Per-thread environment

It looks to me from the documentation that environments are tied to a function. So any time a function is being called, it has access to that environment.

Is it possible to associate an environment with a thread instead? So if a function is executed in that thread it will use the thread’s environment.

Basically I’m trying to simulate TLS. I want any access to a TLS variable to use the local environment, but when accessing a global variable (a variable not in the current environment), I want to access the real global variable.

One way I can do this manually is to manipulate the metatable of _G:

__index=function(g,n)

local env=threadEnvironments[coroutine.running()] -- a table that keeps custom environments for select threads

if env and env[n] then

return env[n]

end

return rawget(g,n)

end

and something similar for __newindex

Is there something like that already built into the language?

Ivo