fix unique_lock<DistributedMutex>::operator=

Summary: It is required to unlock a held lock, if it owns one.

Reviewed By: aary

Differential Revision: D28704148

fbshipit-source-id: c329a3045fa27985fdec4142f00fe11c95394779

folly/synchronization/detail/ProxyLockable-inl.h

@@ -76,6 +76,9 @@ ProxyLockableUniqueLock<Mutex>::ProxyLockableUniqueLock(
 template <typename Mutex>
 ProxyLockableUniqueLock<Mutex>& ProxyLockableUniqueLock<Mutex>::operator=(
     ProxyLockableUniqueLock&& other) noexcept {
+  if (owns_lock()) {
+    unlock();
+  }
   proxy_ = std::move(other.proxy_);
   mutex_ = std::exchange(other.mutex_, nullptr);
   return *this;

folly/synchronization/detail/test/ProxyLockableTest.cpp

@@ -125,6 +125,16 @@ TEST_F(ProxyLockableTest, UniqueLockConstructMoveConstructAssign) {
   EXPECT_FALSE(one.proxy());
 
   EXPECT_EQ(mutex.locked_, 1);
+
+  four = std::move(three);
+  EXPECT_EQ(mutex.locked_, 0);
+  EXPECT_FALSE(four.mutex());
+  EXPECT_FALSE(four.proxy());
+
+  four = ProxyLockableUniqueLock<MockMutex>{mutex};
+  EXPECT_EQ(mutex.locked_, 1);
+  EXPECT_TRUE(four.mutex());
+  EXPECT_TRUE(four.proxy());
 }
 
 TEST_F(ProxyLockableTest, UniqueLockDeferLock) {