From: "Eustaquio Rangel de Oliveira Jr." <eustaquiorangel@...>
Date: 2005-07-07T06:13:50+09:00
Subject: Collecting garbage

Hi.

I have a doubt about garbage collection:

----------------------------------------------------------------------------------------
class CustomObject
	attr_accessor :val, :next
	def initialize(v,n=nil)
		@val	= v
		@next	= n
	end
	def to_s
		"Object #{@val} (#{self.object_id}) points to #{@next.nil? ? 'nothing' : 
@next.val} (#{@next.nil? ? '':@next.object_id})"
	end
end

def list
	print "Listing all CustomObject's with ObjectSpace\n"
	print "#{ObjectSpace.each_object(CustomObject) {|v| puts v}} objects 
found\n\n"
end

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

c1 = nil
c4.next = nil

GC.start		# here I want c1 disappears
sleep(1)
list
----------------------------------------------------------------------------------------

running this program I get

----------------------------------------------------------------------------------------
Listing all CustomObject's with ObjectSpace
Object 6 (-604874926) points to nothing ()
Object 4 (-604874906) points to 5 (-604874896)
Object 5 (-604874896) points to nothing ()
Object 1 (-604874866) points to 2 (-604874856)
Object 2 (-604874856) points to 3 (-604874846)
Object 3 (-604874846) points to 1 (-604874866)
6 objects found

Listing all CustomObject's with ObjectSpace
Object 6 (-604874926) points to nothing ()
Object 4 (-604874906) points to nothing ()
Object 1 (-604874866) points to 2 (-604874856)
Object 2 (-604874856) points to 3 (-604874846)
Object 3 (-604874846) points to 1 (-604874866)
5 objects found
----------------------------------------------------------------------------------------

There's a circular reference there: c1 points to 2 (created internally on 
1), 2 points to 3 (created internally on 2), and 3 points to c1, which is a 
reference at root (?) level there and again points to an internal 2, that 
points to 3, that points to c1 ...

My question is, when assigning nil to c1, it should not invalidate all the 
inner objects and becomes available for garbage collection?
On the example above, I assigned nil to c1 and c4.next (5), and after the 
GC.start I don't have 5, but still have c1 (same id), 2 and 3. On that 
case, that memory will never be sweeped (free)? Because seems that I'll 
always have a Object with id -604874856 and will not have a way to refer to 
it later, for use or free the allocated memory for it.

Thanks.

----------------------------
Eust�quio "TaQ" Rangel
eustaquiorangel@yahoo.com
http://beam.to/taq
Usu�rio GNU/Linux no. 224050