[libcxx] LWG4172 fix self-move-assignment in {unique|shared}_lock

Author: elhewaty

libcxx/include/__mutex/unique_lock.h

@@ -74,13 +74,7 @@ class unique_lock {
   }
 
   _LIBCPP_HIDE_FROM_ABI unique_lock& operator=(unique_lock&& __u) _NOEXCEPT {
-    if (__owns_)
-      __m_->unlock();
-
-    __m_        = __u.__m_;
-    __owns_     = __u.__owns_;
-    __u.__m_    = nullptr;
-    __u.__owns_ = false;
+    unique_lock{std::move(__u)}.swap(*this);
     return *this;
   }
 

libcxx/include/shared_mutex

@@ -340,14 +340,7 @@ public:
   }
 
   _LIBCPP_HIDE_FROM_ABI shared_lock& operator=(shared_lock&& __u) _NOEXCEPT {
-    if (__owns_)
-      __m_->unlock_shared();
-    __m_        = nullptr;
-    __owns_     = false;
-    __m_        = __u.__m_;
-    __owns_     = __u.__owns_;
-    __u.__m_    = nullptr;
-    __u.__owns_ = false;
+    shared_lock{std::move(__u)}.swap(*this);
     return *this;
   }
 

libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.shared/thread.lock.shared.cons/move_assign.pass.cpp

@@ -21,22 +21,32 @@
 
 #include "test_macros.h"
 
-
-int main(int, char**)
-{
-    {
+int main(int, char**) {
+  {
     typedef std::shared_timed_mutex M;
     M m0;
     M m1;
     std::shared_lock<M> lk0(m0);
     std::shared_lock<M> lk1(m1);
+
+    // Test self move assignment for lk0.
+    lk0 = std::move(lk0);
+    assert(lk0.mutex() == std::addressof(m0));
+    assert(lk0.owns_lock() == true);
+
     lk1 = std::move(lk0);
     assert(lk1.mutex() == std::addressof(m0));
     assert(lk1.owns_lock() == true);
     assert(lk0.mutex() == nullptr);
     assert(lk0.owns_lock() == false);
-    }
-    {
+
+    // Test self move assignment for lk1.
+    lk1 = std::move(lk1);
+    assert(lk1.mutex() == std::addressof(m0));
+    assert(lk1.owns_lock() == true);
+
+  }
+  {
     typedef nasty_mutex M;
     M m0;
     M m1;
@@ -47,7 +57,7 @@ int main(int, char**)
     assert(lk1.owns_lock() == true);
     assert(lk0.mutex() == nullptr);
     assert(lk0.owns_lock() == false);
-    }
+  }
 
   return 0;
 }

libcxx/test/std/thread/thread.mutex/thread.lock/thread.lock.unique/thread.lock.unique.cons/move_assign.pass.cpp

@@ -24,13 +24,22 @@ int main(int, char**) {
   std::unique_lock<checking_mutex> lk0(m0);
   std::unique_lock<checking_mutex> lk1(m1);
 
+  // Test self move assignment for lk0.
+  lk0 = std::move(lk0);
+  assert(lk0.mutex() == std::addressof(m0));
+  assert(lk0.owns_lock() == true);
+
   auto& result = (lk1 = std::move(lk0));
 
   assert(&result == &lk1);
   assert(lk1.mutex() == std::addressof(m0));
   assert(lk1.owns_lock());
   assert(lk0.mutex() == nullptr);
-  assert(!lk0.owns_lock());
+  assert(lk0.owns_lock() == false);
 
+  // Test self move assignment for lk1
+  lk1 = std::move(lk1);
+  assert(lk1.mutex() == std::addressof(m0));
+  assert(lk1.owns_lock() == true);
   return 0;
 }