MPI_COMM_DUP(3)

💖 MPI_COMM_DUP 💖

okay bestie, welcome to MPI_COMM_DUP(3) from the Open MPI collection ✨ this is the glow-up-your-communicator page and I'm obsessed with it, let's go 🫶

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🌸 NAME 🌸

MPI_Comm_dup — duplicates an existing communicator with all its cached information. yeah she's a copycat and she's iconic for it 👑

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✨ SYNTAX ✨

💅 C Syntax 💅

#include <mpi.h>

int MPI_Comm_dup(MPI_Comm comm, MPI_Comm *newcomm)

🎀 Fortran Syntax 🎀

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_COMM_DUP(COMM, NEWCOMM, IERROR)
    INTEGER COMM, NEWCOMM, IERROR

🦋 Fortran 2008 Syntax 🦋

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

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🍓 INPUT PARAMETER 🍓

• comm — the communicator, aka a handle. that's her. that's the one you're duplicating 💖

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💜 OUTPUT PARAMETERS 💜

• newcomm — copy of comm (handle). your brand new twin, no cap 🌈
• ierror — Fortran only: error status (integer). yes bestie, Fortran gets a whole extra arg, that's just how she lives ✨

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🔥 DESCRIPTION 🔥

So like — 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 that's associated with that key in the new communicator. and one particular action a copy callback is allowed to take? deleting the attribute from the new communicator entirely. she can just ✨remove it✨, main character behaviour fr fr.

It returns in newcomm a new communicator with the same group, any copied cached information, but a new context — and if you wanna go read the lore on that, it's in the "Functionality" subsection of the "Caching" section in the "Groups, Contexts, and Communicators" chapter of the MPI Standard over at <https://www.mpi-forum.org/docs/> 🫶

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🧚 NOTES 🧚

This operation is used to hand a parallel library call a duplicate communication space that has the same properties as the original communicator. that includes any attributes (see below, bestie) and topologies (see the "Process Topologies" chapter in the MPI Standard at <https://www.mpi-forum.org/docs/> 📚).

and the best part? this call is valid even if there are pending point-to-point communications involving the communicator comm. she does NOT care. she does NOT block. slay 💅

A typical call might be: 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 — you do you, girlie 🌸

This call applies to both intra- and intercommunicators.

⚠️ okay important thing, listen up: the MPI standard does not define 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. don't do it. that's the vibe check and you failed it if you do 😭

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💀 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. classic 💅

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/MPI_Init_thread, after MPI_Finalize, 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 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/MPI_Comm_spawn_multiple. 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. she said everyone's coming with her 💀
• 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 was called on that communicator. If called on a window or file, acts as if MPI_Abort 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. very context-aware of her ✨
• MPI_ERRORS_RETURN — returns an error code to the application. the polite one 🎀

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

• MPI_Comm_create_errhandler then MPI_Comm_set_errhandler
• MPI_File_create_errhandler then MPI_File_set_errhandler
• MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init
• MPI_Win_create_errhandler then MPI_Win_set_errhandler

😭 note that MPI does not guarantee that an MPI program can continue past an error. so like. be normal about it.

See the MPI man page for a full list of MPI error codes.

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

See also:

• MPI_Comm_dup_with_info — she's the cousin, go say hi 🦋

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👑 Copyright 👑

2003-2026, The Open MPI Community

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okay that's the whole page bestie, you ate that, periodt 💅✨ and a lil cute sign-off for you: this was the Sep 10, 2026 edition of MPI_COMM_DUP(3), brought to you by The Open MPI Community 🫶💖 go duplicate something responsibly 🌈