5.3.1. Partition Communication with Threads/Tasks Using OpenMP 4.0 or later

In the following the equal partitioning on send-side and receive-side Example Semantics of Partitioned Point-to-Point Communication is extended to utilize threads. In this case, the receive-side uses the same number of partitions as the send-side as in the previous example, but this example uses multiple threads on the send-side. Note that the MPI_PSEND_INIT and MPI_PRECV_INIT functions match each other like in the previous example.

Example Equal partitioning on send-side and receive-side using threads.

#include <stdlib.h> 
#include "mpi.h" 
#define NUM_THREADS 8 
#define PARTITIONS 8 
#define PARTLENGTH 16 
int main(int argc, char *argv[]) /* same send/recv partitioning */ 
{ 
  double message[PARTITIONS*PARTLENGTH]; 
  int partitions = PARTITIONS; 
  int partlength = PARTLENGTH; 
  int count = 1, source = 0, dest = 1, tag = 1, flag = 0; 
  int myrank; 
  int provided; 
  MPI_Request request; 
  MPI_Info info = MPI_INFO_NULL; 
  MPI_Datatype xfer_type; 
  MPI_Init_thread(&argc, &argv, MPI_THREAD_MULTIPLE, &provided); 
  if (provided < MPI_THREAD_MULTIPLE) 
     MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE); 
  MPI_Comm_rank(MPI_COMM_WORLD, &myrank); 
  MPI_Type_contiguous(partlength, MPI_DOUBLE, &xfer_type); 
  MPI_Type_commit(&xfer_type); 
  if (myrank == 0) 
  { 
     MPI_Psend_init(message, partitions, count, xfer_type, dest, tag, 
                    MPI_COMM_WORLD, info, &request); 
     MPI_Start(&request); 
 
     #pragma omp parallel for shared(request) num_threads(NUM_THREADS) 
     for (int i=0; i<partitions; i++) 
     { 
        /* compute and fill partition #i, then mark ready: */ 
        MPI_Pready(i, request); 
     } 
     while(!flag) 
     { 
        /* Do useful work */ 
        MPI_Test(&request, &flag, MPI_STATUS_IGNORE); 
        /* Do useful work */ 
     } 
     MPI_Request_free(&request); 
  } 
  else if (myrank == 1) 
  { 
     MPI_Precv_init(message, partitions, count, xfer_type, source, tag, 
                    MPI_COMM_WORLD, info, &request); 
     MPI_Start(&request); 
     while(!flag) 
     { 
        /* Do useful work */ 
        MPI_Test(&request, &flag, MPI_STATUS_IGNORE); 
        /* Do useful work */ 
     } 
     MPI_Request_free(&request); 
  } 
  MPI_Finalize(); 
  return 0; 
}