type SpinLock struct {
    // 鎖變量
    lock uint32
}
// Lock locks the SpinLock.
func (sl *SpinLock) Lock() {
    for !sl.TryLock() {
        // 暫停當(dāng)前goroutine，讓其他goroutine先行運算
        runtime.Gosched()
    }
}
// TryLock tries to lock the SpinLock.
func (sl *SpinLock) TryLock() bool {
    // 原子交換，0換成1
    return atomic.CompareAndSwapUint32(&sl.lock, 0, 1)
}
// Unlock unlocks the SpinLock.
func (sl *SpinLock) Unlock() {
    // 原子置零
    atomic.StoreUint32(&sl.lock, 0)
}

func output(s string) {
    for i := 0; i < 3; i++ {
        fmt.Println(s)
    }
}
// 未使用Gosched的代碼
func Test_GoschedDisable(t *testing.T) {
    go output("goroutine 2")
    output("goroutine 1")
}
// === RUN   Test_GoschedDisable
// goroutine 1
// goroutine 1
// goroutine 1
// --- PASS: Test_GoschedDisable (0.00s)

func output(s string) {
    for i := 0; i < 3; i++ {
        fmt.Println(s)
    }
}
// 使用Gosched的代碼
func Test_GoschedEnable(t *testing.T) {
    go output("goroutine 2")
    runtime.Gosched()
    output("goroutine 1")
}
// === RUN   Test_GoschedEnable
// goroutine 2
// goroutine 2
// goroutine 2
// goroutine 1
// goroutine 1
// goroutine 1
// --- PASS: Test_GoschedEnable (0.00s)

func output(s string) {
    for i := 0; i < 3; i++ {
        fmt.Println(s)
    }
}
// 使用Gosched的代碼，并故意延長子協(xié)程的執(zhí)行時間，看主協(xié)程是否一直等待
func Test_GoschedEnableAndSleep(t *testing.T) {
    go func() {
        time.Sleep(5000)
        output("goroutine 2")
    }()
    runtime.Gosched()
    output("goroutine 1")
}
// === RUN   Test_GoschedEnableAndSleep
// goroutine 2
// goroutine 2
// goroutine 2
// goroutine 1
// goroutine 1
// goroutine 1
// --- PASS: Test_GoschedEnableAndSleep (0.00s)

// addr 表示地址
// old  表示uint32值，它是舊的，
// new  表示uint32新值，它將與舊值交換自身。
// 如果交換完成，則返回true，否則返回false。
func CompareAndSwapUint32(addr *uint32, old, new uint32) (swapped bool)

// addr 表示地址
// val  表示uint32值，它是舊的，
func StoreUint32(addr *uint32, val uint32)