[Bug libstdc++/100429] threading support on windows. _GLIBCXX_HAS_GTHREADS macro is not 1 but libgcc is correct

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100429

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to cqwrteur from comment #0)
> It looks like libgcc DOES provide threading support for windows. However,
> _GLIBCXX_HAS_GTHREADS does not get defined for libstdc++, I guess it is
> another libtool issue.
> 
> SO GOOD, if we fix them, we will have our own threading support for GCC on
> windows.
> 
> 
> https://github.com/gcc-mirror/gcc/blob/master/libgcc/config/i386/gthr-win32.h
> 
> 
> _GLIBCXX_HAS_GTHREADS

Just read the comments in libgcc/gthr.h

   If the following are also defined, you should
     #define __GTHREADS_CXX0X 1
   to enable the c++0x thread library.

None of the required functions are defined by gthr-win32.h so it (correctly)
doesn't define __GTHREADS_CXX0X and so libstdc++ doesn't use it.



> In file included from
> d:\toolchains\include\c++\12.0.0\x86_64-w64-mingw32\bits\gthr.h:148,
>                  from b.cc:4:
> d:\toolchains\include\c++\12.0.0\x86_64-w64-mingw32\bits\gthr-default.h: In
> function 'int __gthread_setspecific(__gthread_key_t, const void*)':
> d:\toolchains\include\c++\12.0.0\x86_64-w64-mingw32\bits\gthr-default.h:629:
> 27: error: types may not be defined in casts
>   629 |   if (TlsSetValue (__key, CONST_CAST2(void *, const void *, __ptr))
> != 0)
>       |                           ^~~~~~~~~~~
> 
> BTW. there is another bug in libgcc. This does not work.
> 
> An alternative code should be if (TlsSetValue (__key, void*( __ptr)) != 0)

This seems like an entirely separate issue.