redis 秒杀问题

模拟了一个秒杀的场景，发现count为0，但是有多个用户买了，麻烦大佬看看，谢谢！ 代码如下：

  async buy(ctx) {
    try {
      await redis.watch("goods_count");
      const count = await redis.get("goods_count");
      if (parseInt(count) > 0) {
        console.log(count);
        const time = new Date();
        const at = Math.round(time / 1000);
        const data = await redis.multi().zadd("user_goods_list", at, uuid.v4()).set("goods_count", count - 1).exec();
        console.log(data);
        ctx.body = {
          message: "抢到了"
        }
      } else {
        ctx.body = {
          message: "goods is empty"
        }
      }
    } catch (error) {
      console.log(error)
      ctx.body = {
        message: "fail"
      }
    }
  }