[libcxx-commits] [libcxx] [libc++] Improve performance of std::atomic_flag on Windows (PR #163524)

[David Spickett via libcxx-commits]

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@@ -101,6 +105,37 @@ static void __libcpp_platform_wake_by_address(__cxx_atomic_contention_t const vo
   _umtx_op(const_cast<__cxx_atomic_contention_t*>(__ptr), UMTX_OP_WAKE, __notify_one ? 1 : INT_MAX, nullptr, nullptr);
 }
 
+#elif defined(_WIN32)
+
+static void
+__libcpp_platform_wait_on_address(__cxx_atomic_contention_t const volatile* __ptr, __cxx_contention_t __val) {
+  static auto pWaitOnAddress = reinterpret_cast<BOOL(WINAPI*)(volatile void*, PVOID, SIZE_T, DWORD)>(
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DavidSpickett wrote:

Maybe it's ok for this to not be `__pWaitOnAddress` (see https://libcxx.llvm.org/CodingGuidelines.html#use-ugly-names-for-implementation-details), but reviewers might want `__` added just to be consistent.

https://github.com/llvm/llvm-project/pull/163524