urlQueueService.insert(urlQueue);

        // Poll should return the item
        final OpenSearchUrlQueue polled = urlQueueService.poll(sessionId);
        assertNotNull(polled);
        assertEquals("http://www.example.com/page1", polled.getUrl());
        assertEquals(sessionId, polled.getSessionId());

        // Second poll should return null (queue is empty)

     */
    @Override
    public OpenSearchUrlQueue poll(final String sessionId) {
        final QueueHolder queueHolder = getQueueHolder(sessionId);
        final Queue<OpenSearchUrlQueue> waitingQueue = queueHolder.waitingQueue;
        final Queue<OpenSearchUrlQueue> crawlingQueue = queueHolder.crawlingQueue;

        OpenSearchUrlQueue urlQueue = waitingQueue.poll();
        if (urlQueue == null) {

     */
    public void test_run_noUrlsInQueue() throws Exception {
        when(urlQueueService.poll(anyString())).thenReturn(null);
        crawlerContext.setStatus(CrawlerStatus.RUNNING);
        crawlerContext.maxThreadCheckCount = 1; // Will exit after 1 check

        crawlerThread.run();

        verify(urlQueueService, times(1)).poll(anyString());
    }

    /**
     * Test run method with crawler status DONE.
     */

     *
     * @return an encryption cipher
     */
    protected Cipher pollEncryptoCipher() {
        Cipher cipher = encryptoQueue.poll();
        if (cipher == null) {
            try {
                final SecretKeySpec sksSpec = new SecretKeySpec(key.getBytes(charsetName), algorithm);
                cipher = Cipher.getInstance(algorithm);

            }

            @Override
            public void offerAll(String sessionId, List<UrlQueue<?>> newUrlQueueList) {
            }

            @Override
            public UrlQueue<?> poll(String sessionId) {
                return null;
            }

            @Override
            public void saveSession(String sessionId) {
            }

            @Override

        mockQueue.add(urlQueue);

        when(dataHelper.getUrlQueueList(sessionId)).thenReturn(mockQueue);

        // Execute
        UrlQueueImpl<Long> result = service.poll(sessionId);

        // Verify
        assertNotNull(result);
        assertEquals("https://example.com", result.getUrl());
        assertTrue(mockQueue.isEmpty());
    }

        final List<SearchLog> searchLogList = new ArrayList<>();
        final Map<String, UserInfo> userInfoMap = new HashMap<>();
        while (!queue.isEmpty()) {
            final SearchLog searchLog = queue.poll();
            if (searchLog != null) {
                final String userAgent = searchLog.getUserAgent();
                final boolean isBot =

int maxDepth = -1               // Max depth (-1 = unlimited)
long maxAccessCount = 0         // Max URLs (0 = unlimited)
```

### CrawlerThread (`CrawlerThread.java`)

Worker thread for crawling.

**Flow**: Poll URL → Validate → Get client → Delay → Check last-modified → Execute → Process → Extract children → Queue children → Delay

### CrawlerClientFactory

Pattern-based client selection using `LinkedHashMap<Pattern, CrawlerClient>`.

    }

    @Override
    public synchronized Map<String, Object> read() {
        while (!isFinished.get() && queue.isEmpty()) {
            addDocumentToQueue();
        }

        return queue.poll();
    }

    @Override
    public void close() {
        isFinished.set(true);
        queue.clear();
    }

    /**
     * Sets the scroll size.
     * @param scrollSize The scroll size.

            UrlQueue urlQueue;
            while ((urlQueue = urlQueueService.poll(sessionId1)) != null) {
                assertTrue(urlQueue.getUrl().startsWith(url1));
            }
            while ((urlQueue = urlQueueService.poll(sessionId2)) != null) {
                assertTrue(urlQueue.getUrl().startsWith(url2));
            }