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Diffstat (limited to 'trunk/lib/singleton.rb')
| -rw-r--r-- | trunk/lib/singleton.rb | 313 |
1 files changed, 0 insertions, 313 deletions
diff --git a/trunk/lib/singleton.rb b/trunk/lib/singleton.rb deleted file mode 100644 index c6a2527d9a..0000000000 --- a/trunk/lib/singleton.rb +++ /dev/null @@ -1,313 +0,0 @@ -# The Singleton module implements the Singleton pattern. -# -# Usage: -# class Klass -# include Singleton -# # ... -# end -# -# * this ensures that only one instance of Klass lets call it -# ``the instance'' can be created. -# -# a,b = Klass.instance, Klass.instance -# a == b # => true -# a.new # NoMethodError - new is private ... -# -# * ``The instance'' is created at instantiation time, in other -# words the first call of Klass.instance(), thus -# -# class OtherKlass -# include Singleton -# # ... -# end -# ObjectSpace.each_object(OtherKlass){} # => 0. -# -# * This behavior is preserved under inheritance and cloning. -# -# -# -# This is achieved by marking -# * Klass.new and Klass.allocate - as private -# -# Providing (or modifying) the class methods -# * Klass.inherited(sub_klass) and Klass.clone() - -# to ensure that the Singleton pattern is properly -# inherited and cloned. -# -# * Klass.instance() - returning ``the instance''. After a -# successful self modifying (normally the first) call the -# method body is a simple: -# -# def Klass.instance() -# return @singleton__instance__ -# end -# -# * Klass._load(str) - calling Klass.instance() -# -# * Klass._instantiate?() - returning ``the instance'' or -# nil. This hook method puts a second (or nth) thread calling -# Klass.instance() on a waiting loop. The return value -# signifies the successful completion or premature termination -# of the first, or more generally, current "instantiation thread". -# -# -# The instance method of Singleton are -# * clone and dup - raising TypeErrors to prevent cloning or duping -# -# * _dump(depth) - returning the empty string. Marshalling strips -# by default all state information, e.g. instance variables and -# taint state, from ``the instance''. Providing custom _load(str) -# and _dump(depth) hooks allows the (partially) resurrections of -# a previous state of ``the instance''. - -require 'thread' - -module Singleton - # disable build-in copying methods - def clone - raise TypeError, "can't clone instance of singleton #{self.class}" - end - def dup - raise TypeError, "can't dup instance of singleton #{self.class}" - end - - # default marshalling strategy - def _dump(depth = -1) - '' - end - - module SingletonClassMethods - # properly clone the Singleton pattern - did you know - # that duping doesn't copy class methods? - def clone - Singleton.__init__(super) - end - - def _load(str) - instance - end - - private - - # ensure that the Singleton pattern is properly inherited - def inherited(sub_klass) - super - Singleton.__init__(sub_klass) - end - end - - class << Singleton - def __init__(klass) - klass.instance_eval { - @singleton__instance__ = nil - @singleton__mutex__ = Mutex.new - } - def klass.instance - return @singleton__instance__ if @singleton__instance__ - @singleton__mutex__.synchronize { - return @singleton__instance__ if @singleton__instance__ - @singleton__instance__ = new() - } - @singleton__instance__ - end - klass - end - - private - - # extending an object with Singleton is a bad idea - undef_method :extend_object - - def append_features(mod) - # help out people counting on transitive mixins - unless mod.instance_of?(Class) - raise TypeError, "Inclusion of the OO-Singleton module in module #{mod}" - end - super - end - - def included(klass) - super - klass.private_class_method :new, :allocate - klass.extend SingletonClassMethods - Singleton.__init__(klass) - end - end - -end - - -if __FILE__ == $0 - -def num_of_instances(klass) - "#{ObjectSpace.each_object(klass){}} #{klass} instance(s)" -end - -# The basic and most important example. - -class SomeSingletonClass - include Singleton -end -puts "There are #{num_of_instances(SomeSingletonClass)}" - -a = SomeSingletonClass.instance -b = SomeSingletonClass.instance # a and b are same object -puts "basic test is #{a == b}" - -begin - SomeSingletonClass.new -rescue NoMethodError => mes - puts mes -end - - - -puts "\nThreaded example with exception and customized #_instantiate?() hook"; p -Thread.abort_on_exception = false - -class Ups < SomeSingletonClass - def initialize - self.class.__sleep - puts "initialize called by thread ##{Thread.current[:i]}" - end -end - -class << Ups - def _instantiate? - @enter.push Thread.current[:i] - while false.equal?(@singleton__instance__) - @singleton__mutex__.unlock - sleep 0.08 - @singleton__mutex__.lock - end - @leave.push Thread.current[:i] - @singleton__instance__ - end - - def __sleep - sleep(rand(0.08)) - end - - def new - begin - __sleep - raise "boom - thread ##{Thread.current[:i]} failed to create instance" - ensure - # simple flip-flop - class << self - remove_method :new - end - end - end - - def instantiate_all - @enter = [] - @leave = [] - 1.upto(9) {|i| - Thread.new { - begin - Thread.current[:i] = i - __sleep - instance - rescue RuntimeError => mes - puts mes - end - } - } - puts "Before there were #{num_of_instances(self)}" - sleep 3 - puts "Now there is #{num_of_instances(self)}" - puts "#{@enter.join '; '} was the order of threads entering the waiting loop" - puts "#{@leave.join '; '} was the order of threads leaving the waiting loop" - end -end - - -Ups.instantiate_all -# results in message like -# Before there were 0 Ups instance(s) -# boom - thread #6 failed to create instance -# initialize called by thread #3 -# Now there is 1 Ups instance(s) -# 3; 2; 1; 8; 4; 7; 5 was the order of threads entering the waiting loop -# 3; 2; 1; 7; 4; 8; 5 was the order of threads leaving the waiting loop - - -puts "\nLets see if class level cloning really works" -Yup = Ups.clone -def Yup.new - begin - __sleep - raise "boom - thread ##{Thread.current[:i]} failed to create instance" - ensure - # simple flip-flop - class << self - remove_method :new - end - end -end -Yup.instantiate_all - - -puts "\n\n","Customized marshalling" -class A - include Singleton - attr_accessor :persist, :die - def _dump(depth) - # this strips the @die information from the instance - Marshal.dump(@persist,depth) - end -end - -def A._load(str) - instance.persist = Marshal.load(str) - instance -end - -a = A.instance -a.persist = ["persist"] -a.die = "die" -a.taint - -stored_state = Marshal.dump(a) -# change state -a.persist = nil -a.die = nil -b = Marshal.load(stored_state) -p a == b # => true -p a.persist # => ["persist"] -p a.die # => nil - - -puts "\n\nSingleton with overridden default #inherited() hook" -class Up -end -def Up.inherited(sub_klass) - puts "#{sub_klass} subclasses #{self}" -end - - -class Middle < Up - include Singleton -end - -class Down < Middle; end - -puts "and basic \"Down test\" is #{Down.instance == Down.instance}\n -Various exceptions" - -begin - module AModule - include Singleton - end -rescue TypeError => mes - puts mes #=> Inclusion of the OO-Singleton module in module AModule -end - -begin - 'aString'.extend Singleton -rescue NoMethodError => mes - puts mes #=> undefined method `extend_object' for Singleton:Module -end - -end |