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Author: huixie90

libcxx/src/atomic.cpp

@@ -152,8 +152,10 @@ static void __libcpp_contention_wait(__cxx_atomic_contention_t volatile* __conte
                                      __cxx_atomic_contention_t const volatile* __platform_state,
                                      __cxx_contention_t __old_value) {
   __cxx_atomic_fetch_add(__contention_state, __cxx_contention_t(1), memory_order_relaxed);
-  // We sleep as long as the monitored value hasn't changed.
+  // https://github.com/llvm/llvm-project/issues/109290
+  // There are no platform guarantees of a memory barrier in the platform wait implementation
   __cxx_atomic_thread_fence(memory_order_seq_cst);
+  // We sleep as long as the monitored value hasn't changed.
   __libcpp_platform_wait_on_address(__platform_state, __old_value);
   __cxx_atomic_fetch_sub(__contention_state, __cxx_contention_t(1), memory_order_release);
 }