Re: Adding module+DLL to Lua for Windows (LfW)

[Joshua Jensen <jjensen@...>]

----- Original Message -----
From: Roberto Ierusalimschy
Date: 12/10/2009 10:50 AM
> > What I would like to see (and experimented with once) is for Lua to load
> > the Lua module and call the luaopen_ function by passing in a structure
> > of pointers to all the exported Lua functions.
> >
> > struct lua_Exports
> > {
> >      ...
> >      void  (*lua_pushvalue) (lua_State *L, int idx);
> > };
> >
> > int luaopen_mymodule(lua_State *L, lua_Exports *exports);
> >      
> A variation of that idea is to have lua_Exports accessible via
> lua_State, so that it does not need to be passed as an extra argument to
> luaopen. (E.g., it may be the first pointer in lua_State.)
>    
I prefer the exports table being available in the lua_State.  I was just 
trying to be explicit about my example for discussion's purposes.
> Do you know the performance impact of this approach?
>    
Before Lua had modules and before LuaPlus was LuaPlus, I had implemented 
a form of this approach for dynamically loadable modules.  There was no 
cost on Windows, as I recall, as a DLL accessing another DLL uses a 
function pointer table anyway.  (In fact, delay loaded DLLs on Windows 
use the function pointer table to load the DLL... when the DLL is 
loaded, the proper pointers are filled in.)  If the function pointer 
table is assigned to global variables, it should be just as fast.

lua_exports(L)->lua_pushvalue(L) would require an extra dereference.

I don't know how Linux/Mac OS X resolves this stuff.

It was mentioned that Tcl does this now.  It might be worth some 
investigation as to what they do.

Josh