go锁

var m sync.Mutex

m.Lock()

m.Unlock()

mysql 悲观锁

func (s InventoryServer) Sell(ctx context.Context, request *proto.SellInfo) (*emptypb.Empty, error) {
    tx := global.DB.Begin()

    for _, item := range request.GoodsInfo {
        inventory := model.Inventory{}
        // 需要用tx.Clauses(clause.Locking{Strength: "UPDATE"})
        // SELECT * FROM `inventory` WHERE goods = ? LIMIT 1 FOR UPDATE
        // https://blog.csdn.net/rootzcl/article/details/101597084
        //           👇 👇
        if result := tx.Clauses(clause.Locking{Strength: "UPDATE"}).Where("goods = ?", item.GoodsId).First(&inventory); result.RowsAffected == 0 {
            tx.Rollback()
            return nil, status.Error(codes.InvalidArgument, "没有库存信息")
        }
        if item.Nums > inventory.Stocks {
            tx.Rollback()
            return nil, status.Error(codes.ResourceExhausted, "库存不足")
        }

        inventory.Stocks -= item.Nums
        tx.Save(&inventory)
    }

    tx.Commit()
    return &emptypb.Empty{}, nil
}

mysql 乐观锁

// Sell 使用乐观锁
func (s InventoryServer) Sell(ctx context.Context, request *proto.SellInfo) (*emptypb.Empty, error) {
    tx := global.DB.Begin()
    for _, item := range request.GoodsInfo {
        for {
            inventory := model.Inventory{}
            if result := global.DB.Where("goods = ?", item.GoodsId).First(&inventory); result.RowsAffected == 0 {
                tx.Rollback()
                return nil, status.Error(codes.InvalidArgument, "没有库存信息")
            }
            if item.Nums > inventory.Stocks {
                tx.Rollback()
                return nil, status.Error(codes.ResourceExhausted, "库存不足")
            }

            inventory.Stocks -= item.Nums

            if result := tx.Model(&model.Inventory{}).
            //                     👇
            Where("goods = ? and version = ?", inventory.Goods, inventory.Version).
            Select("stocks", "version"). // 避免0被忽略
            Updates(model.Inventory{
                Stocks:  inventory.Stocks,
                Version: inventory.Version + 1, // 👈
            }); result.RowsAffected == 0 {
                zap.S().Info("库存扣减失败 (乐观锁)")
            } else {
                break
            }
        }
    }
    tx.Commit()

    return &emptypb.Empty{}, nil
}

redis 分布式锁

client := redis.NewClient(&redis.Options{
    Addr:     fmt.Sprintf("%s:%d", global.ServerConfig.RedisConfig.Host, global.ServerConfig.RedisConfig.Port),
    Password: global.ServerConfig.RedisConfig.Password,
})
pool := goredis.NewPool(client) // or, pool := redigo.NewPool(...)

global.RedSync = redsync.New(pool)

mutex := global.RedSync.NewMutex(fmt.Sprintf("goods_%d", item.GoodsId))
// 获取锁
if err := mutex.Lock(); err != nil {
    return nil, status.Error(codes.Internal, "获取redis分布式锁异常")
}
// 释放锁
if ok, err := mutex.Unlock(); !ok || err != nil {
    tx.Rollback()
    return nil, status.Error(codes.Internal, "释放redis分布式锁异常")
}

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