The Great and Terrible implementation of MPI-2

function index


Sets the print name for a communicator
int MPI_Comm_set_name(
  MPI_Comm comm,
  char *comm_name

int MPI_Comm_set_name(
  MPI_Comm comm,
  wchar_t *comm_name


[in] communicator to name (handle)
[in] Name for communicator (string)


MPI_COMM_SET_NAME allows a user to associate a name string with a communicator. The character string which is passed to MPI_COMM_SET_NAME will be saved inside the MPI library (so it can be freed by the caller immediately after the call, or allocated on the stack). Leading spaces in name are significant but trailing ones are not.

MPI_COMM_SET_NAME is a local (non-collective) operation, which only affects the name of the communicator as seen in the process which made the MPI_COMM_SET_NAME call. There is no requirement that the same (or any) name be assigned to a communicator in every process where it exists.

Advice to users.

Since MPI_COMM_SET_NAME is provided to help debug code, it is sensible to give the same name to a communicator in all of the processes where it exists, to avoid confusion.

The length of the name which can be stored is limited to the value of MPI_MAX_OBJECT_NAME in Fortran and MPI_MAX_OBJECT_NAME-1 in C and C++ to allow for the null terminator. Attempts to put names longer than this will result in truncation of the name. MPI_MAX_OBJECT_NAME must have a value of at least 64.

Advice to users.

Under circumstances of store exhaustion an attempt to put a name of any length could fail, therefore the value of MPI_MAX_OBJECT_NAME should be viewed only as a strict upper bound on the name length, not a guarantee that setting names of less than this length will always succeed.

Thread and Interrupt Safety

This routine is thread and interrupt safe only if no MPI routine that updates or frees the same MPI object may be called concurrently with this routine.

The MPI standard defined a thread-safe interface but this does not mean that all routines may be called without any thread locks. For example, two threads must not attempt to change the contents of the same MPI_Info object concurrently. The user is responsible in this case for using some mechanism, such as thread locks, to ensure that only one thread at a time makes use of this routine.

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 communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).

Example Code

The following sample code illustrates MPI_Comm_set_name.

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

int main( int argc, char *argv[] )
    int errs = 0;
    MPI_Comm comm;
int cnt, rlen;

    MPI_Init( &argc, &argv );

    nameout[0] = 0;
    MPI_Comm_get_name( MPI_COMM_WORLD, nameout, &rlen );
    printf( "Name of comm world is: %s\n", nameout );

    strcpy( name, "comm-0" );
    MPI_Comm_set_name( MPI_COMM_WORLD, name );
    nameout[0] = 0;
    MPI_Comm_get_name( MPI_COMM_WORLD, nameout, &rlen );
    printf( "Now the name of comm world is: %s\n", nameout );

    return 0;