[Bug libstdc++/112351] New: libstdc++ locale init doesn't handle __gthread_once failure

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112351

            Bug ID: 112351
           Summary: libstdc++ locale init doesn't handle __gthread_once
                    failure
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

pthread_once called through gthread_once can return "an error number" but the
locale init code isn't prepared for that, instead leaving the object
uninitialized:

src/c++98/locale.cc:

  __c_locale
  locale::facet::_S_get_c_locale()
  {
#ifdef __GTHREADS
    if (__gthread_active_p())
      __gthread_once(&_S_once, _S_initialize_once);
    else
#endif
      {
        if (!_S_c_locale)
          _S_initialize_once();
      }
    return _S_c_locale;
  }

OTOH similar code exists for C++11 locales which doesn't specifically handle
errors but instead executes the non-threaded fallback code in that case:

src/c++11/locale_init.cc:

  void
  locale::_S_initialize()
  {
#ifdef __GTHREADS
    if (!__gnu_cxx::__is_single_threaded())
      __gthread_once(&_S_once, _S_initialize_once);
#endif
    if (__builtin_expect(!_S_classic, 0))
      _S_initialize_once();
  }

Imagine an application overriding pthread_once (and other thread functions)
with an implementation that "fails" before some intitialization is done
(also imagine, just for curiosity, it wouldn't signal failure but success
and do nothing in that case...).

It would be nice to handle the situation consistently and either do the
single-threaded "fallback" or abort on failure.