Re: Lua Memory Allocator and Memory Check

[Rena <hyperhacker@...>]

On Mon, Nov 24, 2014 at 1:02 AM, Santosh Kadam <sanmanik@yahoo.com> wrote:
> Hi,
>
> Greetings....
>
> I am doing a few experiments with Lua and Lua memory consumptions. I have
> following memory allocator function registered with Lua via lua_newstate
>
> lua_State *L = lua_newstate(myl_alloc,NULL);
>
> static void *myl_alloc (void *ud, void *ptr, size_t osize,
>                                                 size_t nsize)
>    {
>        (void)ud;  (void)osize;  /* not used */
>        if (nsize == 0) {
>         memsize-=osize;
> //        printf ("Freeing [%ld] bytes, memory size = [%ld] \n",osize,
> memsize);
>          free(ptr);
>          return NULL;
>        }
>        else
>         {
> /*
>         if (memsize > 31000)
>         {
>           printf ("Memory exceeded 32K \n");
>           return NULL;
>         }
> */
>          memsize+=(nsize-osize);
> //         printf ("Allocating new [%ld] bytes,old size = [%ld], total =
> [%ld] \n",nsize, osize, memsize);
>          return realloc(ptr, nsize);
>         }
>      }
>
> This function adds / subtracts the memory size used by Lua and stores the
> same in the global memsize variable.
>
> At the end of the execution i.e. When I call lua_close - I expected to get a
> "zero" printed by the memsize but I am getting a negative number.
> ----------
> The memory size = [-1165]
> ----------
>
> Why is it that the memory count negative ?
>
> I am pasting the code .....
>
> Thanks and Regards
> Santosh
>
>
>
> Below is my script ..
>
> ------------------
> function add(a, b)
>     a=10
>     b=20
>     print (a+b)
> --    collectgarbage("collect")
>     print(collectgarbage("count"))
>     print ("Add - after garbage collect")
>     return a+b
> end
>
> function subt(a, b)
>     a=10
>     b=20
>     print (b-a)
>     print ("memory in subt")
>  --   collectgarbage("collect")
>     print(collectgarbage("count"))
>     return b-a
> end
>
> add (3,4)
> ---------------------
>
> And the complete program is as below...
>
> ---------------
> #include"lua.h"
> #include"lauxlib.h"
> #include"lualib.h"
> #include<stdlib.h>
> #include<stdio.h>
>
> long memsize = 0;
>
> static void *myl_alloc (void *ud, void *ptr, size_t osize,
>                                                 size_t nsize);
> int main ()
> {
>   char str [80], *str1, *str2;
>   int i;
>
>   FILE *f = fopen("./add.lua", "rb");
>   fseek(f, 0, SEEK_END);
>   long fsize = ftell(f);
>   fseek(f, 0, SEEK_SET);
>
>   str1 = malloc(fsize + 1);
>   fread(str1, fsize, 1, f);
>   fclose(f);
>   printf ("Add String = \n[%s]\n",str1);
>
>   FILE *f1 = fopen("./subt.lua", "rb");
>   fseek(f1, 0, SEEK_END);
>   fsize = ftell(f1);
>   fseek(f1, 0, SEEK_SET);
>
>   str2 = malloc(fsize + 1);
>   fread(str2, fsize, 1, f1);
>   fclose(f1);
>
>   printf ("Factorial String = \n[%s]\n",str2);
>   //lua_State *L = luaL_newstate();
>   lua_State *L = lua_newstate(myl_alloc,NULL);
>   luaL_openlibs(L);
>   luaL_loadstring(L, str1);
>
> /*
>   if (lua_pcall(L,0, 1, 0)) {
>     printf ("Something went wrong during execution [%s\n",lua_tostring(L,
> -1)) ;
>     lua_pop(L,1);
>   }
> */
>
>
>   if (lua_pcall(L,0, LUA_MULTRET, 0)) {
>             printf ("Something went wrong during execution
> [%s\n",lua_tostring(L, -1)) ;
>             lua_pop(L,1);
>   }
>
>
>   do
>   {
>      printf ("Enter the operation: ");
>      scanf ("%79s",str);
>    //  printf ("Memory before loadString = [%ld]\n",memsize);
>      if (strcmp (str, "add") == 0)
>       {
>    //  printf ("Memory after loadString = [%ld]\n",memsize);
>
>
>           lua_getglobal(L, "add");
>           lua_pushnumber(L, 5);
>           lua_pushnumber(L, 5);
>
>           if (lua_pcall(L,2, 1, 0)) {
>             printf ("Something went wrong during execution
> [%s\n",lua_tostring(L, -1)) ;
>             lua_pop(L,1);
>           }
>           lua_pop(L,1);
>     // printf ("Memory after pcall = [%ld]\n",memsize);
>
>       }
>
>      if (strcmp (str, "subt") == 0)
>       {
>         luaL_loadstring(L, str2);
>           lua_getglobal(L, "subt");
>           lua_pushnumber(L, 5);
>           lua_pushnumber(L, 5);
>         printf ("Inside subt [%s]\n", lua_tostring(L, -1));
>           if (lua_pcall(L,2, 1, 0)) {
>             printf ("Something went wrong during execution
> [%s\n",lua_tostring(L, -1)) ;
>             lua_pop(L,1);
>           }
>             lua_pop(L,1);
>
>       }
>
>      printf ("You have entered %s \n",str);
>   } while (strcmp (str, "quit"));
>
>   lua_close(L);
> printf ("The memory size = [%ld]\n",memsize);
>   return 0;
> }
>
>
> static void *myl_alloc (void *ud, void *ptr, size_t osize,
>                                                 size_t nsize)
>    {
>        (void)ud;  (void)osize;  /* not used */
>        if (nsize == 0) {
>         memsize-=osize;
> //        printf ("Freeing [%ld] bytes, memory size = [%ld] \n",osize,
> memsize);
>          free(ptr);
>          return NULL;
>        }
>        else
>         {
> /*
>         if (memsize > 31000)
>         {
>           printf ("Memory exceeded 32K \n");
>           return NULL;
>         }
> */
>          memsize+=(nsize-osize);
>      //   printf ("Allocating new [%ld] bytes,old size = [%ld], total =
> [%ld] \n",nsize, osize, memsize);
>          return realloc(ptr, nsize);
>         }
>      }
> --------------
>

It looks like you aren't accounting for the case when ptr == NULL. In
that case, osize encodes information about the type of object being
allocated, so you don't want to subtract it from memsize. See
http://www.lua.org/manual/5.2/manual.html#lua_Alloc

(also, your message got flagged as spam for some reason.)

-- 
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