[Beowulf] Refactoring an MPI code to call from another MPI code

[Charlie Peck]

It’s hard to tell for certain without looking at the code, but I believe you want to use two different MPI communicators, one for each of the programs, see http://mpitutorial.com/tutorials/introduction-to-groups-and-communicators/

charlie

> On May 6, 2018, at 01:10, Navid Shervani-Tabar <nshervt at gmail.com> wrote:
> 
> Dear All,
> 
> I have a question which is more on the software side, and I was advised that I might find people with related expertise here.
> 
> I have two programs Main and Solver, each of which uses MPI for parallel processing. I am keeping Main as the main code and am modifying Solver as a subroutine which is being called by Main.
> 
> The problem arises when both codes initiate the MPI (since both were originally standalone programs) and then each have their own parallel structure, which leads the code to crash as MPI_init can only be called once in the now combined program.
> 
> I thought this must have been a common problem and there should be discussions on how to approach this; However, to my surprise, I couldn't find anything with this setting on common websites like stackoverflow and the archives of this mailing list. 
> 
> 
> 
> Thanks,
> 
> Navid
> 
> PS1: When connecting the two codes, I decided to call Solver by Main rather than running the Solver as an executable by Main to have a more optimized and robust setting and also avoid the overhead.
> 
> PS2: Code Main is written in c++ and code Solver is written in Fortran.
> 
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