gistfile1.ru

        @@asset_timestamps_cache = {}
        @@asset_timestamps_cache_guard = Mutex.new

        # Use the RAILS_ASSET_ID environment variable or the source's
        # modification time as its cache-busting asset id.
        def rails_asset_id(source)
          if asset_id = ENV["RAILS_ASSET_ID"]
            asset_id
          else
            if @@cache_asset_timestamps && (asset_id = @@asset_timestamps_cache[source])
              asset_id
            else
              path = File.join(ASSETS_DIR, source)
              asset_id = File.exist?(path) ? File.mtime(path).to_i.to_s : ''

              if @@cache_asset_timestamps
                @@asset_timestamps_cache_guard.synchronize do
                  @@asset_timestamps_cache[source] = asset_id
                end
              end

              asset_id
            end
          end
        end

        # Break out the asset path rewrite in case plugins wish to put the asset id
        # someplace other than the query string.
        def rewrite_asset_path(source)
          asset_id = rails_asset_id(source)
          if asset_id.blank?
            source
          else
            source + "?#{asset_id}"
          end
        end