
          } finally {
              lock.unlock();
          }
      }
docs: Inserts the specified element into this delay queue.
  
  @param e the element to add
  @return {@code true}
  @throws NullPointerException if the specified element is null