Chapter Questions - Have fun with MPI in C

Point-to-Poit Communication Questions

What does it mean that an operation is posted?

a send or receive operation is started.

a send or receive operation is ended.

a send or receive operation is ended with an error.

MPI manages system memory..

that is used for sending and receiving messages.

that is used for buffering messages and for storing internal representations of various MPI objects such as groups, communicators, datatypes, etc.

that is used for allocate the user memory.

How many buffer MPI defines?

2, application and internal.

1, application.

1, internal.

3, application, internal and special.

What does the MPI_Buffer_detach do?

removes the buffer currently attached to the MPI buffer space.

removes the buffer currently attached to the user buffer space.

removes the buffer currently attached to the MPI and user buffer space.

MPI_INT?

is a datatype of MPI.

is the int definition of an integer value in C.

What is a MPI program?

An MPI program consists of one MPI process and a number of child processes.

An MPI program consists of autonomous processes, executing their own code.

Change the code in order to avoid the deadlock.

#include "mpi.h"
#include <stdio.h>
int main(argc,argv) int argc; char *argv[];
{
    int numtasks, rank, dest, source, rc, count, tag=1;  
    char inmsg, outmsg='x';
    MPI_Status Stat;
    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    if (rank == 0) {
        dest = 1;
        source = 1;
        rc = MPI_Recv(&inmsg, 1, MPI_CHAR, source, tag, MPI_COMM_WORLD, &Stat);
        rc = MPI_Send(&outmsg, 1, MPI_CHAR, dest, tag, MPI_COMM_WORLD);
    } else if (rank == 1) {
        dest = 0;
        source = 0;
        rc = MPI_Recv(&inmsg, 1, MPI_CHAR, source, tag, MPI_COMM_WORLD, &Stat);
        rc = MPI_Send(&outmsg, 1, MPI_CHAR, dest, tag, MPI_COMM_WORLD);
    }
    rc = MPI_Get_count(&Stat, MPI_CHAR, &count);
    printf("Task %d: Received %d char(s) from task %d with tag %d \n",
           rank, count, Stat.MPI_SOURCE, Stat.MPI_TAG);
    MPI_Finalize();
}

Write on the standard output of the process with rank=1 the total number of received characters.

#include "mpi.h"
#include <stdio.h>
int main(argc,argv) int argc; char *argv[];
{
    int numtasks, rank, dest, source, count;  
    char inmsg, outmsg='x';
    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    if (rank == 0) {
        MPI_Send(&outmsg, 1, MPI_CHAR, 1, 1, MPI_COMM_WORLD);
        MPI_Send(&outmsg, 1, MPI_CHAR, 1, 2, MPI_COMM_WORLD);
        MPI_Send(&outmsg, 1, MPI_CHAR, 1, 3, MPI_COMM_WORLD);
        MPI_Send(&outmsg, 1, MPI_CHAR, 1, 4, MPI_COMM_WORLD);
    } else {
        MPI_Recv(&inmsg, 1, MPI_CHAR, MPI_ANY_SOURCE, MPI_ANY_TAG, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    }
    MPI_Finalize();
}

Remove the deadlock using MPI_Isend and MPI_Irecv.

#include "mpi.h"
#include <stdio.h>
int main(argc,argv) int argc; char *argv[];
{
    int numtasks, rank, dest, source, rc, count, tag=1;  
    char inmsg, outmsg='x';
    MPI_Status Stat;
    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    if (rank == 0) {
        dest = 1;
        source = 1;
        rc = MPI_Recv(&inmsg, 1, MPI_CHAR, source, tag, MPI_COMM_WORLD, &Stat);
        rc = MPI_Send(&outmsg, 1, MPI_CHAR, dest, tag, MPI_COMM_WORLD);
    } else if (rank == 1) {
        dest = 0;
        source = 0;
        rc = MPI_Recv(&inmsg, 1, MPI_CHAR, source, tag, MPI_COMM_WORLD, &Stat);
        rc = MPI_Send(&outmsg, 1, MPI_CHAR, dest, tag, MPI_COMM_WORLD);
    }
    rc = MPI_Get_count(&Stat, MPI_CHAR, &count);
    printf("Task %d: Received %d char(s) from task %d with tag %d \n",
           rank, count, Stat.MPI_SOURCE, Stat.MPI_TAG);
    MPI_Finalize();
}

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