mutex扩展

const (
    mutexLocked = 1 << iota
    mutexWoken
    mutexStarving
    mutexWaiterShift = iota
)

type Mutex struct {
    sync.Mutex
}

func (m *Mutex) TryLock() bool {
    if atomic.CompareAndSwapInt32((*int32)(unsafe.Pointer(&m.Mutex)), 0, mutexLocked) {
        return true
    }

    old := atomic.LoadInt32((*int32)(unsafe.Pointer(&m.Mutex)))

    if old&(mutexLocked|mutexStarving|mutexWoken) != 0 {
        return false
    }

    n := old | mutexLocked

    return atomic.CompareAndSwapInt32((*int32)(unsafe.Pointer(&m.Mutex)), old, n)
}

func (m *Mutex) Count() int {
    v := atomic.LoadInt32((*int32)(unsafe.Pointer(&m.Mutex)))

    v = v >> mutexWaiterShift
    v = v + (v & mutexLocked)

    return int(v)
}

func (m *Mutex) IsLocked() bool {
    return m.isState(mutexLocked)
}

func (m *Mutex) IsWoken() bool {
    return m.isState(mutexWoken)
}

func (m *Mutex) IsStarving() bool {
    return m.isState(mutexStarving)
}

func (m *Mutex) isState(state int32) bool {
    return atomic.LoadInt32((*int32)(unsafe.Pointer(&m.Mutex)))&state == state
}