Is it possible to do a reduction on an array with openmp?

Question

Does OpenMP natively support reduction of a variable that represents an array?

This would work something like the following...

float* a = (float*) c         


        

Answer 1

Array reduction is now possible with OpenMP 4.5 for C and C++. Here's an example:

#include 

int main()
{

  int myArray[6] = {};

  #pragma omp parallel for reduction(+:myArray[:6])
  for (int i=0; i<50; ++i)
  {
    double a = 2.0; // Or something non-trivial justifying the parallelism...
    for (int n = 0; n<6; ++n)
    {
      myArray[n] += a;
    }
  }
  // Print the array elements to see them summed   
  for (int n = 0; n<6; ++n)
  {
    std::cout << myArray[n] << " " << std::endl;
  } 
}

Outputs:

100
100
100
100
100
100

I compiled this with GCC 6.2. You can see which common compiler versions support the OpenMP 4.5 features here: https://www.openmp.org/resources/openmp-compilers-tools/

Note from the comments above that while this is convenient syntax, it may invoke a lot of overheads from creating copies of each array section for each thread.