MPI_Reduce_local − Applies a reduction operator to local arguments.
int MPI_Reduce_local(const void *inbuf, void *inoutbuf, int count, MPI_Datatype datatype, MPI_Op op)
- address of the input buffer (choice)
- number of elements in each buffer (integer)
- data type of elements in the buffers (handle)
- reduction operation (handle)
- address of input-output buffer (choice)
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.
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.
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.
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.
- No error; MPI routine completed successfully.
- Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
- Invalid datatype argument. Additionally, this error can occur if an uncommitted MPI_Datatype (see MPI_Type_commit ) is used in a communication call.
- Invalid buffer pointer. Usually a null buffer where one is not valid.
- This error class is associcated with an error code that indicates that two buffer arguments are aliased ; that is, the describe overlapping storage (often the exact same storage). This is prohibited in MPI (because it is prohibited by the Fortran standard, and rather than have a separate case for C and Fortran, the MPI Forum adopted the more restrictive requirements of Fortran).