C++并行开发11- std__atomic续谈、std__async深入谈

原子操作续谈

std::atomic<int> g_value = 0; //原子操作
void my_thread() {
    for (int i = 0; i < 1000000; i++) {
        g_value++; //支持原子操作
        g_value+=1； //支持原子操作
        g_value = g_value + 1； //不支持原子操作
    }
}

std::async深入谈

F:/网站备份-20221127/zhouaq_backup_20221127.com/zhouaq.com/wp-content/p://zhouaq.com/wp-./uploads/2020/10/wp_editor_md_3264c3613be8ad76733550edd28c5bb3.jpg)](http:./uploads/2020/10/wp_editor_md_3264c3613be8ad76733550edd28c5bb3.jpg)F:/网站备份-20221127/zhouaq_backup_20221127.com/zhouaq.com/wp-content/p://zhouaq.com/wp-
content/uploads/2020/10/wp_editor_md_5a1d3ba8bea412f86fd61b09424d9d0f.jpg)](http://zhouaq.com/wp-
content/uploads/2020/10/wp_editor_md_5a1d3ba8bea412f86fd61b09424d9d0f.jpg)
通过wait_for判断当前是否创建新线程

#include <iostream>
#include <thread>
#include <algorithm>
#include <vector>
#include <list>
#include <mutex>
#include <future>   //引入std::future头文件
using namespace std;

int my_thread() {
    cout << "mythread start" << " threadid is = " << std::this_thread::get_id() << endl;
    std::chrono::milliseconds dura(5000);  //休息了5s
    std::this_thread::sleep_for(dura);
    cout << "over " << endl;
    return 5;
}

int main() {
    cout << "main " << "thread id is " << std::this_thread::get_id() << endl;
    std::future<int> result = std::async(my_thread);  //async:异步; 

    cout << "continue " << endl;

    //枚举类型
    //std::future_status status = result.wait_for(std::chrono::seconds(6)); //等待1s
    std::future_status status = result.wait_for(0s); //(std::chrono::seconds(6)); //等待1s  //重载了后缀s
    if (status == std::future_status::timeout) {
        //超时，表示线程还没有结束完
        cout << "创建了线程" << endl;

        cout << "线程还没有执行完， 超时" << endl;
    }
    else if (status == std::future_status::ready) {
        //表示线程成功返回
        cout << "创建了线程" << endl;
        cout << "线程成功返回" << endl;
        cout << result.get() << endl;
    }
    else if (status == std::future_status::deferred) {
        cout << "没有创建线程" << endl;
        //如果    std::future<int> result = std::async(std::launch::deferred, my_thread);  //async:异步; 
        cout << "线程被延迟执行" << endl;
        cout << result.get() << endl;
    }

    cout << "主线程结束 " << endl;

    return 0;
}