gistfile1.txt

class Foo
  def initialize
    @var = 0
    @updated = false
  end

  def update
    @updated = true
    @var = 42
  end

  def check
    x = @updated
    raise if @var == 42 && !x
    @updated
  end
end

100.times do
  obj = Foo.new
  t1 = Thread.new {
    sleep 0.01
    obj.update
  }
  100.times.map {
    Thread.new {
      Thread.pass while !obj.check
    }
  }.each(&:join)
  t1.join
end

!!CAUTION!! This test has a concurrency bug... '@Updated = true' can be executed by another Thread just after 'x = @Updated' is executed. I cannot emulate volatility issue in JRuby.