How to make soft-realtime schedulers in C?

Hi, I'm a self taught C (and to a lesser degree C++) coder working in music/audio/sequencing apps, and want to get further under the hood. It's hard to find tutorials or books on how good soft real time schedulers are written, so hoping someone might have links to good articles, books, or open source projects to look at. I'm interested in the systems programming, algorithms, and data structures side of this, not in just using some project's existing infrastructure.

For context, soft-real time in the context of music means no one dies if we miss a deadline, so runs on general purpose OS, but temporal accuracy and low latency are the highest priorities. This is typically done with the audio card providing an interrupt callback that one starts from. Thanks!