1--std::async创建异步任务

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

int thread(){
    std::cout << "thread id: " << std::this_thread::get_id() << std::endl;
    return -1;
}

int main(int argc, char *argv[]){
    std::cout << "thread id: " << std::this_thread::get_id() << std::endl;
    // std::future<int> result = std::async(std::launch::deferred, thread); //不会创建一个新线程
    std::future<int> result = std::async(std::launch::async, thread); //强制创建一个新线程
    std::cout << "result.get(): " << result.get() << std::endl;
    return 0;
}

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

int thread(){
    std::cout << "thread id: " << std::this_thread::get_id() << std::endl;
    return -1;
}

int main(int argc, char *argv[]){
    std::cout << "thread id: " << std::this_thread::get_id() << std::endl;
    std::future<int> result = std::async(thread);
    std::future_status status = result.wait_for(std::chrono::seconds(0));
    if(status == std::future_status::deferred) { // 异步任务会延迟执行
        std::cout << "deferred running" << std::endl;
        std::cout << "result.get(): " << result.get() << std::endl;
    }
    else{ // 创建新线程来执行异步任务，还需进一步判断是否超时
        std::cout << "create new thread" << std::endl; 
    }
    return 0;
}