[libc-commits] [libc] [libc] fix lost signal issue in cnd_test (PR #201721)

[Schrodinger ZHU Yifan via libc-commits]

https://github.com/SchrodingerZhu created https://github.com/llvm/llvm-project/pull/201721

None

>From 1bf56b3223c24c9e882fbc44ea5bde42e27532c4 Mon Sep 17 00:00:00 2001
From: Yifan Zhu <yfzhu at google.com>
Date: Thu, 4 Jun 2026 16:55:57 -0700
Subject: [PATCH] [libc] fix lost signal issue in cnd_test

---
 libc/test/integration/src/threads/cnd_test.cpp | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/libc/test/integration/src/threads/cnd_test.cpp b/libc/test/integration/src/threads/cnd_test.cpp
index 297d95e3149a2..222e2c7c8eeef 100644
--- a/libc/test/integration/src/threads/cnd_test.cpp
+++ b/libc/test/integration/src/threads/cnd_test.cpp
@@ -116,7 +116,8 @@ enum class WaitMode {
   Timed,
 };
 
-int waiter_thread_func([[maybe_unused]] void *unused) {
+int waiter_thread_func(void *arg) {
+  auto *waiter_unblocked = static_cast<LIBC_NAMESPACE::cpp::Atomic<bool> *>(arg);
   LIBC_NAMESPACE::mtx_lock(&waiter_mtx);
 
   LIBC_NAMESPACE::mtx_lock(&main_thread_mtx);
@@ -124,6 +125,7 @@ int waiter_thread_func([[maybe_unused]] void *unused) {
   LIBC_NAMESPACE::mtx_unlock(&main_thread_mtx);
 
   LIBC_NAMESPACE::cnd_wait(&waiter_cnd, &waiter_mtx);
+  waiter_unblocked->store(true);
   LIBC_NAMESPACE::mtx_unlock(&waiter_mtx);
 
   return 0x600D;
@@ -140,7 +142,8 @@ void single_waiter_test(WaitMode wait_mode) {
   ASSERT_EQ(LIBC_NAMESPACE::mtx_lock(&main_thread_mtx), int(thrd_success));
 
   thrd_t waiter_thread;
-  LIBC_NAMESPACE::thrd_create(&waiter_thread, waiter_thread_func, nullptr);
+  LIBC_NAMESPACE::cpp::Atomic<bool> waiter_unblocked(false);
+  LIBC_NAMESPACE::thrd_create(&waiter_thread, waiter_thread_func, &waiter_unblocked);
 
   if (wait_mode == WaitMode::Default) {
     ASSERT_EQ(LIBC_NAMESPACE::cnd_wait(&main_thread_cnd, &main_thread_mtx),
@@ -156,9 +159,11 @@ void single_waiter_test(WaitMode wait_mode) {
   }
   ASSERT_EQ(LIBC_NAMESPACE::mtx_unlock(&main_thread_mtx), int(thrd_success));
 
-  ASSERT_EQ(LIBC_NAMESPACE::mtx_lock(&waiter_mtx), int(thrd_success));
-  ASSERT_EQ(LIBC_NAMESPACE::cnd_signal(&waiter_cnd), int(thrd_success));
-  ASSERT_EQ(LIBC_NAMESPACE::mtx_unlock(&waiter_mtx), int(thrd_success));
+  while (!waiter_unblocked.load()) {
+    ASSERT_EQ(LIBC_NAMESPACE::mtx_lock(&waiter_mtx), int(thrd_success));
+    ASSERT_EQ(LIBC_NAMESPACE::cnd_signal(&waiter_cnd), int(thrd_success));
+    ASSERT_EQ(LIBC_NAMESPACE::mtx_unlock(&waiter_mtx), int(thrd_success));
+  }
 
   int retval;
   LIBC_NAMESPACE::thrd_join(waiter_thread, &retval);