[Mpi3-rma] Request-Based RMA Example

[William Gropp]

I've added this and posted an update to the wiki.  There are a few  
bugs in this; please check the wiki version.

Bill

On Apr 19, 2011, at 4:31 PM, James Dinan wrote:

> Hi All,
>
> Example is below, please give any feedback.  I'll work on  
> compressing this down the match the format in the writeup.
>
> Caption: The following example shows how request-based operations  
> can be used to overlap communication with computation.  Each process  
> fetches, processes, and writes the result for $NSTEPS$ chunks of  
> data.  Instead of a single buffer, $M$ local buffers are used to  
> allow up to $M$ communication operations to overlap with computation.
>
> ~Jim.
>
> ---snip---
>
> int i, j;
> MPI_Window  win;
> MPI_Request put_req[M] = { MPI_REQUEST_NULL };
> MPI_Request get_req;
> double      data[M][N];
>
> /* Create win: size M*N*sizeof(double), displacement unit MPI_DOUBLE  
> */
>
> MPI_Win_lock_all(0, win);
>
> for (i = 0; i < NSTEPS; i++) {
>  MPI_Waitany(M, put_req, &j, MPI_STATUS_IGNORE);
>  MPI_RGet(data[j], N, MPI_DOUBLE, target, i*N, N, MPI_DOUBLE, win,  
> &get_req);
>  MPI_Wait(get_req);
>  compute(i, data[M], ...);
>  MPI_RPut(data[j], N, MPI_DOUBLE, target, i*N, N, MPI_DOUBLE, win,  
> &R[j]);
> }
>
> MPI_Waitall(M, put_req, MPI_STATUSES_IGNORE);
> MPI_Win_unlock_all(win);
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William Gropp
Director, Parallel Computing Institute
Deputy Director for Research
Institute for Advanced Computing Applications and Technologies
Paul and Cynthia Saylor Professor of Computer Science
University of Illinois Urbana-Champaign