listeners.add(new PerListenerQueue<>(listener, executor));
  }

  /**
   * Enqueues an event to be run on currently known listeners.
   *
   * <p>The {@code toString} method of the Event itself will be used to describe the event in the
   * case of an error.
   *
   * @param event the callback to execute on {@link #dispatch}
   */
  public void enqueue(Event<L> event) {
    enqueueHelper(event, event);
  }

  /**

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        out the following fields.

  - type: textarea
    attributes:
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      description: Please describe the issue you encountered.
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    }

    /**
     * Creates a {@link ReentrantLock} with the given fairness policy and rank. The values returned
     * by {@link Enum#getDeclaringClass()} and {@link Enum#name()} are used to describe the lock in
     * warning or exception output.
     *
     * @throws IllegalStateException If the factory has already created a {@code Lock} with the
     *     specified rank.
     */

   *
   * @param index a user-supplied index identifying an element of an array, list or string
   * @param size the size of that array, list or string
   * @param desc the text to use to describe this index in an error message
   * @return the value of {@code index}
   * @throws IndexOutOfBoundsException if {@code index} is negative or is not less than {@code size}

  /** Constructor for use by subclasses. */
  protected Equivalence() {}

  /**
   * Returns {@code true} if the given objects are considered equivalent.
   *
   * <p>This method describes an <i>equivalence relation</i> on object references, meaning that for
   * all references {@code x}, {@code y}, and {@code z} (any of which may be null):
   *
   * <ul>

public abstract class Equivalence<T>
{
  /** Constructor for use by subclasses. */
  protected Equivalence() {}

  /**
   * Returns {@code true} if the given objects are considered equivalent.
   *
   * <p>This method describes an <i>equivalence relation</i> on object references, meaning that for
   * all references {@code x}, {@code y}, and {@code z} (any of which may be null):
   *
   * <ul>

       * strip the methods *and* have the test runner not run them (for some unusual cases in which
       * we don't run the stripping test for technical reasons), then we'd be back to the problem
       * described above, since the supermethod is *not* annotated @AndroidIncompatible (since it
       * works fine with the other Table implementations).
       */
      return;
    }
    super.testNullPointerInstance();
  }

    /** Lock used whenever accessing the state variables (runningTasks, shutdown) of the executor */
    private final Object lock = new Object();

    /*
     * Conceptually, these two variables describe the executor being in
     * one of three states:
     *   - Active: shutdown == false
     *   - Shutdown: runningTasks > 0 and shutdown == true
     *   - Terminated: runningTasks == 0 and shutdown == true
     */

   *
   * @param index a user-supplied index identifying an element of an array, list or string
   * @param size the size of that array, list or string
   * @param desc the text to use to describe this index in an error message
   * @return the value of {@code index}
   * @throws IndexOutOfBoundsException if {@code index} is negative or is not less than {@code size}

   * described in the class documentation.
   *
   * @throws NullPointerException if any of {@code elements} is null
   * @since 6.0
   */
  public static <E> ImmutableMultiset<E> copyOf(E[] elements) {
    return copyFromElements(elements);
  }

  /**
   * Returns an immutable multiset containing the given elements, in the "grouped iteration order"
   * described in the class documentation.
   *