MPI_Win_create(3)

NAME
MPI_Win_create - One-sided MPI call that returns a window object for RMA operations.

SYNTAX

C Syntax
#include <mpi.h>
MPI_Win_create(void *base, MPI_Aint size, int disp_unit,
	MPI_Info info, MPI_Comm comm, MPI_Win *win)

Fortran Syntax (see FORTRAN 77 NOTES)
INCLUDE 'mpif.h'
MPI_WIN_CREATE(BASE, SIZE, DISP_UNIT, INFO, COMM, WIN, IERROR)
	<type> BASE(*)
	INTEGER(KIND=MPI_ADDRESS_KIND) SIZE
	INTEGER DISP_UNIT, INFO, COMM, WIN, IERROR

C++ Syntax
#include <mpi.h>
static MPI::Win MPI::Win::Create(const void* base,
	MPI::Aint size, int disp_unit, const
	MPI::Info& info, const MPI::Intracomm& comm)

INPUT PARAMETERS

base
    Initial address of window (choice).

size
    Size of window in bytes (nonnegative integer).

disp_unit
    Local unit size for displacements, in bytes (positive integer).

info
    Info argument (handle).

comm
    Communicator (handle).

OUTPUT PARAMETERS

win Window object returned by the call (handle).

IERROR
    Fortran only: Error status (integer).

DESCRIPTION
MPI_Win_create is a one-sided MPI communication collective call executed by all processes in the group of comm. 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 comm. The window consists of size bytes, starting at address base. A process may elect to expose no memory by specifying size = 0.

If the base 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.

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 disp_unit specified by the target process, at window creation.

The following info key is supported:

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.

NOTES
Common choices for disp_unit are 1 (no scaling), and (in C syntax) sizeof(type), for a window that consists of an array of elements of type type. 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.

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).

FORTRAN 77 NOTES
The MPI standard prescribes portable Fortran syntax for the SIZE argument only for Fortran 90. FORTRAN 77 users may use the non-portable syntax

     INTEGER*MPI_ADDRESS_KIND SIZE

where MPI_ADDRESS_KIND is a constant defined in mpif.h and gives the length of the declared integer in bytes.

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.

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.