@CheckReturnValue
    @NonNull
    public final ParallelFlowable<T> doOnCancel(@NonNull Action onCancel) {
        ObjectHelper.requireNonNull(onCancel, "onCancel is null");
        return RxJavaPlugins.onAssembly(new ParallelPeek<T>(this,
                Functions.emptyConsumer(),
                Functions.emptyConsumer(),
                Functions.emptyConsumer(),
                Functions.EMPTY_ACTION,
                Functions.EMPTY_ACTION,
                Functions.emptyConsumer(),
                Functions.EMPTY_LONG_CONSUMER,
                onCancel
                ));
    }