java----乐观锁

乐观锁实现重试机制

//乐观锁冲突最大重试次数
    private static final int DEFAULT_MAX_RETRIES = 5;
    /**
     * 减少库存，每次减一
     *
     * @return
     */
    public boolean reduceStock(GoodsVo goods) {
        int numAttempts = 0;
        int ret = 0;
        SeckillGoods sg = new SeckillGoods();
        sg.setGoodsId(goods.getId());
        sg.setVersion(goods.getVersion());
        do {
            numAttempts++;
            try {
                sg.setVersion(goodsMapper.getVersionByGoodsId(goods.getId()));
                ret = goodsMapper.reduceStockByVersion(sg);
            } catch (Exception e) {
                e.printStackTrace();
            }
            if (ret != 0)
                break;
        } while (numAttempts < DEFAULT_MAX_RETRIES);

        return ret > 0;
    }

　　

@Mapper
public interface GoodsMapper {
    //stock_count > 0 和 版本号实现乐观锁 防止超卖
    @Update("update sk_goods_seckill set stock_count = stock_count - 1, version= version + 1 where goods_id = #{goodsId} and stock_count > 0 and version = #{version}")
    public int reduceStockByVersion(SeckillGoods seckillGoods);

    // 获取最新版本号
    @Select("select version from sk_goods_seckill  where goods_id = #{goodsId}")
    public int getVersionByGoodsId(@Param("goodsId") long goodsId);
}