trying to pass different values to openMp thread in its thread function parameter-CodePudding

I have this code that I am trying to figure out how to pass differnt value to as thread parameter in openMp threads

so for example I have an simple decrement statement like --t where t is a variable so every time thread function called it gets decremented value of t first then is received as thread parameter. this is what I tried

int main(int argc, char* argv[])
{

    int t=2;
    #pragma omp parallel firstprivate(t=(--t))
    {
        
        printf("%d\n",t);
    }
    
    // Ending of parallel region
}

So I have absolute no clue how this above code is expended to since I assumed firstprivate(...) part of #pragma omp derective is just a way of spawning a thread using open mp but I need different parameters received each thread. Is it doable in openMM C

CodePudding user response：

It is not possible to do that in a firstprivate clause. However, you can change the clause to shared and use the atomic construct to update the value safely. Here is an example:

int main(int argc, char* argv[])
{
    int t=2;

    #pragma omp parallel shared(t)
    {
        int local_t_value;

        #pragma omp atomic capture relaxed
        local_t_value = --t;

        printf("%d\n", local_t_value);
    }
}

Note that capture is used in this context because the atomic value is both fetched and updated at the same time. relaxed is a memory-ordering specifying that this value can be updated without doing any flush. For more information please read this related part of the specification.