Greates a new attribute key


int MPI_Keyval_create(MPI_Copy_function *copy_fn, 
                     MPI_Delete_function *delete_fn, 
                     int *keyval, void *extra_state)

Input Parameters

Copy callback function for keyval
Delete callback function for keyval
Extra state for callback functions

Output Parameters

key value for future access (integer)


Key values are global (available for any and all communicators).

There are subtle differences between C and Fortran that require that the copy_fn be written in the same language that MPI_Keyval_create is called from. This should not be a problem for most users; only programmers using both Fortran and C in the same program need to be sure that they follow this rule.

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.

Deprecated Function

The MPI-2 standard deprecated a number of routines because MPI-2 provides better versions. This routine is one of those that was deprecated. The routine may continue to be used, but new code should use the replacement routine. The replacement for this routine is MPI_Comm_create_keyval.

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.
This error is returned when some part of the MPICH implementation is unable to acquire memory.
Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).

See Also MPI_Keyval_free, MPI_Comm_create_keyval