I wrote about a small fraction of this, CFRunLoop: https://blog.meldstudio.co/macos-cfrunloop-internals-scheduling-high-precision-timers-and-recurring-tasks/ ht

I wrote about a small fraction of this, CFRunLoop: https://blog.meldstudio.co/macos-cfrunloop-internals-scheduling-high-precision-timers-and-recurring-tasks/ https://blog.meldstudio.co/macos-cfrunloop-internals-schedul... libdispatch source code is an enlightening read for those interested in diving deeper into the C Runtime powering Swift concurrency.