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MPI_Win_create.3.rst

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MPI_Win_create

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

USE MPI
! or the older form: 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

Fortran 2008 Syntax

USE mpi_f08
MPI_Win_create(base, size, disp_unit, info, comm, win, ierror)
 TYPE(*), DIMENSION(..), ASYNCHRONOUS :: base
 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(MPI_Win), INTENT(OUT) :: win
 INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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 keys are supported:

no_locks

If set to true, then the implementation may assume that the local window is never locked (by a call to MPI_Win_lock or MPI_Win_lock_all). Setting this value if only active synchronization may allow the implementation to enable certain optimizations.

accumulate_ordering

By default, accumulate operations from one initiator to one target on the same window memory location are strictly ordered. If the info key accumulate_ordering is set to none, no ordering of accumulate operations guaranteed. They key can also be a comma-separated list of required orderings consisting of rar, war, raw, and waw for read-after-read, write-after-read, read-after-write, and write-after-write, respectively. Looser ordering constraints are likely to result in improved performance.

accumulate_ops

If set to same_op, the implementation will assume that all concurrent accumulate calls to the same target address will use the same operation. If set to same_op_no_op, then the implementation will assume that all concurrent accumulate calls to the same target address will use the same operation or MPI_NO_OP. The default is same_op_no_op.

same_size

If set to true, then the implementation may assume that the argument size is identical on all processes, and that all processes have provided this info key with the same value.

same_disp_unit

If set to true, then the implementation may assume that the argument disp_unit is identical on all processes, and that all processes have provided this info key with the same value.

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).

ERRORS

* MPI_Alloc_mem * MPI_Free_mem * MPI_Win_allocate * MPI_Win_allocate_shared