docs: public void clear() {
          final ReentrantLock lock = this.lock;
          lock.lock();
          try {
              for (Node<E> f = first; f != null; ) {
                  f.item = null;
                  Node<E> n = f.next;
                  f.prev = null;
                  f.next = null;
                  f = n;
              }
              first = last = null;
              count = 0;
              notFull.signalAll();
          } finally {
              lock.unlock();
          }
      }