Question

I wish to send a contiguous array of memory between two nodes using MPI. For this purpose, I use the following Non-blocking Send/Receive command (MPI_Isend, MPI_Irecv). While executing the run command, I see two warning statements as follows:

Warning: Program exiting with outstanding receive requests

Basically, I want to see that the array data from “NorthEdge1” is passed to “NorthofNorthEdge3”. How could I fix this? What else could I try to check this communication?

Here is an excerpt from the source code:

 #define Rows 48 
 ...

 double *northedge1 = new double[Rows];
 double *northofnorthedge3 = new double[Rows];
 ...
 ...

 int main (int argc, char *argv[])
 {
  ....
  ....

   MPI_Request send_request, recv_request;
 ...
 ...
 {
   MPI_Isend(northedge1, Rows, MPI_DOUBLE, my_rank+1, 0, MPI_COMM_WORLD, &send_request);        
   MPI_Irecv(northofnorthedge3, Rows, MPI_DOUBLE, my_rank+1, MPI_ANY_TAG, MPI_COMM_WORLD,   
   &recv_request); 
 }

Answer 1

It looks like you haven’t called MPI_Waitall(). The “immediate” send and receive routines only begin the communication. You have to block your process to ensure the communication has finished. Blocking in MPI is with a variant of MPI_Wait(); in your case, you need MPI_Waitall().