#include <iostream>                // std::cout

#include <thread>                // std::thread, std::this_thread::yield

#include <mutex>                // std::mutex, std::unique_lock

#include <condition_variable>    // std::condition_variable

std::mutex mtx;

std::condition_variable cv;

int cargo = ;

bool shipment_available()

{

    return cargo != ;

}

// 消费者线程.

void consume(int n)

{

    for (int i = ; i < n; ++i) {

        std::unique_lock <std::mutex> lck(mtx);

        cv.wait(lck, shipment_available);//当返回false时阻塞，当true时解除阻塞

        std::cout << cargo << '\n';

        cargo = ;

    }

}

int main()

{

    std::thread consumer_thread(consume, ); // 消费者线程.

    // 主线程为生产者线程, 生产 10 个物品.

    for (int i = ; i < ; ++i)

    {

        while (shipment_available())//等待消费者把cargo置成0

            std::this_thread::yield();//相当于sleep一下

        std::unique_lock <std::mutex> lck(mtx);

        cargo = i + ;

        cv.notify_one();//唤醒一个阻塞的线程

    }

    consumer_thread.join();

    getchar();

    return ;

}