shared_timed_mutex not available on older versions of MacOS

[jppelteret]

../include/deal.II/base/thread_local_storage.h:253:10: error: 'shared_timed_mutex' is unavailable: introduced in macOS 10.12
    std::shared_timed_mutex insertion_mutex;
         ^
/Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/shared_mutex:202:58: note: 'shared_timed_mutex' has been explicitly marked unavailable here
class _LIBCPP_TYPE_VIS _LIBCPP_AVAILABILITY_SHARED_MUTEX shared_timed_mutex

I just rolled back to version 9.2, which is OK for now. @tamiko I think that you introduced this change a short while ago. Is there an easy(ish) workaround for this? I know that my OS is old (circa Sept 2015), so if the answer is "no" then I recognise that I might just need to upgrade everything. I wonder, though, if there are users that might hit the same issue.

[masterleinad]

What's your compiler and version?

[bangerth]

That's disappointing -- it's clearly marked as C++14: https://en.cppreference.com/w/cpp/thread/shared_timed_mutex

[jppelteret]

What's your compiler and version?

$ clang -v
Apple LLVM version 8.0.0 (clang-800.0.42.1)
Target: x86_64-apple-darwin15.6.0

It looks like this is based off of LLVM 3.9. So it looks like this falls below our minimum supported version of "Clang version 4.0 or later", and from the table I linked to we should blacklist everything below Apple LLVM version 9.0.0 (clang-900.0.37).

[jppelteret]

It looks like there is a boost version of shared_mutex (which I could use as a workaround) but I feel that we should probably respect our minimum compiler requirements.

[tamiko]

It looks like there is a boost version of `shared_mutex` (which I could use as a workaround) but I feel that we should probably respect our minimum compiler requirements.

We can make a simple feature test for std::shared_timed_mutex/shared_mutex and if not available fall back to the boost version. I will make a pull request for this sometime this week. Best, Matthias

[jppelteret]

We can make a simple feature test for
std::shared_timed_mutex/shared_mutex and if not available fall back to
the boost version. I will make a pull request for this sometime this
week.

Thanks a lot for being willing to do that, but if we go with #10532 then I don't think that a workaround is necessary any more. The next version of MacOS (apparently) shipped with a compiler that provided this feature, and if we test the minimum required version of Clang and GCC then we should be able to verify that all's OK there too. Do you agree with this?

[tamiko]

Thanks a lot for being willing to do that, but if we go with #10532 then I don't think that a workaround is necessary any more. The next version of MacOS (apparently) shipped with a compiler that provided this feature, and if we test the minimum required version of Clang and GCC then we should be able to verify that all's OK there too. Do you agree with this?

Your call entirely :-) I am happy with either solution.

[jppelteret]

Let's do it properly then. If we say that we don't support a certain version of the compiler, then there's no point in doing any further work to support it :-D