1 files changed, 116 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..5570e2a8dc
--- /dev/null
+++ b/actionview/lib/action_view/digestor.rb
@@ -0,0 +1,116 @@
+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
+      def digest(name, format, finder, options = {})
+        details_key = finder.details_key.hash
+        dependencies = Array.wrap(options[:dependencies])
+        cache_key = ([name, details_key, format] + 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, name, format, finder, options)
+          end
+        end
+      end
+
+      private
+      def compute_and_store_digest(cache_key, name, format, finder, options) # called under @@digest_monitor lock
+        klass = if options[:partial] || 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(name, format, finder, 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, :format, :finder, :options
+
+    def initialize(name, format, finder, options={})
+      @name, @format, @finder, @options = name, format, finder, options
+    end
+
+    def digest
+      Digest::MD5.hexdigest("#{source}-#{dependency_digest}").tap do |digest|
+        logger.try :info, "Cache digest for #{name}.#{format}: #{digest}"
+      end
+    rescue ActionView::MissingTemplate
+      logger.try :error, "Couldn't find template for digesting: #{name}.#{format}"
+      ''
+    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(dependency, format, 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.find(logical_name, [], partial?, formats: [ format ])
+      end
+
+      def source
+        template.source
+      end
+
+      def dependency_digest
+        template_digests = dependencies.collect do |template_name|
+          Digestor.digest(template_name, format, 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