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

["kathrin_69@..." <kathrin_69@...>]

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?

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?

Thank you + Regards
Joeerg


Ben Sunshine-Hill schrieb:
> If you want to serialize *everything* in the Lua state, the easiest
> approach is a Lua variant called lper. That basically does your #3.
> It's unix-specific, though... I'm not sure how much work would be
> involved in porting it to win32.
>
> Ben
>
> On Fri, Mar 20, 2009 at 7:10 AM, kathrin_69@gmx.de <kathrin_69@gmx.de> wrote:
>   
> > Hi,
> >
> > I want to save the state of a Lua VM to a file to re-load and restart
> > execution later.
> >
> > Three options come to my mind:
> >
> > 1. Serializing the global index table of the VM. I even found a library
> > called "Pluto" which promises to do this.
> >
> > 2. Trying to make a deep copy of the lua_State* pointing to a VM and
> > save/load the binary data.
> >
> > 3. Trying to overwrite malloc/free for the Lua.dll, place all memory the VM
> > holds in an pre-allocated chunk. Save and re-load that whole chunk. I'm not
> > sure If I'm yet experienced (in C/C++) enough to get this done. Probably
> > not.
> >
> >
> >
> > My Questions are:
> >
> > 1. Which of that options will work or which one are used and which not?
> > 2. Are there any other options I missed?
> > 3. Which option is most promising in terms of time and complexity?
> > 4. Are there any other helper libraries (beside Pluto) which helps doing one
> > of the options?
> >
> > Thank you!
> >
> > Regards
> > Joerg
> >
> >
> >     
>
>