MPI_Win_allocate(3) Open MPI MPI_Win_allocate(3)
NAME
MPI_Win_allocate - One-sided MPI call that allocates memory and returns
a window object for RMA operations.
SYNTAX
C Syntax
#include <mpi.h>
int MPI_Win_allocate (MPI_Aint size, int disp_unit, MPI_Info info,
MPI_Comm comm, void *baseptr, MPI_Win *win)
Fortran Syntax
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_WIN_ALLOCATE(SIZE, DISP_UNIT, INFO, COMM, BASEPTR, WIN, IERROR)
INTEGER(KIND=MPI_ADDRESS_KIND) SIZE, BASEPTR
INTEGER DISP_UNIT, INFO, COMM, WIN, IERROR
Fortran 2008 Syntax
USE mpi_f08
MPI_Win_allocate(size, disp_unit, info, comm, baseptr, win, ierror)
USE, INTRINSIC :: ISO_C_BINDING, ONLY : C_PTR
INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: size
INTEGER, INTENT(IN) :: disp_unit
TYPE(MPI_Info), INTENT(IN) :: info
TYPE(MPI_Comm), INTENT(IN) :: comm
TYPE(C_PTR), INTENT(OUT) :: baseptr
TYPE(MPI_Win), INTENT(OUT) :: win
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
INPUT PARAMETERS
size Size of window in bytes (nonnegative integer).
disp_unit Local unit size for displacements, in bytes (positive inte-
ger).
info Info argument (handle).
comm Communicator (handle).
OUTPUT PARAMETERS
baseptr Initial address of window.
win Window object returned by the call (handle).
IERROR Fortran only: Error status (integer).
DESCRIPTION
MPI_Win_allocate is a collective call executed by all processes in the
group of comm. On each process, it allocates memory of at least size
bytes, returns a pointer to it, and returns a window object that can be
used by all processes in comm to perform RMA operations. The returned
memory consists of size bytes local to each process, starting at ad-
dress baseptr and is associated with the window as if the user called
MPI_Win_create on existing memory. The size argument may be different
at each process and size = 0 is valid; however, a library might allo-
cate and expose more memory in order to create a fast, globally symmet-
ric allocation. The discussion of and rationales for MPI_Alloc_mem and
MPI_Free_mem in MPI-3.1 § 8.2 also apply to MPI_Win_allocate; in par-
ticular, see the rationale in MPI-3.1 § 8.2 for an explanation of the
type used for baseptr.
The displacement unit argument is provided to facilitate address arith-
metic in RMA operations: the target displacement argument of an RMA op-
eration is scaled by the factor disp_unit specified by the target
process, at window creation.
For supported info keys see MPI_Win_create.
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.
ERRORS
Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument.
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.
SEE ALSO
MPI_Alloc_mem MPI_Free_mem MPI_Win_create MPI_Win_allocate_shared
4.1.2 Nov 24, 2021 MPI_Win_allocate(3)
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