private final Executor executor;

  @GuardedBy("queue")
  private final Deque<Runnable> queue = new ArrayDeque<>();

  /** see {@link WorkerRunningState} */
  @LazyInit
  @GuardedBy("queue")
  private WorkerRunningState workerRunningState = IDLE;

  /**
   * This counter prevents an ABA issue where a thread may successfully schedule the worker, the
   * worker runs and exhausts the queue, another thread enqueues a task and fails to schedule the

import java.util.Queue;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Creates queues, containing sample elements, to be tested.
 *
 * @author Jared Levy
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public interface TestQueueGenerator<E extends @Nullable Object> extends TestCollectionGenerator<E> {
  @Override
  Queue<E> create(Object... elements);

   * {@link Iterators#consumingIterator(Iterator)}.
   *
   * <p>Note: If {@code iterable} is a {@link Queue}, the returned iterable will instead use {@link
   * Queue#isEmpty} and {@link Queue#remove()}, since {@link Queue}'s iteration order is undefined.
   * Calling {@link Iterator#hasNext()} on a generated iterator from the returned iterable may cause

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.testing.features.CollectionFeature;
import org.junit.Ignore;

/**
 * A generic JUnit test which tests offer operations on a queue. Can't be invoked directly; please
 * see {@link com.google.common.collect.testing.CollectionTestSuiteBuilder}.
 *
 * @author Jared Levy
 */
@GwtCompatible

import com.google.common.collect.testing.features.CollectionSize;
import java.util.NoSuchElementException;
import org.junit.Ignore;

/**
 * A generic JUnit test which tests {@code remove()} operations on a queue. Can't be invoked
 * directly; please see {@link com.google.common.collect.testing.CollectionTestSuiteBuilder}.
 *
 * @author Jared Levy
 */
@GwtCompatible

                "fess_config.request_header", //
                "fess_config.role_type", //
                "fess_config.scheduled_job", //
                "fess_config.thumbnail_queue", //
                "fess_config.web_authentication", //
                "fess_config.web_config", //
                "fess_user.group", //
                "fess_user.role", //
                "fess_user.user", //

            urlFilterService.delete(sid);
        } catch (final Exception e) {
            logger.warn("Failed to delete UrlFilter for {}", sid, e);
        }

        try {
            // clear queue
            urlQueueService.clearCache();
            urlQueueService.delete(sid);
        } catch (final Exception e) {
            logger.warn("Failed to delete UrlQueue for {}", sid, e);
        }

    assertEquals(0, queue.size());
    assertEquals(3, queue.remainingCapacity());

    assertTrue(queue.add("one"));
    assertTrue(queue.add("two"));
    assertTrue(queue.add("three"));
    assertEquals("one", queue.element());
    assertEquals("one", queue.peek());
    assertEquals(3, queue.size());
    assertEquals(0, queue.remainingCapacity());

    assertTrue(queue.add("four"));
    assertEquals("two", queue.element());

            final Queue<SearchLog> queue = searchLogQueue;
            searchLogQueue = new ConcurrentLinkedQueue<>();
            processSearchLogQueue(queue);
        }

        if (!clickLogQueue.isEmpty()) {
            final Queue<ClickLog> queue = clickLogQueue;
            clickLogQueue = new ConcurrentLinkedQueue<>();
            processClickLogQueue(queue);
        }
    }

      implements PeekingIterator<T> {
    private final Queue<T> queue;

    BreadthFirstIterator(T root) {
      this.queue = new ArrayDeque<>();
      queue.add(root);
    }

    @Override
    public boolean hasNext() {
      return !queue.isEmpty();
    }

    @Override
    public T peek() {
      return queue.element();
    }

    @Override
    public T next() {