text: /* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil ; -*- */
  /*
   *  (C) 2001 by Argonne National Laboratory.
   *      See COPYRIGHT in top-level directory.
   */
  #include "mpi.h"
  #include <stdlib.h>
  #include <string.h>
  #include <stdio.h>
  
  /* A 32^3 array. For other array sizes, change array_of_gsizes below. */
  
  /* Uses collective I/O. Writes a 3D block-distributed array to a file
     corresponding to the global array in row-major (C) order, reads it
     back, and checks that the data read is correct. */
  
  /* The file name is taken as a command-line argument. */
  
  /* Note that the file access pattern is noncontiguous. */
  
  void handle_error(int errcode, const char *str);
  
  void handle_error(int errcode, const char *str)
  {
  	char msg[MPI_MAX_ERROR_STRING];
  	int resultlen;
  	MPI_Error_string(errcode, msg, &resultlen);
  	fprintf(stderr, "%s: %s\n", str, msg);
  	MPI_Abort(MPI_COMM_WORLD, 1);
  }
  
  int main(int argc, char **argv)
  {
      MPI_Datatype newtype;
      int i, ndims, array_of_gsizes[3], array_of_distribs[3];
      int order, nprocs, j, len;
      int array_of_dargs[3], array_of_psizes[3];
      int *readbuf, *writebuf, mynod, *tmpbuf, array_size;
      MPI_Count bufcount;
      char *filename;
      int errs=0, toterrs;
      MPI_File fh;
      MPI_Status status;
      MPI_Request request;
      MPI_Info info = MPI_INFO_NULL;
      int errcode;
  
      MPI_Init(&argc,&argv);
      MPI_Comm_rank(MPI_COMM_WORLD, &mynod);
      MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
  
  /* process 0 takes the file name as a command-line argument and
     broadcasts it to other processes */
      if (!mynod) {
  	i = 1;
  	while ((i < argc) && strcmp("-fname", *argv)) {
  	    i++;
  	    argv++;
  	}
  	if (i >= argc) {
  	    fprintf(stderr, "\n*#  Usage: coll_test -fname filename\n\n");
  	    MPI_Abort(MPI_COMM_WORLD, 1);
  	}
  	argv++;
  	len = strlen(*argv);
  	filename = (char *) malloc(len+1);
  	strcpy(filename, *argv);
  	MPI_Bcast(&len, 1, MPI_INT, 0, MPI_COMM_WORLD);
  	MPI_Bcast(filename, len+1, MPI_CHAR, 0, MPI_COMM_WORLD);
      }
      else {
  	MPI_Bcast(&len, 1, MPI_INT, 0, MPI_COMM_WORLD);
  	filename = (char *) malloc(len+1);
  	MPI_Bcast(filename, len+1, MPI_CHAR, 0, MPI_COMM_WORLD);
      }
  
  
  /* create the distributed array filetype */
      ndims = 3;
      order = MPI_ORDER_C;
  
      array_of_gsizes[0] = 32;
      array_of_gsizes[1] = 32;
      array_of_gsizes[2] = 32;
  
      array_of_distribs[0] = MPI_DISTRIBUTE_BLOCK;
      array_of_distribs[1] = MPI_DISTRIBUTE_BLOCK;
      array_of_distribs[2] = MPI_DISTRIBUTE_BLOCK;
  
      array_of_dargs[0] = MPI_DISTRIBUTE_DFLT_DARG;
      array_of_dargs[1] = MPI_DISTRIBUTE_DFLT_DARG;
      array_of_dargs[2] = MPI_DISTRIBUTE_DFLT_DARG;
  
      for (i=0; i<ndims; i++) array_of_psizes[i] = 0;
      MPI_Dims_create(nprocs, ndims, array_of_psizes);
  
      MPI_Type_create_darray(nprocs, mynod, ndims, array_of_gsizes,
  			   array_of_distribs, array_of_dargs,
  			   array_of_psizes, order, MPI_INT, &newtype);
      MPI_Type_commit(&newtype);
  
