lock while building image

lock.rb

    # Build Docker image and run it as a container.
    def up
      begin
        lock = File.open('/var/lock/subsys/pool.lock', 'w')
        if lock.flock(File::LOCK_EX | File::LOCK_NB )
          image_id = build
          container_id = run image_id
          confirm_running container_id
        else
          @logger.info("Locked! Other environment is under building process")
          @logger.info("Please access after finishing another building process...")
        end
      rescue => ex
        @logger.error ex
        raise
      ensure
        @logger.close
        lock.flock(File::LOCK_UN)
      end
    end