diff options
Diffstat (limited to 'lib/singleton.rb')
| -rw-r--r-- | lib/singleton.rb | 478 |
1 files changed, 191 insertions, 287 deletions
diff --git a/lib/singleton.rb b/lib/singleton.rb index 3c20c13253..74aec8903c 100644 --- a/lib/singleton.rb +++ b/lib/singleton.rb @@ -1,336 +1,240 @@ +# frozen_string_literal: true + # The Singleton module implements the Singleton pattern. # -# Usage: +# == Usage +# +# To use Singleton, include the module in your class. +# # class Klass # include Singleton # # ... # end # -# * this ensures that only one instance of Klass lets call it -# ``the instance'' can be created. +# This ensures that only one instance of Klass can be created. +# +# a,b = Klass.instance, Klass.instance # -# a,b = Klass.instance, Klass.instance -# a == b # => true -# a.new # NoMethodError - new is private ... +# a == b +# # => true # -# * ``The instance'' is created at instanciation time, in other words -# the first call of Klass.instance(), thus +# Klass.new +# # => NoMethodError - new is private ... # -# class OtherKlass +# The instance is created at upon the first call of Klass.instance(). +# +# class OtherKlass # include Singleton # # ... -# end -# ObjectSpace.each_object(OtherKlass){} # => 0. +# end # -# * This behavior is preserved under inheritance and cloning. +# ObjectSpace.each_object(OtherKlass){} +# # => 0 # +# OtherKlass.instance +# ObjectSpace.each_object(OtherKlass){} +# # => 1 # -# This is achieved by marking -# * Klass.new and Klass.allocate - as private -# * removing #clone and #dup and modifying -# * Klass.inherited(sub_klass) and Klass.clone() - -# to ensure that the Singleton pattern is properly -# inherited and cloned. # -# In addition Klass is providing the additional class methods -# * Klass.instance() - returning ``the instance''. After a successful -# self modifying instanciating first call the method body is a simple -# def Klass.instance() -# return @__instance__ -# end -# * Klass._load(str) - calls instance() -# * Klass._instanciate?() - 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 instanciating thread. +# This behavior is preserved under inheritance and cloning. +# +# == Implementation +# +# This above is achieved by: +# +# * Making Klass.new and Klass.allocate private. +# +# * Overriding Klass.inherited(sub_klass) and Klass.clone() to ensure that the +# Singleton properties are kept when inherited and cloned. +# +# * Providing the Klass.instance() method that returns the same object each +# time it is called. +# +# * Overriding Klass._load(str) to call Klass.instance(). +# +# * Overriding Klass#clone and Klass#dup to raise TypeErrors to prevent +# cloning or duping. +# +# == Singleton and Marshal +# +# By default Singleton's #_dump(depth) returns the empty string. Marshalling by +# default will strip state information, e.g. instance variables from the instance. +# Classes using Singleton can provide custom _load(str) and _dump(depth) methods +# to retain some of the previous state of the instance. +# +# require 'singleton' +# +# class Example +# include Singleton +# attr_accessor :keep, :strip +# def _dump(depth) +# # this strips the @strip information from the instance +# Marshal.dump(@keep, depth) +# end +# +# def self._load(str) +# instance.keep = Marshal.load(str) +# instance +# end +# end +# +# a = Example.instance +# a.keep = "keep this" +# a.strip = "get rid of this" +# +# stored_state = Marshal.dump(a) +# +# a.keep = nil +# a.strip = nil +# b = Marshal.load(stored_state) +# p a == b # => true +# p a.keep # => "keep this" +# p a.strip # => nil # -# The sole instance method of Singleton is -# * _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''. - module Singleton - private - # default marshalling strategy - def _dump(depth=-1) '' end - - class << self - # extending an object with Singleton is a bad idea - undef_method :extend_object - private - def append_features(mod) - # This catches ill advisted inclusions of Singleton in - # singletons types (sounds like an oxymoron) and - # helps out people counting on transitive mixins - unless mod.instance_of?