1 files changed, 122 insertions, 0 deletions
diff --git a/actionview/lib/action_view/digestor.rb b/actionview/lib/action_view/digestor.rb
new file mode 100644
index 0000000000..1f103786cb
--- /dev/null
+++ b/actionview/lib/action_view/digestor.rb
@@ -0,0 +1,122 @@
+require 'thread_safe'
+require 'action_view/dependency_tracker'
+require 'monitor'
+
+module ActionView
+  class Digestor
+    cattr_reader(:cache)
+    @@cache          = ThreadSafe::Cache.new
+    @@digest_monitor = Monitor.new
+
+    class << self
+      # Supported options:
+      #
+      # * <tt>name</tt>   - Template name
+      # * <tt>finder</tt>  - An instance of ActionView::LookupContext
+      # * <tt>dependencies</tt>  - An array of dependent views
+      # * <tt>partial</tt>  - Specifies whether the template is a partial
+      def digest(options)
+        options.assert_valid_keys(:name, :finder, :dependencies, :partial)
+
+        cache_key = ([ options[:name], options[:finder].details_key.hash ].compact + Array.wrap(options[:dependencies])).join('.')
+
+        # this is a correctly done double-checked locking idiom
+        # (ThreadSafe::Cache's lookups have volatile semantics)
+        @@cache[cache_key] || @@digest_monitor.synchronize do
+          @@cache.fetch(cache_key) do # re-check under lock
+            compute_and_store_digest(cache_key, options)
+          end
+        end
+      end
+
+      private
+        def compute_and_store_digest(cache_key, options) # called under @@digest_monitor lock
+          klass = if options[:partial] || options[:name].include?("/_")
+            # Prevent re-entry or else recursive templates will blow the stack.
+            # There is no need to worry about other threads seeing the +false+ value,
+            # as they will then have to wait for this thread to let go of the @@digest_monitor lock.
+            pre_stored = @@cache.put_if_absent(cache_key, false).nil? # put_if_absent returns nil on insertion
+            PartialDigestor
+          else
+            Digestor
+          end
+
+          digest = klass.new(options).digest
+          # Store the actual digest if config.cache_template_loading is true
+          @@cache[cache_key] = stored_digest = digest if ActionView::Resolver.caching?
+          digest
+        ensure
+          # something went wrong or ActionView::Resolver.caching? is false, make sure not to corrupt the @@cache
+          @@cache.delete_pair(cache_key, false) if pre_stored && !stored_digest
+        end
+    end
+
+    attr_reader :name, :finder, :options
+
+    def initialize(options)
+      @name, @finder = options.values_at(:name, :finder)
+      @options = options.except(:name, :finder)
+    end
+
+    def digest
+      Digest::MD5.hexdigest("#{source}-#{dependency_digest}").tap do |digest|
+        logger.try :debug, "  Cache digest for #{template.inspect}: #{digest}"
+      end
+    rescue ActionView::MissingTemplate
+      logger.try :error, "  Couldn't find template for digesting: #{name}"
+      ''
+    end
+
+    def dependencies
+      DependencyTracker.find_dependencies(name, template)
+    rescue ActionView::MissingTemplate
+      [] # File doesn't exist, so no dependencies
+    end
+
+    def nested_dependencies
+      dependencies.collect do |dependency|
+        dependencies = PartialDigestor.new(name: dependency, finder: finder).nested_dependencies
+        dependencies.any? ? { dependency => dependencies } : dependency
+      end
+    end
+
+    private
+      def logger
+        ActionView::Base.logger
+      end
+
+      def logical_name
+        name.gsub(%r|/_|, "/")
+      end
+
+      def partial?
+        false
+      end
+
+      def template
+        @template ||= finder.disable_cache { finder.find(logical_name, [], partial?) }
+      end
+
+      def source
+        template.source
+      end
+
+      def dependency_digest
+        template_digests = dependencies.collect do |template_name|
+          Digestor.digest(name: template_name, finder: finder, partial: true)
+        end
+
+        (template_digests + injected_dependencies).join("-")
+      end
+
+      def injected_dependencies
+        Array.wrap(options[:dependencies])
+      end
+  end
+
+  class PartialDigestor < Digestor # :nodoc:
+    def partial?
+      true
+    end
+  end
+end