mtx_trylock
extern int mtx_trylock(mtx_t *);
VERIFY3S(mtx_trylock(&mtx), ==, thrd_busy);
VERIFY3S(mtx_trylock(mtx), ==, thrd_busy);
VERIFY3S(mtx_trylock(&mtx), ==, thrd_success);
VERIFY3S(mtx_trylock(&mtx), ==, thrd_success);