Distributed sort in MPI

sort.cpp

/*
 * ===========================================================================
 *
 *       Filename:  sort.cpp
 *         Author:  Dodon Victor, dodonvictor AT gmail DOT com
 *        Created:  11/22/2012 04:32:15 PM
 *         Editor:  Vim 7.3
 *       Compiler:  clang 3.2
 *             OS:  Archlinux x86_64
 *
 *    Description:  Sortare paralela in MPI
 *
 * ===========================================================================
 */

#include <mpi.h>
#include <iostream>

int values[] = {5, 3, 8, 1, 9, 4, 2, 6, 7, 0};
int n = 10;
int sortedValues[10];

int main(int argc, char *argv[])
{
    int nthreads, rank;
    int tag = 1;

    MPI::Init(argc, argv);
    MPI::COMM_WORLD.Set_errhandler(MPI::ERRORS_THROW_EXCEPTIONS);

    try {
        nthreads = MPI::COMM_WORLD.Get_size();
        rank = MPI::COMM_WORLD.Get_rank();

        if (rank == 0)
        {
            std::cout << "Initial values: ";
            for (int i = 0; i < n; ++i)
            {
                std::cout << values[i] << " ";
            }
            std::cout << std::endl;
        }

        int current;
        int root = 0;
        MPI::COMM_WORLD.Scatter(values, 1, MPI::INT, &current, 1, MPI::INT, root);
        for (int i = 0; i < n; ++i)
        {
            if ((i % 2 == 0 && rank % 2 == 0) || (i % 2 && rank % 2))
            {
                if (rank < nthreads - 1)
                {
                    MPI::COMM_WORLD.Send(&current, 1, MPI::INT, rank + 1, tag);
                    MPI::COMM_WORLD.Recv(&current, 1, MPI::INT, rank + 1, tag);
                }
            }
            else
            {
                if (rank > 0) {
                    int recVal;
                    MPI::COMM_WORLD.Recv(&recVal, 1, MPI::INT, rank - 1, tag);
                    if (recVal > current) {
                        int tmp = current;
                        current = recVal;
                        recVal = tmp;
                    }
                    MPI::COMM_WORLD.Send(&recVal, 1, MPI::INT, rank - 1, tag);
                }
            }
            MPI::COMM_WORLD.Barrier();
        }
        MPI::COMM_WORLD.Gather(&current, 1, MPI::INT, sortedValues, 1, MPI::INT, root);

        if (rank == 0)
        {
            std::cout << "Sorted values: ";
            for (int i = 0; i < n; ++i)
            {
                std::cout << sortedValues[i] << " ";
            }
            std::cout << std::endl;
        }
    } catch (MPI::Exception e) {
        std::cout << "MPI exception: " << e.Get_error_code() << " - " << e.Get_error_string() << std::endl;
    }
    MPI::Finalize();
    return 0;
}