11.4. Dynamically loading libmpi at runtime

If you want to explicitly load Open MPI’s shared library libmpi at runtime by using dlopen() from C/C ++ or something like the ctypes package from Python, extra care is required. The default configuration of Open MPI uses dlopen() internally to load its support components. These components rely on symbols available in libmpi. In order to make the symbols in libmpi available to the components loaded by Open MPI at runtime, your application must load libmpi with the RTLD_GLOBAL option.

In C/C++, this option is specified as the second parameter to the POSIX dlopen(3) function.

When using ctypes with Python, this can be done with the second (optional) parameter to CDLL(). For example (shown below in Mac OS X, where Open MPI’s shared library name ends in .dylib; other operating systems use other suffixes, such as .so):

from ctypes import *

mpi = CDLL('libmpi.0.dylib', RTLD_GLOBAL)

f = pythonapi.Py_GetArgcArgv
argc = c_int()
argv = POINTER(c_char_p)()
f(byref(argc), byref(argv))
mpi.MPI_Init(byref(argc), byref(argv))

# Your MPI program here



The above is just an example showing dynamic loading. If you want to use MPI in Python, you are much better off using MPI4Py.

Other scripting languages should have similar options when dynamically loading shared libraries.