[libcxx-commits] [libcxx] [libc++] Fix flakiness in `atomic_notify_all.pass.cpp` (PR #70436)

[Konstantin Varlamov via libcxx-commits]

https://github.com/var-const updated https://github.com/llvm/llvm-project/pull/70436

>From 99ed4f7b920ef1d80969b4a5fdd1cc989cf84bde Mon Sep 17 00:00:00 2001
From: Konstantin Varlamov <varconsteq at gmail.com>
Date: Fri, 27 Oct 2023 02:22:17 -0700
Subject: [PATCH 1/2] [libc++] Fix flakiness in `atomic_notify_all.pass.cpp`

Avoid relying on sleep for synchronization.
---
 .../atomic_notify_all.pass.cpp                     | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_notify_all.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_notify_all.pass.cpp
index d22ea426057113b..b96691735a4ccbd 100644
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_notify_all.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_notify_all.pass.cpp
@@ -56,15 +56,21 @@ struct TestFn {
     {
       volatile A a(T(2));
       static_assert(noexcept(std::atomic_notify_all(&a)), "");
-      auto f = [&]() {
+
+      std::atomic<bool> is_ready[2] = {false, false};
+      auto f = [&](int index) {
         assert(std::atomic_load(&a) == T(2));
+        is_ready[index].store(true);
+
         std::atomic_wait(&a, T(2));
         assert(std::atomic_load(&a) == T(4));
       };
-      std::thread t1 = support::make_test_thread(f);
-      std::thread t2 = support::make_test_thread(f);
-      std::this_thread::sleep_for(std::chrono::milliseconds(100));
+      std::thread t1 = support::make_test_thread(f, /*index=*/0);
+      std::thread t2 = support::make_test_thread(f, /*index=*/1);
 
+      while (!is_ready[0] || !is_ready[1]) {
+        // Spin
+      }
       std::atomic_store(&a, T(4));
       std::atomic_notify_all(&a);
       t1.join();

>From b2e1717545ab691c5fe1abbdb6ba619c82ed916c Mon Sep 17 00:00:00 2001
From: Konstantin Varlamov <varconsteq at gmail.com>
Date: Fri, 27 Oct 2023 02:23:59 -0700
Subject: [PATCH 2/2] clang-format

---
 .../atomics.types.operations.wait/atomic_notify_all.pass.cpp    | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_notify_all.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_notify_all.pass.cpp
index b96691735a4ccbd..2c8161eedbc4dec 100644
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_notify_all.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/atomic_notify_all.pass.cpp
@@ -58,7 +58,7 @@ struct TestFn {
       static_assert(noexcept(std::atomic_notify_all(&a)), "");
 
       std::atomic<bool> is_ready[2] = {false, false};
-      auto f = [&](int index) {
+      auto f                        = [&](int index) {
         assert(std::atomic_load(&a) == T(2));
         is_ready[index].store(true);