CODEWITHSUNDEEP
go
raminr
raminr

Reputation: 804

Safe to read from shared data structure in goroutines without channels

I am new to Golang and starting to use goroutines. I am curious if it is safe to read from a data structure that is being written to by another goroutines without using channel or mutex. In the example below, the events array is visible to main and goroutine, but main only reads from it and the goroutine is modifying it. Is this considered safe?

var events = []string{}

func main() {

    go func() {
        for {
            if len(events) > 30 {
                events = nil
            }
            event := "The time is now " + time.Now().String()
            events = append(events, event)
            time.Sleep(time.Millisecond * 200)
        }
    }()

    for {
        for i:=0; i < len(events); i++ {
            fmt.Println(events[i])
        }
        time.Sleep(time.Millisecond * 100)
        fmt.Println("--------------------------------------------------------")
    }
}

Thanks.

Upvotes: 1

Views: 522

Answers (1)

Eli Bendersky
Eli Bendersky

Reputation: 273566

No, this is absolutely not safe. You should use synchronization primitives around access to events, or redesign to use channels.

Your code may work fine today, on a specific architecture/OS, but it may break unexpectedly with small changes and/or on another architecture/OS.

Try to run your code with -race to verify. You'll probably see WARNING: DATA RACE.

See also this answer.

Upvotes: 1

Related Questions