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
);

Parameters

comm_copy_attr_fn

[in] Copy callback function for keyval

comm_delete_attr_fn

[in] Delete callback function for keyval

comm_keyval

[out] key value for future access (integer)

extra_state

[in] Extra state for callback functions

Remarks

Default copy and delete functions are available. These are

MPI_COMM_NULL_COPY_FN

empty copy function

MPI_COMM_NULL_DELETE_FN

empty delete function

MPI_COMM_DUP_FN

simple dup function

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

This function replaces MPI_KEYVAL_CREATE, whose use is deprecated. The C binding is identical. The Fortran binding differs in that extra_state is an address-sized integer. Also, the copy and delete callback functions have Fortran bindings that are consistent with address-sized attributes.

The argument comm_copy_attr_fn may be specified as MPI_COMM_NULL_COPY_FN or MPI_COMM_DUP_FN from either C, C++, or Fortran. MPI_COMM_NULL_COPY_FN is a function that does nothing other than returning flag = 0 and MPI_SUCCESS. MPI_COMM_DUP_FN is a simple-minded copy function that sets flag = 1, returns the value of attribute_val_in in attribute_val_out, and returns MPI_SUCCESS. These replace the MPI-1 predefined callbacks MPI_NULL_COPY_FN and MPI_DUP_FN, whose use is deprecated.

The argument comm_delete_attr_fn may be specified as MPI_COMM_NULL_DELETE_FN from either C, C++, or Fortran. MPI_COMM_NULL_DELETE_FN is a function that does nothing, other than returning MPI_SUCCESS. MPI_COMM_NULL_DELETE_FN replaces MPI_NULL_DELETE_FN, whose use is deprecated.

The C callback functions are:

typedef int MPI_Comm_copy_attr_function(MPI_Comm oldcomm, int comm_keyval, void *extra_state, void *attribute_val_in, void *attribute_val_out, int *flag);
 

and

typedef int MPI_Comm_delete_attr_function(MPI_Comm comm, int comm_keyval, void *attribute_val, void *extra_state);
 

which are the same as the MPI-1.1 calls but with a new name. The old names are deprecated.

The Fortran callback functions are:

SUBROUTINE COMM_COPY_ATTR_FN(OLDCOMM, COMM_KEYVAL, EXTRA_STATE, ATTRIBUTE_VAL_IN, ATTRIBUTE_VAL_OUT, FLAG, IERROR)
INTEGER OLDCOMM, COMM_KEYVAL, IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) EXTRA_STATE, ATTRIBUTE_VAL_IN,
ATTRIBUTE_VAL_OUT
LOGICAL FLAG
 

and

SUBROUTINE COMM_DELETE_ATTR_FN(COMM, COMM_KEYVAL, ATTRIBUTE_VAL, EXTRA_STATE, IERROR)
INTEGER COMM, COMM_KEYVAL, IERROR
INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE_VAL, EXTRA_STATE
 

The C++ callbacks are:

typedef int MPI::Comm::Copy_attr_function(const MPI::Comm& oldcomm, int comm_keyval, void* extra_state, void* attribute_val_in, void* attribute_val_out, bool& flag);
 

and

typedef int MPI::Comm::Delete_attr_function(MPI::Comm& comm, int comm_keyval, void* attribute_val, void* extra_state);

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.

See Also

Example Code

The following sample code illustrates MPI_Comm_create_keyval.