(Class) - raise TypeError, "Inclusion of the OO-Singleton module in module #{mod}" - end - unless (class << mod; self end) <= (class << Object; self end) - raise TypeError, "Inclusion of the OO-Singleton module in singleton type" - end - super - end - def included(klass) - # remove build in copying methods - klass.class_eval do - define_method(:clone) {raise TypeError, "can't clone singleton #{self.class}"} - end - - # initialize the ``klass instance variable'' @__instance__ to nil - klass.instance_eval do @__instance__ = nil end - class << klass - # a main point of the whole exercise - make - # new and allocate private - private :new, :allocate - - # declare the self modifying klass#instance method - define_method(:instance, Singleton::FirstInstanceCall) - - # simple waiting loop hook - should do in most cases - # note the pre/post-conditions of a thread-critical state - private - def _instanciate?() - while false.equal?(@__instance__) - Thread.critical = false - sleep(0.08) - Thread.critical = true - end - @__instance__ - end - - # default Marshalling strategy - def _load(str) instance end - - # ensure that the Singleton pattern is properly inherited - def inherited(sub_klass) - super - sub_klass.instance_eval do @__instance__ = nil end - class << sub_klass - define_method(:instance, Singleton::FirstInstanceCall) - end - end - - public - # properly clone the Singleton pattern. Question - Did - # you know that duping doesn't copy class methods? - def clone - res = super - res.instance_eval do @__instance__ = nil end - class << res - define_method(:instance, Singleton::FirstInstanceCall) - end - res - end - end # of << klass - end # of included - end # of << Singleton - - FirstInstanceCall = proc do - # @__instance__ takes on one of the following values - # * nil - before and after a failed creation - # * false - during creation - # * sub_class instance - after a successful creation - # the form makes up for the lack of returns in progs - Thread.critical = true - if @__instance__.nil? - @__instance__ = false - Thread.critical = false - begin - @__instance__ = new - ensure - if @__instance__ - def self.instance() @__instance__ end - else - @__instance__ = nil # failed instance creation - end - end - elsif _instanciate?() - Thread.critical = false - else - @__instance__ = false - Thread.critical = false - begin - @__instance__ = new - ensure - if @__instance__ - def self.instance() @__instance__ end - else - @__instance__ = nil - end - end - end - @__instance__ + # The version string + VERSION = "0.3.0" + + module SingletonInstanceMethods # :nodoc: + # Raises a TypeError to prevent cloning. + def clone + raise TypeError, "can't clone instance of singleton #{self.class}" end -end + # Raises a TypeError to prevent duping. + def dup + raise TypeError, "can't dup instance of singleton #{self.class}" + end + # By default, do not retain any state when marshalling. + def _dump(depth = -1) + '' + end + end + include SingletonInstanceMethods + module SingletonClassMethods # :nodoc: -if __FILE__ == $0 + def clone # :nodoc: + Singleton.__init__(super) + end -def num_of_instances(klass) - "#{ObjectSpace.each_object(klass){}} #{klass} instance(s)" -end + # By default calls instance(). Override to retain singleton state. + def _load(str) + instance + end -# The basic and most important example. The latter examples demonstrate -# advanced features that have no relevance for the general usage + def instance # :nodoc: + @singleton__instance__ || @singleton__mutex__.synchronize { @singleton__instance__ ||= new } + end -class SomeSingletonClass - include Singleton -end -puts "There are #{num_of_instances(SomeSingletonClass)}" + private -a = SomeSingletonClass.instance -b = SomeSingletonClass.instance # a and b are same object -puts "basic test is #{a == b}" + def inherited(sub_klass) + super + Singleton.__init__(sub_klass) + end -begin - SomeSingletonClass.new -rescue NoMethodError => mes - puts mes -end + def set_instance(val) + @singleton__instance__ = val + end + def set_mutex(val) + @singleton__mutex__ = val + end + end + def self.module_with_class_methods # :nodoc: + SingletonClassMethods + end -puts "\nThreaded example with exception and customized #_instanciate?() hook"; p -Thread.abort_on_exception = false + module SingletonClassProperties # :nodoc: -class Ups < SomeSingletonClass - def initialize - self.class.