From: Masatoshi SEKI <m_seki@...>
Date: 2000-07-06T02:27:13+09:00
Subject: [ruby-list:23715] Re: Flyweight (Re: Integer[num])


咳といいます。

一年以上前の話題なのです

From: gotoken@math.sci.hokudai.ac.jp (GOTO Kentaro)
Subject: [ruby-list:13690] Flyweight (Re: Integer[num])
Date: Tue, 13 Apr 1999 20:40:03 +0900

> # いま辞書索いたらFlyweightってフライ級のボクサーのコトだそうで
> 
> -- gotoken
> 
> # 蛇足：FlyweightFactory を実現する mix-in (よーするにハッシュ :-)


ごとけんさんのコードを参考に
  ・GCされる 		… Hashが増え続けない
  ・Marshalできる	… 生成時の引数のみを使って dump/load する
ようなものを書いてみました。

おかしな部分があれば指摘してくださいませ。
# finalizer の中って Thread スイッチするのですか ??
# そうすると危険かも…



# flyaway.rb

require 'thread'
require 'weakref'

module FlyweightFactoryWeak
  def FlyweightFactoryWeak.append_features(mod)
    super
    mod.private_class_method :new
    mod.const_set("FW_HASHTABLE", {})
    mod.const_set("FW_REV_TABLE", {})
    mod.const_set("FW_MUTEX", Mutex.new)

    ObjectSpace.add_finalizer(lambda{|id|
				key = mod::FW_REV_TABLE[id]
				if key
				  mod::FW_HASHTABLE[key] = nil
				  mod::FW_REV_TABLE[id] = nil
				end
			      })
    
    def mod.[](*arg)
      self::FW_MUTEX.synchronize do
	begin
	  key = (arg.size == 1) ? arg[0] : arg
	  ref = self::FW_HASHTABLE[key]
	  begin
	    return ref[] if ref
	  rescue WeakRef::RefError
	  end
	  obj = new(*arg)
	  ref = WeakRef.new(obj)
	  self::FW_HASHTABLE[key] = ref
	  self::FW_REV_TABLE[obj.id] = key
	  return obj
	ensure
	  p self::FW_REV_TABLE if $DEBUG
	end
      end
    end

    def mod._load(s)
      self[*Marshal.load(s)]
    end
  end

  private
  def initialize(*arg)
    @fw_arg = arg
  end

  def _dump(port)
    Marshal.dump(@fw_arg, port)
  end
end


if __FILE__ == $0
  class Foo
    include FlyweightFactoryWeak
    def initialize(name, message='hello')
      @name = name
      @message = message

      super	# ! for dump/load trick
    end

    def to_s
      @name + ': ' + @message
    end
  end

  foo = Foo['mas']
  bar = Foo['bar', 'world']
  baz = Foo['bar', 'world']

  p ['foo', foo.id]
  p ['bar', bar.id]
  p ['baz', baz.id]

  baz = nil

  ObjectSpace.garbage_collect

  foo = Foo['mas']
  bar = Foo['bar', 'world']
  baz = Foo['bar', 'world']

  p ['foo', foo.id]
  p ['bar', bar.id]
  p ['baz', baz.id]

  bar = baz = nil

  ObjectSpace.garbage_collect

  foo = Foo['mas']
  bar = Foo['bar', 'world']
  baz = Foo['bar', 'world']

  p ['foo', foo.id]
  p ['bar', bar.id]
  p ['baz', baz.id]

  foo = Marshal.load(Marshal.dump(bar))

  p ['foo', foo.id]
  p ['bar', bar.id]
end