.TH MPI_Win_allocate_shared 3 "11/12/2019" " " "MPI"
.SH NAME
MPI_Win_allocate_shared \-  Create an MPI Window object for one-sided communication and shared memory access, and allocate memory at each process. 
.SH SYNOPSIS
.nf
int MPI_Win_allocate_shared(MPI_Aint size, int disp_unit, MPI_Info info, MPI_Comm comm,
void *baseptr, MPI_Win * win)
.fi
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 
.I 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.

.SH INPUT PARAMETERS
.PD 0
.TP
.B size 
- size of window in bytes (nonnegative integer)
.PD 1
.PD 0
.TP
.B disp_unit 
- local unit size for displacements, in bytes (positive integer)
.PD 1
.PD 0
.TP
.B info 
- info argument (handle)
.PD 1
.PD 0
.TP
.B comm 
- communicator (handle)
.PD 1

.SH OUTPUT PARAMETERS
.PD 0
.TP
.B baseptr 
- initial address of window (choice)
.PD 1
.PD 0
.TP
.B win 
- window object returned by the call (handle)
.PD 1

.SH 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 
.I malloc
or other non-MPICH runtime routines that are themselves not interrupt-safe.
.SH NOTES FOR FORTRAN
All MPI routines in Fortran (except for 
.I MPI_WTIME
and 
.I MPI_WTICK
) have
an additional argument 
.I ierr
at the end of the argument list.  
.I 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
.I call
statement.

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

.SH ERRORS

All MPI routines (except 
.I MPI_Wtime
and 
.I 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 
.I MPI_Comm_set_errhandler
(for communicators),
.I MPI_File_set_errhandler
(for files), and 
.I MPI_Win_set_errhandler
(for
RMA windows).  The MPI-1 routine 
.I MPI_Errhandler_set
may be used but
its use is deprecated.  The predefined error handler
.I MPI_ERRORS_RETURN
may be used to cause error values to be returned.
Note that MPI does 
.B not
guarentee that an MPI program can continue past
an error; however, MPI implementations will attempt to continue whenever
possible.

.PD 0
.TP
.B MPI_SUCCESS 
- No error; MPI routine completed successfully.
.PD 1
.PD 0
.TP
.B MPI_ERR_ARG 
- Invalid argument.  Some argument is invalid and is not
identified by a specific error class (e.g., 
.I MPI_ERR_RANK
).
.PD 1
.PD 0
.TP
.B MPI_ERR_COMM 
- Invalid communicator.  A common error is to use a null
communicator in a call (not even allowed in 
.I MPI_Comm_rank
).
.PD 1
.PD 0
.TP
.B MPI_ERR_INFO 
- Invalid Info 
.PD 1
.PD 0
.TP
.B MPI_ERR_OTHER 
- Other error; use 
.I MPI_Error_string
to get more information
about this error code. 
.PD 1
.PD 0
.TP
.B MPI_ERR_SIZE 
- 
.PD 1

.SH SEE ALSO
MPI_Win_allocate MPI_Win_create MPI_Win_create_dynamic MPI_Win_free MPI_Win_shared_query
.br