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ruby--ruby/lib/singleton.rb

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# Singleton module that ensures only one object to be allocated.
#
# Usage:
# class SomeSingletonClass
# include Singleton
# #....
# end
# a = SomeSingletonClass.instance
# b = SomeSingletonClass.instance # a and b are same object
# p [a,b]
# a = SomeSingletonClass.new # error (`new' is private)
module Singleton
def Singleton.included(klass)
klass.private_class_method(:new)
klass.instance_eval %{
@__instance__ = nil
def instance
if defined? @__allocating__
until @__instance__
sleep 0.5
end
elsif ! @__instance__
Thread.critical = true
@__allocating__ = true
Thread.critical = false
begin
@__instance__ = new
ensure
remove_instance_variable(:@__allocating__)
end
end
return @__instance__
end
}
end
end
if __FILE__ == $0
class SomeSingletonClass
include Singleton
#....
end
a = SomeSingletonClass.instance
b = SomeSingletonClass.instance # a and b are same object
p [a,b]
a = SomeSingletonClass.new # error (`new' is private)
end