小编Kay*_*gle的帖子

似乎除非你打电话给std::async一个std::future遗嘱永远不会被设置为任何其他状态,future_status::deferred除非你打电话get或wait未来.即使任务已经运行并存储结果wait_for,它wait_until也将继续不阻止和返回future_status::deferred.

这是一个例子:

#include <future>

void main()
{
    auto func = []() { return 5; };
    auto asyncFuture = std::async(std::launch::async, func);
    auto status = asyncFuture.wait_for(std::chrono::seconds(0));   // timeout (1)

    auto deferredFuture = std::async(std::launch::deferred, func);
    status = deferredFuture.wait_for(std::chrono::seconds(0));     // deferred (2)

    std::packaged_task<int()> task(func);
    auto packagedTaskFuture = task.get_future();
    status = packagedTaskFuture.wait_for(std::chrono::seconds(0)); // deferred (2)

    task();

    status = packagedTaskFuture.wait_for(std::chrono::seconds(0)); // deferred (2)
    packagedTaskFuture.wait();
    status = packagedTaskFuture.wait_for(std::chrono::seconds(0)); // ready (0) …