The Great and Terrible implementation of MPI-2

function index


Commits the datatype
int MPI_Type_commit(
  MPI_Datatype *datatype


[in] datatype (handle)


A datatype object has to be committed before it can be used in a communication. A committed datatype can still be used as a argument in datatype constructors. There is no need to commit basic datatypes. They are "pre-committed."

The commit operation commits the datatype, that is, the formal description of a communication buffer, not the content of that buffer. Thus, after a datatype has been committed, it can be repeatedly reused to communicate the changing content of a buffer or, indeed, the content of different buffers, with different starting addresses.

Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.


All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

No error; MPI routine completed successfully.
Invalid datatype argument. May be an uncommitted MPI_Datatype (see MPI_Type_commit).

Example Code

The following sample code illustrates MPI_Type_commit.

#include "mpi.h"
#include <stdio.h>
int main(int argc, char *argv[])
    int myrank;
    MPI_Status status;
    MPI_Datatype type;
    int buffer[100];
    MPI_Init(&argc, &argv);
    MPI_Type_contiguous( 100, MPI_CHAR, &type );
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
if (myrank == 0)
        MPI_Send(buffer, 1, type, 1, 123, MPI_COMM_WORLD);
else if (myrank == 1)
        MPI_Recv(buffer, 1, type, 0, 123, MPI_COMM_WORLD, &status);
    return 0;