第 7 章 并行与并发

#include <iostream>
#include <thread>

int main() {
    std::thread t([](){
        std::cout << "hello world." << std::endl;
    });
    t.join();
    return 0;
}

#include <iostream>
#include <mutex>
#include <thread>

int v = 1;

void critical_section(int change_v) {
    static std::mutex mtx;
    std::lock_guard<std::mutex> lock(mtx);

    // 执行竞争操作
    v = change_v;

    // 离开此作用域后 mtx 会被释放
}

int main() {
    std::thread t1(critical_section, 2), t2(critical_section, 3);
    t1.join();
    t2.join();

    std::cout << v << std::endl;
    return 0;
}

#include <iostream>
#include <mutex>
#include <thread>

int v = 1;

void critical_section(int change_v) {
    static std::mutex mtx;
    std::unique_lock<std::mutex> lock(mtx);
    // 执行竞争操作
    v = change_v;
    std::cout << v << std::endl;
    // 将锁进行释放
    lock.unlock();

    // 在此期间，任何人都可以抢夺 v 的持有权

    // 开始另一组竞争操作，再次加锁
    lock.lock();
    v += 1;
    std::cout << v << std::endl;
}

int main() {
    std::thread t1(critical_section, 2), t2(critical_section, 3);
    t1.join();
    t2.join();
    return 0;
}

#include <iostream>
#include <future>
#include <thread>

int main() {
    // 将一个返回值为7的 lambda 表达式封装到 task 中
    // std::packaged_task 的模板参数为要封装函数的类型
    std::packaged_task<int()> task([](){return 7;});
    // 获得 task 的期物
    std::future<int> result = task.get_future(); // 在一个线程中执行 task
    std::thread(std::move(task)).detach();
    std::cout << "waiting...";
    result.wait(); // 在此设置屏障，阻塞到期物的完成
    // 输出执行结果
    std::cout << "done!" << std:: endl << "future result is "
              << result.get() << std::endl;
    return 0;
}

#include <queue>
#include <chrono>
#include <mutex>
#include <thread>
#include <iostream>
#include <condition_variable>


int main() {
    std::queue<int> produced_nums;
    std::mutex mtx;
    std::condition_variable cv;
    bool notified = false;  // 通知信号

    // 生产者
    auto producer = [&]() {
        for (int i = 0; ; i++) {
            std::this_thread::sleep_for(std::chrono::milliseconds(900));
            std::unique_lock<std::mutex> lock(mtx);
            std::cout << "producing " << i << std::endl;
            produced_nums.push(i);
            notified = true;
            cv.notify_all(); // 此处也可以使用 notify_one
        }
    };
    // 消费者
    auto consumer = [&]() {
        while (true) {
            std::unique_lock<std::mutex> lock(mtx);
            while (!notified) {  // 避免虚假唤醒
                cv.wait(lock);
            }
            // 短暂取消锁，使得生产者有机会在消费者消费空前继续生产
            lock.unlock();
            // 消费者慢于生产者
            std::this_thread::sleep_for(std::chrono::milliseconds(1000));
            lock.lock();
            while (!produced_nums.empty()) {
                std::cout << "consuming " << produced_nums.front() << std::endl;
                produced_nums.pop();
            }
            notified = false;
        }
    };

    // 分别在不同的线程中运行
    std::thread p




    
(producer);
    std::thread cs[2];
    for (int i = 0; i < 2; ++i) {
        cs[i] = std::thread(consumer);
    }
    p.join();
    for (int i = 0; i < 2; ++i) {
        cs[i].join();
    }
    return 0;
}

#include <thread>
#include <iostream>

int main() {
    int a = 0;
    int flag = 0;

    std::thread t1([&]() {
        while (flag != 1);

        int b = a;
        std::cout << "b = " << b << std::endl;
    });

    std::thread t2([&]() {
        a = 5;
        flag = 1;
    });

    t1.join();
    t2.join();
    return 0;
}

std::atomic<int> counter;

#include <atomic>
#include <thread>
#include <iostream>

std::atomic<int> count = {0};

int main() {
    std::thread t1([](){
        count.fetch_add(1);
    });
    std::thread t2([](){
        count++;        // 等价于 fetch_add
        count += 1;     // 等价于 fetch_add
    });
    t1.join();
    t2.join();
    std::cout << count << std::endl;
    return 0;
}

#include <atomic>
#include <iostream>

struct A {
    float x;
    int y;
    long long z;
};

int main() {
    std::atomic<A> a;
    std::cout << std::boolalpha << a.is_lock_free() << std::endl;
    return 0;
}