.TH MPI_Win_start 3 "11/12/2019" " " "MPI"

.SH NAME

MPI_Win_start \-  Start an RMA access epoch for MPI 

.SH SYNOPSIS

.nf

int MPI_Win_start(MPI_Group group, int assert, MPI_Win win)

.fi

.SH INPUT PARAMETERS

.PD 0

.TP

.B group 

- group of target processes (handle)

.PD 1

.PD 0

.TP

.B assert 

- Used to optimize this call; zero may be used as a default.

See notes. (integer)

.PD 1

.PD 0

.TP

.B win 

- window object (handle)

.PD 1

.SH NOTES

The 

.I assert

argument is used to indicate special conditions for the

fence that an implementation may use to optimize the 

.I MPI_Win_start

operation.  The value zero is always correct.  Other assertion values

may be or'ed together.  Assertions tha are valid for 

.I MPI_Win_start

are:

.PD 0

.TP

.B MPI_MODE_NOCHECK 

- the matching calls to 

.I MPI_WIN_POST

have already

completed on all target processes when the call to 

.I MPI_WIN_START

is made.

The nocheck option can be specified in a start call if and only if it is

specified in each matching post call. This is similar to the optimization

of ready-send that may save a handshake when the handshake is implicit in

the code. (However, ready-send is matched by a regular receive, whereas

both start and post must specify the nocheck option.)

.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_WIN 

- Invalid MPI window object

.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