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

       Almost all MPI routines return an error value; C routines as  the  return  result  of  the  function  and
       Fortran routines in the last argument.

       Before  the  error  value  is  returned,  the current MPI error handler associated with the communication
       object (e.g., communicator, window, file) is called.  If no communication object is associated  with  the
       MPI  call,  then  the call is considered attached to MPI_COMM_SELF and will call the associated MPI error
       handler.  When  MPI_COMM_SELF  is  not  initialized   (i.e.,   before   MPI_Init/MPI_Init_thread,   after
       MPI_Finalize,  or  when using the Sessions Model exclusively) the error raises the initial error handler.
       The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF  when  using
       the  World  model,  or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/‐
       MPI_Comm_spawn_multiple.  If no other appropriate error handler has been set, then the  MPI_ERRORS_RETURN
       error  handler  is  called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
         called on a communicator, it acts as if MPI_Abort was called on  that  communicator.  If  called  on  a
         window  or file, acts as if MPI_Abort was called on a communicator containing the group of processes in
         the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

       • MPI_File_create_errhandler then MPI_File_set_errhandler

       • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

       • MPI_Win_create_errhandler then MPI_Win_set_errhandler

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.

       See the Error Handling section of the MPI-3.1 standard for more information.

       SEE ALSO:

          • MPI_Alloc_mem

          • MPI_Free_mem

          • MPI_Win_allocate

          • MPI_Win_allocate_shared

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       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                                 MPI_WIN_CREATE(3)