Re: GC Barriers

[Roberto Ierusalimschy <roberto@...>]

> There is a comment above luaH_set that says:
> 
> "beware: when using this function you probably need to check a GC barrier and invalidate the TM cache"
> 
> I have a function which is called from luaV_execute, it creates a Table object, which may or may not have nested Table objects, which is eventually assigned to 'ra'.
> 
> As I am creating this table entirely during the call to my function from luaV_execute do I need to worry about creating GC barriers? The tables have no metamethods so I do not need to invalidate any caches.
> 
> I am setting the array part of the table every time and potentially the hash part if needed. These values are being set to Lua strings via luaS_new. Right now I do not have any barrier calls in place, I do have lua_assert defined and I do not get any assertions during the execution of my code, nor when the Lua state is torn down, which leads me to believe I probably don't need a barrier call.
> 
> I just thought I would double-check here to be sure! :)

If your entire operation never calls the garbage collector (e.g.,
'luaC_checkGC'), then you do not need barriers. The tables you are
creating are all white (not visited yet); the problem is a black object
refering to a white one. If you are using Lua 5.2, remember also that
you have to anchor your objects while creating them, or an emergency
collection can collect them.

-- Roberto