How to interrupt in asynch thread?

Question

I am trying to make some asynch thread for my project.

and I wonder is that possible to finish "Task 5" by using some way such as interrupt.

Is it possible to change itv_duration in already running 'call_from_async'?

#include <iostream>
#include <future>
#include <vector>

using namespace std;

enum class status{
    STATUS_REVICE = 0,
    STATUS_START = 1,
    STATUS_COMPLETED = 2,
    STATUS_CANCELED = 3
};

int called_from_async(std::string taskName, int creationTime, int itv_duration, int itv_start)
{
    cout << "creationTime : " << creationTime << endl;
    cout << "interval : " << itv_duration << endl;
    cout << "startTime : " << itv_start << endl;

    cout << "status : 1 Event Recevied" << endl;

    bool bExit = false;
    bool bStart = false;

    while(!bExit)
    {
        if(creationTime > itv_start && !bStart)
        {
            bStart = true;
        }

        creationTime++;

        if(bStart)
        {
            itv_duration--;
            if(itv_duration < 0 )
            {
                bExit = true;
            }
        }

        std::this_thread::sleep_for(std::chrono::seconds(1));
    }

    cout << "status : 3 Event Completed : " << taskName.c_str() << endl;

    return 1;
}

class eventManager
{
public:
    eventManager() {};
    ~eventManager() {};

    std::future<int> addTask(std::string taskName, int creationTime, int itv_duration, int itv_start)
    {
        return std::async(std::launch::async, called_from_async, taskName, creationTime, itv_duration, itv_start);
    }

private:
};

int main() {

    std::vector<std::future<int>> futures; // place for asyns tasks

    eventManager evtManager;

   futures.push_back(std::move(evtManager.addTask("Task 1", 1234560, 20, 1234570))); // will be done as 4th
   futures.push_back(std::move(evtManager.addTask("Task 2", 1234560, 15, 1234570)));  // will be done as third
   futures.push_back(std::move(evtManager.addTask("Task 3", 1234560, 10, 1234570))); // will be done as second
   futures.push_back(std::move(evtManager.addTask("Task 4", 1234560, 5, 1234570))); // will be done as first
   futures.push_back(std::move(evtManager.addTask("Task 5", 1234560, 360, 1234570))); // super long task, but will be done as zero because of cancel event.

    return 0;

Answer 1

You could pass the duration (variable you want to change during execution) by reference, instead of by value.

It would also be a good idea to create a dedicated variable to handle cancelation. I used a simple bool in the example below, but you might consider something more fancy, like std::condition_variable for example.

int called_from_async(std::string taskName, int creationTime, int& itv_duration, int itv_start, bool& cancel)
{
    bool bExit = false;
    bool bStart = false;
    while (!bExit && !cancel)
    {
        if (creationTime > itv_start && !bStart)
        {
            bStart = true;
        }

        creationTime++;

        if (bStart)
        {
            if (--itv_duration < 0)
            {
                bExit = true;
            }
        }

        std::this_thread::sleep_for(std::chrono::seconds(1));
    }

    std::cout << taskName << std::endl;

    return 1;
}

class eventManager
{
    public:
    eventManager() { };
    ~eventManager() { };

    std::future<int> addTask(std::string taskName, int creationTime, int& itv_duration, int itv_start, bool& cancel)
    {
        return std::async(std::launch::async, [=, &itv_duration, &cancel]() { return called_from_async(taskName, creationTime, itv_duration, itv_start, cancel); });
    }
};

int main()
{

    std::vector<std::future<int>> futures; // place for asyns tasks

    eventManager evtManager;

    bool cancel1 = false, cancel5 = false;
    int shortDuration = 2, longDuration = 360;
    futures.push_back(std::move(evtManager.addTask("Task 1", 1234560, shortDuration, 1234570, cancel1))); // will be done as 4th
    //...
    futures.push_back(std::move(evtManager.addTask("Task 5", 1234560, longDuration, 1234570, cancel5))); // super long task, but will be done as zero because of cancel event.

    longDuration = 1;
    //cancel5 = true;

    //wait for your tasks to finish, so that references are valid
    //or declare them in the higher scope

    return 0;
}