.\" -*- nroff -*-
.\" Copyright (c) 2014-2015 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" $COPYRIGHT$
.TH MPI_Barrier 3 "May 26, 2022" "4.1.4" "Open MPI"
.SH NAME
\fBMPI_Barrier, MPI_Ibarrier\fP \- Synchronization between MPI processes in a group

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Barrier(MPI_Comm \fIcomm\fP)

int MPI_Ibarrier(MPI_Comm \fIcomm\fP, MPI_Request \fI*request\fP)

.fi
.SH Fortran Syntax
.nf
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_BARRIER(\fICOMM\fP,\fI IERROR\fP)
	INTEGER	\fICOMM\fP,\fI IERROR\fP

MPI_IBARRIER(\fICOMM\fP, \fIREQUEST\fP, \fIIERROR\fP)
	INTEGER	\fICOMM\fP, \fIREQUEST\fP, \fIIERROR\fP

.fi
.SH Fortran 2008 Syntax
.nf
USE mpi_f08
MPI_Barrier(\fIcomm\fP, \fIierror\fP)
	TYPE(MPI_Comm), INTENT(IN) :: \fIcomm\fP
	INTEGER, OPTIONAL, INTENT(OUT) :: \fIierror\fP

MPI_Ibarrier(\fIcomm\fP, \fIrequest\fP, \fIierror\fP)
	TYPE(MPI_Comm), INTENT(IN) :: \fIcomm\fP
	TYPE(MPI_Request), INTENT(OUT) :: \fIrequest\fP
	INTEGER, OPTIONAL, INTENT(OUT) :: \fIierror\fP

.fi
.SH C++ Syntax
.nf
#include <mpi.h>
void MPI::Comm::Barrier() const = 0

.fi
.SH INPUT PARAMETER
.ft R
.TP 1i
comm
Communicator (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
request
Request (handle, non-blocking only).
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
An MPI barrier completes after all group members have entered the
barrier.

.SH WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR
.sp
When the communicator is an inter-communicator, the barrier operation is performed across all processes in both groups.  All processes in the first group may exit the barrier when all processes in the second group have entered the barrier.

.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. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

.SH SEE ALSO
.ft R
MPI_Bcast