ruby 判断是否连接到 postgreSQL 数据库，如下关闭连接怎么写

temp = "host=" + conf['host'].to_s + " port=" + 5432.to_s + " dbname=" + conf['database'].to_s + " user=" + conf['username'].to_s + " password=" + conf['password'].to_s

cardinfos_conf = temp.to_s

# 连接到 MySQL服务器
$CAN_CONNECTION = false
begin
  @conn = PGconn.connect(cardinfos_conf)
  if @conn.status == PGconn::CONNECTION_OK
    $CAN_CONNECTION = true
  end
rescue PGError
  关闭连接？？？
end