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;

/**
 * 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.

   *
   * @param queue the queue to be wrapped in a synchronized view
   * @return a synchronized view of the specified queue
   * @since 14.0
   */
  public static <E extends @Nullable Object> Queue<E> synchronizedQueue(Queue<E> queue) {
    return Synchronized.queue(queue, null);
  }

  /**
   * Returns a synchronized (thread-safe) deque backed by the specified deque. In order to guarantee

  @CanIgnoreReturnValue
  public static Set<Feature<?>> addImpliedFeatures(Set<Feature<?>> features) {
    Queue<Feature<?>> queue = new ArrayDeque<>(features);
    while (!queue.isEmpty()) {
      Feature<?> feature = queue.remove();
      for (Feature<?> implied : feature.getImpliedFeatures()) {
        if (features.add(implied)) {
          queue.add(implied);
        }
      }
    }
    return features;
  }

  /**

   * getting a bunch of different keys), then makes sure all the items in the cache are also in the
   * eviction queue. It will invoke the given {@code operation} on the first element in the eviction
   * queue, and then reverify that all items in the cache are in the eviction queue, and verify that
   * the head of the eviction queue has changed as a result of the operation.
   */
  static void checkRecency(

    private final Queue<T> queue;

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

    @Override
    public Iterator<T> iterator() {
      throw new UnsupportedOperationException();
    }

    @Override
    protected Queue<T> delegate() {
      return queue;
    }
  }

  public void testIndexOf_empty() {

   * {@link MoreExecutors#directExecutor}. Normally, when the first future completes, all the other
   * tasks would be called recursively. Here, we detect that the delegate executor is executing
   * inline, and maintain a queue to dispatch tasks iteratively. There is one instance of this class
   * per call to submit() or submitAsync(), and each instance supports only one call to execute().
   *