Monday, June 4, 2012

Array addition using OpenMP

OpenMP is an application programming interface (API) that supports multi-platform shared memory multiprocessing programming.

To compile this in linux environment
$gcc -fopenmp omp_add.c -o omp_add

Then you need to define number of threads:
$export OMP_NUM_THREADS=10

To run program:
$./omp_add

Here is omp_add.c
#include <omp.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main (int argc, char *argv[]) {
  
    int i, tid, nthreads, n = 10, N = 100000000;
    double *A, *B, tResult, fResult;
    
    time_t start, stop;
    clock_t ticks; long count;

      A = (double *) malloc(N*sizeof(double));
      B = (double *) malloc(N*sizeof(double));

      for (i=0; i<N; i++) {
          A[i] = (double)(i+1);
        B[i] = (double)(i+1);
      }

    time(&start);

    /*
    //this block use single process
    for (i=0; i<N; i++)
    {
            fResult = fResult + A[i] + B[i];
    }
    
    */
    
    //begin of parallel section
    
    #pragma omp parallel private(tid, i,tResult) shared(n,A,B,fResult)
    {
        tid = omp_get_thread_num();
        if (tid == 0) 
        {
            nthreads = omp_get_num_threads();
            printf("Number of threads = %d\n", nthreads);
        }

    #pragma omp for schedule (static, n)
        for (i=0; i < N; i++) {
            tResult = tResult + A[i] + B[i];
        }

    #pragma omp for nowait
        for (i=0; i < n; i++) 
        {
            printf("Thread %d does iteration %d\n", tid, i);
        }
        
    #pragma omp critical 
        fResult = fResult + tResult; 
    }
    //end of parallel section
    
    time(&stop);

      printf("%f\n",fResult);
      
       printf("Finished in about %.0f seconds. \n", difftime(stop, start));
  
     exit(0);
}

Special thanks for Dr. M.C. Jayawardena - BSc (Col), PhD(Uppsala), MIEEE, AMCS(SL) (Lecturer)

For more examples

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