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.TH "MPI_COMM_DUP" "3" "May 30, 2025" "" "Open MPI"
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\fI\%MPI_Comm_dup\fP — Duplicates an existing communicator with all its cached
information.
.SH SYNTAX
.SS C Syntax
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.INDENT 3.5
.sp
.nf
.ft C
#include <mpi.h>

int MPI_Comm_dup(MPI_Comm comm, MPI_Comm *newcomm)
.ft P
.fi
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.SS Fortran Syntax
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.INDENT 3.5
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.nf
.ft C
USE MPI
! or the older form: INCLUDE \(aqmpif.h\(aq

MPI_COMM_DUP(COMM, NEWCOMM, IERROR)
    INTEGER COMM, NEWCOMM, IERROR
.ft P
.fi
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.SS Fortran 2008 Syntax
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.INDENT 3.5
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.nf
.ft C
USE mpi_f08

MPI_Comm_dup(comm, newcomm, ierror)
    TYPE(MPI_Comm), INTENT(IN) :: comm
    TYPE(MPI_Comm), INTENT(OUT) :: newcomm
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror
.ft P
.fi
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.SH INPUT PARAMETER
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.IP \(bu 2
\fBcomm\fP : Communicator (handle).
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.SH OUTPUT PARAMETERS
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.IP \(bu 2
\fBnewcomm\fP : Copy of comm (handle).
.IP \(bu 2
\fBierror\fP : Fortran only: Error status (integer).
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.SH DESCRIPTION
.sp
\fI\%MPI_Comm_dup\fP 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 the “Functionality” subsection of the “Caching”
section in the “Groups, Contexts, and Communicators” chapter in the
\fI\%MPI Standard\fP).
.SH NOTES
.sp
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 the “Process Topologies” chapter in the \fI\%MPI Standard\fP).
This call is valid even if there are pending point\-to\-point
communications involving the communicator comm. A typical call might
involve an \fI\%MPI_Comm_dup\fP at the beginning of the parallel call, and an
\fI\%MPI_Comm_free\fP of that duplicated communicator at the end of the call.
Other models of communicator management are also possible. 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
.sp
Almost all MPI routines return an error value; C routines as the return result
of the function and Fortran routines in the last argument.
.sp
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
\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
Model exclusively) the error raises the initial error handler. The initial
error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
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.
.sp
Open MPI includes three predefined error handlers that can be used:
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.IP \(bu 2
\fBMPI_ERRORS_ARE_FATAL\fP
Causes the program to abort all connected MPI processes.
.IP \(bu 2
\fBMPI_ERRORS_ABORT\fP
An error handler that can be invoked on a communicator,
window, file, or session. When called on a communicator, it
acts as if \fI\%MPI_Abort\fP was called on that communicator. If
called on a window or file, acts as if \fI\%MPI_Abort\fP 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.
.IP \(bu 2
\fBMPI_ERRORS_RETURN\fP
Returns an error code to the application.
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.sp
MPI applications can also implement their own error handlers by calling:
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.IP \(bu 2
\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
.IP \(bu 2
\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
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.sp
Note that MPI does not guarantee that an MPI program can continue past
an error.
.sp
See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
.sp
See the Error Handling section of the MPI\-3.1 standard for
more information.
.sp
\fBSEE ALSO:\fP
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.INDENT 3.5
\fI\%MPI_Comm_dup_with_info\fP
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.SH COPYRIGHT
2003-2025, The Open MPI Community
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