[ruby/singleton] Improve Ractor-compliance; Create PerRactorSingleton

https://github.com/ruby/singleton/commit/ec4f66d9c1

lib/singleton.rb

@@ -93,21 +93,25 @@
 #
 module Singleton
   VERSION = "0.2.0"
+  VERSION.freeze
 
-  # Raises a TypeError to prevent cloning.
-  def clone
-    raise TypeError, "can't clone instance of singleton #{self.class}"
-  end
+  module SingletonInstanceMethods
+    # Raises a TypeError to prevent cloning.
+    def clone
+      raise TypeError, "can't clone instance of singleton #{self.class}"
+    end
 
-  # Raises a TypeError to prevent duping.
-  def dup
-    raise TypeError, "can't dup instance of singleton #{self.class}"
-  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)
-    ''
+    # By default, do not retain any state when marshalling.
+    def _dump(depth = -1)
+      ''
+    end
   end
+  include SingletonInstanceMethods
 
   module SingletonClassMethods # :nodoc:
 
@@ -121,7 +125,7 @@ module Singleton
     end
 
     def instance # :nodoc:
-      @singleton__instance__ || @singleton__mutex__.synchronize { @singleton__instance__ ||= new }
+      @singleton__instance__ || @singleton__mutex__.synchronize { @singleton__instance__ ||= set_instance(new) }
     end
 
     private
@@ -130,22 +134,42 @@ module Singleton
       super
       Singleton.__init__(sub_klass)
     end
+
+    def set_instance(val)
+      @singleton__instance__ = val
+    end
+
+    def set_mutex(val)
+      @singleton__mutex__ = val
+    end
   end
 
-  class << Singleton # :nodoc:
+  def self.module_with_class_methods
+    SingletonClassMethods
+  end
+
+  module SingletonClassProperties
+
+    def self.included(c)
+      # extending an object with Singleton is a bad idea
+      c.undef_method :extend_object
+    end
+
+    def self.extended(c)
+      # extending an object with Singleton is a bad idea
+      c.singleton_class.undef_method :extend_object
+    end
+
     def __init__(klass) # :nodoc:
       klass.instance_eval {
-        @singleton__instance__ = nil
-        @singleton__mutex__ = Thread::Mutex.new
+        set_instance(nil)
+        set_mutex(Thread::Mutex.new)
       }
       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)
@@ -157,10 +181,11 @@ module Singleton
     def included(klass)
       super
       klass.private_class_method :new, :allocate
-      klass.extend SingletonClassMethods
+      klass.extend module_with_class_methods
       Singleton.__init__(klass)
     end
   end
+  extend SingletonClassProperties
 
   ##
   # :singleton-method: _load
@@ -170,3 +195,44 @@ module Singleton
   # :singleton-method: instance
   #  Returns the singleton instance.
 end
+
+module PerRactorSingleton
+  include Singleton::SingletonInstanceMethods
+
+  module PerRactorSingletonClassMethods
+    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
+      :"__PerRactorSingleton_instance_with_class_id_#{object_id}__"
+    end
+
+    def mutex_key
+      :"__PerRactorSingleton_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
+
+  def self.module_with_class_methods
+    PerRactorSingletonClassMethods
+  end
+
+  extend Singleton::SingletonClassProperties
+end