compilation error when invoking parallel_for()

[gajendra_g_]

I am trying to create a 1D array and emulate a 2D matrix multiplication and parallelize it using the tbb. In my previous post I got an error that was due  missing the namespace tbb for the tbb constructs.

However  I further extened my code to create a parallelMatrixMultiply that calls the MatrixMultiply2D and i get a half page terminal error message a part of which is like this:

usr/include/tbb/parallel_for.h:102:37: error: no match for call to ‘(const MatrixMultiply2D) (tbb::blocked_range2d<long unsigned int>&)’
         void run_body( Range &r ) { my_body( r ); }
                                     ^
./tbbMatrix.cpp:36:14: note: candidate: void MatrixMultiply2D::operator()(const tbb::blocked_range2d<long unsigned int>&) <near match>
         void operator()(const blocked_range2d<size_t>& rnge )
              ^
./tbbMatrix.cpp:36:14: note:   passing ‘const MatrixMultiply2D*’ as ‘this’ argument discards qualifiers

Here's my code:

#include <iostream>
#include "tbb/tbb.h"
#include "tbb/parallel_for.h"
#include "tbb/blocked_range2d.h"

using namespace tbb;

const size_t m_rows = 256;
const size_t m_columns = 256;
const size_t m_k = 256;

class MatrixMultiply2D
{
    private:
        double *m_A;
        double *m_B;
        double *m_C;

    public:
        void operator()(const blocked_range2d<size_t>& rnge )
        {
            double *usrA = m_A;
            double *usrB = m_B;
            double *usrC = m_C;

            for(size_t row=rnge.rows().begin(); row<rnge.rows().end(); ++row)
            {
                for(size_t col=rnge.cols().begin(); col <rnge.cols().end(); ++col)
                {
                    double sum = 0.0;
                
                     for(size_t k=0; k<m_k; ++k)
                     {
                        usrC[row*(rnge.cols().end()-rnge.cols().begin()) + col]  += usrA[row*m_k + k]*usrB[k*(rnge.cols().end()-rnge.cols().begin()) + col];     
                    }
                }
            }
        }

        MatrixMultiply2D(double *A, double *B, double *C):
        m_A(A), m_B(B), m_C(C)
        {       }
};

// this line spawns error, if commented the code compiles fine!
void parallelMatrixMultiply(double *A, double *B, double *C, size_t rows, size_t columns, size_t k)
{
    parallel_for( blocked_range2d<size_t>(0, rows, 16, 0, columns, 32), MatrixMultiply2D(A,B,C) );
}

int main(int argc, char **argv)
{
    double *A = new double[m_rows*m_k];
    double *B = new double[m_k*m_columns];
    double *C = new double[m_rows*m_columns];

  


/***************************************************************************/
/********************* CALLING TBB PARALLEL MATRIX *************************/

    parallelMatrixMultiply(A, B, C, m_rows, m_columns, m_k);

  
    
/********************* END OF PARALLEL MATRIX *********************************/
/******************************************************************************/

    delete[] A;
    delete[] B;
    delete[] C;
   
    return 0;
}

Any suggestions is greatly appreciated.

[Vladimir_P_1234567890 · Accepted solution]

Hello, 

documentation for parallel_for requires operator() to be the const member function: https://software.intel.com/en-us/node/506153.

So change line 20 from "void operator()(const blocked_range2d<size_t>& rnge )" to "void operator()(const blocked_range2d<size_t>& rnge ) const"

--Vladimir