#vulnerable code 
                                @Override
    public boolean tryAdvance(Consumer<? super E> action) {
        Objects.requireNonNull(action);
        LinkedBlockingDeque<E> q = queue;
        ReentrantLock lock = queueLock;
        if (!exhausted) {
            E e = null;
            lock.lock();
            try {
                if (current == null) {
                    current = getQueueFirst(q);
                }
                while (current != null) {
                    e = getNodeItem(current);
                    current = getNextNode(current);
                    if (e != null) {
                        break;
                    }
                }
            } finally {
                lock.unlock();
            }
            if (current == null) {
                exhausted = true;
            }
            if (e != null) {
                action.accept(e);
                return true;
            }
        }
        return false;
    } 
                            #location 24 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                @Override
    public boolean tryAdvance(Consumer<? super E> action) {
        Objects.requireNonNull(action);
        if (exhausted)
            return false;
        LinkedBlockingDeque<E> q = queue;
        ReentrantLock lock = queueLock;
        Object p = current;
        E e = null;
        lock.lock();
        try {
            if ((p != null && p != getNextNode(p)) || (p = getQueueFirst(q)) != null) {
                e = getNodeItem(p);
                p = getNextNode(p);
            }
        } finally {
            lock.unlock();
        }
        exhausted = ((current = p) == null);
        if (e == null)
            return false;
        action.accept(e);
        return true;
    }