What is a data race?

Data race — is a situation in multithreaded programs where two or more threads simultaneously access the same variable, and at least one of them performs a write, without proper synchronization.

In Go, a data race leads to undefined behavior because the order of operations is not guaranteed.

Example of a data race in Go:

package main
import (
    "fmt"
    "time"
)

func main() {
    var counter int
    go func() {
        counter = 1
    }()
    go func() {
        counter = 2
    }()
    time.Sleep(time.Second)
    fmt.Println(counter)
}

Here, two goroutines write to the variable counter simultaneously without synchronization, leading to a data race.

To detect a data race in Go, you can use the -race flag during run or test:

go run -race main.go