#C++
Create the file mpi_sections.cpp and copy in the following;
#include <mpi.h>
#include <iostream>
#include <unistd.h>
void times_table(int n)
{
int rank = MPI::COMM_WORLD.Get_rank();
for (int i=1; i<=n; ++i)
{
int i_times_n = i * n;
std::cout << "Process " << rank << " says " << i
<< " times " << n << " equals " << i_times_n << std::endl;
sleep(1);
}
}
void countdown()
{
int rank = MPI::COMM_WORLD.Get_rank();
for (int i=10; i>=1; --i)
{
std::cout << "Process " << rank << " says " << i << "...\n";
sleep(1);
}
std::cout << "Process " << rank << " says \"Lift off!\"\n";
}
void long_loop()
{
double sum = 0;
int rank = MPI::COMM_WORLD.Get_rank();
for (int i=1; i<=10; ++i)
{
sum += (i*i);
sleep(1);
}
std::cout << "Process " << rank << " says the sum of the long loop is "
<< sum << std::endl;
}
int main(int argc, char **argv)
{
MPI::Init(argc, argv);
int rank = MPI::COMM_WORLD.Get_rank();
if (rank == 0)
{
std::cout << "This is the main process\n";
times_table(12);
}
else if (rank == 1)
{
countdown();
}
else if (rank == 2)
{
long_loop();
}
else
{
std::cout << "I am not needed...\n";
}
MPI::Finalize();
return 0;
}Note that we have included the header file unistd.h to use the function sleep, to add one second pauses (via sleep(1)) within each function.
In this example we use the function MPI::COMM_WORLD.Get_rank(). This function returns the rank of the calling process. This allows the if block to be used to control which function is called by which process in the MPI process team. While it is possible to write the code within each block of the if statement directly, the code is more readable if you write each section as a function (e.g. countdown, long_loop and times_table) and just call the function from within each block.
You can compile this program using;
mpicxx mpi_sections.cpp -o mpi_sectionsThis will produce the executable, mpi_sections.