* Breaking AtomicReferenceFieldUpdater not only forces AggregateFutureState to fall back to
         * another implementation but also forces AbstractFutureState to be able to do the
         * same—hence the try-catch here.
         *
         * (Really, we're fortunate that breaking AtomicReferenceFieldUpdater doesn't break _even
         * more_ things.)

      return "UnsafeAtomicHelper";
    }
  }

  /** {@link AtomicHelper} based on {@link AtomicReferenceFieldUpdater}. */
  private static final class AtomicReferenceFieldUpdaterAtomicHelper extends AtomicHelper {
    private static final AtomicReferenceFieldUpdater<Waiter, @Nullable Thread> waiterThreadUpdater =
        AtomicReferenceFieldUpdater.<Waiter, @Nullable Thread>newUpdater(
            Waiter.class, Thread.class, "thread");

     */
    val callStackTrace: Any?,
  ) : WeakReference<RealCall>(referent)

  private companion object {
    val eventListenerUpdater: AtomicReferenceFieldUpdater<RealCall, EventListener> =
      AtomicReferenceFieldUpdater.newUpdater(
        RealCall::class.java,
        EventListener::class.java,
        "eventListener",
      )
  }

// getDeclaredField to throw a NoSuchFieldException when the field is definitely there.
// Since this class only needs CAS on one field, we can avoid this bug by extending AtomicReference
// instead of using an AtomicReferenceFieldUpdater. This reference stores Thread instances
// and DONE/INTERRUPTED - they have a common ancestor of Runnable.
abstract class InterruptibleTask<T extends @Nullable Object>