gistfile1.rb

require 'thread'                                                                 
                                                                                 
class A                                                                          
 def initialize                                                                  
   #Thread.new { foo }                                                           
                                                                                 
   ObjectSpace.define_finalizer self, proc { puts 'yes' }                        
 end                                                                             
                                                                                 
 def foo                                                                         
   sleep                                                                         
 end                                                                             
end                                                                              
                                                                                 
A.new                                                                            
GC.start                                                                         
sleep 0.1 until false