int MPI_Group_free(
  MPI_Group *group
);

Parameters

group

[in] group to free (handle)

Remarks

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

Errors

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.

MPI_SUCCESS

No error; MPI routine completed successfully.

MPI_ERR_ARG

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

MPI_ERR_ARG

This error class is associated with an error code that indicates that an attempt was made to free one of the permanent groups.

Example Code

The following sample code illustrates MPI_Group_free.

#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>
 
int main( int argc, char *argv[] )
{
    MPI_Group g1, g2, g4, g5, g45, selfgroup, g6;
    int ranks[16], size, rank, myrank, range[1][3];
    int errs = 0;
    int i, rin[16], rout[16], result;
 
    MPI_Init(0,0);
 
    MPI_Comm_group( MPI_COMM_WORLD, &g1 );
    MPI_Comm_rank( MPI_COMM_WORLD, &myrank );
    MPI_Comm_size( MPI_COMM_WORLD, &size );
    if (size < 8) {
        fprintf( stderr, "Test requires 8 processes (16 prefered) only %d provided\n", size ); fflush(stdout);
        MPI_Abort(MPI_COMM_WORLD, 1);
    }
 
    /* 16 members, this process is rank 0, return in group 1 */
    ranks[0] = myrank; ranks[1] = 2; ranks[2] = 7;
    if (myrank == 2) ranks[1] = 3;
    if (myrank == 7) ranks[2] = 6;
    MPI_Group_incl( g1, 3, ranks, &g2 );
 
    /* Check the resulting group */
    MPI_Group_size( g2, &size );
    MPI_Group_rank( g2, &rank );
 
    if (size != 3) {
        fprintf( stderr, "Size should be %d, is %d\n", 3, size );fflush(stderr);
        errs++;
    }
    if (rank != 0) {
        fprintf( stderr, "Rank should be %d, is %d\n", 0, rank );fflush(stderr);
        errs++;
    }
 
    rin[0] = 0; rin[1] = 1; rin[2] = 2;
    MPI_Group_translate_ranks( g2, 3, rin, g1, rout );
    for (i=0; i<3; i++) {
        if (rout[i] != ranks[i]) {
            fprintf( stderr, "translated rank[%d] %d should be %d\n", i, rout[i], ranks[i] );fflush(stderr);
            errs++;
        }
    }
 
    /* Translate the process of the self group against another group */
    MPI_Comm_group( MPI_COMM_SELF, &selfgroup );
    rin[0] = 0;
    MPI_Group_translate_ranks( selfgroup, 1, rin, g1, rout );
    if (rout[0] != myrank) {
        fprintf( stderr, "translated of self is %d should be %d\n", rout[0], myrank );fflush(stderr);
        errs++;
    }
 
    for (i=0; i<size; i++)
        rin[i] = i;
    MPI_Group_translate_ranks( g1, size, rin, selfgroup, rout );
    for (i=0; i<size; i++) {
        if (i == myrank && rout[i] != 0) {
            fprintf( stderr, "translated world to self of %d is %d\n", i, rout[i] );fflush(stderr);
            errs++;
        }
        else if (i != myrank && rout[i] != MPI_UNDEFINED) {
            fprintf( stderr, "translated world to self of %d should be undefined, is %d\n", i, rout[i] );
            errs++;
        }
    }
    MPI_Group_free( &selfgroup );
 
    /* Exclude everyone in our group */
    {
        int i, *ranks, g1size;
 
        MPI_Group_size( g1, &g1size );
 
        ranks = (int *)malloc( g1size * sizeof(int) );
        for (i=0; i<g1size; i++) ranks[i] = i;
        MPI_Group_excl( g1, g1size, ranks, &g6 );
        if (g6 != MPI_GROUP_EMPTY) {
            fprintf( stderr, "Group formed by excluding all ranks not empty\n" );fflush(stderr);
            errs++;
            MPI_Group_free( &g6 );
        }
        free( ranks );
    }
 
    MPI_Group_free( &g2 );
 
    range[0][0] = 1;
    range[0][1] = size-1;
    range[0][2] = 2;
    MPI_Group_range_excl( g1, 1, range, &g5 );
 
    range[0][0] = 1;
    range[0][1] = size-1;
    range[0][2] = 2;
    MPI_Group_range_incl( g1, 1, range, &g4 );
 
    MPI_Group_union( g4, g5, &g45 );
 
    MPI_Group_compare( MPI_GROUP_EMPTY, g4, &result );
    if (result != MPI_UNEQUAL) {
        errs++;
        fprintf( stderr, "Comparison with empty group gave %d, not 3\n", result );fflush(stderr);
    }
    MPI_Group_free( &g4 );
    MPI_Group_free( &g5 );
    MPI_Group_free( &g45 );
 
    /* Now, duplicate the test, but using negative strides */
    range[0][0] = size-1;
    range[0][1] = 1;
    range[0][2] = -2;
    MPI_Group_range_excl( g1, 1, range, &g5 );
 
    range[0][0] = size-1;
    range[0][1] = 1;
    range[0][2] = -2;
    MPI_Group_range_incl( g1, 1, range, &g4 );
 
    MPI_Group_union( g4, g5, &g45 );
 
    MPI_Group_compare( MPI_GROUP_EMPTY, g4, &result );
    if (result != MPI_UNEQUAL) {
        errs++;
        fprintf( stderr, "Comparison with empty group (formed with negative strides) gave %d, not 3\n", result );fflush(stderr);
    }
    MPI_Group_free( &g4 );
    MPI_Group_free( &g5 );
    MPI_Group_free( &g45 );
    MPI_Group_free( &g1 );
 
    MPI_Finalize();
    return 0;
}