MPI_Win_allocate - One-sided MPI call that allocates memory and returns a window object for RMA operations.
18.2.427.1.1. C Syntax
#include <mpi.h> int MPI_Win_allocate (MPI_Aint size, int disp_unit, MPI_Info info, MPI_Comm comm, void *baseptr, MPI_Win *win)
18.2.427.1.2. Fortran Syntax
USE MPI ! or the older form: 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
18.2.427.1.3. Fortran 2008 Syntax
USE mpi_f08 MPI_Win_allocate(size, disp_unit, info, comm, baseptr, win, ierror) USE, INTRINSIC :: ISO_C_BINDING, ONLY : C_PTR 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(C_PTR), INTENT(OUT) :: baseptr TYPE(MPI_Win), INTENT(OUT) :: win INTEGER, OPTIONAL, INTENT(OUT) :: ierror
18.2.427.2. INPUT PARAMETERS
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).
18.2.427.3. OUTPUT PARAMETERS
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 section 8.2 also apply to MPI_Win_allocate; in particular, see the rationale in MPI-3.1 section 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.
18.2.427.6. C NOTES
While baseptr is a
void * type, this is to allow easy use of any
pointer object for this parameter. This argument is really a
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_thread, after 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 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_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_FATALCauses the program to abort all connected MPI processes.
MPI_ERRORS_ABORTAn error handler that can be invoked on a communicator, window, file, or session. When called on a communicator, it acts as if MPI_Abort was called on that communicator. If called on a window or file, acts as if 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_RETURNReturns an error code to the application.
MPI applications can also implement their own error handlers by calling:
Note that MPI does not guarantee that an MPI program can continue past an error.
See the Error Handling section of the MPI-3.1 standard for more information.