C++ std::async 不生成新线程

Question

C++11

int main(int argc, char** argv) {
    std::async(std::launch::async, [](){ 
        while(true) cout << "async thread" <<endl; 
    });
    while(true) cout << "main thread" << endl;
    return 0;
}

我预计输出应该与 async thread 和 main thread 交错，因为应该有 2 个不同的线程。

但事实并非如此。

它输出：

async thread
async thread
async thread
async thread
...

我想只有一个线程。有人能告诉我为什么它没有为 std::async 生成新线程吗？谢谢。

Answer 1

改为：

auto _ = std::async(std::launch::async, [](){ 
    while(true) cout << "async thread" <<endl; 
});

文件：

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, essentially making code such as the following synchronous:

std::async(std::launch::async, []{ f(); }); // temporary's dtor waits for f() std::async(std::launch::async, []{ g(); }); // does not start until f() completes

C++ std::async 不生成新线程

C++ std::async does not spawn a new thread

c++

multithreading

asynchronous

stdasync