[libc++][test] atomit wait test take 2

libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp

@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: no-threads
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// This is a stress test for std::atomic::wait for lost wake ups.
+
+// <atomic>
+
+#include <atomic>
+#include <functional>
+#include <thread>
+#include <vector>
+
+#include "make_test_thread.h"
+
+constexpr int num_waiters    = 8;
+constexpr int num_iterations = 10'000;
+
+int main(int, char**) {
+  for (int run = 0; run < 20; ++run) {
+    std::atomic<int> waiter_ready(0);
+    std::atomic<int> state(0);
+
+    auto wait = [&]() {
+      for (int i = 0; i < num_iterations; ++i) {
+        auto old_state = state.load();
+        waiter_ready.fetch_add(1);
+        state.wait(old_state);
+      }
+    };
+
+    auto notify = [&] {
+      for (int i = 0; i < num_iterations; ++i) {
+        while (waiter_ready.load() < num_waiters) {
+          std::this_thread::yield();
+        }
+        waiter_ready.store(0);
+        state.fetch_add(1);
+        state.notify_all();
+      }
+    };
+
+    std::vector<std::jthread> threads;
+    for (int i = 0; i < num_waiters; ++i)
+      threads.push_back(support::make_test_jthread(wait));
+
+    threads.push_back(support::make_test_jthread(notify));
+  }
+
+  return 0;
+}