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MPI_Send

Definition

MPI_Send sends a message in a blocking fashion. The routine returns upon completion; which can be reached in two ways. This routine will implicitly use an asynchronous send (MPI_Bsend) if there is enough space in the buffer attached to MPI (MPI_Buffer_attach) to buffer the message. Otherwise, it is the synchronous counterpart (MPI_Ssend) that will be invoked. Refer to MPI_Isend to see the non-blocking counterpart of this routine. Other blocking sends are MPI_Ssend, MPI_Bsend and MPI_Rsend.

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int MPI_Send(const void* buffer,
             int count,
             MPI_Datatype datatype,
             int recipient,
             int tag,
             MPI_Comm communicator);

Parameters

buffer
The buffer to send.
count
The number of elements to send.
datatype
The type of one buffer element.
recipient
The rank of the recipient MPI process.
tag
The tag to apply to the message.
communicator
The communicator in which the communication takes place.

Returned value

MPI_SUCCESS
The routine successfully completed.

Example

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#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>

/**
 * @brief Illustrates how to send a message in a blocking fashion.
 * @details This program is meant to be run with 2 processes: a sender and a
 * receiver.
 **/
int main(int argc, char* argv[])
{
    MPI_Init(&argc, &argv);

    // Get the number of processes and check only 2 processes are used
    int size;
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    if(size != 2)
    {
        printf("This application is meant to be run with 2 processes.\n");
        MPI_Abort(MPI_COMM_WORLD, EXIT_FAILURE);
    }

    // Get my rank and do the corresponding job
    enum role_ranks { SENDER, RECEIVER };
    int my_rank;
    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
    switch(my_rank)
    {
        case SENDER:
        {
            int buffer_sent = 12345;
            MPI_Request request;
            printf("MPI process %d sends value %d.\n", my_rank, buffer_sent);
            MPI_Send(&buffer_sent, 1, MPI_INT, RECEIVER, 0, MPI_COMM_WORLD);
            break;
        }
        case RECEIVER:
        {
            int received;
            MPI_Recv(&received, 1, MPI_INT, SENDER, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
            printf("MPI process %d received value: %d.\n", my_rank, received);
            break;
        }
    }

    MPI_Finalize();

    return EXIT_SUCCESS;
}