sync 主要用于 golang 中共享资源访问的同步控制。虽然 golang 更推荐 chan 这种通过通信来共享资源的方式，但有时候直接使用 sync 的效果更好，它是 chan 方式的很好的补充。本文对 sync 的使用进行一些简单介绍。

互斥锁

func TestMutex() {
    var mutex sync.Mutex
    sum := 0
    for i := 0; i < 10; i++ {
        go func(t int) {
            mutex.Lock()
            defer mutex.Unlock()
            sum += t
            fmt.Println(t)
        }(i)
    }
    time.Sleep(time.Second)
    fmt.Printf("Sum: %v\n",sum)
}

条件变量

func TestCond() {
    cond := sync.NewCond(&sync.Mutex{})
    for i := 0; i < 10; i++ {
        go func(t int) {
            time.Sleep(time.Second)
            cond.L.Lock()
            defer cond.L.Unlock()
            cond.Wait()
            fmt.Println(t)
        }(i)
    }

    time.Sleep(2 * time.Second)
    //cond.Signal()
    cond.Broadcast()
}

读写锁

func TestRWMutex() {
    var rwMutex sync.RWMutex
    sum := 0
    for i := 0; i < 10; i++ {
        go func(t int) {
            rwMutex.RLock()
            //time.Sleep(time.Second)
            defer rwMutex.RUnlock()
            fmt.Printf("Sum: %v\n",sum)
        }(i)
        go func(t int) {
            rwMutex.Lock()
            defer rwMutex.Unlock()
            sum += t
        }(i)
    }
    time.Sleep(5 * time.Second)
}

Pool

func TestPool() {
    var pool sync.Pool
    pool.New = func() interface{} { return "Hello" }
    for i := 0; i < 10; i++ {
        s := pool.Get()
        fmt.Println(s)
        pool.Put("World" + strconv.FormatInt(int64(i), 10))
    }
}

Once

func TestOnce() {
    once := &sync.Once{}
    for i := 0; i < 10; i++ {
        go func(t int) {
            once.Do(func() {
                fmt.Println("Hello Once!")
            })
            fmt.Println("Hello World!")
        }(i)
    }
    time.Sleep(time.Second)
}

WaitGroup

func TestWaitGroup() {
    var wg sync.WaitGroup
    for i := 0; i < 10; i++ {
        wg.Add(1)
        go func(t int) {
            defer wg.Done()
            fmt.Println(t)
        }(i)
    }
    wg.Wait()
}