Re: Lua in multithread systems

[Paul Smith <paullocal@...>]

At 13:21 29/10/2007, you wrote:
> Hello yall,
>
> I'm developing a multithread system, a server answering to a lot of 
> connections at the same time. I'm using Lua to easier the job of 
> having custom made versions. Everything is in C++ and I'm using Luna.h.
>
> Now I'm at the point of choosing how I will use multi thread with 
> Lua. For now I implemented a lua pool (no queues yet) that gives me 
> an already initialized lua_State* whenever I need one. So, I open a 
> new thread (using PThreads on Linux), get an unused lua_State* from 
> the pool, send the inputs, run the script and get the results back. 
> But this model has 2 problems to me:
> 1 - Scope pollution: and second time I run the script with the same 
> lua_State* from the pool, the global variables set by the first run 
> are still there. Is there a fast way to clean only the variables set 
> by the Lua script?
> 2 - Global variables are not global anymore. One script doesn't have 
> access to the global variables set by another instances. On thread 
> doesn't talk to the other using lua entities: numbers, tables, etc...
>
> I only need a solution to one of the items, the second preferentially.
>
> But, maybe this model is not good at all. What are you using to 
> solve the multi thread problem?

Do you have control over the scripts being used?

If so, I wouldn't use Lua globals at all if you want them to be 
'application global' rather than 'script global'. Instead have some 
global access functions in C (available to your Lua scripts) to 
set/retrieve 'globals' from your C++ program directly. These can then 
do the multi-access protection to make sure that only one thread is 
accessing them at once, etc

So, instead of

x = myglobal;

have

x = getglobal("myglobal");

This is what we do here for some things, but we don't use Luna, so I 
can't give example Luna code for the global access/retrieve functions



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