Setting size of userdata

[Vincent Penne <ziggy@...>]

Hi all,

We are using lua 4 as scripting language in an open source project on 
dreamcast. Since it is a realtime application which create several 
temporary objects every frame, we used the incremental garbage collector 
patch, which works very fine, thanks to Paul Liu !

In this project, in particular we have many temporary  userdata that are 
created and forgot every frame. I found that one problem is that lua 
count the memory used by userdata as only the memory taken to manage it 
internally. So I added some function that let me declare how much 
additional memory does the userdata takes. This amount can be changed 
anytime, so that even complex object that make several reallocation can 
keep up to date memory usage information (of course, this may not be 
desirable to do so in every case). Also , most of the time, giving some 
empirical value may be enough (and more simple to implement).

An example of use is :

lua_pushusertag(L, data, tag);
lua_setsz(L, 1024); /* declare 1024 bytes of memory usage for this userdata */


Also a shortcut may exist to make both at the same time

lua_pushusertagsz(L, data, tag, 1024); /* create a new userdata and declare it's memory usage */



What do you think about adding this feature into lua ?


Vincent Penne.