Waiting for cancelled async method from UI thread?

Question

I have a WPF program appending to a textbox asynchronously. If the user selects a new provider via combobox, the appending should be cancelled and called again with the new provider. problem is the updateMoviesTask?.Wait() deadlocks. I guess it is because UpdateMovies() waits for ui thread and ProviderId property waits for the task. How can I solve this?

CancellationTokenSource source;
Task updateMoviesTask;

async Task UpdateMovies()
{
    source?.Dispose();
    source = new CancellationTokenSource();

    CancellationToken cancel = source.Token;

    var request = new GetPopularRequest(Country.Germany);

    for (int i = 1; i <= TotalPages; i++)
    {
        request.Page = i;
        request.ProviderId = providerId;

        var getPopularResponse = await justWatchClient.GetPopularAsync(request);

        // do ui stuff here        

        if (cancel.IsCancellationRequested)
            return;
    }
}

public GetProviderResponse ProviderId
{
    get { return providerId; }
    set
    {
        this.providerId = value; 
        this.source?.Cancel();
        updateMoviesTask?.Wait();
        updateMoviesTask = this.UpdateMovies();
        this.OnPropertyChanged("");
    }
}

Answer 1

If I understand correctly, then you need to - Look at this version of the code (without taking into account the handling of possible exceptions):

    private CancellationTokenSource source = new();
    private readonly object locker = new();

    private void UpdateMovies() => Task.Run(() =>
    {
        source.Dispose();
        source = new CancellationTokenSource();
        CancellationToken cancel = source.Token;

        lock (locker)
        {
            var request = new GetPopularRequest(Country.Germany);

            for (int i = 1; i <= TotalPages; i++)
            {
                request.Page = i;
                request.ProviderId = providerId;

                // Need a synchronous version of the method
                // var getPopularResponse = await justWatchClient.GetPopularAsync(request);
                var getPopularResponse = justWatchClient.GetPopular(request);

                // do ui stuff here        

                if (cancel.IsCancellationRequested)
                    return;
            }
        }
    });

    public GetProviderResponse ProviderId
    {
        get { return providerId; }
        set
        {
            this.providerId = value;
            UpdateMovies();
            this.OnPropertyChanged(string.Empty);
        }
    }