两个线程可以同时读。但是有写的时候，是全部锁定。

#include <boost/thread.hpp>
#include <thread>

int _tmain(int argc, _TCHAR* argv[])
{
    std::vector<int> items;
    boost::shared_mutex mutex;
    std::thread r1([&]() mutable {
        while (true) {
            std::cout << "1：我要读10秒" << std::endl;
            boost::shared_lock<boost::shared_mutex> lk(mutex);
            std::cout << "1：等着吧" << std::endl;
            std::this_thread::sleep_for(std::chrono::seconds(10));
            std::cout << "1：我读完了" << std::endl;
        }
        });

    std::thread r2([&]() mutable {
        while(1){
            {
                std::cout << "2：我要瞬间读" << std::endl;
                boost::shared_lock<boost::shared_mutex> lk(mutex);
                std::cout << "2：读到了" << std::endl;
            }
            std::this_thread::sleep_for(std::chrono::seconds(1));
        }
        });

    while (true) {
        int value = 0;
        std::cin >> value;
        std::cout << "3：我想要写：" << std::endl;
        {
            boost::unique_lock<boost::shared_mutex> lk(mutex);
            items.push_back(value);
            std::cout << "3：写完了";
        };
    }

    system("pause");
    return 0;
}