[Mpi3-tools] Meaning of meaning of unique_id in mqs_communicator?

Ashley Pittman ashley at pittman.co.uk
Mon May 11 11:37:45 CDT 2009

On Mon, 2009-05-11 at 09:54 -0500, Geoffrey R. Paulsen wrote:
> Ashley,
>   In reading HP-MPI source code, which has implemented the MSQ interface
> quite a while back, I believe that we return a value which conforms to
> the definition (b) below.

Thank you, that's good to know.

>  I'm not sure I understand the difference between (b) and (c).

The difference between (b) and (c) is best explained with reference to
MPI_COMM_SELF, in (b) it can have the same id in every process, in (c)
it has to have different values everywhere.  This has a practical
implication, in (c) you can say "Communicator X in this job is...", with
(b) to be able to describe the communicator you have to also include
some information about the communicator members, for example the global
rank of local rank zero.

In my opinion (c) would make the most logical sense and be easiest for
tools to work with however I know from my time working with MPI
libraries that (b) is a much more sensible option in reality.

Ashley Pittman.

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