Function signaler

test/bthread_countdown_event_unittest.cpp:31–36

};

void *signaler(void *arg) {
    Arg* a = (Arg*)arg;
    a->num_sig.fetch_sub(1, butil::memory_order_relaxed);
    a->event.signal();
    return NULL;
}

TEST(CountdonwEventTest, sanity) {
    std::vector<bthread_t> tids;