MPI\_BARRIER(3) Open MPI MPI\_BARRIER(3)

MPI\_Barrier, MPI\_Ibarrier <#mpi-ibarrier> - Synchronization between MPI processes in a group

# [SYNTAX](#SYNTAX)

## [C Syntax](#C_Syntax)

```
#include <mpi.h>
int MPI_Barrier(MPI_Comm)
int MPI_Ibarrier(MPI_Comm comm, MPI_Request *request)
int MPI_Barrier_init(MPI_Comm comm, MPI_Info info, MPI_Request *request)
```

## [Fortran Syntax](#Fortran_Syntax)

```
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_BARRIER(COMM, IERROR)


    INTEGER COMM, IERROR
MPI_IBARRIER(COMM, REQUEST, IERROR)


    INTEGER COMM, REQUEST, IERROR
MPI_BARRIER_INIT(COMM, INFO, REQUEST, IERROR)


    INTEGER COMM, INFO, REQUEST, IERROR
```

## [Fortran 2008 Syntax](#Fortran_2008_Syntax)

```
USE mpi_f08
MPI_Barrier(comm, ierror)


    TYPE(MPI_Comm), INTENT(IN) :: comm


    INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_Ibarrier(comm, request, ierror)


    TYPE(MPI_Comm), INTENT(IN) :: comm


    TYPE(MPI_Request), INTENT (OUT) :: request


    INTEGER, OPTIONAL, INTENT(OUT) :: ierror
MPI_Barrier_init(comm, info, request, ierror)


    TYPE(MPI_Comm), INTENT(IN) :: comm


    TYPE(MPI_Info), INTENT(IN) :: info


    TYPE(MPI_Request), INTENT (OUT) :: request


    INTEGER, OPTIONAL, INTENT(OUT) :: ierror
```

# [INPUT PARAMETER](#INPUT_PARAMETER)

- **comm** : Communicator (handle).
- **info** : Info (handle, persistent only).

# [OUTPUT PARAMETERS](#OUTPUT_PARAMETERS)

- **request** : Request (handle, non-blocking only).
- **ierror** : Fortran only: Error status (integer).

# [DESCRIPTION](#DESCRIPTION)

An MPI barrier completes after all groups members have entered the barrier.

# [WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR](#WHEN_COMMUNICATOR_IS_AN_INTER-COMMUNICATOR)

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.

# [ERRORS](#ERRORS)

Almost all MPI routines return an error value; C routines as the return result of the function and Fortran routines in the last argument.

Before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. If no communication object is associated with the MPI call, then the call is considered attached to MPI\_COMM\_SELF and will call the associated MPI error handler. When MPI\_COMM\_SELF is not initialized (i.e., before MPI\_Init &lt;#mpi-init&gt;/MPI\_Init\_thread &lt;#mpi-init-thread&gt;, after MPI\_Finalize &lt;#mpi-finalize&gt;, or when using the Sessions Model exclusively) the error raises the initial error handler. The initial error handler can be changed by calling MPI\_Comm\_set\_errhandler &lt;#mpi-comm-set-errhandler&gt; on MPI\_COMM\_SELF when using the World model, or the mpi\_initial\_errhandler CLI argument to mpiexec or info key to MPI\_Comm\_spawn &lt;#mpi-comm-spawn&gt;/MPI\_Comm\_spawn\_multiple &lt;#mpi-comm-spawn-multiple&gt;. If no other appropriate error handler has been set, then the MPI\_ERRORS\_RETURN error handler is called for MPI I/O functions and the MPI\_ERRORS\_ABORT error handler is called for all other MPI functions.

Open MPI includes three predefined error handlers that can be used:

- **MPI\_ERRORS\_ARE\_FATAL** Causes the program to abort all connected MPI processes.
- **MPI\_ERRORS\_ABORT** An error handler that can be invoked on a communicator, window, file, or session. When called on a communicator, it acts as if MPI\_Abort &lt;#mpi-abort&gt; was called on that communicator. If called on a window or file, acts as if MPI\_Abort &lt;#mpi-abort&gt; was called on a communicator containing the group of processes in the corresponding window or file. If called on a session, aborts only the local process.
- **MPI\_ERRORS\_RETURN** Returns an error code to the application.

MPI applications can also implement their own error handlers by calling:

- MPI\_Comm\_create\_errhandler &lt;#mpi-comm-create-errhandler&gt; then MPI\_Comm\_set\_errhandler &lt;#mpi-comm-set-errhandler&gt;
- MPI\_File\_create\_errhandler &lt;#mpi-file-create-errhandler&gt; then MPI\_File\_set\_errhandler &lt;#mpi-file-set-errhandler&gt;
- MPI\_Session\_create\_errhandler &lt;#mpi-session-create-errhandler&gt; then MPI\_Session\_set\_errhandler &lt;#mpi-session-set-errhandler&gt; or at MPI\_Session\_init &lt;#mpi-session-init&gt;
- MPI\_Win\_create\_errhandler &lt;#mpi-win-create-errhandler&gt; then MPI\_Win\_set\_errhandler &lt;#mpi-win-set-errhandler&gt;

Note that MPI does not guarantee that an MPI program can continue past an error.

See the MPI man page &lt;#open-mpi&gt; for a full list of MPI error codes &lt;#open-mpi-errors&gt;.

See the Error Handling section of the MPI-3.1 standard for more information.

**See also:**

•

MPI\_Bcast &lt;#mpi-bcast&gt;

# [Copyright](#Copyright)

2003-2026, The Open MPI Community

September 16, 2026

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Document: MPI_Barrier(3) from openmpi 5.0.11-r1 (Chainguard OS)
Source: https://github.com/open-mpi/ompi