这里有一个使用boost：：asio的例子。
1.为什么这个例子使用boost：：asio：：io_service：：work？
1.为什么不调用srv.run ();来执行线程中的任务？

int main()
{
    boost::asio::io_service srv;
    boost::asio::io_service::work work(srv);
    boost::thread_group thr_grp;
    thr_grp.create_thread(boost::bind(&boost::asio::io_service::run, &srv));
    thr_grp.create_thread(boost::bind(&boost::asio::io_service::run, &srv));
    srv.post(boost::bind(f1, 123));
    srv.post(boost::bind(f1, 321));
    //sync
    srv.post(boost::bind(f2, 456));
    srv.post(boost::bind(f2, 654));
    //sync
    srv.stop();
    thr_grp.join();
}

**更新：**使用io_service而不使用io_service：：work时，轮询和运行有什么区别？

int main()
{
    boost::asio::io_service srv;
    //boost::asio::io_service::work work(srv);
    std::vector<boost::thread> thr_grp;
    srv.post(boost::bind(f1, 123));
    srv.post(boost::bind(f1, 321));
    //sync
    srv.post(boost::bind(f2, 456));
    srv.post(boost::bind(f2, 654));
    //sync
    // What is the difference between the poll and run, when io_service without work?
    thr_grp.emplace_back(boost::bind(&boost::asio::io_service::poll, &srv));// poll or run?
    thr_grp.emplace_back(boost::bind(&boost::asio::io_service::run, &srv));// poll or run? 
    srv.stop();
    for(auto &i : thr_grp) i.join();
    int b;
    std::cin >> b;
    return 0;
}