MPI

Implementations

• Open MPI: [1]

Tips & Tricks

• For safe consecutive communications create new context, for example:

int communication_operation(MPI_Comm comm) {
MPI_Comm newcomm;
MPI_Comm_dup(comm, &newcomm);
... // work with newcomm
MPI_Comm_free(&newcomm);
}

Mind the overhead of MPI_Comm_dup and MPI_Comm_free.

Debugging

• Add the following code:

int rank;
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
if (!rank)
  getc(stdin);
MPI_Barrier(MPI_COMM_WORLD);

• Compile your code with -g option
• Run parallel application
• Attach to process(es) from GDB
  • MPICH-1 runs a background process for each application process: 0, 0b, 1, 1b, ..., therefore, attach to the first ones.