Calling Lua from multiple threads

["Thiago L." <fakedme@...>]

Let's say I have a wrapper program, that calls Lua, and most of my code 
is Lua. Let's say my Lua code calls C plugins, (which were developed for 
a different program) which may or may not be multithreaded.

The plugin does the following on a timer event: release a lock, and 
acquire it again. When other threads want to call my code, they try to 
acquire that lock, then call my code, then release it again.

What's the best way to support this? I obviously can't use the same lua 
thread for it (I need a separate stack and stuff), but I'm not sure how 
I _should_ do it.