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.TH "MPI_WIN_CREATE" "3" "May 30, 2025" "" "Open MPI"
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.sp
\fI\%MPI_Win_create\fP — One\-sided MPI call that returns a window object for
RMA operations.
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#include <mpi.h>

MPI_Win_create(void *base, MPI_Aint size, int disp_unit,
     MPI_Info info, MPI_Comm comm, MPI_Win *win)
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE MPI
! or the older form: INCLUDE \(aqmpif.h\(aq
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
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran 2008 Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
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
.ft P
.fi
.UNINDENT
.UNINDENT
.SH INPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBbase\fP: Initial address of window (choice).
.IP \(bu 2
\fBsize\fP: Size of window in bytes (nonnegative integer).
.IP \(bu 2
\fBdisp_unit\fP: Local unit size for displacements, in bytes (positive integer).
.IP \(bu 2
\fBinfo\fP: Info argument (handle).
.IP \(bu 2
\fBcomm\fP: Communicator (handle).
.UNINDENT
.SH OUTPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBwin\fP: Window object returned by the call (handle).
.IP \(bu 2
\fBierror\fP: Fortran only: Error status (integer).
.UNINDENT
.SH DESCRIPTION
.sp
\fI\%MPI_Win_create\fP is a one\-sided MPI communication collective call executed
by all processes in the group of \fIcomm\fP\&. 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 \fIcomm\fP\&. The window consists of \fIsize\fP
bytes, starting at address \fIbase\fP\&. A process may elect to expose no
memory by specifying \fIsize\fP = 0.
.sp
If the \fIbase\fP value used by \fI\%MPI_Win_create\fP was allocated by
\fI\%MPI_Alloc_mem\fP, the size of the window can be no larger than the value
set by the \fI\%MPI_Alloc_mem\fP function.
.sp
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 \fIdisp_unit\fP specified by the target
process, at window creation.
.sp
The following info keys are supported:
.INDENT 0.0
.TP
.B no_locks
If set to \fItrue\fP, then the implementation may assume that the local
window is never locked (by a call to \fI\%MPI_Win_lock\fP or
MPI_Win_lock_all). Setting this value if only active synchronization
may allow the implementation to enable certain optimizations.
.TP
.B 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 \fInone\fP, no ordering of accumulate
operations guaranteed. They key can also be a comma\-separated list of
required orderings consisting of \fIrar\fP, \fIwar\fP, \fIraw\fP, and \fIwaw\fP 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.
.TP
.B accumulate_ops
If set to \fIsame_op\fP, the implementation will assume that all
concurrent accumulate calls to the same target address will use the
same operation. If set to \fIsame_op_no_op\fP, 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
\fIsame_op_no_op\fP\&.
.TP
.B same_size
If set to \fItrue\fP, then the implementation may assume that the
argument \fIsize\fP is identical on all processes, and that all processes
have provided this info key with the same value.
.TP
.B same_disp_unit
If set to \fItrue\fP, then the implementation may assume that the
argument \fIdisp_unit\fP is identical on all processes, and that all
processes have provided this info key with the same value.
.UNINDENT
.SH NOTES
.sp
Common choices for \fIdisp_unit\fP are 1 (no scaling), and (in C syntax)
\fIsizeof(type)\fP, for a window that consists of an array of elements of
type \fItype\fP\&. 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.
.sp
Use memory allocated by \fI\%MPI_Alloc_mem\fP to guarantee properly aligned
window boundaries (such as word, double\-word, cache line, page frame,
and so on).
.SH ERRORS
.sp
Almost all MPI routines return an error value; C routines as the return result
of the function and Fortran routines in the last argument.
.sp
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
\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
Model exclusively) the error raises the initial error handler. The initial
error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
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.
.sp
Open MPI includes three predefined error handlers that can be used:
.INDENT 0.0
.IP \(bu 2
\fBMPI_ERRORS_ARE_FATAL\fP
Causes the program to abort all connected MPI processes.
.IP \(bu 2
\fBMPI_ERRORS_ABORT\fP
An error handler that can be invoked on a communicator,
window, file, or session. When called on a communicator, it
acts as if \fI\%MPI_Abort\fP was called on that communicator. If
called on a window or file, acts as if \fI\%MPI_Abort\fP 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.
.IP \(bu 2
\fBMPI_ERRORS_RETURN\fP
Returns an error code to the application.
.UNINDENT
.sp
MPI applications can also implement their own error handlers by calling:
.INDENT 0.0
.IP \(bu 2
\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
.IP \(bu 2
\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
.UNINDENT
.sp
Note that MPI does not guarantee that an MPI program can continue past
an error.
.sp
See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
.sp
See the Error Handling section of the MPI\-3.1 standard for
more information.
.sp
\fBSEE ALSO:\fP
.INDENT 0.0
.INDENT 3.5
.INDENT 0.0
.IP \(bu 2
\fI\%MPI_Alloc_mem\fP
.IP \(bu 2
\fI\%MPI_Free_mem\fP
.IP \(bu 2
\fI\%MPI_Win_allocate\fP
.IP \(bu 2
\fI\%MPI_Win_allocate_shared\fP
.UNINDENT
.UNINDENT
.UNINDENT
.SH COPYRIGHT
2003-2025, The Open MPI Community
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