No, wg.Add cannot "switch" to wg.Wait, they're both in the samr goroutine, the go statement will be always the next one to execute after wg.Add within serve().
On Thu, Aug 24, 2017, 19:29 Tom Payne <twpa...@gmail.com> wrote: > I'm not singling out Dave Cheney here, I'd just like to check my > understanding of Go's resource handling and concurrency. > > In this blog post a "prototypical network server" is presented: > > https://dave.cheney.net/2017/08/20/context-isnt-for-cancellation > > Code: > > func serve(l net.Listener) error { > var wg sync.WaitGroup > var conn net.Conn > var err error > for { > conn, err = l.Accept() > if err != nil { > break > } > wg.Add(1) > go func(c net.Conn) { > defer wg.Done() > handle(c) > }(conn) > } > wg.Wait() > return err > } > > My understanding is that this contains a race condition. Specifically, a > goroutine switch can occur at the entry to wg.Add(1), switching to > wg.Wait() in the main goroutine. At this point, a connection has been > accepted, but the WaitGroup counter has not been incremented, so the serve > function will terminate while silently dropping a network connection (the > connection will be accepted, but never handled, so will probably eventually > time out on the client side and leak a file descriptor on the server side). > > Is this understanding correct? Furthermore, I suspect that it's impossible > to implement race-free graceful termination using only sync.WaitGroups. Is > it actually possible to do so? > > Thanks for any correction, and apologies to Dave for picking on his code. > > Cheers, > Tom > > -- > 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. > -- -j -- 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.
