[libc++] Consolidated logic into helper function

Author: Roger Sanders

libcxx/src/atomic.cpp

@@ -108,24 +108,29 @@ static void __libcpp_platform_wake_by_address(__cxx_atomic_contention_t const vo
 
 #elif defined(_WIN32)
 
-static HMODULE win32_get_win_core_synch_api_module() {
-  // HMODULE is documented as being a pointer type to the base address of the module in memory, which means we can
-  // safely use std::unique_ptr here as a wrapper for the handle, with a destructor freeing the handle when this module
-  // is unloaded.
+static void* win32_get_synch_api_function(const char* function_name) {
+  // Attempt to load the API set. Note that HMODULE is documented as being a pointer type, which means we can safely use
+  // std::unique_ptr here as a wrapper for the handle, with a destructor freeing the handle when this module is
+  // unloaded.
   // https://learn.microsoft.com/en-us/windows/win32/winprog/windows-data-types
   // https://devblogs.microsoft.com/oldnewthing/20180307-00/?p=98175
   static auto module_handle = std::unique_ptr<std::remove_pointer<HMODULE>::type, decltype(&FreeLibrary)>(
       LoadLibraryW(L"api-ms-win-core-synch-l1-2-0.dll"), &FreeLibrary);
-  return module_handle.get();
+  if (!module_handle) {
+    return nullptr;
+  }
+
+  // Attempt to locate the function in the API and return the result to the caller. Note that the NULL return from this
+  // method is documented as being interchangeable with nullptr.
+  // https://devblogs.microsoft.com/oldnewthing/20180307-00/?p=98175
+  return GetProcAddress(module_handle.get(), function_name);
 }
 
 static void
 __libcpp_platform_wait_on_address(__cxx_atomic_contention_t const volatile* __ptr, __cxx_contention_t __val) {
   // WaitOnAddress was added in Windows 8 (build 9200)
   static auto wait_on_address = reinterpret_cast<BOOL(WINAPI*)(volatile void*, PVOID, SIZE_T, DWORD)>(
-      (win32_get_win_core_synch_api_module() != NULL
-           ? GetProcAddress(win32_get_win_core_synch_api_module(), "WaitOnAddress")
-           : nullptr));
+      win32_get_synch_api_function("WaitOnAddress"));
   if (wait_on_address != nullptr) {
     wait_on_address(const_cast<__cxx_atomic_contention_t*>(__ptr), &__val, sizeof(__val), INFINITE);
   } else {
@@ -138,10 +143,8 @@ __libcpp_platform_wait_on_address(__cxx_atomic_contention_t const volatile* __pt
 static void __libcpp_platform_wake_by_address(__cxx_atomic_contention_t const volatile* __ptr, bool __notify_one) {
   if (__notify_one) {
     // WakeByAddressSingle was added in Windows 8 (build 9200)
-    static auto wake_by_address_single = reinterpret_cast<void(WINAPI*)(PVOID)>(
-        (win32_get_win_core_synch_api_module() != NULL
-             ? GetProcAddress(win32_get_win_core_synch_api_module(), "WakeByAddressSingle")
-             : nullptr));
+    static auto wake_by_address_single =
+        reinterpret_cast<void(WINAPI*)(PVOID)>(win32_get_synch_api_function("WakeByAddressSingle"));
     if (wake_by_address_single != nullptr) {
       wake_by_address_single(const_cast<__cxx_atomic_contention_t*>(__ptr));
     } else {
@@ -150,10 +153,8 @@ static void __libcpp_platform_wake_by_address(__cxx_atomic_contention_t const vo
     }
   } else {
     // WakeByAddressAll was added in Windows 8 (build 9200)
-    static auto wake_by_address_all = reinterpret_cast<void(WINAPI*)(PVOID)>(
-        (win32_get_win_core_synch_api_module() != NULL
-             ? GetProcAddress(win32_get_win_core_synch_api_module(), "WakeByAddressAll")
-             : nullptr));
+    static auto wake_by_address_all =
+        reinterpret_cast<void(WINAPI*)(PVOID)>(win32_get_synch_api_function("WakeByAddressAll"));
     if (wake_by_address_all != nullptr) {
       wake_by_address_all(const_cast<__cxx_atomic_contention_t*>(__ptr));
     } else {