Add lockfree atomic uint128_type CAS for x86

[Dysrhythmic]

Fixes #

Proposed Changes

• add a lockfree implementation of CAS methods for atomic 128-bit integers for x86
  • add a feature test for if 128 bit atomics are lockfree, and if so define HPX_HAVE_CXX11_STD_ATOMIC_128BIT_LOCKFREE
  • split off the uint128_type struct from tagged_ptr_pair.hpp into its own header file uint128_type.hpp for increased modularity
  • if HPX_HAVE_CXX11_STD_ATOMIC_128BIT_LOCKFREE isn't defined, use specialized methods in lockfree_uint128_type.hpp
• add unit test hpx/libs/core/concurrency/tests/unit/lockfree_128uint.cpp
  • no errors upon running: ctest --output-on-failure -R tests.unit.modules.concurrency.lockfree_128uint
  • output from ./bin/lockfree_128uint_test indicates the implementation is working as expected

Any background context you want to provide?

Next steps will be:

• add implementations for other architectures
• use compiler directives to determine which implementation to use

Checklist

Not all points below apply to all pull requests.

• I have added a new feature and have added tests to go along with it.
• I have fixed a bug and have added a regression test.
• I have added a test using random numbers; I have made sure it uses a seed, and that random numbers generated are valid inputs for the tests.

[jenkins-cscs]

Can one of the admins verify this patch?

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ -0.04%	✅ 88.10%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (f4ff6e8)	232431	198777	85.52%
Head commit (0833ee7)	201540 (-30891)	172287 (-26490)	85.49% (-0.04%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#6521)	42	37	88.10%

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[hkaiser]

Thanks for working on this! There are some compilation and inspect/formatting problems reported by the CIs. Would you be able to address those?

[hkaiser]

The Windows CI's are unhappy for some reason (even the one using the Clang frontend). Could you please have a look?

[Dysrhythmic]

The macOS CI tests seem to be failing after running cmake --build build --target all, with the error pointing to the files:
hpx/libs/core/concurrency/tests/unit/tagged_ptr.cpp
and
hpx/libs/core/testing/include/hpx/modules/testing.hpp
I did not alter either of these files (and it looks like it's been a long time since anyone has), so I am investigating how the changes I made could be affecting them. Neither file uses lockfree_uint128_type.hpp, uint128_type.hpp, or tagged_ptr_pair.hpp, which are the main changes I made.

Error for quick reference:

In file included from /Users/runner/work/hpx/hpx/libs/core/concurrency/tests/unit/tagged_ptr.cpp:9:
/Users/runner/work/hpx/hpx/libs/core/testing/include/hpx/modules/testing.hpp:81:25: error: comparison of integers of different signs: 'const unsigned long' and 'const int' [-Werror,-Wsign-compare]
                if (!(t == u))
                      ~ ^  ~
/Users/runner/work/hpx/hpx/libs/core/concurrency/tests/unit/tagged_ptr.cpp:28:9: note: in instantiation of function template specialization 'hpx::util::detail::fixture::check_equal<unsigned long, int>' requested here
        HPX_TEST_EQ(i.get_tag(), 1);
        ^
/Users/runner/work/hpx/hpx/libs/core/testing/include/hpx/modules/testing.hpp:226:5: note: expanded from macro 'HPX_TEST_EQ'
    HPX_TEST_EQ_(__VA_ARGS__)                                                  \
    ^
/Users/runner/work/hpx/hpx/libs/core/testing/include/hpx/modules/testing.hpp:231:9: note: expanded from macro 'HPX_TEST_EQ_'
        HPX_PP_CAT(HPX_TEST_EQ_, HPX_PP_NARGS(__VA_ARGS__))(__VA_ARGS__))      \
        ^
/Users/runner/work/hpx/hpx/libs/core/preprocessor/include/hpx/preprocessor/cat.hpp:28:26: note: expanded from macro 'HPX_PP_CAT'
#define HPX_PP_CAT(a, b) HPX_PP_CAT_I(a, b)
                         ^
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
<scratch space>:232:1: note: expanded from here
HPX_TEST_EQ_2
^
/Users/runner/work/hpx/hpx/libs/core/testing/include/hpx/modules/testing.hpp:234:5: note: expanded from macro 'HPX_TEST_EQ_2'
    HPX_TEST_EQ_IMPL(::hpx::util::detail::global_fixture(), expr1, expr2)
    ^
/Users/runner/work/hpx/hpx/libs/core/testing/include/hpx/modules/testing.hpp:239:13: note: expanded from macro 'HPX_TEST_EQ_IMPL'
    fixture.check_equal(__FILE__, __LINE__, HPX_ASSERT_CURRENT_FUNCTION,       \
            ^
1 error generated.

I was able to run the same command locally on my Macbook and it completed without error. I currently have it running cmake --build build --target tests to see if that passes locally as well.

[hkaiser]

@Dysrhythmic I think the solution to the compilation problem would be to create a new type while derving from std::atomic:

namespace hpx::lockfree {

    struct uint128_atomic : std::atomic<uint128_type> {

        // implement your overloaded functions here
    };
}

[hkaiser]

@Dysrhythmic I still believe that the new uint128_atomic type -- while it is part of this PR -- is not used anywhere in the change set. Could you verify this, please?