Question

在此处使用以下信息：How to check if a thread is still running我尝试使用lambda function中的std::future在专用member function中拨打课程thread这样就可以使用std::future

监视future.wait_for()线程的完成状态

TestClass创建std::future＆amp;在其构造函数中启动一个线程。目的是允许其他成员函数监视进度并在必要时终止该线程。

#include <future>
#include <thread>
#include <chrono>
#include <iostream>
#include <atomic>
#include <functional>

class TestClass
{
public:
TestClass(const int &np) : nap(np), run(true)
{       
    //Run member function in a thread, crucially be able to monitor the  thread status using the future;
    function = std::bind(&TestClass::Snooze, this, std::placeholders::_1, std::placeholders::_2);
    future = std::async(std::launch::async, [this] {
        function(nap, &run);
        return true;
    });

}


~TestClass()
{
//If future thread is still executing then terminate it by setting run = false
//Use wait_for() with zero milliseconds to check thread status.
auto status = future.wait_for(std::chrono::milliseconds(1));//needs to have a value > 0
if (status != std::future_status::ready)//execution not complete
{
    run = false;//terminate Snooze
    future.wait();//wait for execution to complete
}
std::cout << "TestClass: Destructor Completed" << std::endl;
}

void Snooze(const int &napLen, std::atomic<bool>* ptrRun)
{
while (*ptrRun)//check ok to to loop on.
{
std::cout << "zzzz...." << std::endl;
std::this_thread::sleep_for(std::chrono::seconds(napLen));//take a nap
}
std::cout << "TestClass: Finished Snoozing." << std::endl;
}

//Getter
bool isThreadFinished() const
{
auto status = future.wait_for(std::chrono::milliseconds(0));
if (status == std::future_status::ready)//execution complete
{
    return true;
}
else
{ 
    return false;
}   
}

//Setter
void stopSnooze()
{
run = false;
std::cout << "TestClass: stopSnooze(): run = " << run << std::endl;
}

private:
int nap;
std::function<void(int, std::atomic<bool>*)> function;
std::future<bool> future;
std::atomic<bool> run;
};



int main() {    

TestClass tc(1);//should see some zzzz's here
std::this_thread::sleep_for(std::chrono::seconds(5));

tc.stopSnooze();//demonstrate stopping the thread by setting run = false

std::this_thread::sleep_for(std::chrono::seconds(2));
std::cout << "TestClass: Next test." << std::endl;

TestClass tc1(1);//should see some zzzz's here
std::this_thread::sleep_for(std::chrono::seconds(5));
}

编辑：更正了代码以按预期运行。

Answer 1

我把这个作为重复投票，但实际上你只是有一个错字：

auto function = std::bind(&TestClass::Snooze, this, nap, &run);
auto future = std::async(std::launch::async, [&function]{
    function();
    return true;
});

应该是：

function = std::bind(&TestClass::Snooze, this, nap, &run);
future = std::async(std::launch::async, [this] {
    function();
    return true;
});

您想要分配给您的会员，而不是创建临时工。原样，您的构造函数是blocking on the future destructor。

使用std :: future来监视和控制线程执行类成员函数（c ++）？

1 个答案: