setjmp()/longjmp() will work, but they're sort of inefficient as, at least under POSIX, they will save and restore the signal mask, which makes for two round-trips to the kernel just for a coroutine context switch.

My web server uses coroutines, and for x86 and x86-64 it uses open-coded assembly routines to yield/resume, with fallbacks to setjmp()/longjmp() on other architectures.

It works fairly well, performance-wise. In fact, it's one of the top-performing servers/frameworks in the TechEmpower's Web Framework benchmarks[1].

I wrote a similar article explaining how everything is put together here[2].

[1] https://www.techempower.com/benchmarks/ [2] http://tia.mat.br/blog/html/2014/10/06/life_of_a_http_reques...