[Mpi-forum] MPI_Comm_split_type question

[Jeff Hammond]

On Thu, Dec 15, 2016 at 10:29 AM, Guillaume Mercier <
guillaume.mercier at 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 at gmail.com
http://jeffhammond.github.io/
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