For example, in _createView, the DB and CollectionLock are acquired for the view's namespace, but Top::LockType::NotLocked is reported. According to the mongodb documentation, even commands should increment the "readLock" and "writeLock" counts. 

It looks like we rely on the Top::LockType to increment "readLock" and "writeLock". 

If today's usage of Top::LockType::NotLocked is correct, we should at least add a comment on when to use which LockType in the enum class declaration.