Advice on running and reusing multiple threaded Lua states

[Rodrigo Dias Arruda Senra <rodrigo.senra@...>]

Dear colleagues,

I seek your advice on a system we (www.hitecnologia.com) have been building.

We are using Lua as the embedded scripting language for a supervisory 
system for
Industrial Automation Control. So far it was an excellent choice.
Since it was my first contact with Lua, I am uncertain about some design 
decisions.

In the C++ app kernel, every time there is a demand for script 
execution, we create
the Lua state, populate it with contextual info, load the standard Lua 
libs and assign
it to a (system-)thread retrieved from a pre-allocated thread pool.
The user code for the script is wrapped in a template "function 
<scriptName>(Param) <user code> end".
When the script finishes execution, the thread is returned to the pool 
and the lua state
is destroyed. This is working, but I guess it can be improved.

My assumptions:

1) I did not use co-routines because the <user code> can do
   arbitrary blocking operations (DBs, file system, etc).
   Moreover, OS threads provide a simpler programming model
   for the script developer (sometimes they are Engineers with
   little background in programming).

   If I could detect the absence of blocking calls, perhaps I could
   transparently run the script in a coroutine instead of a OS thread.
   But I decided not even to try this, even though it sounds a nice
   research project.

My doubts:

1) Is it worth to pre-allocate a lua_State pool instead of creating it 
every time ?

2) If so, in between executions is it enough to clean it using 
settop(L,0) and
   replacing its _ENV for a empty table ?

3) Instead of wrapping <user code> in the template function, could I 
just push it
   as a Lua chunk and pcall()-it ?

4) I have a common set of wrapped C-callbacks that are registered in 
every Lua state.
   Could I prepare a prototypical Lua State and clone it in the new Lua 
state created
   with some performance gain instead of registering its contents ?

I thank you for your time.

Cheers
Rod Senra
http://rodrigo.senra.nom.br--

Atenciosamente

_Rodrigo Dias Arruda Senra_
*Engenheiro de Computação*//