Multiple Program Multiple Data programming with MPI

This is a simple C++ class to help to easily make programs for MPMD running. It is contained in a single .hpp file for ease of use.

Usage

The class can be used as a global static, or just as a local variable in main. Either way, you need to only initialize it after you initialize MPI:

   MPMDHelper MPMD;

   MPI_Init(&argc, &argv);

   MPMD.Init(MPI_COMM_WORLD, "my program");

Then, you can communicate within a single program through MPMD.local communicator, and with other programs with MPMD["other program"].local inter-communicator.

Additionaly, one can exclude some of the processes from the communication, which would be common in MPI programs with master-workers architecture.

You can use the library to combine programs both by running them simultaniously, and by dynamic spawning of processes:

Reference

Initialization

You initialize the helper object with name of the program:

   MPMD.Init(MPI_COMM_WORLD, "my program");

The name is used to split the common world communicator into smaller communicators. You can use the name of the executable as the name:

   MPMD.Init(MPI_COMM_WORLD, argv[0]);

If your program has a master-workers architecture, you can create a subgrup, by excluding the master process (for instance 0):

   std::vector<int> excl;
   excl.push_back(0);
   MPMD.Init(MPI_COMM_WORLD, "my program with workers", excl);

Communicators

After initialization, you can use:

• MPMD.world - the original MPI_COMM_WORLD
• MPMD.local - the communicator for the single program (the processes which declared the same name)
• MPMD.work - the communicator for the workers (all processes excluding excl)

Inter-communicators

You can communicate with other program (let's say B) with:

• MPMD["B"].local - inter-communicator with the whole B program
• MPMD["B"].work - inter-communicator with the worker processes of B

Spawn

You can also dynamically spawn processes:

MPMD.Spawn("./slave", MPI_ARGV_NULL, N, MPI_INFO_NULL);

After you do, you can access inter-communicators the same way as above

Running MPMD programs

The simplest way to run MPMD program with OpenMPI is:

mpirun -np 2 ./program_A : -np 3 ./program_B