Add thread_m/cattr_accessor/reader/writer suite of methods for declaring class and module variables that live per-thread

3 files changed, 144 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/core_ext/module.rb b/activesupport/lib/active_support/core_ext/module.rb
index b4efff8b24..ef038331c2 100644
--- a/activesupport/lib/active_support/core_ext/module.rb
+++ b/activesupport/lib/active_support/core_ext/module.rb
@@ -3,6 +3,7 @@ require 'active_support/core_ext/module/introspection'
 require 'active_support/core_ext/module/anonymous'
 require 'active_support/core_ext/module/reachable'
 require 'active_support/core_ext/module/attribute_accessors'
+require 'active_support/core_ext/module/attribute_accessors_per_thread'
 require 'active_support/core_ext/module/attr_internal'
 require 'active_support/core_ext/module/concerning'
 require 'active_support/core_ext/module/delegation'
diff --git a/activesupport/lib/active_support/core_ext/module/attribute_accessors_per_thread.rb b/activesupport/lib/active_support/core_ext/module/attribute_accessors_per_thread.rb
new file mode 100644
index 0000000000..36fe52cea1
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/module/attribute_accessors_per_thread.rb
@@ -0,0 +1,140 @@
+require 'active_support/core_ext/array/extract_options'
+
+# Extends the module object with class/module and instance accessors for
+# class/module attributes, just like the native attr* accessors for instance
+# attributes, but does so on a per-thread basis.
+# 
+# So the values are scoped within the Thread.current space under the class name
+# of the module.
+class Module
+  # Defines a per-thread class attribute and creates class and instance reader methods.
+  # The underlying per-thread class variable is set to +nil+, if it is not previously defined.
+  #
+  #   module Current
+  #     thread_mattr_reader :user
+  #   end
+  #
+  #   Current.user # => nil
+  #   Thread.current[:attr_Current_user] = "DHH"
+  #   Current.user # => "DHH"
+  #
+  # The attribute name must be a valid method name in Ruby.
+  #
+  #   module Foo
+  #     thread_mattr_reader :"1_Badname"
+  #   end
+  #   # => NameError: invalid attribute name: 1_Badname
+  #
+  # If you want to opt out the creation on the instance reader method, pass
+  # <tt>instance_reader: false</tt> or <tt>instance_accessor: false</tt>.
+  #
+  #   class Current
+  #     thread_mattr_reader :user, instance_reader: false
+  #   end
+  #
+  #   Current.new.user # => NoMethodError
+  def thread_mattr_reader(*syms)
+    options = syms.extract_options!
+
+    syms.each do |sym|
+      raise NameError.new("invalid attribute name: #{sym}") unless sym =~ /^[_A-Za-z]\w*$/
+      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
+        def self.#{sym}
+          Thread.current[:"attr_#{name}_#{sym}"]
+        end
+      EOS
+
+      unless options[:instance_reader] == false || options[:instance_accessor] == false
+        class_eval(<<-EOS, __FILE__, __LINE__ + 1)
+          def #{sym}
+            Thread.current[:"attr_#{self.class.name}_#{sym}"]
+          end
+        EOS
+      end
+    end
+  end
+  alias :thread_cattr_reader :thread_mattr_reader
+
+  # Defines a per-thread class attribute and creates a class and instance writer methods to
+  # allow assignment to the attribute.
+  #
+  #   module Current
+  #     thread_mattr_writer :user
+  #   end
+  #
+  #   Current.user = "DHH"
+  #   Thread.current[:attr_Current_user] # => "DHH"
+  #
+  # If you want to opt out the instance writer method, pass
+  # <tt>instance_writer: false</tt> or <tt>instance_accessor: false</tt>.
+  #
+  #   class Current
+  #     thread_mattr_writer :user, instance_writer: false
+  #   end
+  #
+  #   Current.new.user = "DHH" # => NoMethodError
+  def thread_mattr_writer(*syms)
+    options = syms.extract_options!
+    syms.each do |sym|
+      raise NameError.new("invalid attribute name: #{sym}") unless sym =~ /^[_A-Za-z]\w*$/
+      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
+        def self.#{sym}=(obj)
+          Thread.current[:"attr_#{name}_#{sym}"] = obj
+        end
+      EOS
+
+      unless options[:instance_writer] == false || options[:instance_accessor] == false
+        class_eval(<<-EOS, __FILE__, __LINE__ + 1)
+          def #{sym}=(obj)
+            Thread.current[:"attr_#{self.class.name}_#{sym}"] = obj
+          end
+        EOS
+      end
+    end
+  end
+  alias :thread_cattr_writer :thread_mattr_writer
+
+  # Defines both class and instance accessors for class attributes.
+  #
+  #   class Current
+  #     thread_mattr_accessor :user
+  #   end
+  #
+  #   Current.user = "DHH"
+  #   Current.user     # => "DHH"
+  #   Current.new.user # => "DHH"
+  #
+  # If a subclass changes the value then that will not change the value for
+  # parent class. Similarly if parent class changes the value then that will not
+  # change the value of subclasses either.
+  #
+  #   class Customer < Account
+  #   end
+  #
+  #   Customer.user = "CHH"
+  #   Account.user # => "DHH"
+  #
+  # To opt out of the instance writer method, pass <tt>instance_writer: false</tt>.
+  # To opt out of the instance reader method, pass <tt>instance_reader: false</tt>.
+  #
+  #   class Current
+  #     thread_mattr_accessor :user, instance_writer: false, instance_reader: false
+  #   end
+  #
+  #   Current.new.user = "DHH"  # => NoMethodError
+  #   Current.new.user          # => NoMethodError
+  #
+  # Or pass <tt>instance_accessor: false</tt>, to opt out both instance methods.
+  #
+  #   class Current
+  #     mattr_accessor :user, instance_accessor: false
+  #   end
+  #
+  #   Current.new.user = "DHH"  # => NoMethodError
+  #   Current.new.user          # => NoMethodError
+  def thread_mattr_accessor(*syms, &blk)
+    thread_mattr_reader(*syms, &blk)
+    thread_mattr_writer(*syms, &blk)
+  end
+  alias :thread_cattr_accessor :thread_mattr_accessor
+end
diff --git a/activesupport/lib/active_support/per_thread_registry.rb b/activesupport/lib/active_support/per_thread_registry.rb
index a909a65bb6..88e2b12cc7 100644
--- a/activesupport/lib/active_support/per_thread_registry.rb
+++ b/activesupport/lib/active_support/per_thread_registry.rb
@@ -1,6 +1,9 @@
 require 'active_support/core_ext/module/delegation'
 
 module ActiveSupport
+  # NOTE: This approach has been deprecated for end-user code in favor of thread_mattr_accessor and friends.
+  # Please use that approach instead.
+  #
   # This module is used to encapsulate access to thread local variables.
   #
   # Instead of polluting the thread locals namespace: