LWG 4172 was approved in Hagenberg, February 2025, fixing
std::unique_lock and std::shared_lock to work correctly for
self-move-assignment.
Our std::shared_lock was already doing the right thing (contradicting
the standard) so just add a comment there. Our std::unique_lock needs to
be fixed to do the right thing.
libstdc++-v3/ChangeLog:
* include/bits/unique_lock.h (unique_lock::operator=): Fix for
self-move-assignment.
* include/std/shared_mutex (shared_lock::operator=): Add
comment.
* testsuite/30_threads/shared_lock/cons/lwg4172.cc: New test.
* testsuite/30_threads/unique_lock/cons/lwg4172.cc: New test.
---
Tested x86_64-linux.
libstdc++-v3/include/bits/unique_lock.h | 9 ++----
libstdc++-v3/include/std/shared_mutex | 2 ++
.../30_threads/shared_lock/cons/lwg4172.cc | 28 +++++++++++++++++++
.../30_threads/unique_lock/cons/lwg4172.cc | 27 ++++++++++++++++++
4 files changed, 59 insertions(+), 7 deletions(-)
create mode 100644
libstdc++-v3/testsuite/30_threads/shared_lock/cons/lwg4172.cc
create mode 100644
libstdc++-v3/testsuite/30_threads/unique_lock/cons/lwg4172.cc
diff --git a/libstdc++-v3/include/bits/unique_lock.h
b/libstdc++-v3/include/bits/unique_lock.h
index 22ea7e9d772..5b1518745ca 100644
--- a/libstdc++-v3/include/bits/unique_lock.h
+++ b/libstdc++-v3/include/bits/unique_lock.h
@@ -126,14 +126,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
unique_lock& operator=(unique_lock&& __u) noexcept
{
- if(_M_owns)
- unlock();
-
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 4172. unique_lock self-move-assignment is broken
unique_lock(std::move(__u)).swap(*this);
-
- __u._M_device = 0;
- __u._M_owns = false;
-
return *this;
}
diff --git a/libstdc++-v3/include/std/shared_mutex
b/libstdc++-v3/include/std/shared_mutex
index cbdf58f403b..94c8532399d 100644
--- a/libstdc++-v3/include/std/shared_mutex
+++ b/libstdc++-v3/include/std/shared_mutex
@@ -780,6 +780,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
shared_lock&
operator=(shared_lock&& __sl) noexcept
{
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 4172. unique_lock self-move-assignment is broken
shared_lock(std::move(__sl)).swap(*this);
return *this;
}
diff --git a/libstdc++-v3/testsuite/30_threads/shared_lock/cons/lwg4172.cc
b/libstdc++-v3/testsuite/30_threads/shared_lock/cons/lwg4172.cc
new file mode 100644
index 00000000000..0a3bf10b8bb
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/shared_lock/cons/lwg4172.cc
@@ -0,0 +1,28 @@
+// { dg-do run { target c++14 } }
+
+// LWG 4172. unique_lock self-move-assignment is broken
+
+#include <shared_mutex>
+#include <testsuite_hooks.h>
+
+void
+test_self_move()
+{
+ struct Lockable
+ {
+ bool locked = false;
+ void lock_shared() { locked = true; }
+ void unlock_shared() { locked = false; }
+ bool try_lock_shared() { if (locked) return false; return locked = true; }
+ };
+
+ Lockable x;
+ std::shared_lock<Lockable> l(x);
+ l = std::move(l);
+ VERIFY(x.locked);
+}
+
+int main()
+{
+ test_self_move();
+}
diff --git a/libstdc++-v3/testsuite/30_threads/unique_lock/cons/lwg4172.cc
b/libstdc++-v3/testsuite/30_threads/unique_lock/cons/lwg4172.cc
new file mode 100644
index 00000000000..37542b586a9
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/unique_lock/cons/lwg4172.cc
@@ -0,0 +1,27 @@
+// { dg-do run { target c++11 } }
+
+// LWG 4172. unique_lock self-move-assignment is broken
+
+#include <mutex>
+#include <testsuite_hooks.h>
+
+void
+test_self_move()
+{
+ struct Lockable
+ {
+ bool locked = false;
+ void lock() { locked = true; }
+ void unlock() { locked = false; }
+ };
+
+ Lockable x;
+ std::unique_lock<Lockable> l(x);
+ l = std::move(l);
+ VERIFY(x.locked);
+}
+
+int main()
+{
+ test_self_move();
+}
--
2.48.1
