openmpi/ompi/mpi/man/man3/MPI_Win_create.3

.\"Copyright 2007, Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.TH MPI_Win_create 3OpenMPI "March 2007" "Open MPI 1.2" " "
.SH NAME
\fBMPI_Win_create\fP \- One-sided MPI call that returns a window object for RMA operations.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
MPI_Win_create(void *\fIbase\fP, MPI_Aint \fIsize\fP, int \fIdisp_unit\fP, 
	MPI_Info \fIinfo\fP, MPI_Comm \fIcomm\fP, MPI_Win *\fIwin\fP)

.SH Fortran Syntax (see FORTRAN 77 NOTES)
.nf
INCLUDE 'mpif.h'
MPI_WIN_CREATE(\fIBASE, SIZE, DISP_UNIT, INFO, COMM, WIN, IERROR\fP)
	<type> \fIBASE\fP(*)
	INTEGER(KIND=MPI_ADDRESS_KIND) \fISIZE\fP
	INTEGER \fIDISP_UNIT, INFO, COMM, WIN, IERROR\fP

.SH C++ Syntax
.nf
#include <mpi.h>
static MPI::Win MPI::Win::Create(const void* \fIbase\fP, 
	MPI::Aint \fIsize\fP, int \fIdisp_unit\fP, const 
	MPI::Info& \fIinfo\fP, const MPI::Intracomm& \fIcomm\fP)

.SH INPUT PARAMETERS
.ft R
.TP 1i
base
Initial address of window (choice).
.TP 1i
size
Size of window in bytes (nonnegative integer).
.TP 1i
disp_unit
Local unit size for displacements, in bytes (positive integer).
.TP 1i
info
Info argument (handle).
.TP 1i
comm
Communicator (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
win
Window object returned by the call (handle). 
.TP 1i
IERROR
Fortran only: Error status (integer). 

.SH DESCRIPTION
.ft R
MPI_Win_create is a one-sided MPI communication collective call executed by all processes in the group of \fIcomm\fP that are in the same node. It returns a window object that can be used by these processes to perform RMA operations. Each process specifies a window of existing memory that it exposes to RMA accesses by the processes in the group of \fIcomm\fP. The window consists of \fIsize\fP bytes, starting at address \fIbase\fP. A process may elect to expose no memory by specifying \fIsize\fP = 0.
.sp
If the \fIbase\fP value used by MPI_Win_create was allocated by MPI_Alloc_mem, the size of the window can be no larger than the value set by the MPI_ALLOC_MEM function.
.sp
The displacement unit argument is provided to facilitate address arithmetic in RMA operations: the target displacement argument of an RMA operation is scaled by the factor \fIdisp_unit\fP specified by the target process, at window creation.
.sp
The following info key is supported:
.ft R
.TP 1i
no_locks 
If MPI_Win_lock is called on a window created with this info key, the
call will fail. If this info key is present, it is assumed that the
local window is never locked, allowing several internal checks to be
skipped, permitting a more efficient implementation.
.sp 

.SH NOTES
Common choices for \fIdisp_unit\fP are 1 (no scaling), and (in C syntax) \fIsizeof(type)\fP, for a window that consists of an array of elements of type \fItype\fP. The later choice will allow one to use array indices in RMA calls, and have those scaled correctly to byte displacements, even in a heterogeneous environment. 
.sp
Use memory allocated by MPI_Alloc_mem to guarantee properly aligned window boundaries (such as word, double-word, cache line, page frame, and so on).
.sp
If the base address argument specified in the MPI_Win_create call
points to a memory region allocated using MPI_Alloc_mem, any permissions
or effective uid/gid paremeters specified in the info key passed to
the MPI_Alloc_mem call will overwrite the ones specified in the
MPI_Win_create call. 
.sp
If infokeys are not specified in MPI_Alloc_mem but used in
MPI_Win_create, then default infokey values are used and not the ones
specified in MPI_Win_create. 


.SH FORTRAN 77 NOTES
.ft R
The MPI standard prescribes portable Fortran syntax for
the \fISIZE\fP argument only for Fortran 90. FORTRAN 77
users may use the non-portable syntax
.sp
.nf
     INTEGER*MPI_ADDRESS_KIND \fISIZE\fP
.fi
.sp
where MPI_ADDRESS_KIND is a constant defined in mpif.h
and gives the length of the declared integer in bytes.

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI:Exception object.
.sp
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.