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Subject: Re: [OMPI users] MPI_Gatherv and 0 size?
From: Eugene Loh (Eugene.Loh_at_[hidden])
Date: 2009-02-23 15:55:49


I think the question is about passing NULL as a buffer pointer. E.g.,

MPI_Send(NULL, 0, mytype,dst, tag,comm);

vs

MPI_Send(&dummy,0,mytype,dst,tag,comm);

George Bosilca wrote:

> The only restriction the MPI standard impose on the sendcounts and
> recvcounts arrays is that the values be non-negative, so zero is a
> legal value.
>
> I don't really understand your second question. Where do you want to
> use NULL ? In general NULL is not accepted in MPI as an argument for
> any function ...
>
> On Feb 23, 2009, at 02:55 , jody wrote:
>
>> I have an application in which various processes create different
>> amounts of data (including no data at all).
>> I have found that MPI_Scatterv and MPI_Gatherv do work with arrays
>> sendcounts or receivecounts containing zeros.
>>
>> Since i didn't find the case of 0 sizes in the descriptions
>> of these functions in the MPI reference, i wondered whether
>> the use of zeroes is legal or if i was simply lucky that it worked.
>>
>> An other point: currently i use 1-sized buffers in the
>> case of a 0-sized data transfer.
>> Now if 0-sized data transfer is legal, would it be ok to
>> pass NULL for the buffer?
>