The standard way is to use libraries like libevent, libuv that wraps system calls such as epoll, kqueue etc.

The other palatable way is to register consumer coroutines on a system provided event-loop. In C one does so with macro magic, or using stack switching with the help of tiny bit of insight inline assembly.

Take a look at Simon Tatham's page on coroutines in C.

To get really fast you may need to bypass the kernel. Or have more control on the event loop / scheduler. Database implementations would be the place to look.