template< class Lock, class Rep, class Period >
std::cv_status wait_for( Lock& lock,
const std::chrono::duration<Rep, Period>& rel_time); (1) (since C++11) template< class Lock, class Rep, class Period, class Predicate >
bool wait_for( Lock& lock,
const std::chrono::duration<Rep, Period>& rel_time,
Predicate pred); (2) (since C++11)
1) Atomically releases lock, blocks the current execut