Decreasing (Worsening) performance in C++ code

Question

I need to add some artificial latency to my code without using std::this_thread::sleep_for() to test some hardware. In fact, I need a function like:

addLatency(10m) // Do dummy computation for 10 milli second

I know that one possible solution is by doing a dummy calculation like:

long int j=0;
for (long int = 0; i < MAX_SIZE < i++)
    j++;

But, Is there any easier or logical way to do this? I searched a lot and could find out a lot of solutions to improve performance, but I could not find anything how to make the performance worst.

Answer 1

This loop on its own is not reliable to have any effect:

long int j=0;
for (long int = 0; i < MAX_SIZE < i++)
    j++;

Unless you use the value of j afterwards the compiler may remove the loop entirely. If you want to keep the CPU busy for some time you need to measure the elapsed time (copy-pasted & modified from here):

void addLatency(long ms) {
    std::chrono::steady_clock::time_point begin = std::chrono::steady_clock::now();
    auto duration_ms = [&](){
        std::chrono::steady_clock::time_point end = std::chrono::steady_clock::now();
        return std::chrono::duration_cast<std::chrono::milliseconds>(end - begin).count();
    };
    while( duration_ms() < ms) {}
}