gistfile1.rb

puts "---Starting run---"

threads = []

@mutex = Mutex.new
thread1_ids = []
thread2_ids = []
o = nil
a = nil

threads << Thread.new do 
  50000.times do
    @mutex.synchronize { a = Object.new } 
    thread1_ids << a.object_id
  end
end

threads << Thread.new do 
  50000.times do
    @mutex.synchronize { o = Object.new }
    thread2_ids << o.object_id
  end
end

threads.each {|th| th.join}

thread1_ids.sort!
thread2_ids.sort!

dups = thread1_ids & thread2_ids

puts "Duplicates: #{dups.inspect}"
puts "Total dups: #{dups.length}"
puts "---DONE---"