Re: Garbage collection

[Shmuel Zeigerman <shmuz@...>]

Lyte _ wrote:
> I have some problems with adding a metatable to userdata for garbage 
> collection. This is what I have now... When i start lua I do the following.
>
> luaL_newmetatable(L, "LuaBook.gc_event");
>
> /* set its __gc field */
> lua_pushstring(L, "__gc");
> lua_pushcfunction(L, gc_function);
> lua_settable(L, -3);
>
> I then call a factory function from lua which creates an object in C. I 
> want to be able to free this object the right way when it is not used 
> anymore, but it does not seem to work. This is what I do in the factory 
> function.
>
> lua_newuserdata(L,sizeof(...))
> luaL_getmetatable(L, "LuaBook.gc_event");
> lua_setmetatable(L, -2);'
>
> In the Lua program, I then do something like this.
>
> o = CreateObject()
> o = nil
> collectgarbage()
>
> When I run this the function I added to the metatable does not get 
> called. What am I doing wrong here?

You probably forgot to assign the "__index" field
of the metatable to the metatable itself:

  luaL_newmetatable(L, "LuaBook.gc_event");
  lua_pushliteral(L, "__index");
  lua_pushvalue(L, -2);         /* push metatable */
  lua_rawset(L, -3);            /* metatable.__index = metatable */

--
Shmuel