[PATCH] libstdc++: Only use __gthread_yield if gthreads is available

[Jonathan Wakely]

On Tue, 29 Jun 2021, 22:09 Matheus Castanho via Libstdc++, <
libstdc++@gcc.gnu.org> wrote:

> When building libstdc++ with --disable-threads g++ complains that no
> __gthread_yield declaration is available. The code should check
> _GLIBCXX_HAS_GTHREADS before trying to use it.
>


Yes, thanks for the patch. Do you have write access? If not I'll commit it
tomorrow.



> libstdc++-v3/ChangeLog:
>
>         * include/std/mutex (__lock_impl): Check _GLIBCXX_HAS_GTHREADS
> before
>         using __gthread_yield
> ---
>  libstdc++-v3/include/std/mutex | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/include/std/mutex
> b/libstdc++-v3/include/std/mutex
> index eeb51fdb840..7ab4ee12690 100644
> --- a/libstdc++-v3/include/std/mutex
> +++ b/libstdc++-v3/include/std/mutex
> @@ -618,7 +618,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>                       return;
>                     }
>                 }
> -#ifdef _GLIBCXX_USE_SCHED_YIELD
> +#if defined _GLIBCXX_HAS_GTHREADS && defined _GLIBCXX_USE_SCHED_YIELD
>                 __gthread_yield();
>  #endif
>                 constexpr auto __n = 1 + sizeof...(_L1);
> --
> 2.31.1
>
>