The Push Queue is mostly a normal queue, but it has some special logic to merge push requests for each given proxy. This results in each proxy having 0 or 1 outstanding push requests; if additional updates come in the existing push request is just expanded.

Another job polls this queue and triggers each client to start a push.

```mermaid
graph TD

    }

    @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();
    }

    public void setScrollSize(final int scrollSize) {
        this.scrollSize = scrollSize;
    }

import java.lang.reflect.Method;
import java.util.ArrayDeque;
import java.util.Collection;
import java.util.LinkedList;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.LinkedBlockingQueue;

  @Param({"100", "10000"})
  private int size;

  @Param private HeapType heap;

  private Queue<Integer> queue;

  private final Random random = new Random();

  @BeforeExperiment
  void setUp() {
    queue = heap.create(comparator.get());
    for (int i = 0; i < size; i++) {
      queue.add(random.nextInt());
    }
  }

  @Benchmark
  void pollAndAdd(int reps) {

    startNs = queue.taskRunner.backend.nanoTime()
    log(task, queue, "starting")
  }

  var completedNormally = false
  try {
    val result = block()
    completedNormally = true
    return result
  } finally {
    if (loggingEnabled) {
      val elapsedNs = queue.taskRunner.backend.nanoTime() - startNs
      if (completedNormally) {
        log(task, queue, "finished run in ${formatDuration(elapsedNs)}")

    assertEquals(6, queue.size());
    assertEquals(8, queue.capacity());
    checkUnbounded(queue);
    checkNatural(queue);
  }

  public void testCreation_maximumSize_withContents() {
    MinMaxPriorityQueue<Integer> queue =
        rawtypeToWildcard(MinMaxPriorityQueue.maximumSize(42)).create(NUMBERS);
    assertEquals(6, queue.size());
    assertEquals(11, queue.capacity());
    assertEquals(42, queue.maximumSize);

  private final Queue<T> queue;

  ConsumingQueueIterator(Queue<T> queue) {
    this.queue = checkNotNull(queue);
  }

  @Override
  @CheckForNull
  protected T computeNext() {
    // TODO(b/192579700): Use a ternary once it no longer confuses our nullness checker.
    if (queue.isEmpty()) {
      return endOfData();
    }
    return queue.remove();
  }

        final Queue<String> queue = new LinkedList<>();
        queue.add(text);
        final List<String> convertedTexts = new ArrayList<>(getMaxReadingNum());
        convertedTexts.add(text);

        for (final ReadingConverter converter : converters) {
            String s;
            while ((s = queue.poll()) != null && convertedTexts.size() <= getMaxReadingNum()) {

        urlQueueService.insert(urlQueue);
        assertTrue(fesenClient.prepareSearch("fess_crawler.queue").setQuery(QueryBuilders.termQuery("sessionId", "sessionId")).setSize(0)
                .execute().actionGet().getHits().getTotalHits().value > 0);

        urlQueueService.delete("sessionId");
        assertFalse(fesenClient.prepareSearch("fess_crawler.queue").setQuery(QueryBuilders.termQuery("sessionId", "sessionId")).setSize(0)

 *
 */
public interface UrlQueueService<QUEUE extends UrlQueue<?>> {

    void updateSessionId(String oldSessionId, String newSessionId);

    void add(String sessionId, String url);

    void insert(QUEUE urlQueue);

    void delete(String sessionId);

    void deleteAll();

    void offerAll(String sessionId, List<QUEUE> newUrlQueueList);

    QUEUE poll(String sessionId);