From: Wyss Clemens <WYS@...>
Date: 2001-05-20T01:37:00+09:00
Subject: [ruby-talk:15400] Re: PROPOSAL: Java-like method-based synchr	onization mechanism in Rub y



>> class Module
>>   def synchronized(*methods)
>>     if methods.size() > 0 then
>>       # we need a Mutex (-getter)
>>       module_eval  <<-EOS
>>       def __mutex__()
>> 	if (@__mutex__.nil?()) then 
>> 	  @__mutex__ = Mutex.new() 
>> 	end

>Is this thread safe, or could two different threads each generate
>their own mutex?

You are right, we need to apply the "Double-Checked Locking" as described in
POSA2 ;-)

class Module 
  def synchronized(*methods)
    if methods.size() > 0 then
      instance_eval("@@__dcl_mutex__ = Mutex.new()")

      # we need a Mutex (-getter)
      module_eval  <<-EOS
      def __mutex__()
	if (@__mutex__.nil?()) then 
	  @@__dcl_mutex__.synchronize {
	    if (@__mutex__.nil?()) then 
	      @__mutex__ = Mutex.new() 
	    end
	  }
	end 
	return @__mutex__
      end
      EOS
    end
    methods.each { | method |
      synchronizeMethod(method.to_s())
    }
  end # synchronize(*methods)


>> Note: �synchronized� is to be applied in the same manner as
�attr_reader�,
>> �attr_writer�, etc.

>I wonder if it should be more like 'protected', 'private', and
>'public'? That is, it can apply to a list of methods, or to all
>subsequent methods.

Not sure. Best would be if we could use "def_synchronized" or "def
synchronized" (or...) to denote synchronized methods. But this would require
changes to the ruby interpreter.

Clemens