Re: [mpich-discuss] where mpi waitsome only returns one request each time

19 Oct 2014

      Because I want to understand the behavior of MPI_Waitsome, I change the program as fellow. MPI can waitsome 10 Isend request once time, while waitsome 1 Irecv request each time. Why waitsome-Irecv can not be more than 1 as I expect?
=====
     MPI_Init(&argc, &argv);
     MPI_Comm_size(MPI_COMM_WORLD, &size);
     MPI_Comm_rank(MPI_COMM_WORLD, &rank);

     if(rank==0) {
         for(i =0; i< 10;i++){
             MPI_Isend(buf[i], 10, MPI_BYTE, 1, 123, MPI_COMM_WORLD, &req[i]);
         }
         printf("post send\n");
     }else {
         for(i=0; i< 10;i++){
             MPI_Irecv(buf[i], 10, MPI_BYTE, 0, 123, MPI_COMM_WORLD, &req[i]);
         }
         printf("post recv\n");
     }

     for (;;){
         MPI_Waitsome(10, req, &outcount, array_of_indices, stat);
         complete += outcount;
         printf("rank %d %d index %d\n", rank, outcount, array_of_indices[0]);
         if(complete == 10)
             break;
     }
     printf("rank %d complete\n", rank);
     MPI_Finalize();
=====
$ mpirun -n 2 ./tests
post send
post recv
rank 0 10 index 0
rank 0 complete
rank 1 1 index 0
rank 1 1 index 1
rank 1 1 index 2
rank 1 1 index 3
rank 1 1 index 4
rank 1 1 index 5
rank 1 1 index 6
rank 1 1 index 7
rank 1 1 index 8
rank 1 1 index 9
rank 1 complete

At 2014-10-19 22:36:25, "Bland, Wesley B." <[email protected]> wrote:

You need to move your waitany outside of the if statement so both ranks execute it. 

On Oct 19, 2014, at 9:33 AM, myself <[email protected]> wrote:

Here is my test program

======

 #include "mpi.h"
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/time.h>

 typedef unsigned char byte;

 int main(int argc, char *argv[]){
     MPI_Init(&argc, &argv);
     int rank,size;
     MPI_Comm_size(MPI_COMM_WORLD, &size);
     MPI_Comm_rank(MPI_COMM_WORLD, &rank);
     byte buf[10][10];
     MPI_Request req[10];
     MPI_Status stat[10];
     int outcount;
     int array_of_indices[10];
     int i;

     if(rank==0) {
         for(i =0; i< 10;i++){
             MPI_Isend(buf[i], 10, MPI_BYTE, 1, 123, MPI_COMM_WORLD, &req[i]);
         }
         printf("post send\n");
         MPI_Waitall(10, req, stat);
         printf("send over\n");
     }else {
         for(i=0; i< 10;i++){
             MPI_Irecv(buf[i], 10, MPI_BYTE, 0, 123, MPI_COMM_WORLD, &req[i]);
         }

         printf("post recv\n");
         for (i=0;i<10;i++){
             MPI_Waitsome(10, req, &outcount, array_of_indices, stat);
             printf("%d index %d\n", outcount, array_of_indices[0]);
         }
     }
     MPI_Finalize();
 }

======
 get the result like this
======
$ mpirun -n 2 ./tests
post send
send over
post recv
1 index 0
1 index 1
1 index 2
1 index 3
1 index 4
1 index 5
1 index 6
1 index 7
1 index 8
1 index 9

======

I think I should get some completed receive connection, not just 1.

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