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Subject: Re: [OMPI users] Calling a variable from another processor
From: Jeff Squyres (jsquyres) (jsquyres_at_[hidden])
Date: 2014-01-09 06:39:19


MPI one-sided stuff is actually pretty complicated; I wouldn't suggest it for a beginner (I don't even recommend it for many MPI experts ;-) ).

Why not look at the MPI_SOURCE in the status that you got back from the MPI_RECV? In fortran, it would look something like (typed off the top of my head; forgive typos):

-----
integer, dimension(MPI_STATUS_SIZE) :: status
...
call MPI_Recv(buffer, ..., status, ierr)
-----

The rank of the sender will be in status(MPI_SOURCE).

On Jan 9, 2014, at 6:29 AM, Christoph Niethammer <niethammer_at_[hidden]> wrote:

> Hello,
>
> I suggest you have a look onto the MPI one-sided functionality (Section 11 of the MPI Spec 3.0).
> Create a window to allow the other processes to access the arrays A directly via MPI_Get/MPI_Put.
> Be aware of synchronization which you have to implement via MPI_Win_fence or manual locking.
>
> Regards
> Christoph
>
> --
>
> Christoph Niethammer
> High Performance Computing Center Stuttgart (HLRS)
> Nobelstrasse 19
> 70569 Stuttgart
>
> Tel: ++49(0)711-685-87203
> email: niethammer_at_[hidden]
> http://www.hlrs.de/people/niethammer
>
>
>
> ----- Ursprüngliche Mail -----
> Von: "Pradeep Jha" <pradeep_at_[hidden]>
> An: "Open MPI Users" <users_at_[hidden]>
> Gesendet: Donnerstag, 9. Januar 2014 12:10:51
> Betreff: [OMPI users] Calling a variable from another processor
>
>
>
>
>
> I am writing a parallel program in Fortran77. I have the following problem: 1) I have N number of processors.
> 2) Each processor contains an array A of size S.
> 3) Using some function, on every processor (say rank X), I calculate the value of two integers Y and Z, where Z<S. (the values of Y and Z are different on every processor)
> 4) I want to get the value of A(Z) on processor Y to processor X.
>
> I thought of first sending the numerical value X to processor Y from processor X and then sending A(Z) from processor Y to processor X. But it is not possible as processor Y does not know the numerical value X and so it won't know from which processor to receive the numerical value X from.
>
> I tried but I haven't been able to come up with any code which can implement this action. So I am not posting any codes.
>
> Any suggestions?
>
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-- 
Jeff Squyres
jsquyres_at_[hidden]
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