[libcxx-commits] [libcxx] [libc++] atomic_wait refactor experiment (PR #85086)

[Louis Dionne via libcxx-commits]

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@@ -120,40 +122,83 @@ static __libcpp_contention_table_entry* __libcpp_contention_state(void const vol
 /* Given an atomic to track contention and an atomic to actually wait on, which may be
    the same atomic, we try to detect contention to avoid spuriously calling the platform. */
 
-static void __libcpp_contention_notify(__cxx_atomic_contention_t volatile* __contention_state,
+static void __libcpp_contention_notify(__cxx_atomic_contention_t volatile* __waiter_count,
                                        __cxx_atomic_contention_t const volatile* __platform_state,
                                        bool __notify_one) {
-  if (0 != __cxx_atomic_load(__contention_state, memory_order_seq_cst))
+  if (0 != __cxx_atomic_load(__waiter_count, memory_order_seq_cst))
     // We only call 'wake' if we consumed a contention bit here.
     __libcpp_platform_wake_by_address(__platform_state, __notify_one);
 }
-static __cxx_contention_t
-__libcpp_contention_monitor_for_wait(__cxx_atomic_contention_t volatile* /*__contention_state*/,
-                                     __cxx_atomic_contention_t const volatile* __platform_state) {
-  // We will monitor this value.
-  return __cxx_atomic_load(__platform_state, memory_order_acquire);
-}
-static void __libcpp_contention_wait(__cxx_atomic_contention_t volatile* __contention_state,
+static void __libcpp_contention_wait(__cxx_atomic_contention_t volatile* __waiter_count,
                                      __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_seq_cst);
+  __cxx_atomic_fetch_add(__waiter_count, __cxx_contention_t(1), 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);
+  __cxx_atomic_fetch_sub(__waiter_count, __cxx_contention_t(1), memory_order_release);
+}
+
+namespace {
+
+_LIBCPP_EXPORTED_FROM_ABI const auto __get_contention_table_entry = &__libcpp_contention_state;
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ldionne wrote:

`__libcpp_contention_state` can be renamed to whatever you see fit instead! It's just a local helper in the dylib.

https://github.com/llvm/llvm-project/pull/85086