Untested ...

threadsafe.rb

class ThreadSafeWrapper < Delegator
  def initialize(obj)
    super
    @mutex = Mutex.new
  end

  def method_missing(m, *args, &block)
    @mutex.synchronize { super }
  end

  def __getobj__
    @delegate
  end
  
  def __setobj__(obj)
    @delegate = obj
  end
end