Re: Lua GC

[Andre Leiradella <andre@...>]

 On 16/09/2010 18:58, jgiors@threeeyessoftware.com wrote:
> > -------- 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.
Sure, I overlooked it when I typed the code. The point is, given t will 
be available for garbage collection, will the GC collect get_t.lua's 
script from memory? I could say yes from your post, but you didn't say 
it out loud.

Thanks,

Andre
> > 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