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MPI_Win_allocate - One-sided MPI call that allocates memory and
returns a window object for RMA operations.
#include <mpi.h>
int MPI_Win_allocate (MPI_Aint size, int disp_unit, MPI_Info info,
MPI_Comm comm, void *baseptr, MPI_Win *win)
INCLUDE ’mpif.h’
MPI_WIN_ALLOCATE(SIZE, DISP_UNIT, INFO, COMM, BASEPTR, WIN, IERROR)
INTEGER(KIND=MPI_ADDRESS_KIND) SIZE, BASEPTR
INTEGER DISP_UNIT, INFO, COMM, WIN, IERROR
- 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).
- baseptr
- Initial address of window.
- win
- Window object returned by the call (handle).
- IERROR
- Fortran only: Error status (integer).
MPI_Win_allocate
is a collective call executed by all processes in the group of comm. On
each process, it allocates memory of at least size bytes, returns a pointer
to it, and returns a window object that can be used by all processes in
comm to perform RMA operations. The returned memory consists of size bytes
local to each process, starting at address baseptr and is associated with
the window as if the user called MPI_Win_create on existing memory. The
size argument may be different at each process and size = 0 is valid; however,
a library might allocate and expose more memory in order to create a fast,
globally symmetric allocation. The discussion of and rationales for MPI_Alloc_mem
and MPI_Free_mem in MPI-3.1 [char167] 8.2 also apply to MPI_Win_allocate;
in particular, see the rationale in MPI-3.1 [char167] 8.2 for an explanation
of the type used for baseptr.
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.
For supported info keys see MPI_Win_create.
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.
Almost all MPI routines return an error value; C routines
as the value of the function and Fortran routines in the last argument.
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.
MPI_Alloc_mem MPI_Free_mem MPI_Win_create
MPI_Win_allocate_shared
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