From: Tim Pease <tim.pease@...>
Date: 2008-01-11T05:25:41+09:00
Subject: Re: why does this code leak?

On Jan 10, 2008, at 1:03 PM, Rick DeNatale wrote:

> Right, this analysis is correct for Robert's code, and I was thinking
> the same thing about Ara's "leaky_finalizer" code as well, but that
> code, here simplified, doesn't have the same problem as far as I can
> tell:
>
> class Class
>
>
>   def leaky_finalizer
>     lambda{}
>   end
>
>   def new *a, &b
>     object = allocate
>     object.send :initialize, *a, &b
>     object
>   ensure
>     ObjectSpace.define_finalizer object, leaky_finalizer
>   end
> end
>
> end
>
> Note that we are in class Class so self when the lambda is created is
> not the new instance but Class itself.  In this case it looks as if
> the lambda (or something else) is holding on to the binding of the
> caller of the finalize method where object is bound to the object to
> be finalized.
>

Hmmm ... I get the same results as my previous example:

$ cat a.rb
class Class
   def leaky_finalizer
     lambda {|object_id|
       puts "#{object_id} #{local_variables.inspect}  
#{instance_variables.inspect}"
     }
   end

   def new(*a, &b)
     object = allocate
     object.send :initialize, *a, &b
     object
   ensure
     ObjectSpace.define_finalizer object, leaky_finalizer
   end
end

class Foo; end

10.times {
   GC.start
   Foo.new
   p "Foo" => ObjectSpace.each_object(Foo){}
}


$ ruby a.rb
{"Foo"=>1}
{"Foo"=>2}
{"Foo"=>3}
84800 ["object_id"] []
{"Foo"=>3}
89480 ["object_id"] []
84470 ["object_id"] []
{"Foo"=>2}
{"Foo"=>3}
84360 ["object_id"] []
83880 ["object_id"] []
{"Foo"=>2}
89480 ["object_id"] []
{"Foo"=>2}
83740 ["object_id"] []
{"Foo"=>2}
84730 ["object_id"] []
{"Foo"=>2}
84770 ["object_id"] []
84800 ["object_id"] []


It looks like everything is getting cleaned up -- just not as quickly  
as one would assume. But by the end of the program, all 10 finalizers  
have been called.

Blessings,
TwP