private @Nullable Runnable setUp;
  private @Nullable Runnable tearDown;

  // public so that it can be referenced in generated GWT tests.
  @Override
  public void setUp() throws Exception {
    if (setUp != null) {
      setUp.run();
    }
  }

  // public so that it can be referenced in generated GWT tests.
  @Override
  public void tearDown() throws Exception {
    if (tearDown != null) {

      return created;
    }

    // N.B. Draining the queue is only necessary to ensure that we don't accumulate empty references
    // in the array. We could skip this if we decide we don't care about holding on to Reference
    // objects indefinitely.
    private void drainQueue() {
      Reference<? extends L> ref;
      while ((ref = queue.poll()) != null) {

  private @Nullable Runnable setUp;
  private @Nullable Runnable tearDown;

  // public so that it can be referenced in generated GWT tests.
  @Override
  public void setUp() throws Exception {
    if (setUp != null) {
      setUp.run();
    }
  }

  // public so that it can be referenced in generated GWT tests.
  @Override
  public void tearDown() throws Exception {
    if (tearDown != null) {

    }
  }

  /**
   * Cleans up the given reference and any other references already in the queue. Catches and logs
   * all throwables.
   *
   * @return true if the caller should continue to wait for more references to be added to the
   *     queue, false if the associated FinalizableReferenceQueue is no longer referenced.
   */
  private boolean cleanUp(Reference<?> firstReference) {

     * type.
     *
     * In practice, we are very unlikely to see `null`: The `WeakReference` to the enum constant
     * won't be cleared as long as the enum constant is referenced somewhere, and the enum constant
     * is referenced somewhere for as long as the enum class is loaded. *Maybe in theory* the enum
     * class could be unloaded after the above call to `getEnumConstants` but before we call

      assertBasicInvariants(striped);
    }
  }

  private static void assertBasicInvariants(Striped<?> striped) {
    Set<Object> observed = Sets.newIdentityHashSet(); // for the sake of weakly referenced locks.
    // this gets the stripes with #getAt(index)
    for (int i = 0; i < striped.size(); i++) {
      Object object = striped.getAt(i);
      assertNotNull(object);

   *   <li>clearing weak references to unreachable referents
   *   <li>enqueuing weak references to unreachable referents in their reference queue
   * </ul>
   */
  @DoNotMock("Implement with a lambda")
  public interface FinalizationPredicate {
    boolean isDone();
  }

  /**
   * Waits until the given weak reference is cleared, invoking the garbage collector as necessary to

      assertBasicInvariants(striped);
    }
  }

  private static void assertBasicInvariants(Striped<?> striped) {
    Set<Object> observed = Sets.newIdentityHashSet(); // for the sake of weakly referenced locks.
    // this gets the stripes with #getAt(index)
    for (int i = 0; i < striped.size(); i++) {
      Object object = striped.getAt(i);
      assertNotNull(object);

    assertNotNull(sepStopwatchA.get());
    // Clear all references to the Stopwatch and wait for it to be gc'd.
    sepStopwatchA.set(null);
    GcFinalization.awaitClear(sepStopwatchRef.get());
    // Return a weak reference to the parallel ClassLoader. This is the reference that should
    // eventually become clear if there are no other references to the ClassLoader.
    return new WeakReference<ClassLoader>(sepLoader);
  }

      }
    }
  }

  /** A weakly referenced value that also has a reference to its containing entry. */
  interface WeakValueReference<K, V, E extends InternalEntry<K, V, E>> {
    /**
     * Returns the current value being referenced, or {@code null} if there is none (e.g. because