  /* initialize writebuf */
  
      MPI_Type_size_x(newtype, &bufcount);
      bufcount = bufcount/sizeof(int);
      writebuf = (int *) malloc(bufcount * sizeof(int));
      for (i=0; i<bufcount; i++) writebuf[i] = 1;
  
      array_size = array_of_gsizes[0]*array_of_gsizes[1]*array_of_gsizes[2];
      tmpbuf = (int *) calloc(array_size, sizeof(int));
      MPI_Irecv(tmpbuf, 1, newtype, mynod, 10, MPI_COMM_WORLD, &request);
      MPI_Send(writebuf, bufcount, MPI_INT, mynod, 10, MPI_COMM_WORLD);
      MPI_Wait(&request, &status);
  
      j = 0;
      for (i=0; i<array_size; i++)
  	if (tmpbuf[i]) {
  	    writebuf[j] = i;
  	    j++;
  	}
      free(tmpbuf);
  
      if (j != bufcount) {
  	fprintf(stderr, "Error in initializing writebuf on process %d\n", mynod);
  	MPI_Abort(MPI_COMM_WORLD, 1);
      }
  /* end of initialization */
  
      /* write the array to the file */
      errcode = MPI_File_open(MPI_COMM_WORLD, filename,
  		    MPI_MODE_CREATE | MPI_MODE_RDWR, info, &fh);
      if (errcode != MPI_SUCCESS) handle_error(errcode, "MPI_File_open");
  
      errcode = MPI_File_set_view(fh, 0, MPI_INT, newtype, "native", info);
      if (errcode != MPI_SUCCESS) handle_error(errcode, "MPI_File_set_view");
  
      errcode = MPI_File_write_all(fh, writebuf, bufcount, MPI_INT, &status);
      if (errcode != MPI_SUCCESS) handle_error(errcode, "MPI_File_write_all");
      errcode = MPI_File_close(&fh);
      if (errcode != MPI_SUCCESS) handle_error(errcode, "MPI_File_close");
  
      if (!mynod) {
          /* wkl suggests potential for false " No Errors" if both read
  	 * and write use the same file view */
          /* solution: rank 0 reads entire file and checks write values */
  	errcode = MPI_File_open(MPI_COMM_SELF, filename,
  			MPI_MODE_RDONLY, info, &fh);
          if (errcode != MPI_SUCCESS) handle_error(errcode, "MPI_File_open");
  
          readbuf = (int *) malloc(array_size * sizeof(int));
          errcode = MPI_File_read(fh, readbuf, array_size, MPI_INT, &status);
          if (errcode != MPI_SUCCESS) handle_error(errcode, "MPI_File_read");
  
          errcode = MPI_File_close(&fh);
          if (errcode != MPI_SUCCESS) handle_error(errcode, "MPI_File_close");
  
          for (i=0; i<array_size; i++)
              if (readbuf[i] != i) {
                  errs++;
                  fprintf(stderr, "Error: write integer %d but read %d\n",
  				i,readbuf[i]);
                  break;
              }
          free(readbuf);
      }
      MPI_Barrier(MPI_COMM_WORLD);
  
      /* now read it back */
      readbuf = (int *) malloc(bufcount * sizeof(int));
      errcode = MPI_File_open(MPI_COMM_WORLD, filename,
  		    MPI_MODE_CREATE | MPI_MODE_RDWR, info, &fh);
      if (errcode != MPI_SUCCESS) handle_error(errcode, "MPI_File_open");
  
      errcode = MPI_File_set_view(fh, 0, MPI_INT, newtype, "native", info);
      if (errcode != MPI_SUCCESS) handle_error(errcode, "MPI_File_set_view");
      errcode = MPI_File_read_all(fh, readbuf, bufcount, MPI_INT, &status);
      if (errcode != MPI_SUCCESS) handle_error(errcode, "MPI_File_read_all");
      errcode = MPI_File_close(&fh);
      if (errcode != MPI_SUCCESS) handle_error(errcode, "MPI_File_close");
  
      /* check the data read */
      for (i=0; i<bufcount; i++) {
  	if (readbuf[i] != writebuf[i]) {
  	    errs++;
  	    fprintf(stderr, "Process %d, readbuf %d, writebuf %d, i %d\n", mynod, readbuf[i], writebuf[i], i);
  	}
      }
  
      MPI_Allreduce( &errs, &toterrs, 1, MPI_INT, MPI_SUM, MPI_COMM_WORLD );
      if (mynod == 0) {
  	if( toterrs > 0) {
  	    fprintf( stderr, "Found %d errors\n", toterrs );
  	}
  	else {
  	    fprintf( stdout, " No Errors\n" );
  	}
      }
  
      MPI_Type_free(&newtype);
      free(readbuf);
      free(writebuf);
      free(filename);
  
      MPI_Finalize();
      return 0;
  }
  