/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil ; -*- */

/*

 *

 *  (C) 2003 by Argonne National Laboratory.

 *      See COPYRIGHT in top-level directory.

 */

#include <mpi.h>

#include <stdio.h>

#include <assert.h>

#include "mpitest.h"

#define NSTEPS 100

#define N 1000

#define M 10

/* This is example 11.21 from the MPI 3.0 spec:

 *

 * 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.

 */

/* Use a global variable to inhibit compiler optimizations in the compute

 * function. */

double junk = 0.0;

void compute(int step, double *data)

{

    int i;

    for (i = 0; i < N; i++)

        junk += data[i] * (double) step;

}

int main(int argc, char *argv[])

{

    int i, rank, nproc;

    int errors = 0, all_errors = 0;

    MPI_Win win;

    MPI_Request put_req[M] = { MPI_REQUEST_NULL };

    MPI_Request get_req;

    double *baseptr;

    double data[M][N];          /* M buffers of length N */

    MPI_Info win_info;

    MPI_Init(&argc, &argv);

    MPI_Comm_rank(MPI_COMM_WORLD, &rank;;

    MPI_Comm_size(MPI_COMM_WORLD, &nproc);

    assert(M < NSTEPS);

    MPI_Info_create(&win_info);

#ifdef USE_WIN_ALLOC_SHM

    MPI_Info_set(win_info, "alloc_shm", "true");

#else

    MPI_Info_set(win_info, "alloc_shm", "false");

#endif

    MPI_Win_allocate(NSTEPS * N * sizeof(double), sizeof(double), win_info,

                     MPI_COMM_WORLD, &baseptr, &win);

    MPI_Win_lock_all(0, win);

    for (i = 0; i < NSTEPS; i++) {

        int target = (rank + 1) % nproc;

        int j;

        /* Find a free put request */

        if (i < M) {

            j = i;

        }

        else {

            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, MPI_STATUS_IGNORE);

        compute(i, data[j]);

        MPI_Rput(data[j], N, MPI_DOUBLE, target, i * N, N, MPI_DOUBLE, win, &put_req[j]);

    }

    MPI_Waitall(M, put_req, MPI_STATUSES_IGNORE);

    MPI_Win_unlock_all(win);

    MPI_Win_free(&win);

    MPI_Info_free(&win_info);

    MPI_Reduce(&errors, &all_errors, 1, MPI_INT, MPI_SUM, 0, MPI_COMM_WORLD);

    if (rank == 0 && all_errors == 0)

        printf(" No Errors\n");

    MPI_Finalize();

    return 0;

}