Re: one-time-set, many-times-use data

["Robert G. Jakabosky" <bobby@...>]

On Saturday 02, C++ RTMP Server wrote:
> On Apr 3, 2011, at 2:42 AM, Peter Cawley wrote:
> > On Sun, Apr 3, 2011 at 12:40 AM, C++ RTMP Server <crtmpserver@gmail.com> 
wrote:
> >> However, I didn't find any way of pulling it out from a lua_State.
> > 
> > lua_getallocf
> 
> Jackpot!!! That's exactly what I needed :)

I don't recommend messing with allocator's userdata value.  There is a better 
option for doing what you want.

In the luaconf.h redefine these:

#define LUAI_EXTRASPACE  sizeof(void *) /* or the size of your custom state */

#define LUA_TO_CUSTOM_STATE(L) ((((unsigned char *)L) - LUAI_EXTRASPACE))
inline void init_custom_state(lua_State *L) {
  void **custom_state = LUA_TO_CUSTOM_STATE(L);
  *custom_state = NULL;
  /* or allocate your custom state. */
}

inline void cleanup_custom_state(lua_State *L) {
  void **custom_state = LUA_TO_CUSTOM_STATE(L);
  if(*custom_state) free(*custom_state);
}

inline void copy_custom_state(lua_State *L, lua_State *L1) {
  void **custom_state = LUA_TO_CUSTOM_STATE(L);
  void **custom_state1 = LUA_TO_CUSTOM_STATE(L1);
  *custom_state1 = *custom_state;
  /* or allocate a new custom state. */
}

/* these are for the main states. */
#define luai_userstateopen(L)		init_custom_state(L)
#define luai_userstateclose(L)		cleanup_custom_state(L)
/* these are for lua threads (i.e. coroutines) */
#define luai_userstatethread(L,L1)	copy_custom_state(L, L1)
#define luai_userstatefree(L)		((void)L)
/* you might not need these. */
#define luai_userstateresume(L,n)	((void)L)
#define luai_userstateyield(L,n)	((void)L)

Now you can always get your custom state object from a lua state pointer using 
the LUA_TO_CUSTOM_STATE(L) macro.  Note that you could pre-append your custom 
state object to have a 1-to-1 mapping both ways.  Remember that coroutines 
have there own lua_State object, which is different from the main lua_State.

-- 
Robert G. Jakabosky