Ask HN: How to learn how to develop real time applications?

I am a C++ programmer and I want to learn how to develop real-time programs. It looks like it's a "lost art" these days.I think we all use such programs every day to one degree or another. For example, if you work with a network, then you probably use wireshark. If you work with audio, then you probably use something from this field. What do I mean by real-time apps? These are applications where we have a part that creates data (or a data stream, with high frequency) and a part that processes it (or gui part, if we somehow process it). I would like to focus specifically on network applications. I'll say right away that I've already read Richard Stevens book[1], but it doesn't seem to be enough to develop applications of this level.

[1] Richard Stevens - Unix Network Programming