c++ - std::async int 函数可以在任务完成之前退出吗？

Question

我的代码如下:

void f1() {
    for (int i = 0; i < 1000; ++i) {
        std::cout << "f1: " << i << std::endl;
    }
}

void f2() {
    for (int i = 0; i < 10; ++i) {
        std::cout << "f2: " << i << std::endl;
    }
}
auto fz = []() {
        auto l_future = std::async(std::launch::async, f1);
        auto r_future = std::async(std::launch::async, f2);
        while (!is_ready(r_future)) {}
        std::cout << "right done" << std::endl;
    };

fz();
std::cout << "one of task done" << std::endl;

结果是打印了“正确完成”但 fz() 没有完成。“完成任务之一”被打印，直到 f1 完成。现在我想在 f1 完成之前打印“完成的任务之一”。我该怎么办？

Answer 1

来自 this std::async reference :

If the std::future obtained from std::async is not moved from or bound to a reference, the destructor of the std::future will block at the end of the full expression until the asynchronous operation completes

当 lambda 结束时，两个 std::future对象被破坏，破坏l_future将阻塞直到函数 f1返回。