<condition_variable>: condition_variable_any::wait_until may cause infinite wait

[achabense]

The following code will cause infinite wait (unexpectedly).

#include<thread>
#include<condition_variable>
#include<mutex>

int main() {
	using namespace std;
	using ull_sec = std::chrono::duration<unsigned long long>;
	auto ull_point_sec = chrono::time_point_cast<ull_sec>(chrono::system_clock::now());
	std::this_thread::sleep_for(2s);

	std::mutex m;
	std::unique_lock lock{m};
	std::condition_variable_any cond;
	cond.wait_until(lock, ull_point_sec);//infinite wait.
}

In this case, in wait_until, _Abs_time - _Clock::now() will result in a large unsigned value. A quick fix would be adding a comparison before calling wait_for (return at once if _Abs_time <= now).

In the current implementation, there are both wait_until calling wait_for(see below) and wait_for calling wait_until(example). For better consistency and conformance to the standard(ref), a thorough fix would be ensuring that every wait_for will call a matching wait_until.

STL/stl/inc/condition_variable

Lines 92 to 99 in c8d1efb

	template <class _Lock, class _Clock, class _Duration>
	cv_status wait_until(_Lock& _Lck, const chrono::time_point<_Clock, _Duration>& _Abs_time) {
	// wait until time point
	#if _HAS_CXX20
	static_assert(chrono::is_clock_v<_Clock>, "Clock type required");
	#endif // _HAS_CXX20
	return wait_for(_Lck, _Abs_time - _Clock::now());
	}