From: Yohanes Santoso <ysantoso-rubytalk@...>
Date: 2005-07-08T05:47:03+09:00
Subject: Re: Collecting garbage

"Eustaquio Rangel de Oliveira Jr." <eustaquiorangel@yahoo.com> writes:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Hi!
>
> Thanks for the answer. :-)
>
> | Ruby's GC is lazy and conservative. Lazy meaning, it does not
> | exhaustively try to do path-finding on each object because for some
> | objects, path-finding is an expensive process. Conservative meaning,
> | if it is not doing a path-finding on an object, that object is not
> | freed.
> |
> | Hate it or love it. It has both advantages and disadvantages. You have
> | just shown a disadvantage. But it can be mitigated by exiting the
> | scope which should make path-finding to those objects cheaper.
>
> I'll search about lazy and conversative gc's. :-)
> Just another question: if I use a method there, and not a begin/end block,
> like this
>
> - --------------------------------------------------------------------------
> def test
> 	c1 = CustomObject.new("1",CustomObject.new("2",CustomObject.new("3")))
> 	c4 = CustomObject.new("4",CustomObject.new("5"))
> 	c6 = CustomObject.new("6")
> 	c1.next.next.next = c1	# comment this and check again
> 	list
> end
>
> test
> GC.start			
> sleep(1)
> list
> - --------------------------------------------------------------------------
>
> After run this, only c6 remains. It's about scope also?
>

Funny, I couldn't reproduce what you are seeing. I cut and paste the
code you have and run it:

vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
/tmp $ ruby1.8 ./gc.rb
Listing all CustomObject's with ObjectSpace
Object 6 (-604561642) points to nothing ()
Object 4 (-604561622) points to 5 (-604561612)
Object 5 (-604561612) points to nothing ()
Object 1 (-604561582) points to 2 (-604561572)
Object 2 (-604561572) points to 3 (-604561562)
Object 3 (-604561562) points to 1 (-604561582)
6 objects found

Listing all CustomObject's with ObjectSpace
0 objects found
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Nothing remains.

Probably you are seeing c6 remaining because you were playing with
your code like so: 

vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
def test
	c1 = CustomObject.new("1",CustomObject.new("2",CustomObject.new("3")))
	c4 = CustomObject.new("4",CustomObject.new("5"))
	c6 = CustomObject.new("6")
end

test
GC.start			
sleep(1)
list
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Notice that c6 is returned from test, so the object refered to by c6
is now accessible from where you invoke GC.start and that is the
original problem.


YS.