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)

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 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).

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.

SEE ALSO

MPI_Alloc_mem MPI_Free_mem MPI_Win_allocate MPI_Win_allocate_shared