Re: [PATCH] libstdc++/112351 - deal with __gthread_once failure during locale init

[Jonathan Wakely <jwakely@redhat.com>]

On Mon, 6 Nov 2023 at 12:16, Jakub Jelinek <jakub@redhat.com> wrote:
>
> On Mon, Nov 06, 2023 at 11:52:08AM +0000, Richard Biener wrote:
> > The following makes the C++98 locale init path follow the way the
> > C++11 performs initialization.  This way we deal with pthread_once
> > failing, falling back to non-threadsafe initialization which, given we
> > initialize from the library, should be serialized by the dynamic
> > loader already.
> >
> > Bootstrapped and tested on x86_64-unknown-linux-gnu, OK for trunk?
> > And GCC 13 branch?
> >
> > Thanks,
> > Richard.
> >
> >       PR libstdc++/112351
> > libstdc++-v3/
> >       * src/c++98/locale.cc (locale::facet::_S_get_c_locale):
> >       Always perform non-threadsafe init when threadsafe init
> >       failed.
> > ---
> >  libstdc++-v3/src/c++98/locale.cc | 7 ++-----
> >  1 file changed, 2 insertions(+), 5 deletions(-)
> >
> > diff --git a/libstdc++-v3/src/c++98/locale.cc b/libstdc++-v3/src/c++98/locale.cc
> > index d308140bab7..e9bec1db3b6 100644
> > --- a/libstdc++-v3/src/c++98/locale.cc
> > +++ b/libstdc++-v3/src/c++98/locale.cc
> > @@ -216,12 +216,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >  #ifdef __GTHREADS
> >      if (__gthread_active_p())
> >        __gthread_once(&_S_once, _S_initialize_once);
> > -    else
> >  #endif
> > -      {
> > -     if (!_S_c_locale)
> > -       _S_initialize_once();
> > -      }
> > +    if (__builtin_expect (!_S_c_locale, 0))
> > +      _S_initialize_once();
> >      return _S_c_locale;
>
> Wouldn't it be better to just test __gthread_once return value
> #ifdef __THREADS
>   if ((!__gthread_active_p()
>        || __gthread_once(&_S_once, _S_initialize_once)))
> #endif
>     if (!_S_c_locale)
>       _S_initialize_once();
> ?


This still has the problem of calling the function twice, once because
__gthread_once fails and one because it succeeds.