omp_bug5.c

/******************************************************************************
 * FILE: omp_bug5.c
 * DESCRIPTION:
 *   Using SECTIONS, two threads initialize their own array and then add
 *   it to the other's array, however a deadlock occurs.
 * AUTHOR: Blaise Barney  01/29/04
 * LAST REVISED: 04/06/05
 ******************************************************************************/
#include <omp.h>
#include <stdio.h>
#include <stdlib.h>
#define N 1000000
#define PI 3.1415926535
#define DELTA .01415926535

int main (int argc, char *argv[]) 
{
  int nthreads, tid, i;
  float a[N], b[N];
  omp_lock_t locka, lockb;

  /* Initialize the locks */
  omp_init_lock(&locka);
  omp_init_lock(&lockb);

  /* Fork a team of threads giving them their own copies of variables */
#pragma omp parallel shared(a, b, nthreads, locka, lockb) private(tid)
  {

    /* Obtain thread number and number of threads */
    tid = omp_get_thread_num();
#pragma omp master
    {
      nthreads = omp_get_num_threads();
      printf("Number of threads = %d\n", nthreads);
    }
    printf("Thread %d starting...\n", tid);
#pragma omp barrier

#pragma omp sections nowait
    {
#pragma omp section
      {
        printf("Thread %d initializing a[]\n",tid);
        omp_set_lock(&locka);
        for (i=0; i<N; i++)
          a[i] = i * DELTA;
        omp_set_lock(&lockb);
        printf("Thread %d adding a[] to b[]\n",tid);
        for (i=0; i<N; i++)
          b[i] += a[i];
        omp_unset_lock(&lockb);
        omp_unset_lock(&locka);
      }

#pragma omp section
      {
        printf("Thread %d initializing b[]\n",tid);
        omp_set_lock(&lockb);
        for (i=0; i<N; i++)
          b[i] = i * PI;
        omp_set_lock(&locka);
        printf("Thread %d adding b[] to a[]\n",tid);
        for (i=0; i<N; i++)
          a[i] += b[i];
        omp_unset_lock(&locka);
        omp_unset_lock(&lockb);
      }
    }  /* end of sections */
  }  /* end of parallel region */

}