I'm guessing that Michal is flagging is there no way to write safe code if your using stmt.QueryContext(ctx) and rows.Scan into a sql.RawBytes as QueryContext kicks off a go routine that monitors the ctx, closing rows if cancelled and that ctx can be cancelled at any time.
The only thing that springs to mind is to only allow the cancellation processing to happen while in sql functions which would mean that sql.RawBytes can't be updated while the consumer, user code, is processing it. It's interesting that there is a related comment in row.Scan <https://github.com/golang/go/blob/176b63e7113b82c140a4ecb2620024526c2c42e3/src/database/sql/sql.go#L3356>, which prevents the use of sql.RawBytes because it always closes the underlying rows before returning. On Thu, 21 Jul 2022 at 20:02, Ian Lance Taylor <i...@golang.org> wrote: > On Thu, Jul 21, 2022 at 11:02 AM Michal Hruby <michal....@gmail.com> > wrote: > > > > Hello, I have a code snippet equivalent to this one: > > > > rows, err := stmt.QueryContext(ctx) > > if err != nil { > > return info, nil, err > > } > > defer rows.Close() > > > > var data sql.RawBytes > > for rows.Next() { > > err = rows.Scan(&data) > > if err != nil { > > return nil, err > > } > > // if ctx is canceled around this point, rows.Close() will be called > and the data can e overwritten, causing a data race > > _ = data[0] // <--- possible concurrent read here and write inside > driver.Rows.Close() > > } > > > > And as the comments say, if the context is cancelled, there's a > possibility of a data race where this goroutine is trying to read data[0], > and another goroutine can be writing to it, cause the sql package calls > driver.Rows.Close() (from > https://github.com/golang/go/blob/176b63e7113b82c140a4ecb2620024526c2c42e3/src/database/sql/sql.go#L2974 > ) > > > > I've opened an issue about this on github ( > https://github.com/golang/go/issues/53970 ), but was told that's not the > proper forum to talk about data races. > > > > Any help would be appreciated, thanks. > > I don't quite understand what you are asking. I think you're correct > that there is a data race there. It seems to me that the answer is to > not cancel the context. > > What kind of answer are you looking for? > > 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. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/CAOyqgcUwGN5b-DEwCqLRu6kWwpAnCvO7o6u5TjzS3bmbUgksdw%40mail.gmail.com > . > -- 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/CAHEMsqYKu5wNtZybfNzz4xbBmfZOCDew6zo-v5R8QDsDH%3D43Ug%40mail.gmail.com.
