The code in sync/atomic.once.go is :
func (o *Once) Do(f func()) { if atomic.LoadUint32(&o.done) == 1 { //A //if o.done == 1 { return } // Slow-path. o.m.Lock() defer o.m.Unlock() if o.done == 0 { f() atomic.CompareAndSwapUint32(&o.done, 0, 1) //B //o.done = 1 } }I don't think the two 'atomic-style' code A,B above is necessary or useful. I think the lock is enough, and it could be ok if A,B are not atomic style. I must miss something, please be kind to tell me the purpose of the code A,B. Thank you.