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have you consider using different virtual machines for each entity?
that's what i am going to do for mine not too sure if it's better than
threads but i can hope.

On Thu, May 14, 2009 at 8:39 PM, Guy Junk <> wrote:
> I am developing a game using C++ where the logic of different entities
> are controlled by Lua scripts. So, I'd have a collection of scripts
> that each have a standard set of functions like "nextAction", as well
> as any internal state (most likely in the form of global variables)
> the C++ side doesn't and shouldn't know about.
> Since I don't want my scripts overwriting each other, some form of
> sandboxing is in order. The behaviour I want can be achieved by having
> multiple lua_State objects for each script instance; i.e. each
> script-controlled entity has its own lua_State. I heard that this was
> wasteful though, so I've been looking at threads and environment
> tables.
> So far I've been trying to use lua threads. I start off by creating my
> main lua_State. For every script I load, I create a new thread:
> -----------------------------------------------------------------------
> lua_State *scriptThread = lua_newthread(mainLuaState);
> lua_newtable(scriptThread);
> lua_replace(scriptThread, LUA_GLOBALSINDEX );
> //lua_setfenv(scriptThread, 1); // Doesn't seem to work
> luaL_openlibs(scriptThread); // I could have loaded this once in the
>                             // main Lua state and then manipulated the
>                             // current thread's metatable, but I want
>                             // to illustrate a bug here later.
> if (luaL_dofile(scriptThread, path.c_str()))
> {
>    throw runtime_error("Could not load file '" + path + "': "
>      + lua_tostring(scriptThread, -1));
> }
> -----------------------------------------------------------------------
> Whenever I need to call a function for a particular script instance, I
> access its thread. This seems to work for running general script
> logic. However, including libraries seems to only work for the first
> script I load.
> The call to luaL_openlibs only works for the first script I load. If I
> have print() in two scripts and I run those scripts, only the first
> script I loaded and ran will recognize the print() while the second
> script will think it's a nil value.
> Similarly, require doesn't work for scripts that weren't loaded first.
> I made two scripts that call a function inside a common Lua file (i.e.
> they both require() this file). The first script to be loaded is able
> to call this function, while the second thinks the function is a nil
> value.