NAME¶
MPI_Op_create - Creates a user-defined combination function handle
SYNOPSIS¶
#include <mpi.h>
int MPI_Op_create(MPI_User_function func, int commute,
MPI_Op *pop)
- func
- - user defined function (function)
- commute
- - true if commutative; false otherwise.
OUTPUT PARAMETER¶
- pop
- - 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.
NOTES¶
When the
MPI_Op created by this function is no longer being used, it
should be freed with
MPI_Op_free .
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 (e.g.,
MPI_ERRORS_RETURN ), then no error may be indicated.
The reason for this is the performance problems that arise in ensuring that all
collective routines return the same error value.
ERRORS¶
If an error occurs in an MPI function, the current MPI error handler is called
to handle it. By default, this error handler aborts the MPI job. The error
handler may be changed with
MPI_Errhandler_set ; the predefined error
handler
MPI_ERRORS_RETURN may be used to cause error values to be
returned (in C and Fortran; this error handler is less useful in with the C++
MPI bindings. The predefined error handler
MPI::ERRORS_THROW_EXCEPTIONS
should be used in C++ if the error value needs to be recovered). Note that MPI
does
not guarantee that an MPI program can continue past an error.
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. The C++ bindings for MPI do not return error values; instead,
error values are communicated by throwing exceptions of type
MPI::Exception (but not by default). Exceptions are only thrown if the
error value is not
MPI::SUCCESS .
Note that if the
MPI::ERRORS_RETURN handler is set in C++, while MPI
functions will return upon an error, there will be no way to recover what the
actual error value was.
- MPI_SUCCESS
- - No error; MPI routine completed successfully.
- MPI_ERR_OP
- - Invalid operation. MPI operations (objects of type MPI_Op ) must
either be one of the predefined operations (e.g., MPI_SUM ) or
created with MPI_Op_create . Additionally, only certain datatypes
are alloed with given predefined operations. See MPI-1, section
4.9.2.
- MPI_ERR_ARG
- - Invalid argument. Some argument is invalid and is not identified by a
specific error class. This is typically a NULL pointer or other such
error.
- MPI_ERR_OTHER
- - This error is returned when some part of the LAM/MPI implementation is
unable to acquire memory.
SEE ALSO¶
MPI_Op_free
For more information, please see the official MPI Forum web site, which contains
the text of both the MPI-1 and MPI-2 standards. These documents contain
detailed information about each MPI function (most of which is not duplicated
in these man pages).
http://www.mpi-forum.org/
ACKNOWLEDGEMENTS¶
The LAM Team would like the thank the MPICH Team for the handy program to
generate man pages ("doctext" from
ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the initial
formatting, and some initial text for most of the MPI-1 man pages.
LOCATION¶
opcreate.c