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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <mpi.h>
#define DATASIZE 64
#define WRITER_ID 0
void single_writer(int, int *, int);
void many_writers(int, int *, int);
int main(int argc, char *argv[])
{
int my_id, ntasks, i, localsize;
int *localvector;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &ntasks);
MPI_Comm_rank(MPI_COMM_WORLD, &my_id);
if (ntasks > 64) {
fprintf(stderr, "Datasize (64) should be divisible by number "
"of tasks.\n");
MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
}
if (DATASIZE % ntasks != 0) {
fprintf(stderr, "Datasize (64) should be divisible by number "
"of tasks.\n");
MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
}
localsize = DATASIZE / ntasks;
localvector = (int *) malloc(localsize * sizeof(int));
for (i = 0; i < localsize; i++) {
localvector[i] = i + 1 + localsize * my_id;
}
many_writers(my_id, localvector, localsize);
free(localvector);
MPI_Finalize();
return 0;
}
void single_writer(int my_id, int *localvector, int localsize)
{
FILE *fp;
int *fullvector;
fullvector = (int *) malloc(DATASIZE * sizeof(int));
MPI_Gather(localvector, localsize, MPI_INT, fullvector, localsize,
MPI_INT, WRITER_ID, MPI_COMM_WORLD);
if (my_id == WRITER_ID) {
if ((fp = fopen("singlewriter.dat", "wb")) == NULL) {
fprintf(stderr, "Error: %d (%s)\n", errno, strerror(errno));
MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
} else {
fwrite(fullvector, sizeof(int), DATASIZE, fp);
fclose(fp);
printf("Wrote %d elements to file singlewriter.dat\n", DATASIZE);
}
}
free(fullvector);
}
void many_writers(int my_id, int *localvector, int localsize)
{
FILE *fp;
char filename[64];
sprintf(filename, "manywriters-%d.dat", my_id);
if ((fp = fopen(filename, "wb")) == NULL) {
fprintf(stderr, "Error: %d (%s)\n", errno, strerror(errno));
MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
} else {
fwrite(localvector, sizeof(int), localsize, fp);
fclose(fp);
printf("Wrote %d elements to file manywriters-%d.dat\n", localsize,
my_id);
}
}