2.8 sync.Mutex

1. What Is Mutex

• A mutual-exclusion lock
• Implements the Locker interface; its zero value is the unlocked state
• Locking and unlocking can be done in different goroutines

2. Usage

2.1. Without Mutex

const TIMES = 1000

var data int = 0

func TestSync2(t *testing.T) {
	var wg sync.WaitGroup
	wg.Add(2)
	go func() {
		defer wg.Done()
		for i := 0; i < TIMES; i++ {
			data--
			time.Sleep(2*time.Millisecond)
		}
	}()

	go func() {
		defer wg.Done()
		for i := 0; i < TIMES; i++ {
			data++
			time.Sleep(time.Millisecond)
		}
	}()

	wg.Wait()
	fmt.Println(data, data == 0)
}
// output
-1 false

2.2. With Mutex

const TIMES = 1000

var data int = 0

func TestSync2(t *testing.T) {
	var wg sync.WaitGroup
	var lock sync.Mutex
	wg.Add(2)
	go func() {
		defer wg.Done()
		for i := 0; i < TIMES; i++ {
			lock.Lock()
			data--
			lock.Unlock()
			time.Sleep(2 * time.Millisecond)
		}
	}()

	go func() {
		defer wg.Done()
		for i := 0; i < TIMES; i++ {
			lock.Lock()
			data++
			lock.Unlock()
			time.Sleep(time.Millisecond)
		}
	}()

	wg.Wait()
	fmt.Println(data, data == 0)
}


// output
0 true