RE: Lua GC

[<jgiors@...>]

> -------- Original Message --------
> Subject: Re: Lua GC
> From: <jgiors@threeeyessoftware.com>
> Date: Thu, September 16, 2010 2:49 pm
> To: lua-l@lists.lua.org
> 
> >>> Andre Leiradella <andre@leiradella.com> wrote:
> >Hi All,
> >Given the following script held in a get_t.lua file:
> >
> >----------8<----------
> >local t = {
> >-- Initialization of fields in t.
> >}
> >
> >-- Code that manipulates fields in t.
> >
> >return t
> >----------8<----------
> >
> >and the following main.lua file:
> >
> >----------8<----------
> >local t = loadfile( 'get_t.lua' )()
> >
> >-- Use t.
> >
> >-- Code that runs for a long time and that doesn't
> >-- reference t anymore follows...
> >----------8<----------
> >
> >Can I count on t being garbage-collected, and also the bytecode 
> >generated by loading get_t.lua along with all local variables and 
> >functions declared in it? Consider that main.lua will be creating 
> >tables, strings and userdata so the GC will be triggered eventually.
> >
> >I'm aware of require and stuff but since the results of get_t.lua will 
> >be used just once I don't want it to be lying around while main.lua runs.
> >
> >Thanks,
> >
> >Andre
> 
> Table t will not be garbage-collected (unless there is some optimizer
> magic I don't know about). t is in scope throughout the main file, and
> will not be dereferenced until main.lua terminates.
> 
> However, there is a very simple solution. Just change your main.lua to
> this:
> 
> ----------8<----------
> local t = loadfile( 'get_t.lua' )()
> 
> -- Use t.
> 
> t = nil     --This will dereference t.
>             --You could also call collectgarbage("collect")
> 
> -- Code that runs for a long time and that doesn't
> -- reference t anymore follows...
> ----------8<----------
> 
> An alternative is to package the operations on t into a function, which
> I find "cleaner" (please excuse any typos!):
> 
> ----------8<----------
> local function init()
>     local t = loadfile( 'get_t.lua' )()
>     --Use t.
>     --optional collectgarbage("collect")
> end
> 
> init()
> 
> --Rest of main. t is not in scope.
> ----------8<----------

I made a mistake in that second version, it should be:

----------8<----------
local function init()
    local t = loadfile( 'get_t.lua' )()
    --Use t.
end

init()
--optional collectgarbage("collect") --GC HERE, NOT IN INIT()

--Rest of main. t is not in scope.
----------8<----------

Sorry for any potential confusion.

John Giors
Independent Programmer
Three Eyes Software
jgiors@ThreeEyesSoftware.com
http://www.ThreeEyesSoftware.com