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

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libc

Author: Schrodinger ZHU Yifan (SchrodingerZhu)

<details>
<summary>Changes</summary>

Fix another spot of potential hanging test.

The timeout time is too short in cnd_test which results in missed signals. This patch adds an atomic flag and make the main thread looping on it to ensure the last signal to unblock waiter is delivered.

---
Full diff: https://github.com/llvm/llvm-project/pull/201721.diff


1 Files Affected:

- (modified) libc/test/integration/src/threads/cnd_test.cpp (+12-5) 


``````````diff
diff --git a/libc/test/integration/src/threads/cnd_test.cpp b/libc/test/integration/src/threads/cnd_test.cpp
index 297d95e3149a2..03c9ff3b45dd2 100644
--- a/libc/test/integration/src/threads/cnd_test.cpp
+++ b/libc/test/integration/src/threads/cnd_test.cpp
@@ -116,7 +116,9 @@ 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 +126,7 @@ 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 +143,9 @@ 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 +161,11 @@ 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);

``````````

</details>


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