flock.rb

class File
  def flocked? &block
    status = flock LOCK_EX|LOCK_NB
    case status
      when false
        return true
      when 0
        begin
          block ? block.call : false
        ensure
          flock LOCK_UN
        end
      else
        raise SystemCallError, status
    end
  end
  alias_method "if_not_flocked", "flocked?"
end

dpkg = File.open("/var/lib/apt/lists/lock","r")
#puts dpkg.flocked?
dpkg.flocked? do
  puts "not locked"
  sleep(60)
end

test.rb

  def flocked? &block
    status = flock LOCK_EX|LOCK_NB
    case status
      when false
        return true
      when 0
        flock LOCK_UN
        return false
      else
        raise SystemCallError, status
    end
  end
  alias_method "if_not_flocked", "flocked?"