Appendix

MPI-enabled Python interpreter

Warning

These days it is no longer required to use the MPI-enabled Python interpreter in most cases, and, therefore, it is not built by default anymore because it is too difficult to reliably build a Python interpreter across different distributions. If you know that you still really need it, see below on how to use the build_exe and install_exe commands.

Some MPI-1 implementations (notably, MPICH 1) do require the actual command line arguments to be passed at the time MPI_Init() is called. In this case, you will need to use a re-built, MPI-enabled, Python interpreter binary executable. A basic implementation (targeting Python 2.X) of what is required is shown below:

#include <Python.h>
#include <mpi.h>

int main(int argc, char *argv[])
{
   int status, flag;
   MPI_Init(&argc, &argv);
   status = Py_Main(argc, argv);
   MPI_Finalized(&flag);
   if (!flag) MPI_Finalize();
   return status;
}

The source code above is straightforward; compiling it should also be. However, the linking step is more tricky: special flags have to be passed to the linker depending on your platform. In order to alleviate you for such low-level details, MPI for Python provides some pure-distutils based support to build and install an MPI-enabled Python interpreter executable:

$ cd mpi4py-X.X.X
$ python setup.py build_exe [--mpi=<name>|--mpicc=/path/to/mpicc]
$ [sudo] python setup.py install_exe [--install-dir=$HOME/bin]

After the above steps you should have the MPI-enabled interpreter installed as prefix/bin/pythonX.X-mpi (or $HOME/bin/pythonX.X-mpi). Assuming that prefix/bin (or $HOME/bin) is listed on your PATH, you should be able to enter your MPI-enabled Python interactively, for example:

$ python2.7-mpi
Python 2.7.8 (default, Nov 10 2014, 08:19:18)
[GCC 4.9.2 20141101 (Red Hat 4.9.2-1)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.executable
'/usr/bin/python2.7-mpi'
>>>

Building MPI from sources

In the list below you have some executive instructions for building some of the open-source MPI implementations out there with support for shared/dynamic libraries on POSIX environments.

• MPICH

  $ tar -zxf mpich-X.X.X.tar.gz
  $ cd mpich-X.X.X
  $ ./configure --enable-shared --prefix=/usr/local/mpich
  $ make
  $ make install
  

• Open MPI

  $ tar -zxf openmpi-X.X.X tar.gz
  $ cd openmpi-X.X.X
  $ ./configure --prefix=/usr/local/openmpi
  $ make all
  $ make install
  

• MPICH 1

  $ tar -zxf mpich-X.X.X.tar.gz
  $ cd mpich-X.X.X
  $ ./configure --enable-sharedlib --prefix=/usr/local/mpich1
  $ make
  $ make install
  

Perhaps you will need to set the LD_LIBRARY_PATH environment variable (using export, setenv or what applies to your system) pointing to the directory containing the MPI libraries . In case of getting runtime linking errors when running MPI programs, the following lines can be added to the user login shell script (.profile, .bashrc, etc.).

• MPICH

  MPI_DIR=/usr/local/mpich
  export LD_LIBRARY_PATH=$MPI_DIR/lib:$LD_LIBRARY_PATH
  

• Open MPI

  MPI_DIR=/usr/local/openmpi
  export LD_LIBRARY_PATH=$MPI_DIR/lib:$LD_LIBRARY_PATH
  

• MPICH 1

  MPI_DIR=/usr/local/mpich1
  export LD_LIBRARY_PATH=$MPI_DIR/lib/shared:$LD_LIBRARY_PATH:
  export MPICH_USE_SHLIB=yes
  

  Warning

  MPICH 1 support for dynamic libraries is not completely transparent. Users should set the environment variable MPICH_USE_SHLIB to yes in order to avoid link problems when using the mpicc compiler wrapper.