How to start a thread in another function but inside IF statement-CodePudding

I have a function that I want to run it inside another function, so the main function I have , have a while loop running and the other function outside also have a while loop, and I wanna run both together without any of each other interrupting each other,

so the main function will keep its main while loop running normally and the other function.

I want it to run as a thread in the background but only inside IF statement and its also a while loop and only if this IF statement was TRUE it will start the thread and will also run while the main loop function running I will show here the problem by example:

    void MatchChecker()
    {
    
        while (1)
        {
    
            if (g_pOBJ->checkInMatch() == 2)
            {
    
                std::cout <<  "In Match! " << std::endl;

            }
    }

    void mainFunc()
    {
        while (1)
        {
            if (checkIngame() == true) {
                std::thread checker(MatchChecker);
                checker.join();
                break;

                       
            }
        }
    
        while (1)
        {
            std::cout << "Im doing some stuff here in this main loop" << std::endl;
    
            someOtherThread.join();
        }
    }

so the main problem is with the checker.join(); when I add it inside that if , the second loop doesn't start and its stuck with the mainchecker loop, and I cant put the checker.join inside the other loop because its not defined, so what can I do to solve my problem? any suggestions?

CodePudding user response：

If you want to run 2 threads concurrently, but let's say the execution of one of them is subject to a condition, you could maybe do the following:

Run the one whose execution is subject to a condition as an async task. This way, you can declare a future for that task and later check if that future is valid (i.e. if a task was created for that future).
Run the other one in a normal thread (another async task would serve as well).

This way, you can wait in your mainFunc for your tasks/threads to finish (with a get on the future and a join on the thread). Demo

#include <iostream>  // cout
#include <future>  // async
#include <thread>

void f() { for (auto i{0}; i < 10000;   i) std::cout << "a\n"; }
void g() { for (auto i{0}; i < 10000;   i) std::cout << "b\n"; }

int main()
{
    std::future<void> fut{};
    if (0)  // 0 just for testing; your condition would come here
    {
        fut = std::async(std::launch::async, f);
    }
    std::thread t_g(g);
    t_g.join();
    if (fut.valid())
    {
        fut.get();
    }
}

CodePudding user response：

ITNOA

You can change your code like below

    void MatchChecker()
    {
    
        while (1)
        {
    
            if (g_pOBJ->checkInMatch() == 2)
            {
    
                std::cout <<  "In Match! " << std::endl;

            }
    }

    void mainFunc()
    {
        std::thread checker;

        while (1)
        {
            if (checkIngame() == true) {
                checker = std::thread(MatchChecker);
                break;
            }
        }
    
        while (1)
        {
            std::cout << "Im doing some stuff here in this main loop" << std::endl;
    
            someOtherThread.join();
        }

        if (checker.joinable())
            checker.join();
    }

In the above code, I separate thread definition and running by define empty thread, and start when I needed.

For gracefully joining thread, in the end of function I check thread is joinable or not, if it is joinable, I try to join it.