[libcxx-commits] [libcxx] [libc++] Add thread safety annotations for std::lock (PR #154078)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 created https://github.com/llvm/llvm-project/pull/154078

Fixes #151733


>From e4f2c244eaf3a1001a2334d6e353d8da7e40ae73 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Mon, 18 Aug 2025 10:46:02 +0200
Subject: [PATCH] [libc++] Add thread safety annotations for std::lock

---
 libcxx/include/mutex                          |  5 ++-
 .../clang/thread/thread.mutex/lock.verify.cpp | 43 +++++++++++++++++++
 2 files changed, 46 insertions(+), 2 deletions(-)
 create mode 100644 libcxx/test/extensions/clang/thread/thread.mutex/lock.verify.cpp

diff --git a/libcxx/include/mutex b/libcxx/include/mutex
index 78d8c8a9bcc6e..3f546f039f4c7 100644
--- a/libcxx/include/mutex
+++ b/libcxx/include/mutex
@@ -351,7 +351,7 @@ _LIBCPP_HIDE_FROM_ABI int try_lock(_L0& __l0, _L1& __l1, _L2& __l2, _L3&... __l3
 #    endif // _LIBCPP_CXX03_LANG
 
 template <class _L0, class _L1>
-_LIBCPP_HIDE_FROM_ABI void lock(_L0& __l0, _L1& __l1) {
+_LIBCPP_HIDE_FROM_ABI void lock(_L0& __l0, _L1& __l1) _LIBCPP_ACQUIRE_CAPABILITY(__l0, __l1) {
   while (true) {
     {
       unique_lock<_L0> __u0(__l0);
@@ -411,7 +411,8 @@ void __lock_first(int __i, _L0& __l0, _L1& __l1, _L2& __l2, _L3&... __l3) {
 }
 
 template <class _L0, class _L1, class _L2, class... _L3>
-inline _LIBCPP_HIDE_FROM_ABI void lock(_L0& __l0, _L1& __l1, _L2& __l2, _L3&... __l3) {
+inline _LIBCPP_HIDE_FROM_ABI void lock(_L0& __l0, _L1& __l1, _L2& __l2, _L3&... __l3)
+    _LIBCPP_ACQUIRE_CAPABILITY(__l0, __l1, __l2, __l3...) {
   std::__lock_first(0, __l0, __l1, __l2, __l3...);
 }
 
diff --git a/libcxx/test/extensions/clang/thread/thread.mutex/lock.verify.cpp b/libcxx/test/extensions/clang/thread/thread.mutex/lock.verify.cpp
new file mode 100644
index 0000000000000..0b3f87068589a
--- /dev/null
+++ b/libcxx/test/extensions/clang/thread/thread.mutex/lock.verify.cpp
@@ -0,0 +1,43 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+// <mutex>
+
+// GCC doesn't have thread safety attributes
+// UNSUPPORTED: gcc
+
+// ADDITIONAL_COMPILE_FLAGS: -Wthread-safety -Wno-comment
+
+// XFAIL: FROZEN-CXX03-HEADERS-FIXME
+
+#include <mutex>
+
+std::mutex m0;
+std::mutex m1;
+std::mutex m2;
+std::mutex m3;
+
+void f1() {
+  std::lock(m0, m1);
+} // expected-warning {{mutex 'm0' is still held at the end of function}} \
+     expected-warning {{mutex 'm1' is still held at the end of function}}
+
+void f2() {
+  std::lock(m0, m1, m2);
+} // expected-warning {{mutex 'm0' is still held at the end of function}} \
+     expected-warning {{mutex 'm1' is still held at the end of function}} \
+     expected-warning {{mutex 'm2' is still held at the end of function}}
+
+void f3() {
+  std::lock(m0, m1, m2, m3);
+} // expected-warning {{mutex 'm0' is still held at the end of function}} \
+     expected-warning {{mutex 'm1' is still held at the end of function}} \
+     expected-warning {{mutex 'm2' is still held at the end of function}} \
+     expected-warning {{mutex 'm3' is still held at the end of function}}