有没有办法在 std::async 方法中实现超时，所以如果线程在指定的时间内没有完成，我希望这个调用超时并完成。我该如何实现此功能。

最佳答案

没有(标准的)方法可以进入线程并杀死它，无论如何这通常不是一个好主意。更简洁的选择是将开始时间和最长持续时间传递给函数，然后(可能随着计算的进行多次)检查当前时间减去开始时间是否太长。

我会做这样的事情:

#include <chrono>

template <typename Clock = std::chrono::steady_clock>
class timeout
{
public:
    typedef Clock clock_type;
    typedef typename clock_type::time_point time_point;
    typedef typename clock_type::duration duration;

    explicit timeout(duration maxDuration) :
    mStartTime(clock_type::now()),
    mMaxDuration(maxDuration)
    {}

    time_point start_time() const
    {
        return mStartTime;
    }

    duration max_duration() const
    {
        return mMaxDuration;
    }

    bool is_expired() const
    {
        const auto endTime = clock_type::now();

        return (endTime - start_time()) > max_duration();
    }

    static timeout infinity()
    {
        return timeout(duration::max());
    }

private:
    time_point mStartTime;
    duration mMaxDuration;
};

这个简单的实用程序跟踪开始时间和最大持续时间(并提供一种指定无穷大的方法)，并允许用户查询简单的事实，最重要的是是否发生超时。

下面测试；您可以通过定义/取消定义 FAKE_DELAY 来添加伪延迟:

#include <iostream>
#include <future>

#define FAKE_DELAY

void fake_delay()
{
    #ifdef FAKE_DELAY
    std::this_thread::sleep_for(std::chrono::milliseconds(1000));
    #endif
}

void short_running_function(timeout<> timelimit)
{
    fake_delay();

    if (timelimit.is_expired())
        std::cout << "short running thread ran out of time" << std::endl;
    else
        std::cout << "short running function finished" << std::endl;
}

void long_running_function(timeout<> timelimit)
{
    for (unsigned i = 0; i < 10; ++i) {
        if (timelimit.is_expired())
        {
            std::cout << "long running thread ran out of time" << std::endl;
            return;
        }

        std::cout << "long running thread doing work" << std::endl;
        fake_delay();
    }

    std::cout << "long running function finished" << std::endl;
}

int main()
{
    std::async(short_running_function,
               timeout<>(std::chrono::milliseconds(500))).wait();

    std::async(short_running_function,
               timeout<>(std::chrono::milliseconds(5000))).wait();

    std::async(long_running_function,
               timeout<>(std::chrono::milliseconds(500))).wait();

    std::async(long_running_function,
               timeout<>(std::chrono::milliseconds(5000))).wait();

    std::async(long_running_function,
               timeout<>::infinity()).wait();
}

FAKE_DELAY off 的一种可能输出:

short running function finished
short running function finished
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running function finished
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running function finished
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running function finished

FAKE_DELAY on 的一种可能输出:

short running thread ran out of time
short running function finished
long running thread doing work
long running thread ran out of time
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread ran out of time
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running thread doing work
long running function finished

关于c++ - std::async 超时，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14203584/