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MPI_Win_create - One-sided MPI call that returns a window object
for RMA operations.
#include <mpi.h>
MPI_Win_create(void *base, MPI_Aint size, int disp_unit,
MPI_Info info, MPI_Comm comm, MPI_Win *win)
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
#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).
- win
- Window object returned by the call (handle).
- IERROR
- Fortran only: Error status (integer).
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.
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).
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.
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.
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