__sleep - puts "initialize called by thread ##{Thread.current[:i]}" - end - class << self - def _instanciate? - @enter.push Thread.current[:i] - while false.equal?(@__instance__) - Thread.critical = false - sleep 0.04 - Thread.critical = true - end - @leave.push Thread.current[:i] - @__instance__ - end - def __sleep - sleep(rand(0.08)) - end - def allocate - __sleep - def self.allocate; __sleep; super() end - raise "boom - allocation in thread ##{Thread.current[:i]} aborted" - end - def instanciate_all - @enter = [] - @leave = [] - 1.upto(9) do |i| - Thread.new do - begin - Thread.current[:i] = i - __sleep - instance - rescue RuntimeError => mes - puts mes - end - end - end - puts "Before there were #{num_of_instances(self)}" - sleep 5 - 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 + def self.included(c) + # extending an object with Singleton is a bad idea + c.undef_method :extend_object end -end - -Ups.instanciate_all -# results in message like -# Before there were 0 Ups instances -# boom - allocation in thread #8 aborted -# initialize called by thread #3 -# Now there is 1 Ups instance -# 2; 3; 6; 1; 7; 5; 9; 4 was the order of threads entering the waiting loop -# 3; 2; 1; 7; 6; 5; 4; 9 was the order of threads leaving the waiting loop - -puts "\nLets see if class level cloning really works" -Yup = Ups.clone -def Yup.allocate - __sleep - def self.allocate; __sleep; super() end - raise "boom - allocation in thread ##{Thread.current[:i]} aborted" -end -Yup.instanciate_all + def self.extended(c) + # extending an object with Singleton is a bad idea + c.singleton_class.send(:undef_method, :extend_object) + end -puts "\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) + def __init__(klass) # :nodoc: + klass.instance_eval { + set_instance(nil) + set_mutex(Thread::Mutex.new) + } + klass end -end -def A._load(str) - instance.persist = Marshal.load(str) - instance -end -a = A.instance -a.persist = ["persist"] -a.die = "die" -a.taint + private -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 + 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 -puts "\n\nSingleton with overridden default #inherited() hook" -class Up - def Up.inherited(sub_klass) - puts "#{sub_klass} subclasses #{self}" + def included(klass) + super + klass.private_class_method :new, :allocate + klass.extend module_with_class_methods + Singleton.__init__(klass) end -end + end + extend SingletonClassProperties + ## + # :singleton-method: _load + # By default calls instance(). Override to retain singleton state. -class Middle < Up - undef_method :dup - include Singleton + ## + # :singleton-method: instance + # Returns the singleton instance. end -class Down < Middle; end - -puts "basic test is #{Down.instance == Down.instance}" - -puts "\n","Various exceptions" - -begin - module AModule - include Singleton +if defined?(Ractor) + module RactorLocalSingleton # :nodoc: + include Singleton::SingletonInstanceMethods + + module RactorLocalSingletonClassMethods # :nodoc: + include Singleton::SingletonClassMethods + def instance + set_mutex(Thread::Mutex.new) if Ractor.current[mutex_key].nil? + return Ractor.current[instance_key] if Ractor.current[instance_key] + Ractor.current[mutex_key].synchronize { + return Ractor.current[instance_key] if Ractor.current[instance_key] + set_instance(new()) + } + Ractor.current[instance_key] + end + + private + + def instance_key + :"__RactorLocalSingleton_instance_with_class_id_#{object_id}__" + end + + def mutex_key + :"__RactorLocalSingleton_mutex_with_class_id_#{object_id}__" + end + + def set_instance(val) + Ractor.current[instance_key] = val + end + + def set_mutex(val) + Ractor.current[mutex_key] = val + end end -rescue TypeError => mes - puts mes #=> Inclusion of the OO-Singleton module in module AModule -end -begin - class << 'aString' - include Singleton + def self.module_with_class_methods + RactorLocalSingletonClassMethods end -rescue TypeError => mes - puts mes # => Inclusion of the OO-Singleton module in singleton type -end - -begin - 'aString'.extend Singleton -rescue NoMethodError => mes - puts mes #=> undefined method `extend_object' for Singleton:Module -end + extend Singleton::SingletonClassProperties + end end |