From: Juergen Strobel <strobel@...>
Date: 2006-07-08T14:30:38+09:00
Subject: Re: GC oddness

--qGV0fN9tzfkG3CxV
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Fri, Jul 07, 2006 at 12:46:50AM +0900, Alex Young wrote:
> nobu@ruby-lang.org wrote:
> >Hi,
> >
> >At Thu, 6 Jul 2006 23:58:27 +0900,
> >Alex Young wrote in [ruby-talk:200382]:
> >
> >>Can someone smarter tell me why this fails?  I'm expecting the TestDir=
=20
> >>to get GC'd when I call GC.start in the test, but something's obviously=
=20
> >>keeping a reference lying around.  I just can't see what it is...
> >
> >
> >The finalizer proc refers testdir.
> I thought it might be that, but this also fails:
>=20
> -----------------------------
> require 'test/unit'
> require 'fileutils'
>=20
> class TestDir
>   @@dir =3D nil
>   @@clearup =3D proc {|id| FileUtils.rm_rf(@@dir)}
>=20
>   def TestDir.set_finalizer(testdir, dir)
>     @@dir =3D dir
>     ObjectSpace.define_finalizer(testdir, @@clearup)
>   end
>   def initialize(dir)
>     FileUtils.mkdir(dir)
>     TestDir.set_finalizer(self, dir)
>   end
> end
>=20
> class DestroyTest < Test::Unit::TestCase
>   def test_destroy
>     a =3D TestDir.new('test_dir')
>     a =3D nil
>     GC.start
>     assert !File.directory?('test_dir')
>   end
> end
> ----------------------------
>=20
> testdir hasn't come into existence when the proc's created this time, so=
=20
> I don't see how it can be keeping a reference to it, or how a finalizer=
=20
> proc keeping a reference to the object that's being finalized can stop=20
> GC - if that's the case, how does the object ever get GC'd?  What have I=
=20
> missed?
>=20
> --=20
> Alex

To get slightly off the track, I don't think using finalizers is the
best way to tackle your problem.

Are you per chance coming from C++? The RAI-pattern (Resource
Aquisition is Initialisation) is very C++-specific and doesn't work
well for any language where destructors (or finalizers) don't get to
run at fixed times. Consider instead something more rubyish like this:

def with_testdir(dir)
  raise "needs a block" unless block_given?
  setup(dir)
  yield dir     # calls your given block
ensure
  cleanup(dir)  # is executed right after your block finishes
end

with_test_dir("/tmp/test") do |dir|
 puts "now working in #{dir}"
 # your code
end

-J=FCrgen

--=20
 The box said it requires Windows 95 or better so I installed Linux

--qGV0fN9tzfkG3CxV
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: Digital signature
Content-Disposition: inline

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.3 (GNU/Linux)

iQEVAwUBRK9C9fy64gyiEfXtAQLrwQgAn8kydbi1H7WER78I5qJZvyIt3MtsmnP4
M316tWes7hd7Mb3tD+RhSLAHBK7HOh2xApKJe9pBAIO+F4ExpHs9bJPupvdN2VRF
nkCtZuubUVVUkYa0bOMwQfOnl4Js7d+of5EsevnhMOb4Au+OAUQaN9BI4Fg9+1KM
mTX7RGaDfwnKs1H25y4rW7/WUXQxgGoe+Nbm7KRxoGvVWpJTtqcqo//0K6dmMHqi
4eXNWa3Lffnkv73o+A2Cw3WHFcP5bwKcWjhc8L9gPjm/sHrCr6KmoFgTM9VV5Ni0
drUizA4dQb1FJeoDr9ei40bC2suMn6pPtsRXmQuGbmyHJRmFxTEXww==
=Kfos
-----END PGP SIGNATURE-----

--qGV0fN9tzfkG3CxV--