var m sync.Mutexfunc (*InventoryServer) LockSell(ctx context.Context, req *proto.SellInfo) (*emptypb.Empty, error) {
    tx := global.DB.Begin()
    m.Lock() 
    for _, good := range req.GoodsInfo {
        var i model.Inventory        if result := global.DB.Where(&model.Inventory{Goods: good.GoodsId}).First(&i); 
             result.RowsAffected == 0 {
            tx.Rollback() // 回滚
            return nil, status.Errorf(codes.InvalidArgument, "未找到此商品的库存信息。")
        }
        if i.Stocks < good.Num {
            tx.Rollback() 
            return nil, status.Errorf(codes.ResourceExhausted, "此商品的库存不足")
        }
        i.Stocks -= good.Num
        tx.Save(&i)
    }
    tx.Commit()
    m.Unlock()
    return &emptypb.Empty{}, nil}

func (*InventoryServer) ForUpdateSell(ctx context.Context, req *proto.SellInfo) (*emptypb.Empty, error) {
    tx := global.DB.Begin()
    for _, good := range req.GoodsInfo {
        var i model.Inventory        if result := tx.Clauses(clause.Locking{
            Strength: "UPDATE",
        }).Where(&model.Inventory{Goods: good.GoodsId}).First(&i);
            result.RowsAffected == 0 {
            tx.Rollback()
            return nil, status.Errorf(codes.InvalidArgument, "未找到此商品的库存信息。")
        }
        if i.Stocks < good.Num {
            tx.Rollback()
            return nil, status.Errorf(codes.ResourceExhausted, "此商品的库存不足")
        }

        i.Stocks -= good.Num
        tx.Save(&i)
    }

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

func (*InventoryServer) VersionSell(ctx context.Context, req *proto.SellInfo) (*emptypb.Empty, error) {
    tx := global.DB.Begin()
    for _, good := range req.GoodsInfo {
        var i model.Inventory        for { // 并发请求相同条件比较多，防止放弃掉一些请求
            if result := global.DB.Where(&model.Inventory{Goods: good.GoodsId}).First(&i);
                result.RowsAffected == 0 {

                tx.Rollback()
                return nil, status.Errorf(codes.InvalidArgument, "未找到此商品的库存信息.")
            }
            if i.Stocks < good.Num {
                tx.Rollback() // 回滚
                return nil, status.Errorf(codes.ResourceExhausted, "此商品的库存不足")
            }
            i.Stocks -= good.Num
            version := i.Version + 1
            if result := tx.Model(&model.Inventory{}).
                Select("Stocks", "Version").
                Where("goods = ? and version= ?", good.GoodsId, i.Version).
                Updates(model.Inventory{Stocks: i.Stocks, Version: version});
                result.RowsAffected == 0 {
                
                zap.S().Info("库存扣减失败!")
            } else {
                break
            }
        }
    }
    tx.Commit() // 提交
    return &emptypb.Empty{}, nil}

func (*InventoryServer) RedisSell(ctx context.Context, req *proto.SellInfo) (*emptypb.Empty, error) {
    // redis 分布式锁
    pool := goredis.NewPool(global.Redis)
    rs := redsync.New(pool)
    tx := global.DB.Begin()
    for _, good := range req.GoodsInfo {
        mutex := rs.NewMutex(fmt.Sprintf("goods_%d", good.GoodsId))
        if err := mutex.Lock(); err != nil {
            return nil, status.Errorf(codes.Internal, "redis:分布式锁获取异常")
        }
        var i model.Inventory        if result := global.DB.Where(&model.Inventory{Goods: good.GoodsId}).First(&i); result.RowsAffected == 0 {
            tx.Rollback()
            return nil, status.Errorf(codes.InvalidArgument, "未找到此商品的库存信息")
        }
        if i.Stocks < good.Num {
            tx.Rollback()
            return nil, status.Errorf(codes.ResourceExhausted, "此商品的库存不足")
        }
        i.Stocks -= good.Num
        tx.Save(&i)
        if ok, err := mutex.Unlock(); !ok || err != nil {
            return nil, status.Errorf(codes.Internal, "redis:分布式锁释放异常")
        }
    }
    tx.Commit()
    return &emptypb.Empty{}, nil}

func main() {
  var w sync.WaitGroup
  w.Add(20)
  for i := 0; i < 20; i++ {
      go TestForUpdateSell(&w) // 模拟并发请求
  }
  w.Wait()}func TestForUpdateSell(wg *sync.WaitGroup) {
     defer wg.Done()
  _, err := invClient.Sell(context.Background(), &proto.SellInfo{
      GoodsInfo: []*proto.GoodsInvInfo{
     {GoodsId: 16, Num: 1},
  //{GoodsId: 16, Num: 10},
      },
  })
  if err != nil {
      panic(err)
 } 
 fmt.Println("库存扣减成功")}