Hi.
I have written this library https://github.com/jaracil/pubsub-c to be able to face complex multi-thread developments.The main idea is decoupled programming using the actor model https://en.wikipedia.org/wiki/Actor_model.
The pubsub-c library works with POSIX (Pthreads) and FreeRTOS.
It is working in production on embedded systems based on the ESP32.
The documentation for now is in the pubsub.h file and in the tests.