Refactor optimized relation reader

Author: flash-gordon

core/lib/rom/container.rb

@@ -110,6 +110,18 @@ def self.new(gateways, relations, mappers, commands)
       end
     end
 
+    # Container lock
+    #
+    # @api private
+    attr_reader :lock
+
+    # @api private
+    def initialize
+      super
+
+      @lock = ::Mutex.new
+    end
+
     # Return registered gateways
     #
     # @return [Hash<Symbol=>Gateway>]

core/lib/rom/plugins/relation/registry_reader.rb

@@ -14,9 +14,9 @@ class RegistryReader < ::Module
         EMPTY_REGISTRY = RelationRegistry.build(EMPTY_HASH).freeze
 
         # @api private
-        def initialize(klass:, relation_readers_module:)
+        def initialize(readers:)
           super()
-          klass.include relation_readers_module
+          include readers
         end
 
         # @api private

core/lib/rom/setup/finalize/finalize_relations.rb

@@ -9,14 +9,12 @@ class Finalize
     class FinalizeRelations
       attr_reader :notifications
 
-      module BuildRelationReaders
-        def self.build(relations)
-          Module.new do
-            relations.each do |name|
-              define_method(name) do
-                __registry__[name]
-              end
-            end
+      class RegistryReaders < ::Module
+        def initialize(relations)
+          super()
+
+          relations.each do |name|
+            define_method(name) { __registry__[name] }
           end
         end
       end
@@ -44,7 +42,7 @@ def initialize(gateways, relation_classes, notifications:, mappers: nil, plugins
       # rubocop:disable Metrics/AbcSize, Metrics/MethodLength
       def run!
         relation_registry = RelationRegistry.new do |registry, relations|
-          relation_readers_module = BuildRelationReaders.build(relation_names)
+          registry_readers = RegistryReaders.new(relation_names)
           @relation_classes.each do |klass|
             unless klass.adapter
               raise MissingAdapterIdentifierError,
@@ -58,7 +56,7 @@ def run!
                     "Relation with name #{key.inspect} registered more than once"
             end
 
-            klass.use(:registry_reader, klass: klass, relation_readers_module: relation_readers_module)
+            klass.use(:registry_reader, readers: registry_readers)
 
             notifications.trigger(
               'configuration.relations.class.ready',

repository/lib/rom/repository/class_interface.rb

@@ -60,8 +60,12 @@ def new(container = nil, **options)
         container ||= options.fetch(:container)
 
         unless relation_reader
-          relation_reader(RelationReader.new(self, container.relations.elements.keys))
-          include(relation_reader)
+          reader = RelationReader.new(
+            relations: container.relations.elements.keys,
+            lock: container.lock
+          )
+          relation_reader(reader)
+          include(reader)
         end
 
         super(**options, container: container)

repository/lib/rom/repository/relation_reader.rb

@@ -7,70 +7,77 @@ class RelationReader < ::Module
       extend ::Dry::Core::ClassAttributes
 
       # @api private
-      attr_reader :klass
-
-      # @api private
-      attr_reader :relations
-
       defines :relation_readers
 
-      defines :mutex
-      mutex(Mutex.new)
-
-      defines :relation_cache
-      relation_cache(Concurrent::Hash.new)
-
       module InstanceMethods
         # @api private
-        def set_relation(name) # rubocop:disable Naming/AccessorMethodName
+        def prepare_relation(name)
           container
             .relations[name]
-            .with(auto_struct: auto_struct, struct_namespace: struct_namespace)
+            .with(
+              auto_struct: auto_struct,
+              struct_namespace: struct_namespace
+            )
         end
 
+        # @api private
         def relation_reader(name, relation_cache)
           key = [name, auto_struct, struct_namespace]
-          relation_cache[key] ||= set_relation(name)
+          relation_cache[key] ||= prepare_relation(name)
         end
       end
 
       # @api private
-      def mutex
-        ROM::Repository::RelationReader.mutex
-      end
+      class Readers < ::Module
+        # @api private
+        attr_reader :cache
 
-      # @api private
-      def initialize(klass, relations)
-        super()
-        @relations = relations
-        mutex.synchronize do
-          unless self.class.relation_readers
-            self.class.relation_readers(
-              build_relation_readers(relations, self.class.relation_cache)
-            )
+        def initialize(relations)
+          super()
+          cache = ::Concurrent::Hash.new
+
+          relations.each do |name|
+            define_readers_for_relation(name, cache)
+          end
+        end
+
+        # @api private
+        def define_readers_for_relation(name, cache)
+          define_method(name) do
+            relation_reader(name, cache)
           end
         end
-        klass.include self.class.relation_readers
       end
 
       # @api private
-      def included(klass)
-        super
-        klass.include(InstanceMethods)
-      end
+      def initialize(relations:, lock:)
+        super()
 
-      private
+        include relation_readers(relations:, lock:)
+      end
 
       # @api private
-      def build_relation_readers(relations, relation_cache)
-        Module.new do
-          relations.each do |name|
-            define_method(name) do
-              relation_reader(name, relation_cache)
+      def relation_readers(relations:, lock:)
+        existing = self.class.relation_readers
+
+        if existing.nil?
+          lock.synchronize do
+            unless self.class.relation_readers
+              self.class.relation_readers Readers.new(relations)
             end
           end
+
+          self.class.relation_readers
+        else
+          existing
         end
       end
+
+      # @api private
+      def included(klass)
+        super
+        klass.include(InstanceMethods)
+      end
     end
   end
 end

repository/lib/rom/repository/root.rb

@@ -58,7 +58,7 @@ def self.inherited(klass)
       # @see Repository#initialize
       def initialize(*, **)
         super
-        @root = set_relation(self.class.root)
+        @root = prepare_relation(self.class.root)
       end
     end
   end

repository/spec/integration/plugin_spec.rb

@@ -12,7 +12,7 @@ def self.apply(target, **)
         target.prepend(self)
       end
 
-      def set_relation(*)
+      def prepare_relation(*)
         super.where { `1 = 0` }
       end
     end

repository/spec/spec_helper.rb

@@ -59,7 +59,6 @@ def self.remove_constants
   config.after do
     Test.remove_constants
     ROM::Repository::RelationReader.relation_readers(nil)
-    ROM::Repository::RelationReader.relation_cache(Concurrent::Hash.new)
   end
 
   Dir[SPEC_ROOT.join('support/*.rb').to_s].each do |f|