OpenMP collapse and private

OpenMP collapse and private

After updating into Intel(R) C++ Compiler XE [IA-32] I found a different treatment for variables in collapsed control loops. Previously I used Intel C++ 13.x.  For version, the following code was correct :

int i,j,k;

#pragma omp parallel for collapse(3)
    for (k=0; k< h->nz;  k++)
    for (j=0; j< h->ny ; j++)
    for (i=0; i< h->nx ; i++)
       Point3DType p3d;

       XYZ(h, i, j, k, &p3d);
       d2pc[(h->nx * h->ny)*k + h->nx * j + i] = kdNNS(&p3d);

For version it needs to be modified into:

#pragma omp parallel for collapse(3) private (k,j,i)

I had to declare as private at less j and i.

I do not know if it is mandatory to declare i and j as private according to OpenMP definition. But I found important to share my case with others because it was not easy to locate the source of the problem and there are lot of examples of use of "collapse" omitting private declaration for the control variables affected.

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duplicate thread

Sorry for posting several times, it took 7 hours to be published and I keep trying...

Closed as duplication ,please refer to Tim's advice and my answer in this thread


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