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. _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss