NAME

       MPI_Win_allocate_shared  -   Create  an  MPI Window object for one-sided communication and
       shared memory access, and allocate memory at each process.

SYNOPSIS

       int MPI_Win_allocate_shared(MPI_Aint size, int disp_unit, MPI_Info info, MPI_Comm comm,
                                    void *baseptr, MPI_Win *win)
       This is a collective call executed by all processes in the group of comm. On each  process
       i,  it allocates memory of at least size bytes that is shared among all processes in comm,
       and returns a pointer to the locally allocated segment in baseptr that  can  be  used  for
       load/store accesses on the calling process. The locally allocated memory can be the target
       of load/store accesses by remote processes; the base pointers for other processes  can  be
       queried using the function MPI_Win_shared_query .

       The call also returns a window object that can be used by all processes in comm to perform
       RMA operations. The size argument may be different at each process and size = 0 is  valid.
       It is the user's responsibility to ensure that the communicator comm represents a group of
       processes that can create a shared memory segment that can be accessed by all processes in
       the  group.  The  allocated  memory is contiguous across process ranks unless the info key
       alloc_shared_noncontig is specified. Contiguous across process ranks means that the  first
       address  in  the  memory  segment of process i is consecutive with the last address in the
       memory segment of process i − 1.  This may enable the user  to  calculate  remote  address
       offsets with local information only.

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)

OUTPUT PARAMETERS

       baseptr
              - initial address of window (choice)
       win    - window object returned by the call (handle)

THREAD AND INTERRUPT SAFETY

       This  routine is thread-safe.  This means that this routine may be safely used by multiple
       threads without the need for any user-provided thread locks.  However, the routine is  not
       interrupt  safe.   Typically, this is due to the use of memory allocation routines such as
       malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.

NOTES FOR FORTRAN

       All MPI routines in Fortran (except for MPI_WTIME  and  MPI_WTICK  )  have  an  additional
       argument  ierr  at  the  end  of  the  argument list.  ierr is an integer and has the same
       meaning as the  return  value  of  the  routine  in  C.   In  Fortran,  MPI  routines  are
       subroutines, and are invoked with the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran.

ERRORS

       All  MPI  routines  (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as
       the value of the function and Fortran routines in the last argument.  Before the value  is
       returned,  the current MPI error handler is called.  By default, this error handler aborts
       the MPI  job.   The  error  handler  may  be  changed  with  MPI_Comm_set_errhandler  (for
       communicators),  MPI_File_set_errhandler  (for files), and MPI_Win_set_errhandler (for RMA
       windows).  The MPI-1 routine MPI_Errhandler_set may be used but  its  use  is  deprecated.
       The  predefined  error  handler  MPI_ERRORS_RETURN may be used to cause error values to be
       returned.  Note that MPI does not guarentee that an  MPI  program  can  continue  past  an
       error; however, MPI implementations will attempt to continue whenever possible.

       MPI_SUCCESS
              - No error; MPI routine completed successfully.
       MPI_ERR_ARG
              -  Invalid  argument.  Some argument is invalid and is not identified by a specific
              error class (e.g., MPI_ERR_RANK ).
       MPI_ERR_COMM
              - Invalid communicator.  A common error is to use a null  communicator  in  a  call
              (not even allowed in MPI_Comm_rank ).
       MPI_ERR_INFO
              - Invalid Info
       MPI_ERR_OTHER
              - Other error; use MPI_Error_string to get more information about this error code.
       MPI_ERR_SIZE
              -

SEE ALSO

       MPI_Win_allocate MPI_Win_create MPI_Win_create_dynamic MPI_Win_free MPI_Win_shared_query

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