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)
- 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 key is supported:
- no_locks
- If MPI_Win_lock is called on a window created with this
info key, the call will fail. If this info key is present, it is assumed
that the local window is never locked, allowing several internal checks to
be skipped, permitting a more efficient implementation.
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.