yaxt_c_external.c

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/*
  --------------------------------------------------------------------
  Example plugin for the ICON Community Interface (ComIn)
  to demonstrate the usage of YAXT: External process.
 
  @authors 08/2021 :: ICON Community Interface  <icon@dwd.de>
 
  Note that in order to demonstrate ComIn's language interoperability,
  a similar plugin has been implemented in Fortran, see the subdirectory
  "yaxt_fortran".
  --------------------------------------------------------------------
 */
 
#include <stdio.h>
 
#include <mpi.h>
#include <mpi_handshake.h>
#include <yaxt.h>
 
double mean(double* data, int size) {
  double sum = 0;
  for (int i = 0; i < size; ++i)
    sum += data[i];
  return sum / size;
}
 
int main(int argc, char** argv) {
 
  MPI_Init(&argc, &argv);
 
  const char* group_names[] = {"comin", "yaxt_c_external"};
  MPI_Comm group_comms[2];
  mpi_handshake(group_names, group_comms, 2, MPI_COMM_WORLD);
 
  MPI_Comm plugin_comm;
  const char* plugin_comm_name = "yaxt_c";
  mpi_handshake(&plugin_comm_name, &plugin_comm, 1, group_comms[0]);
 
  xt_initialize(plugin_comm);
 
  int ncells               = atoi(argv[1]);
  struct Xt_stripe stripe  = {.start = 1, .stride = 1, .nstrides = ncells};
  Xt_idxlist tgt_idxlist   = xt_idxstripes_new(&stripe, 1);
  Xt_idxlist empty_idxlist = xt_idxempty_new();
 
  Xt_xmap xmap = xt_xmap_all2all_new(empty_idxlist, tgt_idxlist, plugin_comm);
 
  Xt_redist yaxt_redist = xt_redist_p2p_new(xmap, MPI_DOUBLE);
  xt_xmap_delete(xmap);
  xt_idxlist_delete(empty_idxlist);
  xt_idxlist_delete(tgt_idxlist);
 
  double* buffer = malloc(ncells * sizeof(*buffer));
  int ntimesteps = atoi(argv[2]);
  for (int i = 0; i < ntimesteps; ++i) {
    xt_redist_s_exchange1(yaxt_redist, NULL, buffer);
    // now we have the whole field available and can compute things
    printf("mean: %.2lf\n", mean(buffer, ncells));
  }
  MPI_Finalize();
  return 0;
}