Re: Reducing memory consumption

[Rici Lake <lua@...>]

On 27-Aug-04, at 9:05 PM, Edgar Toernig wrote:

> /* C side */
> int
> gimme_funcs(lua_State *L)
> {
>     lua_pushcfunction(L, myFnCallback1);
>     lua_pushcfunction(L, myFnCallback2);
>     lua_pushcfunction(L, myFnCallback3);
>     lua_pushcfunction(L, myFnCallback4);
>     lua_pushcfunction(L, myFnCallbackN);
>     return 5;
> }

Nice, but it won't work with thousands of functions.

Here's one that will, provided that an individual script file only
references, say, 100:

/* C side */

#define N_FUNCS 1500
static const lua_CFunction funcs[N_FUNCS] = {
  myFnCallback1,
  myFnCallback2,
  myFnCallback3,
  ...
  myFnCallback1500
};

int i;

/* Fast but maybe not future proof way of creating a vector */
static const char *makevec = "return function(...) return arg end";
luaL_loadbuffer(L, makevec, strlen(makevec), "");
lua_call(L, 0, 1);

lua_checkstack(L, N_FUNCS);
for (i = 0, i < N_FUNCS, i++) {
  lua_pushcfunction(L, funcs[i]);
}
lua_call(L, N_FUNCS, 1);
lua_setglobal(L, "funcs");


-- Lua side, each script
local ThisFunctionNameIsVeryDescriptive1,
      ThisFunctionNameIsVeryDescriptive23,
      ThisFunctionNameIsVeryDescriptive117,
      ...
do
  local function setvals()
    ThisFunctionNameIsVeryDescriptive1,
    ThisFunctionNameIsVeryDescriptive23,
    ThisFunctionNameIsVeryDescriptive117, ...
    = funcs[1], funcs[23], funcs[117], ...
  end

  setvals()
end  -- Poof!

-- rest of script

and after loading all the scripts, you could do:

funcs = nil -- Poof, again!

Personally, I would implement this by using the same name in
both C and Lua. A simple pattern match against the C files
could construct the index from function names to index values
(and also generate the funcs array). You could use a simple
pattern match against the Lua scripts, too, or you could
run lparse against them and then iterate over the globals
that it discovers.

For maximum poof-ness, you would want to arrange to get
rid of the C funcs vector as well. Perhaps it could become
a fixed-length buffer or something :)

The end result is the creation of an upvalue for each unique
function in each script, plus a closure for each function
actually used. But no character strings.

Not that I've actually tried it... :)

R.