BackgroundDownloader Max Parallelism

Question

Is there a way to set the max number of concurrent downloads from BackgroundDownloader?

This is roughly what I'm doing.

var downloader = new BackgroundDownloader();
foreach( var uri in uriList )
{
    var download = downloader.CreateDownload( uri, storageFile );
    download.StartAsync().AsTask( cancellationTokenSource.Token, progress );
}

I'd like to be able to set a max download parallelism of say 4. Is this built in, or do I need to manage this myself?

If I need to manage this myself, what is the recommended way? I have thought about just doing a Parallel.ForEach and setting the max amount there, but I don't know if that's a good solution.

Answer 1

This is what I ended up doing. This isn't complete, but it's the gist of it.

private void StartDownloadsAsync()
{
    var downloadQueue = new Queue<DownloadOperation>();
    // Create all the download operations and add them to the queue.
    await CreateDownloadsAsync();
    var maxConcurrentDownloads = 4;
    var loopAmount = Math.Min( maxConcurrentDownloads, downloadQueue.Count );
    for( var i = 0; i < loopAmount; i++ )
    {
        DownloadAsync();
    }
}

private void DownloadAsync()
{
    var download = downloadQueue.Dequeue();

    HandleDownloadAsync( download ).ContinueWith( task => DownloadComplete( download ) );
}

private void DownloadComplete( DownloadOperation download )
{
    // Update progress counter here.

    if( downloadQueue.Count > 0 )
    {
        DownloadAsync();
    }
    else
    {
        // Downloads are done. Do something.
    }
}

private async Task HandleDownloadAsync( DownloadOperation download, bool isActive = false )
{
    if( !isActive )
    {
        await download.StartAsync().AsTask( cancellationTokenSource.Token );
    }
    {
        await download.AttachAsync().AsTask( cancellationTokenSource.Token );
    }
}