Ubuntu Manpage: MPI_Win_create - One-sided MPI call that returns a window object for RMA operations.

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 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.