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?

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     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." <wbland@anl.gov> 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 <chcdlf@126.com> 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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