.TH MPI_Comm_create_keyval 3 "11/12/2019" " " "MPI"

.SH NAME

MPI_Comm_create_keyval \-  Create a new attribute key 

.SH SYNOPSIS

.nf

int MPI_Comm_create_keyval(MPI_Comm_copy_attr_function * comm_copy_attr_fn,

MPI_Comm_delete_attr_function * comm_delete_attr_fn,

int *comm_keyval, void *extra_state)

.fi

.SH INPUT PARAMETERS

.PD 0

.TP

.B comm_copy_attr_fn 

- Copy callback function for 

.I keyval

.PD 1

.PD 0

.TP

.B comm_delete_attr_fn 

- Delete callback function for 

.I keyval

.PD 1

.PD 0

.TP

.B extra_state 

- Extra state for callback functions

.PD 1

.SH OUTPUT PARAMETERS

.PD 0

.TP

.B comm_keyval 

- key value for future access (integer)

.PD 1

.SH NOTES

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

Default copy and delete functions are available.  These are

.PD 0

.TP

.B MPI_COMM_NULL_COPY_FN   

- empty copy function

.PD 1

.PD 0

.TP

.B MPI_COMM_NULL_DELETE_FN 

- empty delete function

.PD 1

.PD 0

.TP

.B MPI_COMM_DUP_FN         

- simple dup function

.PD 1

There are subtle differences between C and Fortran that require that the

copy_fn be written in the same language from which 

.I MPI_Comm_create_keyval

is called.

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.

.SH RETURN VALUE FROM ATTRIBUTE CALLBACKS

The MPI-2 versions of the attribute callbacks should return either

.I MPI_SUCCESS

on success or a valid MPI error code or class on failure.

The MPI standard is ambiguous on this point, but as MPI-2 provides

the routines 

.I MPI_Add_error_class

and 

.I MPI_Add_error_code

that allow the

user to define and use MPI error codes and classes.

.SH 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 

.I malloc

or other non-MPICH runtime routines that are themselves not interrupt-safe.

.SH NOTES FOR FORTRAN

All MPI routines in Fortran (except for 

.I MPI_WTIME

and 

.I MPI_WTICK

) have

an additional argument 

.I ierr

at the end of the argument list.  

.I 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

.I call

statement.

All MPI objects (e.g., 

.I MPI_Datatype

, 

.I MPI_Comm

) are of type 

.I INTEGER

in Fortran.

.SH ERRORS

All MPI routines (except 

.I MPI_Wtime

and 

.I 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 

.I MPI_Comm_set_errhandler

(for communicators),

.I MPI_File_set_errhandler

(for files), and 

.I MPI_Win_set_errhandler

(for

RMA windows).  The MPI-1 routine 

.I MPI_Errhandler_set

may be used but

its use is deprecated.  The predefined error handler

.I MPI_ERRORS_RETURN

may be used to cause error values to be returned.

Note that MPI does 

.B not

guarentee that an MPI program can continue past

an error; however, MPI implementations will attempt to continue whenever

possible.

.PD 0

.TP

.B MPI_SUCCESS 

- No error; MPI routine completed successfully.

.PD 1

.SH SEE ALSO

MPI_Comm_free_keyval

.br