[libcxx-commits] [libcxx] [libc++] Allows any types of size 4 and 8 to use native platform ulock_wait (PR #161086)

[Louis Dionne via libcxx-commits]

================
@@ -70,42 +77,97 @@ __libcpp_atomic_monitor(__cxx_atomic_contention_t const volatile*) _NOEXCEPT;
 _LIBCPP_EXPORTED_FROM_ABI void
 __libcpp_atomic_wait(__cxx_atomic_contention_t const volatile*, __cxx_contention_t) _NOEXCEPT;
 
+// new dylib interface
+_LIBCPP_AVAILABILITY_NEW_SYNC _LIBCPP_EXPORTED_FROM_ABI __cxx_contention_t
+__libcpp_atomic_monitor_global(void const volatile* __address) _NOEXCEPT;
+
+_LIBCPP_AVAILABILITY_NEW_SYNC _LIBCPP_EXPORTED_FROM_ABI void
+__libcpp_atomic_wait_global_table(void const volatile* __address, __cxx_contention_t __monitor_value) _NOEXCEPT;
+
+_LIBCPP_AVAILABILITY_NEW_SYNC _LIBCPP_EXPORTED_FROM_ABI void
+__libcpp_atomic_notify_one_global_table(void const volatile*) _NOEXCEPT;
+_LIBCPP_AVAILABILITY_NEW_SYNC _LIBCPP_EXPORTED_FROM_ABI void
+__libcpp_atomic_notify_all_global_table(void const volatile*) _NOEXCEPT;
+
+template <std::size_t _Size>
+_LIBCPP_AVAILABILITY_NEW_SYNC _LIBCPP_EXPORTED_FROM_ABI void
+
+__libcpp_atomic_wait_native(void const volatile* __address, void const* __old_value) _NOEXCEPT;
+template <std::size_t _Size>
+_LIBCPP_AVAILABILITY_NEW_SYNC _LIBCPP_EXPORTED_FROM_ABI void
+__libcpp_atomic_notify_one_native(const volatile void*) _NOEXCEPT;
+
+template <std::size_t _Size>
+_LIBCPP_AVAILABILITY_NEW_SYNC _LIBCPP_EXPORTED_FROM_ABI void
+__libcpp_atomic_notify_all_native(const volatile void*) _NOEXCEPT;
+
+// concepts defines the types are supported natively by the platform's wait
+
+#    if defined(_LIBCPP_ABI_ATOMIC_WAIT_NATIVE_BY_SIZE)
+
+#      ifdef __linux__
+
+#        define _LIBCPP_ATOMIC_WAIT_SIZES_LIST(_APPLY) _APPLY(4)
+
+#      elif defined(__APPLE__)
+
+#        define _LIBCPP_ATOMIC_WAIT_SIZES_LIST(_APPLY)                                                                 \
+          _APPLY(4)                                                                                                    \
+          _APPLY(8)
+
+#      elif defined(__FreeBSD__) && __SIZEOF_LONG__ == 8
+
+#        define _LIBCPP_ATOMIC_WAIT_SIZES_LIST(_APPLY) _APPLY(8)
+
+#      else
+
+#        define _LIBCPP_ATOMIC_WAIT_SIZES_LIST(_APPLY) _APPLY(sizeof(__cxx_contention_t))
+
+#      endif // __linux__
+
+inline constexpr std::size_t __supported_native_wait_sizes[] = {
+#      define _IDENTITY(_SIZE) _SIZE,
+    _LIBCPP_ATOMIC_WAIT_SIZES_LIST(_IDENTITY)
+#      undef _IDENTITY
+};
+
+template <class _Tp>
+concept __atomic_wait_native_type =
+    has_unique_object_representations_v<_Tp> &&
+    std::ranges::find(__supported_native_wait_sizes, sizeof(_Tp)) != ranges::end(__supported_native_wait_sizes);
+
+#    else // _LIBCPP_ABI_ATOMIC_WAIT_NATIVE_BY_SIZE
+
+template <class _Tp>
+concept __atomic_wait_native_type = is_same_v<_Tp, __cxx_contention_t>;
+
+#    endif // _LIBCPP_ABI_ATOMIC_WAIT_NATIVE_BY_SIZE
+
 template <class _AtomicWaitable, class _Poll>
 struct __atomic_wait_backoff_impl {
   const _AtomicWaitable& __a_;
   _Poll __poll_;
   memory_order __order_;
 
   using __waitable_traits _LIBCPP_NODEBUG = __atomic_waitable_traits<__decay_t<_AtomicWaitable> >;
-
-  _LIBCPP_HIDE_FROM_ABI bool
-  __update_monitor_val_and_poll(__cxx_atomic_contention_t const volatile*, __cxx_contention_t& __monitor_val) const {
----------------
ldionne wrote:

We should keep the old code around and only call the new code when `_LIBCPP_AVAILABILITY_NEW_SYNC` is defined. Once we improve the story for back deployment on older platforms, we can go back and remove the old code.

https://github.com/llvm/llvm-project/pull/161086