NAME¶
MPI_Op_create - Creates a user-defined combination function handle
SYNOPSIS¶
int MPI_Op_create(MPI_User_function *user_fn, int commute, MPI_Op *op)
- user_fn
- - user defined function (function)
- commute
- - true if commutative; false otherwise. (logical)
OUTPUT PARAMETERS¶
- op
- - operation (handle)
NOTES ON THE USER FUNCTION¶
The calling list for the user function type is
typedef void (MPI_User_function) ( void * a,
void * b, int * len, MPI_Datatype * );
where the operation is
b[i] = a[i] op b[i] , for
i=0,...,len-1 . A
pointer to the datatype given to the MPI collective computation routine (i.e.,
MPI_Reduce ,
MPI_Allreduce ,
MPI_Scan , or
MPI_Reduce_scatter ) is also passed to the user-specified routine.
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 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.
NOTES ON COLLECTIVE OPERATIONS¶
The reduction functions (
MPI_Op ) do not return an error value. As a
result, if the functions detect an error, all they can do is either call
MPI_Abort or silently skip the problem. Thus, if you change the error
handler from
MPI_ERRORS_ARE_FATAL to something else, for example,
MPI_ERRORS_RETURN , then no error may be indicated.
The reason for this is the performance problems in ensuring that all collective
routines return the same error value.
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¶
MPI_Op_free
LOCATION¶
/tmp/gyCYfBi4J6/mpich-3.1/src/mpi/coll/op_create.c