Ordered thread ids in OpenMP in c++

Question

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?

How long do your calculations take? How many threads does your CPU support? It's possible that, for example, each OMP thread runs two of your calculations, do the tids would be duplicated. Have you tried a (for) loop? — 1201ProgramAlarm
– 1201ProgramAlarm, Commented Apr 14, 2017 at 0:36
I'm running on a cluster so it has 16 processors per node. Is there a way to force them to run one calculation per thread even if they don't take long? (They take anywhere from a minute to hours, depending on the dataset) — Chris Kervick
– Chris Kervick, Commented Apr 14, 2017 at 0:40
I'm afraid the question is unclear, not reproducible and extremely broad. You have to be more precise with describing what you do, what you expect and what you observe. Provide a minimal reproducible example with an exact description how you compile and execute it and what environment you run it on (compiler!). Are you running on multiple nodes? What is a "calculation"? — Zulan
– Zulan, Commented Apr 14, 2017 at 11:52

Sklert · Accepted Answer · 2017-04-14 00:53:43Z

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.

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