On Thu, Dec 15, 2016 at 10:29 AM, Guillaume Mercier <guillaume.mercier@u-bordeaux.fr> wrote:

Hi Jeff,

On 15/12/2016 18:48, Jeff Hammond wrote:
The number of output communicators from MPI_Comm_split(_type) is always
one.

 Yes, obviously.

Different ranks may get different outputs, but one cannot transfer
a communicator object from one rank to another.

 That's my issue actually.

If you want to do how many total output communicators there are, you can
perform an MPI_Allgather on the color arguments and see how many unique
values there are.

 I'm not sure about that: tae the case of MPI_Comm_split_type with
MPI_COMM_TYPE_SHARED. According to tha standards :"this type splits
the communicator into subcommunicators each of which can create  a shared memory region".
So, there is only one color, but several subcommunicators.
Or am I understanding this the wrong way?


Each rank gets its own subcommunicator object that captures the ranks of the shared memory domain, as supported by MPI_Win_allocate_shared.

I'm still not sure I understand what the issue is.  What are you trying to do?

Jeff
 
Regards
Guillaume

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--
Jeff Hammond
jeff.science@gmail.com
http://jeffhammond.github.io/