Merge pull request #191 from alphagov/resolver-cache

Fix memory leak in components

CHANGELOG.md

@@ -1,3 +1,5 @@
+* Fix memory leak in components
+
 # 10.1.2
 
 * Bugfix for request URI's encoded as ASCII

lib/slimmer/component_resolver.rb

@@ -5,12 +5,6 @@ module Slimmer
   class ComponentResolver < ::ActionView::Resolver
     TEST_TAG_NAME = 'test-govuk-component'
 
-    def self.caching
-      # this turns off the default ActionView::Resolver caching which caches
-      # all templates for the duration of the current process in production
-      false
-    end
-
     def find_templates(name, prefix, partial, details, outside_app_allowed = false)
       return [] unless prefix == 'govuk_component'
 

lib/slimmer/govuk_components.rb

@@ -17,17 +17,41 @@ def self.included into
 
     # @private
     def add_govuk_components
-      append_view_path Slimmer::ComponentResolver.new
+      append_view_path GovukComponents.expiring_resolver_cache.resolver
 
       return if slimmer_backend_included?
       I18n.backend = I18n::Backend::Chain.new(I18n.backend, Slimmer::I18nBackend.new)
     end
 
+    # @private
+    def self.expiring_resolver_cache
+      @expiring_resolver_cache ||= TimedExpirationResolverCache.new
+    end
+
   private
 
     def slimmer_backend_included?
       I18n.backend.is_a?(I18n::Backend::Chain) &&
         I18n.backend.backends.any? { |b| b.is_a? Slimmer::I18nBackend }
     end
+
+    # Slimmer::ComponentResolver instantiates a lot of large objects and leaks
+    # memory. This class will cache the resolver so that it doesn't have to
+    # create new ActionView::Template objects for each request. The cache is
+    # timed to allow frontends to pick up changes made to components in `static`.
+    class TimedExpirationResolverCache
+      def initialize
+        @cache_last_reset = Time.now
+      end
+
+      def resolver
+        if (@cache_last_reset + Slimmer::CACHE_TTL) < Time.now
+          @resolver = nil
+          @cache_last_reset = Time.now
+        end
+
+        @resolver ||= Slimmer::ComponentResolver.new
+      end
+    end
   end
 end