The Great and Terrible implementation of MPI-2

function index


Adds a (key,value) pair to info
int MPI_Info_set(
  MPI_Info info,
  char *key,
  char *value

int MPI_Info_set(
  MPI_Info info,
  wchar_t *key,
  wchar_t *value


[in] info object (handle)
[in] key (string)
[in] value (string)


MPI_INFO_SET adds the (key,value) pair to info, and overrides the value if a value for the same key was previously set. key and value are null-terminated strings in C. In Fortran, leading and trailing spaces in key and value are stripped. If either key or value are larger than the allowed maximums, the errors MPI_ERR_INFO_KEY or MPI_ERR_INFO_VALUE are raised, respectively.

Thread and Interrupt Safety

The user is responsible for ensuring that multiple threads do not try to update the same MPI object from different threads. This routine should not be used from within a signal handler.

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 or null key string for info.
Invalid or null value string for info
This error is returned when some part of the MPICH implementation is unable to acquire memory.

Example Code

The following sample code illustrates MPI_Info_set.

#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main( int argc, char *argv[] )
int errs = 0;
    MPI_Info info1, infodup;
int nkeys, nkeysdup, i, vallen, flag, flagdup;
char key[MPI_MAX_INFO_KEY], keydup[MPI_MAX_INFO_KEY];
char value[MPI_MAX_INFO_VAL], valdup[MPI_MAX_INFO_VAL];
    MPI_Init( &argc, &argv );
    MPI_Info_create( &info1 );
    MPI_Info_set( info1, "host", "" );
    MPI_Info_set( info1, "file", "runfile.txt" );
    MPI_Info_set( info1, "soft", "2:1000:4,3:1000:7" );
    MPI_Info_dup( info1, &infodup );
    MPI_Info_get_nkeys( infodup, &nkeysdup );
    MPI_Info_get_nkeys( info1, &nkeys );
    if (nkeys != nkeysdup) {
        printf( "Dup'ed info has a different number of keys; is %d should be %d\n", nkeysdup, nkeys );fflush(stdout);
    vallen = MPI_MAX_INFO_VAL;
for (i=0; i<nkeys; i++) {
        /* MPI requires that the keys are in the same order after the dup */
        MPI_Info_get_nthkey( info1, i, key );
        MPI_Info_get_nthkey( infodup, i, keydup );
        if (strcmp(key, keydup)) {
            printf( "keys do not match: %s should be %s\n", keydup, key );fflush(stdout);
        vallen = MPI_MAX_INFO_VAL;
        MPI_Info_get( info1, key, vallen, value, &flag );
        MPI_Info_get( infodup, keydup, vallen, valdup, &flagdup );
        if (!flag || !flagdup) {
            printf( "Info get failed for key %s\n", key );fflush(stdout);
else if (strcmp( value, valdup )) {
            printf( "Info values for key %s not the same after dup\n", key );fflush(stdout);
    /* Change info and check that infodup does NOT have the new value (ensure that lazy dups are still duped) */
    MPI_Info_set( info1, "path", "/a:/b:/c/d" );
    MPI_Info_get( infodup, "path", vallen, value, &flag );
if (flag) {
        printf( "inserting path into info changed infodup\n" );fflush(stdout);

    MPI_Info_free( &info1 );
    MPI_Info_free( &infodup );

return errs;