MPI_COMM_SET_NAME(3)

💅 MPI_COMM_SET_NAME(3) — an Open MPI moment

okay so bestie, welcome to MPI_Comm_set_name(3) from the Open MPI manual. this is the page where we give communicators ✨names✨. yes it's that simple and yes it slaps. let's get into it 🫶

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🌸 NAME

MPI_Comm_set_name — associates a name with a communicator. that's it. that's the whole gig. iconic behavior honestly 👑

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✨ SYNTAX

💖 C Syntax

#include <mpi.h>

int MPI_Comm_set_name(MPI_Comm comm, const char *comm_name)

💜 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_COMM_SET_NAME(COMM, COMM_NAME, IERROR)
     INTEGER COMM, IERROR
     CHARACTER*(*) COMM_NAME

🦋 Fortran 2008 Syntax

USE mpi_f08
MPI_Comm_set_name(comm, comm_name, ierror)
     TYPE(MPI_Comm), INTENT(IN) :: comm
     CHARACTER(LEN=*), INTENT(IN) :: comm_name
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🎀 INPUT/OUTPUT PARAMETER

• comm — the communicator whose identifier is getting set, bestie. it's a handle, so it's both coming and going. main character energy fr 👑

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🍓 INPUT PARAMETER

• comm_name — the character string that's gonna be the new identifier for the communicator. this is the actual name. the glow-up. a string 🧚

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🌈 OUTPUT PARAMETER

• ierror — Fortran only, bestie: error status as an integer. only the Fortran girlies get this one 💅

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💫 DESCRIPTION

so what does MPI_Comm_set_name even do? it lets you associate a name string with a communicator. you hand it a string, the MPI library saves it inside itself — which means you can free that string immediately after the call, or even allocate it on the stack. the library keeps its own copy, no cap 🫶

leading spaces in the name are significant (they count, they're part of the vibe), but trailing ones are not. so " hello " and " hello" are basically the same girl. noted ✍️

MPI_Comm_set_name is a local (noncollective) operation — like, it only affects the name of the communicator as seen in the process that made the call. it is NOT a group activity. there is absolutely no requirement that the same name — or any name — be assigned to that communicator in every process where it exists. you do you, boo 🙈

now the length thing, and this is important. the length of the name that can be stored is limited to:

• the value of MPI_MAX_OBJECT_NAME in Fortran
• MPI_MAX_OBJECT_NAME-1 in C (that extra -1 is so we have room for the null terminator, obviously 💀)

if you try to set a name longer than that, it will get truncated. sobs. and just so you know, MPI_MAX_OBJECT_NAME must have a value of at least 64. that's the floor, not the vibe check ⭐

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🔥 NOTES

okay so MPI_Comm_set_name exists to help you debug your code — which is literally why it's sensible (genuinely, bestie) to give the same name to a communicator in all the processes where it exists. otherwise you're out here confused in the group chat and nobody knows who's who 😭

about that name length again — heads up: under circumstances of store exhaustion, an attempt to set a name of any length could fail. so MPI_MAX_OBJECT_NAME should be viewed as a strict upper bound on the name length only. it is NOT a guarantee that setting names shorter than that length will always succeed. don't come for me, that's just how it is 🙏

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💀 ERRORS

almost all MPI routines return an error value — C routines give it back as the return result of the function, and Fortran routines stick it in the last argument. classic 🌸

before that error value comes back at you, the current MPI error handler associated with the communication object (e.g., communicator, window, file) gets called. and 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 — that's before MPI_Init/MPI_Init_thread, after MPI_Finalize, or when you're using the Sessions Model exclusively — the error raises the initial error handler. that initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or via the mpi_initial_errhandler CLI argument to mpiexec, or the info key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. if no other appropriate error handler has been set, then MPI_ERRORS_RETURN is called for MPI I/O functions, and MPI_ERRORS_ABORT is called for all other MPI functions. got all that? slay 💅

Open MPI ships three predefined error handlers you can use:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. everyone. gone. dramatic but effective 💀
• 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, it 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, it aborts only the local process. situational awareness, love that for it 🎀
• MPI_ERRORS_RETURN — returns an error code to the application. the chill one. hands you the L politely 🫶

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… don't count on it, bestie 😭

see the MPI man page for a full list of MPI error codes. and see the Error Handling section of the MPI-3.1 standard for more information 📚

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🔍 SEE ALSO

• MPI_Comm_get_name — the other half of this duo, go read it 💖

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👑 COPYRIGHT

2003-2026, The Open MPI Community — that's the source and version tea ☕

and that's the page!! it was dated Sep 11, 2026, it's MPI_COMM_SET_NAME(3) from Open MPI, and honestly? naming your communicators is self-care. go forth and be legible in your debuggers 🦋✨💜