8-5

def synchronized(o)
  if block_given?
    o.mutex.synchronize { yield }
  else
    SynchronizedObject.new(o)
  end
end

# A delegating wrapper class using method_missing for thread safety
# Instead of extending Object and deleting our methods we just extend
# BasicObject, which is defined in Ruby 1.9. BasicObject does not 
# inherit from Object or Kernel, so the methods of a BasicObject cannot
# invoke any top-level methods: they are just not there.
class SynchronizedObject  < BasicObject
  def initialize(o); @delegate = o;  end
  def __delegate; @delegate; end

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