CODEWITHSUNDEEP
c++multithreadingopenmp
Chris Kervick
Chris Kervick

Reputation: 11

Ordered thread ids in OpenMP in c++

I'm using OpenMP in c++. I want to specify the number of threads (16) and then run each thread with an id from 0 to 15. I have an array of 16 numbers which I want to use as parameters in each separate thread. So I have

    omp_set_dynamic(0);
    omp_set_num_threads(16);
    int tid;
#pragma omp parallel shared(myvector) private(tid)
{
    tid = omp_get_thread_num();
    // Do some calculations using myvector[tid]
}

However, the (tid)s are not ordered as 0 to 15, as some are repeated twice or more. How do I force it to run one task with each of the 16 parameters?

Upvotes: 1

Views: 303

Answers (1)

Sklert
Sklert

Reputation: 242

Each thread in the team executes all statements within a parallel region except for work-sharing constructs.

I tried this simple code

#include <omp.h>
#include <stdio.h>

int main(){
    omp_set_dynamic(0);
    omp_set_num_threads(32);
    int tid;
    double *myvector;
#pragma omp parallel shared(myvector) private(tid)
    {
        tid = omp_get_thread_num();
        printf("Thread number = %d\n",tid);
        // Do some calculations using myvector[tid]
    }
    return 0;
}

and got right result:

Thread number = 3
Thread number = 4
Thread number = 0
Thread number = 5
Thread number = 6
Thread number = 7
Thread number = 8
Thread number = 9
Thread number = 10
Thread number = 11
Thread number = 12
Thread number = 13
Thread number = 14
Thread number = 15
Thread number = 1
Thread number = 2

Please, check it on your machine or write more information about code you tried and output you got.

Upvotes: 1

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