6.4 Locking shared resources

Atomic functions

Atomic functions provide low-level locking mechanisms for synchronizing access to integers and pointers.

var (
    counter int64
    wg sync.WaitGroup
)
func main() {
    wg.Add(2)
    go incCounter(1)
    go incCounter(2)
    wg.Wait()
    fmt.Println("Final Counter:", counter)
}
func incCounter(id int) {
    defer wg.Done()
    for count := 0; count < 2; count++ {
        atomic.AddInt64(&counter, 1)
        runtime.Gosched()
    }
}

Mutexes

A mutex is used to create a critical section around code that ensures only one goroutine at a time can execute that code section.

var (
    counter int
    wg      sync.WaitGroup
    mutex   sync.Mutex
)
func main() {
    wg.Add(2)
    go incCounter(1)
    go incCounter(2)
    wg.Wait()
    fmt.Printf("Final Counter: %d\\n", counter)
}
func incCounter(id int) {
    defer wg.Done()
    for count := 0; count < 2; count++ {
        mutex.Lock()
        // The use of the curly brackets is just to make the
        // critical section easier to see; they’re not necessary.
        {
            value := counter
            runtime.Gosched()
            value++
            counter = value
        }
        mutex.Unlock()
    }
}