Doesn't the statement "32-bit compilers to not ensure [64 bit alignment at the start of an allocation]" contradict the sync/atomic statement "The first word in a global variable or in an allocated struct or slice can be relied upon to be 64-bit aligned."?
On Fri, Feb 3, 2017 at 6:44 AM Ian Lance Taylor <i...@golang.org> wrote: > On Fri, Feb 3, 2017 at 5:38 AM, T L <tapir....@gmail.com> wrote: > > Why does WaitGroup.state method check 64-bit alignment at run time? > > Why not make the state field as the first word of WaitGroup struct? > > > > // https://golang.org/src/sync/waitgroup.go?s=1857:1892#L20 > > > > type WaitGroup struct { > > > > noCopy noCopy > > > > // 64-bit value: high 32 bits are counter, low 32 bits are waiter count. > > > > // 64-bit atomic operations require 64-bit alignment, but 32-bit > > > > // compilers do not ensure it. So we allocate 12 bytes and then use > > > > // the aligned 8 bytes in them as state. > > Doesn't this comment explain the problem? > > Ian > > -- > 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. > For more options, visit https://groups.google.com/d/optout. > -- 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. For more options, visit https://groups.google.com/d/optout.
