public delegate UniTask ActionAsync(CancellationToken cancellationToken);

public delegate UniTask ActionAsync<in T>(T value, CancellationToken cancellationToken);

public static class ActionAsyncExtensions
{
    public static UniTask InvokeAsync(this ActionAsync handler, CancellationToken cancellationToken)
    {
        Delegate[] delegates = handler?.GetInvocationList();

        if (delegates == null || delegates.Length == 0)
            return UniTask.CompletedTask;

        var tasks = new UniTask[delegates.Length];

        for (var i = 0; i < delegates.Length; i++)
            tasks[i] = (UniTask) delegates[i].DynamicInvoke(cancellationToken);

        return UniTask.WhenAll(tasks);
    }
    
    public static UniTask InvokeAsync<T>(this ActionAsync<T> handler, T value, CancellationToken cancellationToken)
    {
        Delegate[] delegates = handler?.GetInvocationList();

        if (delegates == null || delegates.Length == 0)
            return UniTask.CompletedTask;

        var tasks = new UniTask[delegates.Length];

        for (var i = 0; i < delegates.Length; i++)
            tasks[i] = (UniTask) delegates[i].DynamicInvoke(value, cancellationToken);

        return UniTask.WhenAll(tasks);
    }
}