The Great and Terrible implementation of MPI-2

function index


Create a datatype with a new lower bound and extent from an existing datatype
int MPI_Type_create_resized(
  MPI_Datatype oldtype,
  MPI_Aint lb,
  MPI_Aint extent,
  MPI_Datatype *newtype


[in] input datatype (handle)
[in] new lower bound of datatype (integer)
[in] new extent of datatype (integer)
[out] output datatype (handle)


Returns in newtype a handle to a new datatype that is identical to oldtype, except that the lower bound of this new datatype is set to be lb, and its upper bound is set to be lb + extent. Any previous lb and ub markers are erased, and a new pair of lower bound and upper bound markers are put in the positions indicated by the lb and extent arguments. This affects the behavior of the datatype when used in communication operations, with count >1, and when used in the construction of new derived datatypes.

Advice to users.

It is strongly recommended that users use this new function, rather than the old MPI-1 function to set and access lower bound, upper bound and extent of datatypes.

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_create_resized.

#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>
int main( int argc, char *argv[] )
    int errs = 0, i;
    int rank, size, source, dest;
    int count;
    int *buf;
    MPI_Comm comm;
    MPI_Status status;
    MPI_Datatype newtype;
    MPI_Init( &argc, &argv );
    comm = MPI_COMM_WORLD;
    /* Determine the sender and receiver */
    MPI_Comm_rank( comm, &rank );
    MPI_Comm_size( comm, &size );
    source = 0;
    dest = size - 1;

    MPI_Type_create_resized( MPI_INT, 0, 3 *
sizeof(int), &newtype );
    MPI_Type_commit( &newtype );
    for (count = 1; count < 65000; count = count * 2) {
        buf = (
int *)malloc( count * 3 * sizeof(int) );
        if (!buf) {
            MPI_Abort( comm, 1 );
for (i=0; i<3*count; i++) buf[i] = -1;
        if (rank == source) {
            for (i=0; i<count; i++) buf[3*i] = i;
            MPI_Send( buf, count, newtype, dest, 0, comm );
            MPI_Send( buf, count, newtype, dest, 1, comm );
        else if (rank == dest) {
            MPI_Recv( buf, count, MPI_INT, source, 0, comm, &status );
            for (i=0; i<count; i++) {
                if (buf[i] != i) {
                    printf( "buf[%d] = %d\n", i, buf[i] );fflush(stdout);
for (i=0; i<count*3; i++) buf[i] = -1;
            MPI_Recv( buf, count, newtype, source, 1, comm, &status );
for (i=0; i<count; i++) {
                if (buf[3*i] != i) {
                    printf( "buf[3*%d] = %d\n", i, buf[i] );fflush(stdout);
    MPI_Type_free( &newtype );
    return errs;