std::condition_variable(2)复习

#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 = 0;
bool shipment_available()
{
    return cargo != 0;
}

// 消费者线程.
void consume(int n)
{
    for (int i = 0; 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 = 0;
    }
}

int main()
{
    std::thread consumer_thread(consume, 10); // 消费者线程.

    // 主线程为生产者线程, 生产 10 个物品.
    for (int i = 0; i < 10; ++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 + 1;
        cv.notify_one();//唤醒一个阻塞的线程
    }

    consumer_thread.join();
    getchar();
    return 0;
}