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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/100429] threading support on windows.
 _GLIBCXX_HAS_GTHREADS macro is not 1 but libgcc is correct
Date: Wed, 05 May 2021 12:11:47 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100429

--- 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.
>=20
> SO GOOD, if we fix them, we will have our own threading support for GCC on
> windows.
>=20
>=20
> https://github.com/gcc-mirror/gcc/blob/master/libgcc/config/i386/gthr-win=
32.h
>=20
>=20
> _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:6=
29:
> 27: error: types may not be defined in casts
>   629 |   if (TlsSetValue (__key, CONST_CAST2(void *, const void *, __ptr=
))
> !=3D 0)
>       |                           ^~~~~~~~~~~
>=20
> BTW. there is another bug in libgcc. This does not work.
>=20
> An alternative code should be if (TlsSetValue (__key, void*( __ptr)) !=3D=
 0)

This seems like an entirely separate issue.=