Re: [Boost-users] [mpi] what is the equivalent of MPI_COMM_SELF?

Subject: Re: [Boost-users] [mpi] what is the equivalent of MPI_COMM_SELF?
From: Matthias Troyer (troyer_at_[hidden])
Date: 2009-08-12 18:03:31

On Aug 12, 2009, at 2:41 PM, Alfredo Correa wrote:

>> Do you need this regularly? I have never seen any need for this
>> before. Have you have a real need?
>
> I just started using both MPI and Boost.MPI so I don't know, and most
> of the use is only investigative.
> I just found that sometimes replacing "world" by "self" can change
> from parallel syncronized behavior to unsyncronized behavior very
> easily, for example when debugging.
>
> here it is an example in which just changing WORLD by SELF changes de
> behavior of the program:
> https://computation.llnl.gov/casc/ppf/ppf.html
>
> But maybe you are right, maybe there is no real need and I can live
> without it. I noticed that world and self (or null) are treated
> asymmetrically in the Boost.MPI syntax. just that.

I never saw any need for using MPI_COMM_SELF in many years of parallel  
programming. When I want to debug using one process I just start the  
program using one process only.

As you write yourself, it is trivial to construct a communicator based  
on MPI_COMM_SELF - a single line. Furthermore you don't even need  
MPI_COMM_SELF. Even the MPI manual states that MPI_COMM_SELF is just  
convenience. Unless I see real demand I hesitate to add something to  
the library for which I have never seen any use in a real application.

Matthias