[libcxx-commits] [libcxx] [libc++] Make sure the test for compare-and-wait bug doesn't hang forever (PR #97907)
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Sat Jul 6 11:30:43 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxx
Author: Louis Dionne (ldionne)
<details>
<summary>Changes</summary>
This patch adds an explicit timeout mechanism in the compare-and-wait test for std::atomic, ensuring that it doesn't run forever when the bug is present. This is not an issue when we run inside the CI because we specify a timeout manually, but it can be a problem when running locally, for example.
---
Full diff: https://github.com/llvm/llvm-project/pull/97907.diff
1 Files Affected:
- (renamed) libcxx/test/libcxx/atomics/atomics.syn/wait.issue_85107.pass.cpp (+24-6)
``````````diff
diff --git a/libcxx/test/libcxx/atomics/atomics.syn/wait.pass.cpp b/libcxx/test/libcxx/atomics/atomics.syn/wait.issue_85107.pass.cpp
similarity index 57%
rename from libcxx/test/libcxx/atomics/atomics.syn/wait.pass.cpp
rename to libcxx/test/libcxx/atomics/atomics.syn/wait.issue_85107.pass.cpp
index 6ae1c0997aad72..03eaa0e55ac6a8 100644
--- a/libcxx/test/libcxx/atomics/atomics.syn/wait.pass.cpp
+++ b/libcxx/test/libcxx/atomics/atomics.syn/wait.issue_85107.pass.cpp
@@ -15,22 +15,40 @@
// XFAIL: availability-synchronization_library-missing
+// This is a regression test for https://github.com/llvm/llvm-project/issues/85107, which describes
+// how we were using UL_COMPARE_AND_WAIT instead of UL_COMPARE_AND_WAIT64 in the implementation of
+// atomic::wait, leading to potential infinite hangs.
+
#include <atomic>
#include <cassert>
+#include <chrono>
+
+#include "make_test_thread.h"
-void test_85107() {
+int main(int, char**) {
if constexpr (sizeof(std::__cxx_contention_t) == 8 && sizeof(long) > 4) {
+ std::atomic<bool> done = false;
+ auto const timeout = std::chrono::system_clock::now() + std::chrono::seconds(600); // fail after 10 minutes
+
+ auto timeout_thread = support::make_test_thread([&] {
+ while (!done) {
+ assert(std::chrono::system_clock::now() < timeout); // make sure we don't hang forever
+ }
+ });
+
// https://github.com/llvm/llvm-project/issues/85107
// [libc++] atomic_wait uses UL_COMPARE_AND_WAIT when it should use UL_COMPARE_AND_WAIT64 on Darwin
constexpr std::__cxx_contention_t old_val = 0;
constexpr std::__cxx_contention_t new_val = old_val + (1ll << 32);
std::__cxx_atomic_contention_t ct(new_val);
- std::__libcpp_atomic_wait(&ct, old_val); // this will hang forever if the bug is present
- }
-}
-int main(int, char**) {
- test_85107();
+ // This would hang forever if the bug is present, but the test will fail in a bounded amount of
+ // time due to the timeout above.
+ std::__libcpp_atomic_wait(&ct, old_val);
+
+ done = true;
+ timeout_thread.join();
+ }
return 0;
}
``````````
</details>
https://github.com/llvm/llvm-project/pull/97907
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