Asynchronous Library Build

Upon creation or update the library backend needs to call Last.fm's API for each track (or, given the current design, on each unique artist) which results in a LOT of calls making the library's building process very slow, especially for big library's. Since these calls can't be removed as they are essential pieces of information, the program should start anyway regardless of library status, checking periodically to use the most updated information. This means the methods called by the frontend to access bulk library information (getTags, getPlaylist) should be asynchronous/non-blocking in nature.
Implementing this would mean a more fluid and dynamic experience for the end user.