MPI-/ calls may associate callback functions with MPI-/ objects: error handlers are associated with communicators and files, attribute copy and delete functions are associated with attribute keys, reduce operations are assciated with operation objects, etc. In a multilanguage environment, a function passed in an MPI-/ call in one language may be invoked by an MPI-/ call in another language. MPI-/ implementations must make sure that such invocation will use the calling convention of the language the function is bound to.
MPI-Standard for MARMOT