Dave,
i made PR #1644 to abort with a user friendly error message
https://github.com/open-mpi/ompi/pull/1644
Cheers,
Gilles
On 5/5/2016 2:05 AM, Dave Love wrote:
Gilles Gouaillardet <gilles.gouaillar...@gmail.com> writes:
Dave,
yes, this is for two MPI tasks only.
the MPI subroutine could/should return with an error if the communicator is
made of more than 3 tasks.
an other option would be to abort at initialization time if no collective
modules provide a barrier implementation.
or maybe the tuned module should have not used the two_procs algorithm, but
what should it do instead ? use a default one ? do not implement barrier ?
warn/error the end user ?
note the error message might be a bit obscure.
I write "could" because you explicitly forced something that cannot work,
and I am not convinced OpenMPI should protect end users from themselves,
even when they make an honest mistake.
I just looped over the available algorithms, not expecting any not to
work. One question is how I'd know it can't work; I can't find
documentation on the algorithms, just the more-or-less suggestive names
that I might be able to find in the literature, or not. Is there a good
place to look?
In the absence of a good reason why not -- I haven't looked at the code
-- but I'd expect it to abort with a message about the algorithm being
limited to two processes at some stage. Of course, this isn't a common
case, and people probably have more important things to do.
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