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

   * {@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.collect.Lists;
import com.google.common.util.concurrent.AbstractFutureBenchmarks.OldAbstractFuture;
import com.google.errorprone.annotations.concurrent.GuardedBy;
import java.util.Queue;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executor;
import java.util.concurrent.Future;
import java.util.concurrent.ThreadPoolExecutor;

import java.util.NavigableSet;
import java.util.Optional;
import java.util.OptionalDouble;
import java.util.OptionalInt;
import java.util.OptionalLong;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.Random;
import java.util.Set;
import java.util.SortedMap;
import java.util.SortedSet;
import java.util.TreeMap;
import java.util.TreeSet;
import java.util.UUID;

                "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);
        }

   * formally, removes an element {@code e} such that {@code o.equals(e)}, if this queue contains
   * one or more such elements. Returns {@code true} if and only if this queue contained the
   * specified element (or equivalently, if this queue changed as a result of the call).
   *
   * @param o element to be removed from this queue, if present

/**
 * A bounded {@linkplain BlockingQueue blocking queue} backed by an array. This queue orders
 * elements FIFO (first-in-first-out). The head of the queue is that element that has been
 * on the queue the longest time. The tail of the queue is that element that has been on
 * the queue the shortest time. New elements are inserted at the tail of the queue, and the queue
 * retrieval operations obtain elements at the head of the queue.

    private final BlockingQueue<String> queue;

    public EnableWrites(BlockingQueue<String> queue, long tMinus) {
      super(tMinus);
      assertFalse(queue.isEmpty());
      assertFalse(queue.offer("shouldBeRejected"));
      this.queue = queue;
    }

    @Override
    protected void doAction() {
      assertNotNull(queue.remove());
    }
  }

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

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