Thanks for your good hints.

I see there 's a good no-blocking mysql client Libdrizzle from https://launchpad.net/drizzle.

With Nginx-lua or Openresty , Libdrizzle has been used in production.

I won't hope every thing is no-blocking and I think it is unnecessary.

Only when blocking hurt us we have to conside using no-blocking methods.

For design of no-blocking api we can only use a simple callback pattern, let user to determine whether use threads or not.

Even in Nginx-Clojure 0.1.0, developers can also use his owner thread or thread pool.