modify_value

# File activesupport/lib/active_support/cache/memory_store.rb, line 155
        def modify_value(name, amount, options)
          synchronize do
            options = merged_options(options)
            if num = read(name, options)
              num = num.to_i + amount
              write(name, num, options)
              num
            end
          end
        end