在閱讀 Go 的源代碼時(shí)，我對 src/sync/once.go 中的代碼有疑問：func (o *Once) Do(f func()) {    // Note: Here is an incorrect implementation of Do:    //    //  if atomic.CompareAndSwapUint32(&o.done, 0, 1) {    //      f()    //  }    //    // Do guarantees that when it returns, f has finished.    // This implementation would not implement that guarantee:    // given two simultaneous calls, the winner of the cas would    // call f, and the second would return immediately, without    // waiting for the first's call to f to complete.    // This is why the slow path falls back to a mutex, and why    // the atomic.StoreUint32 must be delayed until after f returns.    if atomic.LoadUint32(&o.done) == 0 {        // Outlined slow-path to allow inlining of the fast-path.        o.doSlow(f)    }}func (o *Once) doSlow(f func()) {    o.m.Lock()    defer o.m.Unlock()    if o.done == 0 {        defer atomic.StoreUint32(&o.done, 1)        f()    }}為什么使用，而不是說？這些不是等價(jià)的嗎？有什么區(qū)別？atomic.StoreUint32o.done = 1我們是否必須使用原子運(yùn)算（）來確保其他goroutines可以在內(nèi)存較弱的機(jī)器上觀察到之前設(shè)置為1的效果？atomic.StoreUint32f()o.done