From: Alex Young <alex@...>
Date: 2006-07-07T00:46:50+09:00
Subject: Re: GC oddness

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 
>>to get GC'd when I call GC.start in the test, but something's obviously 
>>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:

-----------------------------
require 'test/unit'
require 'fileutils'

class TestDir
   @@dir = nil
   @@clearup = proc {|id| FileUtils.rm_rf(@@dir)}

   def TestDir.set_finalizer(testdir, dir)
     @@dir = dir
     ObjectSpace.define_finalizer(testdir, @@clearup)
   end
   def initialize(dir)
     FileUtils.mkdir(dir)
     TestDir.set_finalizer(self, dir)
   end
end

class DestroyTest < Test::Unit::TestCase
   def test_destroy
     a = TestDir.new('test_dir')
     a = nil
     GC.start
     assert !File.directory?('test_dir')
   end
end
----------------------------

testdir hasn't come into existence when the proc's created this time, so 
I don't see how it can be keeping a reference to it, or how a finalizer 
proc keeping a reference to the object that's being finalized can stop 
GC - if that's the case, how does the object ever get GC'd?  What have I 
missed?

-- 
Alex