MPI_WIN_CREATE(3)				     Open MPI					 MPI_WIN_CREATE(3)

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 <#mpi-alloc-mem>, the size  of  the
       window can be no larger than the value set by the MPI_Alloc_mem <#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	<#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 <#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>/MPI_Init_thread <#mpi-init-thread>,
       after MPI_Finalize <#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 <#
       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>/MPI_Comm_spawn_multiple	<#
       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 <#mpi-abort> was called on that communicator. If called
	 on  a window or file, acts as if MPI_Abort <#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	<#mpi-comm-create-errhandler>	  then	   MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	 <#mpi-file-create-errhandler>	   then	    MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

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

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

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

       See also:

	  • MPI_Alloc_mem <#mpi-alloc-mem>

	  • MPI_Free_mem <#mpi-free-mem>

	  • MPI_Win_allocate <#mpi-win-allocate>

	  • MPI_Win_allocate_shared <#mpi-win-allocate-shared>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					 MPI_WIN_CREATE(3)
