c++11之std::async 和std::thread的区别小结

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

int task()
{
    std::cout << "Task is running in thread " << std::this_thread::get_id() << std::endl;
    return 42;
}

int main()
{
    // 使用std::async创建异步任务
    std::future<int> f1 = std::async(std::launch::async, task);
    std::cout << "Async task has been started." << std::endl;

    // 使用std::thread创建新线程
    std::thread t(task);
    std::cout << "Thread has been started." << std::endl;

    // 等待异步任务完成并获取结果
    int result1 = f1.get();
    std::cout << "Async task has been finished with result " << result1 << std::endl;

    // 等待线程完成并退出
    t.join();
    std::cout << "Thread has been finished." << std::endl;

    return 0;
}

#include <iostream>
#include <future>

int main() {
    auto f1 = std::async(std::launch::deferred, []() {
        std::cout << "This is a deferred async task." << std::endl;
        return 1;
        });
    auto f2 = std::async(std::launch::async, []() {
        std::cout << "This is a async task." << std::endl;
        return 2;
        });
    std::cout << "Waiting..." << std::endl;
    std::cout << f1.get() << std::endl;
    std::cout << f2.get() << std::endl;
    return 0;
}

#include<iostream>
#include<thread>
#include<string>
#include<vector>
#include<list>
#include<mutex>
#include<future>
using namespace std;
int mythread() //线程入口函数
{
    cout << "mythread start" << "threadid= " << std::this_thread::get_id() << endl; //打印线程id
    std::chrono::milliseconds dura(5000); //定一个5秒的时间
    std::this_thread::sleep_for(dura);  //休息一定时常
    cout << "mythread end" << "threadid= " << std::this_thread::get_id() << endl; //打印线程id
    return 5;
}
int main()
{
    cout << "main" << "threadid= " << std::this_thread::get_id() << endl;
    std::future<int> result = std::async(mythread);//流程并不卡在这里
    cout << "continue....." << endl;
    //枚举类型
    std::future_status status = result.wait_for(std::chrono::seconds(0));//等待一秒
    
    if (status == std::future_status::deferred)
    {
        //线程被延迟执行了，系统资源紧张
        cout << result.get() << endl; //此时采取调用mythread()
    }
    else if (status == std::future_status::timeout)//
    {
        //超时：表示线程还没执行完；我想等待你1秒，希望你返回，你没有返回，那么 status = timeout
        //线程还没执行完
        cout << "超时：表示线程还没执行完!" << endl;
    }
    else if (status == std::future_status::ready)
    {
        //表示线程成功返回
        cout << "线程成功执行完毕，返回!" << endl;
        cout << result.get() << endl;
    }
    cout << "I love China!" << endl;
    return 0;
}