turnstile_trywait
ts = turnstile_trywait(&invl_gen_ts);
ts = turnstile_trywait(&m->lock_object);
ts = turnstile_trywait(&rm->lock_object);
ts = turnstile_trywait(&rw->lock_object);
ts = turnstile_trywait(&rw->lock_object);
ts = turnstile_trywait(&rw->lock_object);
struct turnstile *turnstile_trywait(struct lock_object *);