MPIExchangeBoundaries1D.c

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#include <stdlib.h>
#include <basic.h>
#include <arrayfunctions.h>
#include <mpivars.h>

int MPIExchangeBoundaries1D(
                              void    *m,     
                              double  *x,     
                              int     N,      
                              int     ghosts, 
                              int     dir,    
                              int     ndims   
                           )
{
#ifndef serial
  MPIVariables  *mpi = (MPIVariables*) m;
  int           i;
  
  int *ip     = mpi->ip;
  int *iproc  = mpi->iproc;
  int non      = 0; /* number of neighbours */

  int neighbor_rank[2] = {-1,-1};
  int nip[ndims];

  /* each process has 2 neighbors (except at physical boundaries)       */
  /* calculate the rank of these neighbors (-1 -> none)                 */
  _ArrayCopy1D_(ip,nip,ndims);  nip[dir]--;
  if (ip[dir] == 0)             neighbor_rank[0] = -1;
  else                          neighbor_rank[0] = MPIRank1D(ndims,iproc,nip);
  _ArrayCopy1D_(ip,nip,ndims);  nip[dir]++;
  if (ip[dir] == (iproc[dir]-1))neighbor_rank[1] = -1;
  else                          neighbor_rank[1] = MPIRank1D(ndims,iproc,nip);

  /* Allocate send and receive buffers */
  double sendbuf[2][ghosts], recvbuf[2][ghosts];

  /* count number of neighbors and copy data to send buffers */
  non = 0;
  if (neighbor_rank[0] != -1) {
    non++;
    for (i = 0; i < ghosts; i++) sendbuf[0][i] = x[i+ghosts];
  }
  if (neighbor_rank[1] != -1) {
    non++;
    for (i = 0; i < ghosts; i++) sendbuf[1][i] = x[i+N];
  }
  MPI_Request requests[2*non];
  MPI_Status  statuses[2*non];

  /* exchange the data */
  int tick = 0;
  if (neighbor_rank[0]!= -1) {
    MPI_Irecv(recvbuf[0],ghosts,MPI_DOUBLE,neighbor_rank[0],1631,mpi->world,&requests[tick]);
    MPI_Isend(sendbuf[0],ghosts,MPI_DOUBLE,neighbor_rank[0],1631,mpi->world,&requests[tick+non]);
    tick++;
  }
  if (neighbor_rank[1] != -1) {
    MPI_Irecv(recvbuf[1],ghosts,MPI_DOUBLE,neighbor_rank[1],1631,mpi->world,&requests[tick]);
    MPI_Isend(sendbuf[1],ghosts,MPI_DOUBLE,neighbor_rank[1],1631,mpi->world,&requests[tick+non]);
    tick++;
  }

  /* Wait till data transfer is done */
  MPI_Waitall(2*non,requests,statuses);

  /* copy received data to ghost points */
  if (neighbor_rank[0] != -1) for (i = 0; i < ghosts; i++) x[i]          = recvbuf[0][i];
  if (neighbor_rank[1] != -1) for (i = 0; i < ghosts; i++) x[i+N+ghosts] = recvbuf[1][i];
  
#endif
  return(0);
}