struct WorkingQueue{
    WorkingQueue()=default;

    void push(std::function<void()> task){
        std::lock_guard<std::mutex> lock{mutex};
        queue.push(std::move(task));
    }

    std::optional<std::function<void()>> popIfNotEmpty(){
        std::lock_guard<std::mutex> lock{mutex};
        if(queue.empty()){
            return std::nullopt;
        }
        auto task = queue.front();
        queue.pop();
        return task;
    }

    bool empty(){
        std::lock_guard<std::mutex> lock{mutex};
        return queue.empty();
    }

    mutable std::mutex mutex;
    std::queue<std::function<void()>> queue;
};

int main(){
    WorkingQueue queue;
    std::atomic<bool> stopFlag{false};
    auto f = std::async(std::launch::async, [&queue, &stopFlag](){
        while(!stopFlag || !queue.empty()){
            auto task = queue.popIfNotEmpty();
            if(task){
                (*task)();
            }
        }
    });
    auto sp = std::make_shared<int>(5);
    queue.push([sp](){
        std::cout << *sp;
    });

    stopFlag = true;
    f.get();
}