[Bug c++/63287] New: __STDCPP_THREADS__ is not defined

[Bug c++/63287] New: __STDCPP_THREADS__ is not defined

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63287

            Bug ID: 63287
           Summary: __STDCPP_THREADS__ is not defined
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org

16.8 [cpp.predefined] in C++11 says:

  __STDCPP_THREADS__
  Defined, and has the value integer constant 1, if and only if a program can
  have more than one thread of execution (1.10).

I'm not sure what the best way to meet that requirement is, given that . For
some platforms we could make -pthread imply -D__STDCPP_THREADS__, or maybe we
just want to define it unconditionally in every gthr-xxx.h header except
gthr-single.h

[Bug c++/63287] __STDCPP_THREADS__ is not defined

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63287

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #0)
> I'm not sure what the best way to meet that requirement is, given that .

Oops, I was going to say "... given that the availability of threads may not be
known until link-time, depending whether libpthread is used.

[Bug c++/63287] __STDCPP_THREADS__ is not defined

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63287

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-01-17
     Ever confirmed|0                           |1

[Bug c++/63287] __STDCPP_THREADS__ is not defined

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63287

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I tried to implement this by adding a macro definition to c_cpp_builtins in
gcc/c-family/c-cppbuiltin.c but failed. I think we want to inspect the
'thread_model' global variable and see if it is "single", but that might only
be available to the driver, not cc1plus.

Maybe the driver needs to check THREAD_MODEL_SPEC and thread_model and then
pass -D__STDCPP_THREADS__=1 to cc1plus when strcmp(thread_model, "single").

For now, I think we can define it in libstdc++'s <bits/c++config.h> based on
the value of the _GLIBCXX_HAS_GTHREADS macro.

[Bug c++/63287] __STDCPP_THREADS__ is not defined

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63287

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Library patch:

diff --git a/libgcc/gthr.h b/libgcc/gthr.h
index f31cf083cbe5..e6462679b362 100644
--- a/libgcc/gthr.h
+++ b/libgcc/gthr.h
@@ -147,6 +147,13 @@ see the files COPYING3 and COPYING.RUNTIME respectively. 
If not, see
 #endif
 #include "gthr-default.h"

+#if defined __GTHREADS_CXX0X && ! defined __STDCPP_THREADS__
+// The C++ standard says that __STDCPP_THREADS__ should be defined to 1,
+// but G++ does not currently do that (PR c++/63287).
+// Define it here if gthr-default.h defined __GTHREADS_CXX0X.
+# define __STDCPP_THREADS__ 1
+#endif
+
 #ifndef HIDE_EXPORTS
 #pragma GCC visibility pop
 #endif
diff --git a/libstdc++-v3/include/Makefile.am
b/libstdc++-v3/include/Makefile.am
index 292d89da8ba7..74e3e4932579 100644
--- a/libstdc++-v3/include/Makefile.am
+++ b/libstdc++-v3/include/Makefile.am
@@ -1316,6 +1316,7 @@ uppercase = [ABCDEFGHIJKLMNOPQRSTUVWXYZ_]

 ${host_builddir}/gthr.h: ${toplevel_srcdir}/libgcc/gthr.h stamp-${host_alias}
        sed -e '/^#pragma/b' \
+           -e '/__STDCPP_THREADS__/b' \
            -e '/^#/s/\(${uppercase}${uppercase}*\)/_GLIBCXX_\1/g' \
            -e 's/_GLIBCXX_SUPPORTS_WEAK/__GXX_WEAK__/g' \
            -e 's/_GLIBCXX___MINGW32_GLIBCXX___/__MINGW32__/g' \

[Bug c++/63287] __STDCPP_THREADS__ is not defined

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63287

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://bugs.llvm.org/show_
                   |                            |bug.cgi?id=33230

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
FWIW libc++ does it in the library:

#if !defined(_LIBCPP_HAS_NO_THREADS) && !defined(__STDCPP_THREADS__)
#define __STDCPP_THREADS__ 1
#endif

[Bug c++/63287] __STDCPP_THREADS__ is not defined

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63287

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:1d9a8675d379f02f5e39639f469ae8dfcf33fea9

commit r11-5017-g1d9a8675d379f02f5e39639f469ae8dfcf33fea9
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Nov 13 23:23:33 2020 +0100

    c++: Predefine __STDCPP_THREADS__ in the compiler if thread model is not
single [PR63287]

    The following patch predefines __STDCPP_THREADS__ macro to 1 if c++11 or
    later and thread model (e.g. printed by gcc -v) is not single.
    There are two targets not handled by this patch, those that define
    THREAD_MODEL_SPEC.  In one case - QNX - it looks just like a mistake
    to me, instead of setting thread_model=posix in config.gcc it uses
    THREAD_MODEL_SPEC macro to set it unconditionally to posix.
    The other is hpux10, which uses -threads option to decide if threads
    are enabled or not, but that option isn't really passed to the compiler.
    I think that is something that really should be solved in config/pa/
    instead, e.g. in the config/xxx/xxx-c.c targets usually set their own
    predefined macros and it could handle this, and either pass the option
    also to the compiler, or say predefine __STDCPP_THREADS__ if _DCE_THREADS
    macro is defined already (or -D_DCE_THREADS found on the command line),
    or whatever else.

    2020-11-13  Jakub Jelinek  <jakub@redhat.com>

            PR c++/63287
            * c-cppbuiltin.c: Include configargs.h.
            (c_cpp_builtins): For C++11 and later if THREAD_MODEL_SPEC is not
            defined, predefine __STDCPP_THREADS__ to 1 unless thread_model is
            "single".