User datatypes

C | Fortran-2008 | Fortran-90

MPI_Type_commit

Definition

MPI_Type_commit must be called on user-defined datatypes before they may be used in communications. User-defined datatypes can be created via MPI_Type_contiguous, MPI_Type_vector, MPI_Type_create_hvector, MPI_Type_indexed, MPI_Type_create_hindexed, MPI_Type_create_indexed_block, MPI_Type_create_hindexed_block, MPI_Type_create_struct, MPI_Type_create_subarray, MPI_Type_create_darray. To free an MPI datatype created with MPI_Type_commit, see MPI_Type_free.

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int MPI_Type_commit(MPI_Datatype* datatype);

Return value

The error code returned from the type commit.

Example

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

/**
 * @brief Illustrates how to create a contiguous MPI datatype.
 * @details This program is meant to be run with 2 processes: a sender and a
 * receiver. These two MPI processes will exchange a message made of two
 * integers. To that end, they each create a datatype representing that layout.
 * The corresponding MPI_Datatype is created, then committed before being used
 * in communications, to eventually be freed.
 **/
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);
    }

    // Create the datatype
    MPI_Datatype double_int_type;
    MPI_Type_contiguous(2, MPI_INT, &double_int_type);

    // Commit the datatype so we can use it in communications
    MPI_Type_commit(&double_int_type);

    // 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:
        {
            // Send the message
            int buffer_sent[2] = {12345, 67890};
            printf("MPI process %d sends values %d and %d.\n", my_rank, buffer_sent[0], buffer_sent[1]);
            MPI_Send(&buffer_sent, 1, double_int_type, RECEIVER, 0, MPI_COMM_WORLD);
            break;
        }
        case RECEIVER:
        {
            // Receive the message
            int received[2];
            MPI_Recv(&received, 1, double_int_type, SENDER, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
            printf("MPI process %d received values: %d and %d.\n", my_rank, received[0], received[1]);
            break;
        }
    }

    // Free the datatype created
    MPI_Type_free(&double_int_type);

    MPI_Finalize();

    return EXIT_SUCCESS;
}