class Module

def synchronize(*methods)

end
synchronize :expire, :with => :@@lock
end
...
def expire
@@lock = Mutex.new
class SharedCache
Example:
constant, or instance or class variable.
The :with option should be a symbol or string, and can represent a method,
#synchronize and yields to a block) must be provided as a final :with option.
particular mutex. A mutex (either a Mutex, or any object that responds to
Synchronize access around a method, delegating synchronization to a 
def synchronize(*methods)
  options = methods.extract_options!
  unless options.is_a?(Hash) && with = options[:with]
    raise ArgumentError, "Synchronization needs a mutex. Supply an options hash with a :with key as the last argument (e.g. synchronize :hello, :with => :@mutex)."
  end
  methods.each do |method|
    aliased_method, punctuation = method.to_s.sub(/([?!=])$/, ''), $1
    if method_defined?("#{aliased_method}_without_synchronization#{punctuation}")
      raise ArgumentError, "#{method} is already synchronized. Double synchronization is not currently supported."
    end
    module_eval(<<-EOS, __FILE__, __LINE__ + 1)
      def #{aliased_method}_with_synchronization#{punctuation}(*args, &block)     # def expire_with_synchronization(*args, &block)
        #{with}.synchronize do                                                    #   @@lock.synchronize do
          #{aliased_method}_without_synchronization#{punctuation}(*args, &block)  #     expire_without_synchronization(*args, &block)
        end                                                                       #   end
      end                                                                         # end
    EOS
    alias_method_chain method, :synchronization
  end
end