Function get_bthread_singleton

test/bthread_once_unittest.cpp:91–96

};

void get_bthread_singleton() {
    auto instance = bthread::get_leaky_singleton<BthreadSingleton>();
    ASSERT_NE(nullptr, instance);
    // Only one BthreadSingleton instance has been created.
    ASSERT_EQ(1, g_bthread_singleton_count.load(butil::memory_order_relaxed));
}

void* first_get_bthread_singleton(void*) {
    g_bthread_started = true;