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. This leads to undefined behavior and hard-to-detect bugs.

In Go, data races can be detected using the -race tool when running a program:

 go run -race main.go

Example of a data race:

package main

import (
    "fmt"
    "time"
)

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

Here, two goroutines write to counter simultaneously without synchronization, which causes a data race. To avoid this, mutexes, channels, or other synchronization mechanisms are used.