The Great and Terrible implementation of MPI-2

function index


Frees the datatype
int MPI_Type_free(
  MPI_Datatype *datatype


[in] datatype that is freed (handle)


Marks the datatype object associated with datatype for deallocation and sets datatype to MPI_DATATYPE_NULL. Any communication that is currently using this datatype will complete normally. Derived datatypes that were defined from the freed datatype are not affected.

Predefined types

The MPI standard states that (in Opaque Objects) qs MPI provides certain predefined opaque objects and predefined, static handles to these objects. Such objects may not be destroyed. qe

Thus, it is an error to free a predefined datatype. The same section makes it clear that it is an error to free a null datatype.

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).
Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).

Example Code

The following sample code illustrates MPI_Type_free.

#include "mpi.h"
#include <stdio.h>
int main(int argc, char *argv[])
    int myrank;
    MPI_Status status;
    MPI_Datatype type, type2;
    int buffer[100];
    MPI_Init(&argc, &argv);
    MPI_Type_contiguous( 100, MPI_CHAR, &type );
    MPI_Type_dup(type, &type2);
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
    if (myrank == 0)
        MPI_Send(buffer, 1, type2, 1, 123, MPI_COMM_WORLD);
else if (myrank == 1)
        MPI_Recv(buffer, 1, type2, 0, 123, MPI_COMM_WORLD, &status);
    return 0;