Re: Best way to save/re-load an lua state

[Timothy Hunter <rmagick@...>]

kathrin_69@gmx.de wrote:
> Hello Ben and every buddy else,
>
> I investigated a bit and it seems much simpler: If I call lua_Newstate 
> instead of luaL_Newstate as I did until now, I am able to pass an 
> allocator function which is used exclusively for memory management by 
> Lua regarding the lua_State* it is assigned to.
>
>
> The default allocator function used by luaL_Newstate() is this:
>
> -----------------------------
> static void *l_alloc (void *ud, void *ptr, size_t osize, size_t nsize) {
>  (void)ud;
>  (void)osize;
>  if (nsize == 0) {
>    free(ptr);
>    return NULL;
>  }
>  else
>    return realloc(ptr, nsize);
> }
> -----------------------------
>
> If I would overwrite it in a way so that all memory used by  my 
> lua_State* is inside my own (pre-allocated) buffer, I could just save 
> and re-load that buffer to/from disc and resume execution. What do you 
> think, will this work? It sounds pretty easy so far.
>
> Two questions to the l_alloc function shown above:
> 1. What is void* ud for? The src code says something about "auxiliary 
> data to  the allocation function". Why is it not used by that function?
It's there for custom allocation functions that need to keep extra 
state. That state can be stored in memory addressed by ud.
> 2. What are the first two lines for?
>  (void)ud;
>  (void)osize;
> They do absolutely nothing, right? Are they there to let the compiler 
> check something?
I explained ud above. The osize argument is necessary if the custom 
memory manager doesn't track the size of each piece of allocated memory 
the way the standard C malloc function does. In that case, the memory 
manager needs to be told how much memory to free as well as the address 
of the memory.

The default allocation function doesn't need to use those two arguments, 
but a custom allocation function may find them useful.

If you intend to write your own memory manager you may find those 
arguments useful as well.