From: Karsten Meier <discussionruby@...>
Date: 2004-08-24T07:10:43+09:00
Subject: Re: Circular References: How to prove that they are garbage collected

Thanks, this is doing the trick.
Even when I put the assignments to nil also in the function
(just to be sure that there is has nothing to do with C++ style
destruction of objects on the stack when leaving the function)


Joel VanderWerf wrote:
> Karsten Meier wrote:
> 
>> Hello Ruby Fans
>>
>> I'm converting a perl example which deals with the circular data 
>> structures, and how to make sure they are destroyed properly.
>> (For the pleac cookbook, pleac.sourceforge.net)
>>
>> I have read several times that the garbage collector has no problems 
>> with circular references, so I tried to prove it.
>> But with my ruby 1.8.0 it looks like the garbage collector
>> does not destroys the Node A, B and C, but only the lonely node:
> 
> 
> "Only the lonely
>  Node the way I feel tonight"
> 
>   ... hehe. Sorry Roy Orbison.
> 
> Anyway, try it with the following 3 additional lines. All four nodes 
> print their message before the "Garbage colection called" message. I 
> think what's going on is conservatism. Keeping the local vars in a 
> method makes sure that stack frame is gone begore the GC starts.
> 
>> GC.enable
>>
>> class RingNode
>>   attr_accessor :next
>>   attr_accessor :prev
>>   attr_reader :name
>>
>>   def initialize(aName)
>>       @name = aName
>>       ObjectSpace.define_finalizer(self,
>>             self.class.method(:finalize).to_proc)
>>   end
>>
>>   def RingNode.finalize(id)
>>       puts "Node #{id} dying"
>>   end
>>
>>   def RingNode.show_all_objects
>>       ObjectSpace.each_object {|id|
>>           puts id.name if id.class == RingNode
>>       }
>>   end
>> end
>>
> def main
> 
>> a = RingNode.new("Node A")
>> b = RingNode.new("Node B")
>> c = RingNode.new("Node C")
>> a.next = b
>> b.next = c
>> c.next = a
>> a.prev = c
>> c.prev = b
>> b.prev = a
>> lonely = RingNode.new("Lonely node")
> 
> end
> 
>>
>> a = nil
>> b = nil
>> c = nil
>> lonely = nil
>>
> main
> 
>> GC.start
>> puts "Garbage Collection called"
>> RingNode.show_all_objects
>> puts "End of Program"
>>
>>
>> What happens is that Noda A,B,C get destroyed, but after the end of 
>> the program. If I comment out the finalizer (in case I made an error 
>> with it) and only use the ObjectSpace.each_object, I see also Node 
>> A,B,C after the garbage collection.
>>
> 
> 
>