C++ Having two "processes" run at the same time

Question

In a command line application I'm building I'd like to have two "processes" running at the same time. By processes, I mean such as:

Every 57 seconds, I would like to do task A, and every 250 seconds do task B. Those are arbitrarily chosen numbers, but you get the point.

How can I have both of these "processes" being checked at the same time?

Thanks guys

What's a thread? As for sleeps, if I were to do a 57000 sleep, and then a 250000 sleep, the 57 second task would be skipped. — Josh Beckwith, Jan 19 '15 at 19:18
btw you can also use std::thread (C++11) regardless of the OS — Axalo, Jan 19 '15 at 19:21
why not set a `cron` job rather than adding the complexity in the code? — qqibrow, Jan 19 '15 at 19:22

score 2 · Answer 1 · answered Jan 19 '15 at 19:22

2

You could do something like this, if neither of the process takes long.

float Atime = 57.f;
float Btime = 250.f;
float startTime = someTimerFunc();
while(true) {
    sleep(a few milliseconds);


    float endTime = someTimerFunc();
    float deltaTime = endTime - startTime;
    startTime = endTime;



    Atime -= deltaTime;
    Btime -= deltaTime;
    if(Atime < 0) {
        Atime += 57.f;
        AProcess();
    }
    if(Btime < 0) {
        Btime += 250.f;
        BProcess();
    }
}

Or you could look up what threads do.

answered Jan 19 '15 at 19:22

BWG

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Interesting. Thank you very much! I'll try this out. – Josh Beckwith Jan 19 '15 at 19:26
@JoshBeckwith I hope it helps. It might not work, I didn't test it but you can try it. – BWG Jan 19 '15 at 19:27

David · Answer 2 · 2015-01-19T19:37:01.487

Running 2 threads would be a good way to handle this unless you have a reason to need different processes. Something like this:

void taskA() { /*...*/ }
void taskB() { /*...*/ }

/*...*/

bool exit = false;
std::mutex mutex;
std::condition_variable cv;

auto runLoop = [&](auto duration, auto task)
    {
        std::unique_lock<std::mutex> lock{mutex};

        while(true)
        {
            if(!cv.wait_for(lock, duration, [&]{ return !exit; }))
                task();
            else
                return;
        }
    };

std::thread a{ [&]{ runLoop(std::chrono::seconds{57}, taskA); }};
std::thread b{ [&]{ runLoop(std::chrono::seconds{250}, taskB); }};

Doing it this way is cross platform standard C++, which is a major benefit. It uses C++11: lambdas and threading library.

http://stackoverflow.com/questions/7709894/using-auto-in-a-lambda-function — amdn, Jan 19 '15 at 19:42

score 1 · Answer 3 · answered Jan 19 '15 at 19:46

As said above, you can use threads instead of processes. If you are using c++11, have a look here on how you can create a thread.

In the example of the link, just replace foo and bar with the code that you want task A and task B to execute.

Also you can have a look here for how you can make your program wait for some time with sleep.

C++ Having two "processes" run at the same time

3 Answers3