A Field Guide to Lua Coroutines

Coroutine are a powerful low-level tool to build higher level, user friendly environments. That's true of most of Lua's advanced features, BTW: they tend to be complex tools letting you build simple-to-use stuff (as opposed e.g. to C++'s templates, where you need a fairly advanced understanding of C++ metaprogramming features to use even simple containers correctly).

Anyway, coroutines are intended to let people build their own high-level concurrency system. It's used e.g. to share the CPU among scripted entities in video games.

Mihini (http://www.eclipse.org/mihini/) offers higher-level concurrency within a single OS thread, primarily targetting Linux-based embedded communicating applications.

Copas (https://github.com/keplerproject/copas) is much simpler, but probably sufficient if you only need to handle several sockets concurrently without wasting many OS threads.

There are also some attempts to wrap luvit (https://github.com/luvit/luvit), Lua's porting of libuv, with coroutines, getting callback-based performances without it's tendency to make one's code write-only. I don't know what's usable and maintained, nor even whether it really exists.

> "The main limitation of Lua coroutines is that, since they are implemented with setjmp(3) and longjmp(3), you cannot use them to call from Lua into C code that calls back into Lua that calls back into C, because the nested longjmp will clobber the C function’s stack frames. (This is detected at runtime, rather than failing silently.)"

Lua 5.2 provides a mechanism to help with this: http://www.lua.org/manual/5.2/manual.html#4.7

Relevant: super lightweight co-routines in C, with (limited) support for blocking as well: https://github.com/halayli/lthread