oracular (3) MPI_Win_create.openmpi.3.gz

Provided by: openmpi-doc_4.1.6-13.3ubuntu2_all bug

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)

       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

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.

SEE ALSO

       MPI_Alloc_mem MPI_Free_mem MPI_Win_allocate MPI_Win_allocate_shared