Program Examples

#include <mpi.h> 
#include <pthread.h> 
#define n 2 
int thread_id[n]; 
MPI_Comm split_comm[n]; 
pthread_t thread[n]; 
void *worker(void *arg) { 
    int i = *((int*)arg), j = i; 
    MPI_Comm comm = split_comm[i]; 
    MPI_Allreduce(MPI_IN_PLACE, &j, 1, MPI_INT, MPI_SUM, comm); 
    printf("Thread %d: allreduce returned %d\n", i, j); 
} 
int main() { 
    MPI_Info info; 
    int i, provided; 
    char s[16]; 
    MPI_Init_thread(NULL, NULL, MPI_THREAD_MULTIPLE, &provided); 
    MPI_Info_create(&info); 
    for (i = 0; i < n; i++) { 
        MPI_Comm_dup(MPI_COMM_WORLD, &split_comm[i]); 
        sprintf(s, "%d", i); 
        MPI_Info_set(info, "thread_id", s); 
        MPI_Comm_set_info(split_comm[i], info); 
        thread_id[i] = i; 
        pthread_create(&thread[i], NULL, worker, (void*) &thread_id[i]); 
    } 
    for (i = 0; i < n; i++) { 
        pthread_join(thread[i], NULL); 
    } 
    MPI_Info_free(&info); 
    MPI_Finalize(); 
}

#include <mpi.h> 
#include <omp.h> 
#define n 2 
MPI_Comm split_comm[n]; 
int main() { 
    int i, provided; 
    MPI_Init_thread(NULL, NULL, MPI_THREAD_MULTIPLE, &provided); 
    for (i = 0; i < n; i++) 
        MPI_Comm_dup(MPI_COMM_WORLD, &split_comm[i]);                                                    
#pragma omp parallel for num_threads(n) 
    for (i = 0; i < n; i++) { 
        int j = i; 
        MPI_Allreduce(MPI_IN_PLACE, &j, 1, MPI_INT, MPI_SUM, split_comm[i]); 
        printf("Thread %d: allreduce returned %d\n", i, j); 
    } 
    MPI_Finalize(); 
}

#include <mpi.h>
#include <omp.h>
#define n 2
MPI_Comm split_comm[n];
int main() {
    MPI_Info info;
    int i, provided;
    char s[16];
    MPI_Init_thread(NULL, NULL, MPI_THREAD_MULTIPLE, &provided);
    MPI_Info_create(&info);
    for (i = 0; i < n; i++) {
        MPI_Comm_dup(MPI_COMM_WORLD, &split_comm[i]);
        sprintf(s, "%d", i);
        MPI_Info_set(info, "thread_id", s);
        MPI_Comm_set_info(split_comm[i], info);
    }
#pragma omp parallel num_threads(n)
    {
#pragma omp task
        {
            int j = 1;
            MPI_Allreduce(MPI_IN_PLACE, &j, 1, MPI_INT, MPI_SUM, split_comm[1]);
            printf("OMP thread %d, logical thread %d: allreduce returned %d\n",
                    omp_get_thread_num(), 1, j);
        }
#pragma omp task
        {
            int j = 0;
            MPI_Allreduce(MPI_IN_PLACE, &j, 1, MPI_INT, MPI_SUM, split_comm[0]);
            printf("OMP thread %d, logical thread %d: allreduce returned %d\n",
                    omp_get_thread_num(), 0, j);
        }
    }
    MPI_Info_free(&info);
    MPI_Finalize();
}