英文:
How to use mutex to lock on a specific value or identifier in golang
问题
我想在更新余额时避免任何竞态条件。以下是示例代码：
type BalanceHandler struct {
repo Repository
provider Provider
mutex sync.Mutex
}
func (h *BalanceHandler) AddToBalance(userID int64, amount int64) {
h.mutex.Lock()
defer h.mutex.Unlock()
user := h.repo.GetUser(userID)
bal := h.provider.GetBalance(user.Email())
newBalance := bal + amount
h.provider.UpdateBalance(user.Email(), newBalance)
}
我想知道是否有一种方法可以为userID创建互斥锁，以便不同的用户可以并发访问，但对于相同的userID，访问应该是同步的。
英文:
I want to avoid any race condition while updating the balance. Below is the example code
type BalanceHandler struct {
repo Repository
provider Provider
}
func(h *BalanceHandler) AddToBalance(userID int64, amount int64){
user := h.repo.GetUser(userID)
bal := h.provider.GetBalance(user.Email())
newBalance := bal + amount
h.provider.UpdateBalance(user.Email(), newBalance)
}
I want to know if there is a way to create mutex specifically for the userID so that different users are allowed concurrent access but for the same userID the access should be synchronised
答案1
得分: 2
解决方案取决于代码中不明显的几个因素。
如果repo.GetUser对于相同的userID返回相同的user实例，并且该用户是指向用户结构体的指针，那么你可以为该用户添加一个互斥锁，在获取后锁定它，在完成后解锁它。
另一个选项是使用共享的map[string]struct{}对象，并记录已锁定的用户ID。你需要一个互斥锁来保护该映射。
英文:
The solution depends on several things not evident from the code.
If repo.GetUser returns the same user instance for the same userID, and if that user is a pointer to a user struct, then you can add a mutex to that user, lock it after you get it, and unlock it when you're done.
Another option is to have a shared map[string]struct{} object, and record locked user IDs. You need a mutex to protect that map.
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