On Saturday, February 4, 2017 at 11:03:11 AM UTC+8, Matt Harden wrote: > > Never mind; I just realized that a WaitGroup is not necessarily at the > start of an allocation or global variable. >
Not very get it. Do you mean WaitGroup will be embedded in other types? So we can't use the 64bit atomic functions for all exported types in libraries? > > On Fri, Feb 3, 2017 at 7:01 PM Matt Harden <matt....@gmail.com > <javascript:>> wrote: > >> 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 <ia...@golang.org >> <javascript:>> wrote: >> >>> On Fri, Feb 3, 2017 at 5:38 AM, T L <tapi...@gmail.com <javascript:>> >>> 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...@googlegroups.com <javascript:>. >>> 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.
