I'm not sure under what situations you get misaligned values. But note that atomic.Int64 has other benefits besides alignment guarantees. Most importantly, it prevents you from accidentally mixing atomic and non-atomic accesses to the same address - every access of an atomic.Int64 is always atomic.
On Thu, Sep 1, 2022, 13:29 Benz <wei.z...@zentertain.net> wrote: > Since go `1.19`, the [`atomic.Int64`]( > https://github.com/golang/go/blob/go1.19/src/sync/atomic/type.go#L82) was > added > > ```go > type Int64 struct { > _ noCopy > _ align64 > v int64 > } > ``` > > There is one additional [`align64`]( > https://github.com/golang/go/blob/go1.19/src/sync/atomic/type.go#L191) in > `atomic.Int64` > > ```go > // align64 may be added to structs that must be 64-bit aligned. > // This struct is recognized by a special case in the compiler > // and will not work if copied to any other package. > type align64 struct{} > ``` > > With the test codes under go 1.19 > > ```go > var i64 int64 > var a64 atomic.Int64 > fmt.Println(unsafe.Alignof(i64)) > fmt.Println(unsafe.Alignof(a64)) > ``` > > The result is > > ``` > 8 > 8 > ``` > > The test environment is MacOS with CPU info > > ``` > hw.ncpu: 12 > hw.activecpu: 12 > hw.perflevel0.cpusperl2: 2 > hw.perflevel0.cpusperl3: 12 > hw.perflevel0.logicalcpu: 12 > hw.perflevel0.logicalcpu_max: 12 > hw.perflevel0.physicalcpu: 6 > hw.perflevel0.physicalcpu_max: 6 > hw.cpu64bit_capable: 1 > ``` > > It seems both `int64` and `atomic.Int64` have the same align size `8`. > What does `align64 may be added to structs that must be 64-bit aligned` > means? What situations can `atomic.Int64` be used？ > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/c800d445-deb7-4683-b353-e1bc17d457abn%40googlegroups.com > <https://groups.google.com/d/msgid/golang-nuts/c800d445-deb7-4683-b353-e1bc17d457abn%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAEkBMfFUQmrfxfhu-wQ%2B75kp%3Dj2W3zTWk%3Dpz5HQcfF_ZB%2BcjNw%40mail.gmail.com.
