MPI Send and Receive

Processes and Pipes

     MPI_Send (
     void * data ,
     int count ,
     MPI_Datatype datatype ,
     int destination ,
     int tag ,
     MPI_Comm communicator )
 		      MPI_Recv (
     void * data ,
     int count ,
     MPI_Datatype datatype ,
     int source ,
     int tag ,
     MPI_Comm communicator ,
     MPI_Status * status )

Details

Same Tag Data Types

#include "mpi.h"
#include <stdio.h>
#include <string.h>

int main(int argc, char *argv[])  {
    int numtasks, rank, dest, source, rc, count,len;  
    char inmsg[30],outmsg0[]="Using Tag1", outmsg1[]="Again Using Tag1",
       outmsg2[]="Using Tag2",outmsg3[]=" Again Using Tag2";
    int Tag1=6,Tag2=10;  /*Just Random int s. There is a max size consideration.*/
    char name[MPI_MAX_PROCESSOR_NAME];
    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Get_processor_name(name, &len);
    if (rank == 0) {      
        dest = 1;
        source = 1;
        MPI_Send(&outmsg0,strlen(outmsg0), MPI_CHAR, dest, Tag1, MPI_COMM_WORLD);
        MPI_Send(&outmsg2,strlen(outmsg2), MPI_CHAR, dest, Tag2, MPI_COMM_WORLD);
        MPI_Send(&outmsg1,strlen(outmsg1), MPI_CHAR, dest, Tag1, MPI_COMM_WORLD);
        MPI_Send(&outmsg3,strlen(outmsg3), MPI_CHAR, dest, Tag2, MPI_COMM_WORLD);
        printf("\nTask 0 on processor %s has sent its  messages to Task 1. \n\n",name);
    } else if (rank == 1) {
        dest = 0;
        source = 0;
        memset(inmsg, 0, 30);
        MPI_Recv(&inmsg,30, MPI_CHAR, source, Tag2, MPI_COMM_WORLD,  MPI_STATUS_IGNORE);
        printf("Task 1 on processor %s listening for Tag2 received this  message:\n   %s\n",name,inmsg);
        memset(inmsg, 0, 30);
        MPI_Recv(&inmsg,30, MPI_CHAR, source, Tag2, MPI_COMM_WORLD,  MPI_STATUS_IGNORE);
        printf("Task 1 on processor %s listening for Tag2 received this  message:\n   %s\n",name,inmsg);
        memset(inmsg, 0, 30);
        MPI_Recv(&inmsg,30, MPI_CHAR, source, Tag1, MPI_COMM_WORLD,  MPI_STATUS_IGNORE);
        printf("Task 1 on processor %s listening for Tag1 received this  message:\n   %s\n",name,inmsg);
        memset(inmsg, 0, 30);
        MPI_Recv(&inmsg,30, MPI_CHAR, source, Tag1, MPI_COMM_WORLD,  MPI_STATUS_IGNORE);
        printf("Task 1 on processor %s listening for Tag1 received this  message:\n   %s\n",name,inmsg);
    }
    MPI_Finalize();
}



Different Tag Data Types

#include "mpi.h"
#include <stdio.h>
#include <string.h>

int main ( int argc , char *argv [])   {
     int numtasks , rank , dest , source , rc , count , len ;  
     char inmsg[30],inmsg1 [30], outmsg0 []= "Hello Task 1" ,
          outmsg1 []= "You are Welcome Task 0" , outmsg2 [ ]= "Another message from Task 0" ;
     int nummsg1 = 10 , nummsg2 = 7 , nummsg3 ;   /*Just Random int s.*/
     int Tag_char = 27 , Tag_int = 15 ;   /*Just Random int s. There is a max size consideration.*/
     char name [MPI_MAX_PROCESSOR_NAME];
     MPI_Init (&argc ,&argv );
     MPI_Comm_size ( MPI_COMM_WORLD , &numtasks );
     MPI_Comm_rank ( MPI_COMM_WORLD , &rank );
     MPI_Get_processor_name ( name , &len );
     if (rank==0) {      
         dest = 1 ;
         source = 1 ;
         MPI_Send (&outmsg0 , strlen ( outmsg0 ), MPI_CHAR , dest , Tag_char ,MPI_COMM_WORLD );
         MPI_Send (&nummsg1 , 1 , MPI_INT , dest , Tag_int , MPI_COMM_WORLD );
         MPI_Send (&outmsg2 , strlen ( outmsg2 ), MPI_CHAR , dest , Tag_char ,MPI_COMM_WORLD );
         printf( "\nTask 0 on processor %s has sent its  messages to Task 1. \n" , name );
         MPI_Recv (&nummsg3 , 1 , MPI_INT , source , Tag_int , MPI_COMM_WORLD,MPI_STATUS_IGNORE );
         memset(inmsg, 0, 30);
         MPI_Recv(&inmsg , 30 , MPI_CHAR , source , Tag_char , MPI_COMM_WORLD ,MPI_STATUS_IGNORE );
         printf( "Task 0 received this  message from Task 1:   %s\n" , inmsg );
         printf( "Task 0 also received this  message:   %i\n\n" , nummsg3 );
     } else if( rank == 1 ) {
         dest = 0 ;
         source = 0 ;
         memset(inmsg, 0, 30);
         MPI_Recv (&inmsg , 30 , MPI_CHAR , source , Tag_char , MPI_COMM_WORLD ,   MPI_STATUS_IGNORE );
         MPI_Recv (&nummsg3 , 1 , MPI_INT , source , Tag_int , MPI_COMM_WORLD ,   MPI_STATUS_IGNORE );
         printf ( "Task 1 on processor %s received this  message:   %s\n" , name , inmsg );
         memset(inmsg1, 0, 30);
         MPI_Recv (&inmsg1 , 30 , MPI_CHAR , source , Tag_char , MPI_COMM_WORLD ,   MPI_STATUS_IGNORE );
         printf ( "Task 1 also received this  message:   %i\n" , nummsg3 );
         printf ( "Task 1 received this  message as well: %s\n" , inmsg1 );
         printf ( "Task 1 has not sent its  message to Task 0 yet.\n\n" );
         MPI_Send (&outmsg1 , strlen (outmsg1), MPI_CHAR , dest , Tag_char , MPI_COMM_WORLD );
         MPI_Send (&nummsg2 , 1 , MPI_INT , dest , Tag_int , MPI_COMM_WORLD );
     }
     MPI_Finalize ();
}

 

  
Task 0 on processor tc-node157.red.lan has sent its  messages to Task 1.
Task 1 on processor tc-node158.red.lan received this  message:   Hello Task 1
Task 1 also received this  message:   10
Task 1 received this  message as well: Another message from Task 0
Task 1 has not sent its  message to Task 0 yet.

Task 0 received this  message from Task 1:   You are Welcome Task 0
Task 0 also received this  message:   7