MPI_Op_create(3) MPI MPI_Op_create(3)
NAME
MPI_Op_create - Creates a user-defined combination function handle
SYNOPSIS
int MPI_Op_create(MPI_User_function *function, int commute, MPI_Op *op)
INPUT PARAMETERS
function
- user defined function (function)
commute
- true if commutative; false otherwise. (logical)
OUTPUT PARAMETER
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 exam-
ple, 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
op_create.c
3/5/2011 MPI_Op_create(3)