| `contact` | `dict` | The contact information for the exposed API. It can contain several fields. <details><summary><code>contact</code> fields</summary><table><thead><tr><th>Parameter</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code>name</code></td><td><code>str</code></td><td>The identifying name of the contact person/organization.</td></tr><tr><td><code>url</code></td><td><code>str</code></td><td>The URL pointing to the...

      // unpark even though the thread has already removed itself from the list. But even if we did
      // use a CAS, that race would still exist (it would just be ever so slightly smaller).
      Thread w = thread;
      if (w != null) {
        thread = null;
        LockSupport.unpark(w);
      }
    }
  }

  /*

      // unpark even though the thread has already removed itself from the list. But even if we did
      // use a CAS, that race would still exist (it would just be ever so slightly smaller).
      Thread w = thread;
      if (w != null) {
        thread = null;
        LockSupport.unpark(w);
      }
    }
  }

  /*

    }

    /**
     * Cleans up the transport thread.
     *
     * @param timeout the maximum time to wait for thread cleanup in milliseconds
     * @throws TransportException if thread cleanup fails
     */
    private synchronized void cleanupThread(final long timeout) throws TransportException {
        final Thread t = this.thread;
        if (t != null && Thread.currentThread() != t) {
            this.thread = null;

            te = null;
            thread = new Thread(this, name);
            thread.setDaemon(true);

            synchronized (thread) {
                thread.start();
                thread.wait(timeout); /* wait for doConnect */

                switch (state) {
                case 1: /* doConnect never returned */
                    state = 0;
                    thread = null;

import jakarta.annotation.Resource;

/**
 * The {@code CrawlerThread} class represents a thread that executes the crawling process.
 * It is responsible for fetching URLs from the queue, accessing the content,
 * processing the response, and extracting child URLs.
 *
 * <p>
 * This class implements the {@link Runnable} interface, allowing it to be executed in a separate thread.

     *       observing a null thread does not mean the object is safe to reuse.
     *   <li>If this field's value is some other thread object, we know that it's not our thread.
     *   <li>If this field's value == null because it originally belonged to another thread and that
     *       thread cleared it, we still know that it's not associated with our thread

    Node<K, V> head;
    Node<K, V> tail;
    int count;

    KeyList(Node<K, V> firstNode) {
      this.head = firstNode;
      this.tail = firstNode;
      firstNode.previousSibling = null;
      firstNode.nextSibling = null;
      this.count = 1;
    }
  }

  private transient @Nullable Node<K, V> head; // the head for all keys

                    if (fessConfig.isSmbRoleFromFile() || fessConfig.isFileRoleFromFile() || fessConfig.isFtpRoleFromFile()) {
                        // head method
                        responseData =
                                client.execute(RequestDataBuilder.newRequestData().head().url(url).weight(urlQueue.getWeight()).build());
                        if (responseData == null) {
                            return true;

    }

    // Test constructor with different thread context
    public void test_constructorInDifferentThread() throws Exception {
        // Test that constructor works in different thread
        final CrawlerEngineClient[] clientHolder = new CrawlerEngineClient[1];
        final Exception[] exceptionHolder = new Exception[1];

        Thread thread = new Thread(() -> {
            try {