_twait
error = _twait(&cond->seq, seq, clock, abs);
while (_twait(&mutex->type, type, CLOCK_REALTIME,
error = _twait(&mutex->lock, CONTENDED, CLOCK_REALTIME, abs);
error = _twait(&rwlock->value, new, CLOCK_REALTIME,
error = _twait(&rwlock->value, new, CLOCK_REALTIME,
error = _twait(&sem->value, 0, CLOCK_REALTIME, abstime);