Golang封装块变量的线程安全吗？

Question

According to the Go spec:

"The scope of an identifier denoting a constant, type, variable, or function (but not method) declared at top level (outside any function) is the package block."

Are package block variables thread safe? E.G. If I have a package block variable to store the current user for a web app:

var CurrentUser *string

Request 1 comes in: Set CurrentUser to "John" Request 2 comes in: Set CurrentUser to "Fred"

In Request 1 what is the value of CurrentUser?

Answer 1

No, package variables are not thread safe.

In your example, CurrentUser could change from "John" to "Fred" at any time—although the goroutine handling Request 1 is not guaranteed to see the change.

So you need to use a local variable to store any data that is different for different goroutines.