MPI_BARRIER, MPI_Barrier

Purpose

Blocks each task until all tasks have called it. in comm

C synopsis

#include <mpi.h>
int MPI_Barrier(MPI_Comm comm);

C++ synopsis

#include mpi.h
void MPI::Comm::Barrier() const;

FORTRAN synopsis

include 'mpif.h' or use mpi
MPI_BARRIER(INTEGER COMM,INTEGER IERROR)

Description

This subroutine blocks until all tasks have called it. Tasks cannot exit
the operation until all group members have entered.

When you use this subroutine in a threads application, make sure all
collective operations on a particular communicator occur in the same order
at each task. See IBM Parallel Environment for AIX: MPI Programming Guide
for more information on programming with MPI in a threads environment.

Parameters

comm
     is a communicator (handle) (IN)
IERROR
     is the FORTRAN return code. It is always the last argument.

Notes

comm can be an intercommunicator or an intracommunicator. If comm is an
intercommunicator, the barrier is performed across all tasks in the
intercommunicator. In this case, all tasks in the local group of the
intercommunicator can exit the barrier when all of the tasks in the remote
group have entered the barrier.

In the 64-bit library, this function uses a shared memory optimization
among the tasks on a node. This optimization is discussed in the chapter
"Using shared memory" of IBM Parallel Environment for AIX: MPI Programming
Guide, and is enabled by default. This optimization is not available to
32-bit programs.

Errors

Fatal errors:

Invalid communicator

MPI not initialized

MPI already finalized

Related information

     MPE_IBARRIER