POCO NotificationQueue Sample疑问

为啥打印这一句地方需要加锁互斥？

WorkNotification::Ptr pWorkNf = pNf.cast<WorkNotification>();if (pWorkNf){{FastMutex::ScopedLock lock(_mutex);std::cout << _name << " got work notification " << pWorkNf->data() << std::endl;}Thread::sleep(rnd.next(200));