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Sending

C | FORTRAN-legacy | FORTRAN-2008

MPI_Ssend

Definition

MPI_Ssend is the synchronous blocking send (the capital ’S’ standing for synchronous); it will block until the recipient has received the message. As a blocking send, MPI_Ssend guarantees that the buffer passed can be safely reused once MPI_Ssend returns. Also, this routine may be invoked implicitly by the standard blocking send (MPI_Send). Refer to MPI_Issend to see the non-blocking counterpart of this routine. Other blocking sends are MPI_Send, MPI_Bsend and MPI_Rsend.

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int MPI_Ssend(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 assign to the message.
communicator
The communicator in which the synchronous send takes place.

Returned value

The error code returned from the synchronous send.

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 synchronous 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:
        {
            // The "master" MPI process issues the MPI_Ssend.
            int buffer_sent = 12345;
            MPI_Request request;
            printf("MPI process %d sends value %d.\n", my_rank, buffer_sent);
            MPI_Ssend(&buffer_sent, 1, MPI_INT, RECEIVER, 0, MPI_COMM_WORLD);
            break;
        }
        case RECEIVER:
        {
            // The "slave" MPI process receives the message.
            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;
}