go: 通过原子变量实现roundrobin切换

type RoundRobin struct{ 
    index int64 
} 
func (m *RoundRobin) GetIndex(max int) int64 { 
 for { 
        index := atomic.LoadInt64(&m.index) 
        newIndex := index + 1 
 if int(newIndex) >= max { 
            newIndex = 0 
 } 
 if atomic.CompareAndSwapInt64(&m.index, index, newIndex) { 
 return newIndex 
 } else { 
 continue 
 } 
 } 
}