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

/*

 *  (C) 2017 by Argonne National Laboratory.

 *      See COPYRIGHT in top-level directory.

 */

#include "mpiimpl.h"

/* Algorithm: Inplace Alltoallw

 *

 * We use pair-wise sendrecv_replace in order to conserve memory usage, which

 * is keeping with the spirit of the MPI-2.2 Standard.  But because of this

 * approach all processes must agree on the global schedule of sendrecv_replace

 * operations to avoid deadlock.

 *

 * Note that this is not an especially efficient algorithm in terms of time and

 * there will be multiple repeated malloc/free's rather than maintaining a

 * single buffer across the whole loop.  Something like MADRE is probably the

 * best solution for the MPI_IN_PLACE scenario.

 */

#undef FUNCNAME

#define FUNCNAME MPIR_Ialltoallw_sched_intra_inplace

#undef FCNAME

#define FCNAME MPL_QUOTE(FUNCNAME)

int MPIR_Ialltoallw_sched_intra_inplace(const void *sendbuf, const int sendcounts[],

                                        const int sdispls[], const MPI_Datatype sendtypes[],

                                        void *recvbuf, const int recvcounts[], const int rdispls[],

                                        const MPI_Datatype recvtypes[], MPIR_Comm * comm_ptr,

                                        MPIR_Sched_t s)

{

    int mpi_errno = MPI_SUCCESS;

    int comm_size, i, j;

    int dst, rank;

    int recv_extent;

    MPI_Aint true_extent, true_lb;

    int max_size;

    void *tmp_buf = NULL, *adj_tmp_buf = NULL;

    MPIR_SCHED_CHKPMEM_DECL(1);

    comm_size = comm_ptr->local_size;

    rank = comm_ptr->rank;

    /* The regular MPI_Alltoallw handles MPI_IN_PLACE using pairwise

     * sendrecv_replace calls.  We don't have a sendrecv_replace, so just

     * malloc the maximum of the counts array entries and then perform the

     * pairwise exchanges manually with schedule barriers instead.

     *

     * Because of this approach all processes must agree on the global

     * schedule of "sendrecv_replace" operations to avoid deadlock.

     *

     * This keeps with the spirit of the MPI-2.2 standard, which is to

     * conserve memory when using MPI_IN_PLACE for these routines.

     * Something like MADRE would probably generate a more optimal

     * algorithm. */

    max_size = 0;

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

        /* only look at recvtypes/recvcounts because the send vectors are

         * ignored when sendbuf==MPI_IN_PLACE */

        MPIR_Type_get_true_extent_impl(recvtypes[i], &true_lb, &true_extent);

        MPIR_Datatype_get_extent_macro(recvtypes[i], recv_extent);

        max_size = MPL_MAX(max_size, recvcounts[i] * MPL_MAX(recv_extent, true_extent));

    }

    MPIR_SCHED_CHKPMEM_MALLOC(tmp_buf, void *, max_size, mpi_errno, "Ialltoallw tmp_buf",

                              MPL_MEM_BUFFER);

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

        /* start inner loop at i to avoid re-exchanging data */

        for (j = i; j < comm_size; ++j) {

            if (rank == i && rank == j) {

                /* no need to "sendrecv_replace" for ourselves */

            } else if (rank == i || rank == j) {

                if (rank == i)

                    dst = j;

                else

                    dst = i;

                MPIR_Type_get_true_extent_impl(recvtypes[i], &true_lb, &true_extent);

                adj_tmp_buf = (void *) ((char *) tmp_buf - true_lb);

                mpi_errno = MPIR_Sched_send(((char *) recvbuf + rdispls[dst]),

                                            recvcounts[dst], recvtypes[dst], dst, comm_ptr, s);

                if (mpi_errno)

                    MPIR_ERR_POP(mpi_errno);

                mpi_errno =

                    MPIR_Sched_recv(adj_tmp_buf, recvcounts[dst], recvtypes[dst], dst, comm_ptr, s);

                if (mpi_errno)

                    MPIR_ERR_POP(mpi_errno);

                MPIR_SCHED_BARRIER(s);

                mpi_errno = MPIR_Sched_copy(adj_tmp_buf, recvcounts[dst], recvtypes[dst],

                                            ((char *) recvbuf + rdispls[dst]),

                                            recvcounts[dst], recvtypes[dst], s);

                if (mpi_errno)

                    MPIR_ERR_POP(mpi_errno);

                MPIR_SCHED_BARRIER(s);

            }

        }

    }

    MPIR_SCHED_CHKPMEM_COMMIT(s);

  fn_exit:

    return mpi_errno;

  fn_fail:

    MPIR_SCHED_CHKPMEM_REAP(s);

    goto fn_exit;

}