_thr_ucond_wait
_thr_ucond_wait(&bar->b_cv, &bar->b_lock, NULL, 0);
_thr_ucond_wait(&bar->b_cv, &bar->b_lock, NULL, 0);
error = _thr_ucond_wait(&cvp->kcond, &mp->m_lock, abstime,
int _thr_ucond_wait(struct ucond *cv, struct umutex *m,