Re: [PATCH v8 1/8] nptl: Add C11 threads thrd_* functions

[Florian Weimer <fweimer at redhat dot com>]

On 07/12/2018 09:19 PM, Adhemerval Zanella wrote:
> Also on GCC BZ#53769 [1] Joseph wrote that check for __STDC_VERSION__
> and/or __STDC_NO_THREADS__ is not meaningful to documented incomplete
> compiler support for language standard.  This is at least for GCC
> standpoint, not sure about other compilers.
>
> We could add a check like:
>
> #if (defined (__GNUC__) && !__GNUC_PREREQ (4.9))
>      || (!defined (__cpluscplus) &&  __cplusplus < 201103L)
> #  define __STDC_NO_THREADS__   1
> #endif
>
> [1]https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53769

I think your first patch was fine.  The <threads.h> header exists after 
your change.

We could polish the definition of thread_local in the header file with 
some conditionals, though, so that we fall back to __thread for GCC 
prior to 4.9.  The definition of the thread_local macro will be 
non-confirming, but that's what you get for using a non-conforming 
implementation.

(If the C compiler is not known to be C, we need to use _Thread_local, 
even though __thread probably covers more old implementations out there.)

Thanks,
Florian