.\" -*- nroff -*-
.\" Copyright (c) 2010-2014 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" $COPYRIGHT$
.TH MPI_Comm_dup 3 "Dec 18, 2020" "4.1.0" "Open MPI"
.SH NAME
\fBMPI_Comm_dup \fP \-  Duplicates an existing communicator with all its cached information.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Comm_dup(MPI_Comm \fIcomm\fP, MPI_Comm\fI *newcomm\fP)

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

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

.fi
.SH C++ Syntax
.nf
#include <mpi.h>
Intracomm Intracomm::Dup() const

Intercomm Intercomm::Dup() const

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

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
newcomm
Copy of comm (handle).
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
MPI_Comm_dup duplicates the existing communicator comm with associated key
values. For each key value, the respective copy callback function determines the attribute value associated with this key in the new communicator; one particular action that a copy callback may take is to delete the attribute from the new communicator. Returns in newcomm a new communicator with the same group, any copied cached information, but a new context (see Section 5.7.1 of the MPI-1 Standard, "Functionality").

.SH NOTES
This operation is used to provide a parallel
library call with a duplicate communication space that has the same properties as the original communicator. This includes any attributes (see below) and topologies (see Chapter 6, "Process Topologies," in the MPI-1 Standard). This call is valid even if there are pending point-to-point communications involving the communicator comm. A typical call might involve an MPI_Comm_dup at the beginning of the parallel call, and an MPI_Comm_free of that duplicated communicator at the end of the call. Other models of communicator management are also possible.
.sp
This call applies to both intra- and intercommunicators.

Note that it is not defined by the MPI standard what happens if the
attribute copy callback invokes other MPI functions.  In Open MPI, it
is not valid for attribute copy callbacks (or any of their children)
to add or delete attributes on the same object on which the attribute
copy callback is being invoked.

.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
.nf
MPI_Comm_dup_with_info
MPI_Comm_idup