.\" -*- nroff -*-
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines
.\" $COPYRIGHT$
.TH MPI_Comm_get_parent 3 "Sep 30, 2023" "4.1.6" "Open MPI"
.SH NAME
\fBMPI_Comm_get_parent\fP \- Returns the parent intercommunicator of current spawned process.

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

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

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

.fi
.SH C++ Syntax
.nf
#include <mpi.h>
static MPI::Intercomm MPI::Comm::Get_parent()


.fi
.SH OUTPUT PARAMETERS
.ft R
.TP 1i
parent
The parent communicator (handle).
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
If a process was started with MPI_Comm_spawn or MPI_Comm_spawn_multiple, MPI_Comm_get_parent returns the "parent" intercommunicator of the current process. This parent intercommunicator is created implicitly inside of MPI_Init and is the same intercommunicator returned by the spawn call made in the parents.
.sp
If the process was not spawned, MPI_Comm_get_parent returns MPI_COMM_NULL.
.sp
After the parent communicator is freed or disconnected, MPI_Comm_get_parent returns MPI_COMM_NULL.

.SH NOTES
.ft R
MPI_Comm_get_parent returns a handle to a single intercommunicator. Calling MPI_Comm_get_parent a second time returns a handle to the same intercommunicator. Freeing the handle with MPI_Comm_disconnect or MPI_Comm_free will cause other references to the intercommunicator to become invalid (dangling). Note that calling MPI_Comm_free on the parent communicator is not useful.

.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
.sp
.nf
MPI_Comm_spawn
MPI_Comm_spawn_multiple