Example #4 (original) (raw)

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The following example is meant to illustrate ``safety'' between point-to-point and collective communication. MPI guarantees that a single communicator can do safe point-to-point and collective communication.

#define TAG_ARBITRARY 12345 #define SOME_COUNT 50

int main(int argc, char *argv[]) { int me; MPI_Request request[2]; MPI_Status status[2]; MPI_Group group_world, subgroup; int ranks[] = {2, 4, 6, 8}; MPI_Comm the_comm; ... MPI_Init(&argc, &argv); MPI_Comm_group(MPI_COMM_WORLD, &group_world);

 MPI_Group_incl(group_world, 4, ranks, &subgroup); /* local */ 
 MPI_Group_rank(subgroup, &me);     /* local */ 

 MPI_Comm_create(MPI_COMM_WORLD, subgroup, &the_comm); 

 if(me != MPI_UNDEFINED) 
 { 
     MPI_Irecv(buff1, count, MPI_DOUBLE, MPI_ANY_SOURCE, TAG_ARBITRARY, 
                       the_comm, request); 
     MPI_Isend(buff2, count, MPI_DOUBLE, (me+1)%4, TAG_ARBITRARY, 
                       the_comm, request+1); 
     for(i = 0; i < SOME_COUNT; i++) 
       MPI_Reduce(..., the_comm); 
     MPI_Waitall(2, request, status); 
 
     MPI_Comm_free(&the_comm); 
 } 

 MPI_Group_free(&group_world); 
 MPI_Group_free(&subgroup); 
 MPI_Finalize(); 
 return 0; 

}

Up: Motivating Examples Next: Library Example #1 Previous: (Approximate) Current Practice #3

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