Race Condition Detected

Why This Happens

Go's race detector (go run -race) finds concurrent unsynchronized access to shared variables. A data race occurs when two goroutines access the same variable and at least one is writing. This leads to unpredictable behavior and bugs that are hard to reproduce.

The Problem

var counter int

func main() {
    for i := 0; i < 1000; i++ {
        go func() {
            counter++ // data race
        }()
    }
    time.Sleep(time.Second)
    fmt.Println(counter)
}

The Fix

var (
    counter int
    mu      sync.Mutex
)

func main() {
    var wg sync.WaitGroup
    for i := 0; i < 1000; i++ {
        wg.Add(1)
        go func() {
            defer wg.Done()
            mu.Lock()
            counter++
            mu.Unlock()
        }()
    }
    wg.Wait()
    fmt.Println(counter)
}

Step-by-Step Fix

1. 1

   Identify the race

   Run your program with go run -race or go test -race to get a detailed report of the conflicting accesses.

2. 2

   Understand the shared state

   Determine which variable is shared and which goroutines are reading and writing to it.

3. 3

   Add synchronization

   Protect the shared variable with sync.Mutex, sync.RWMutex, sync/atomic operations, or redesign to use channels.