void swap(unique_lock& u) noexcept;
Effects: Swaps the data members of *this and u.
mutex_type* release() noexcept;
Returns: The previous value of pm.
Postconditions: pm == 0 and owns == false.
template <class Mutex>
void swap(unique_lock<Mutex>& x, unique_lock<Mutex>& y) noexcept;
Effects: x.swap(y)