Re: Another collectgarbage question. (Inherited class)

I changed the code using only LUA functionalities as followes, and garbage
collection works perfectly. So I tends to believe that this's a LUABIND's
problem.
(luabind classes are collected eventually in the lua_close() function.
However, collectgarbage function never worked for a derived luabind class.
I suspect that Luabind might set some cyclic reference somewhere.)

When not using luabind, collectgarbage function always collected an object
whose reference count==0, and one can always make reference count==0 by
manually setting all references to the variable nil. (It can be tedious
sometimes though.) As an example, I attached a sample code including a class
inheritance implementation written by myself below.

This was not the case when the luabind 'class' was used. (Especially, a
derived one.)
Memory was not freed when collectgarbage(..) was called, but freed later in
lua_close() function.
That was unacceptable in my case because a lot of temporary class instances
are generated in a loop, and all though instances were not freed in the loop
even though I called collectgarbage() many times.

---------------------------------------------------------------

function LUAclass(baseClass)

-- A function to define a class only using native lua calls.
-- usage: MotionLoader=LUAclass()  -- define a class.
--        VRMLloader=LUAclass(MotionLoader) -- define a derived class

--  loader=VRMLloader:create({a,b,c}) -- Create an instance of the class.
-- Note that parameters are enclosed by {}

   local classobj={}
   if __classMTs==nil then
      __classMTs={}
      __classMTs.N=0
   end

   __classMTs.N=__classMTs.N+1
   local classId=__classMTs.N
   __classMTs[classId]={__index=classobj}
   classobj.__classId=classId

   classobj.create=function (classobj, tbl)
              local new_inst={}
              setmetatable(new_inst, __classMTs[classobj.__classId])
              new_inst:__init(unpack(tbl))
              return new_inst
           end

   if baseClass~=nil then
      setmetatable(classobj, {__index=baseClass})
   end

   return classobj
end


class 'VVV' -- I used luabind class only here to check if dtor is called.
You can also use a C++ class instead.
function VVV:__init(ss)
   print("ctor VVV",ss)
   self.name=ss
end

function VVV:__finalize()
   print("dtor VVV", self.name)
end

GCtest=LUAclass()

function GCtest:__init(ss)

   self.skel=VVV(ss)

end



GCtest2=LUAclass(GCtest)
function GCtest2:__init(ss)
   GCtest.__init(self,ss)
end

function gcTest()
   do
      local test=GCtest:create({"name1"})
   end
   collectgarbage("collect") -- dtor of VVV called

   do
      local test=GCtest2:create({"name2"})
   end
   collectgarbage("collect") -- dtor of VVV called

end




On Fri, Sep 25, 2009 at 4:48 AM, Jason McKesson <[email protected]> wrote:

> Taesoo Kwon wrote:
> > Hello,
> >
> > I am using luabind 0.8.1, lua5.1.4, MSVC2005.
> > I have an example where garbage collection doesn't work for a derived
> > lua class.
> > Is this a normal behavior? What should I modify?
> >
> > class 'VVV'
> >
> > function VVV:__init()
> >    print("ctor VVV")
> > end
> >
> > function VVV:__finalize()
> >    print("dtor VVV")
> > end
> >
> >
> > class 'GCtest'
> >
> > function GCtest:__init()
> >    self.skel=VVV()
> > end
> >
> > class 'GCtest2'(GCtest) -- derived class
> > function GCtest2:__init()
> >    GCtest.__init(self)
> > end
> >
> > function gctest()
> >    do
> >       local test=GCtest()
> >    end
> >    collectgarbage() -- dtor of VVV is called.
> >    collectgarbage()
> >    collectgarbage()
> >
> >    do
> >       local test=GCtest2()
> >    end
> >    collectgarbage()
> >    collectgarbage()
> >    collectgarbage() -- dtor of VVV is not called.
> >
> > end
> >
> > Thank you.
> > ------------------------------------------------------------------------
> >
> >
> ------------------------------------------------------------------------------
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> >
> It is Lua that decides when the finalize method of a table will be
> called. It will do it eventually, but it does not guarantee that it will
> be called at any particular time. And if Lua's garbage collection
> functions don't want to do a full CG on everything in memory when you
> call the function, then there's nothing you can do.
>
> This is the price you pay for having a fast garbage collector.
>
>
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> developing skills, take BlackBerry mobile applications to market and stay
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>

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