.\"Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.TH MPI_File_set_atomicity 3 "Dec 08, 2009" "1.4" "Open MPI"
.SH NAME
\fBMPI_File_set_atomicity\fP \- Sets consistency semantics for data-access operations (collective).

.SH SYNTAX
.ft R
.nf
C Syntax
    #include <mpi.h>
    int MPI_File_set_atomicity(MPI_File \fIfh\fP, int \fIflag\fP)

Fortran Syntax
    INCLUDE 'mpif.h'
    MPI_FILE_SET_ATOMICITY(\fIFH\fP,\fI FLAG\fP,\fI IERROR\fP)
    	      INTEGER 	  FH, FLAG, IERROR

.SH C++ Syntax
.nf
#include <mpi.h>
void MPI::File::Set_atomicity(bool \fIflag\fP)

.SH INPUT PARAMETERS
.ft R
.TP 1i
fh
File handle (handle).
.TP 1i
flag
\fBtrue\fP to enable atomic mode, \fBfalse\fP to enable nonatomic mode (boolean).

.SH OUTPUT PARAMETER
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer). 

.SH DESCRIPTION
.ft R
The consistency semantics for data-access operations using the set of
file handles created by one collective MPI_File_open is set by collectively
calling MPI_File_set_atomicity. All processes in the group must pass identical values for 
.I fh 
and
.I flag.
If 
.I flag 
is 
.I true,
atomic mode is set; if 
.I flag 
is 
.I false,
nonatomic mode is set.
.sp
The default value on a call to MPI_File_open in Open MPI is \fItrue\fP for jobs running on more than one node, \fIfalse\fP for jobs running on a single SMP. For more information, see the MPI-2 standard. 

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI:Exception object.
.sp
Before the error value is returned, the current MPI error handler is
called. For MPI I/O function errors, the default error handler is set to MPI_ERRORS_RETURN. The error handler may be changed with MPI_File_set_errhandler; the predefined error handler MPI_ERRORS_ARE_FATAL may be used to make I/O errors fatal. Note that MPI does not guarantee that an MPI program can continue past an error.