Comment 3 for bug 1551524

Not sure whether this is a duplicate, I don't know enough about the internals of the music app.

In terms of performance, it does matter, even though you are async. It won't block the UI, but it does prevent album art from arriving because of (unneeded) artist art ahead of it in the queue. There are only so many thumbnail requests we can have outstanding at a time. So, each artist request that we get prevents an album request from being processed that, otherwise, could have gone ahead straight away. Requests to the remote server have turn-around times of around 6 seconds, so this is significant.

Whatever you can do to avoid making requests for images that aren't actually needed will do a lot to improve the user experience.

The thumbnailer can't help. It's image provider is simply told "fetch this", and the thumbailer goes ahead and fetches it. The thumbnailer has absolutely no idea of what's visible and what isn't.