namespace std { class thread; void swap(thread& x, thread& y) noexcept; namespace this_thread { thread::id get_id() noexcept; void yield() noexcept; template <class Clock, class Duration> void sleep_until(const chrono::time_point<Clock, Duration>& abs_time); template <class Rep, class Period> void sleep_for(const chrono::duration<Rep, Period>& rel_time); } }