Are you sure about that? I thought that yields across C functions were added in Lua 5.2. Not to mention that in a controlled environment like the runtime that Wikipedia exposes to you, you can take care of avoiding exposing APIs that would allow people to code themselves into a corner like that (if the C calls are leaves, you're OK even in 5.1).

You are right that they could use a carefully crafted API to work around the problems. Its also true that yields across C were added in 5.2 but you need to code the C functions in continuation-passing-style using a special API to take advantage of that.

http://www.lua.org/manual/5.2/manual.html#4.7

Well, two other options for you are using the coco library with stock Lua 5.1.x, or simply using LuaJIT.