cnd_wait
extern int cnd_wait(cnd_t *, mtx_t *);
VERIFY3S(cnd_wait(&broadcast_cnd, &broadcast_mtx), ==,
VERIFY3S(cnd_wait(&signal_cnd, &signal_mtx), ==,
VERIFY3S(cnd_wait(&ct_cnd, &ct_mtx), ==, thrd_success);
(void) cnd_wait(&co_cnd, &co_mtx);