MPI_COMM_SET_ATTR(3)

💅 MPI_COMM_SET_ATTR(3) — the Open MPI glow-up 👑

okay bestie, gather round, because today we're talking about MPI_Comm_set_attr — the Open MPI manual page, but make it make sense. It "Stores attribute value associated with a key." That's the whole assignment. Slay. ✨

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🌸 NAME 🌸

MPI_Comm_set_attr — stores an attribute value, and that value is associated with a key. that's it, that's the vibe 🎀

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✨ SYNTAX ✨

C Syntax

#include <mpi.h>

int MPI_Comm_set_attr(MPI_Comm comm, int comm_keyval, void *attribute_val)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_COMM_SET_ATTR(COMM, COMM_KEYVAL, ATTRIBUTE_VAL, IERROR)
     INTEGER COMM, COMM_KEYVAL, IERROR
     INTEGER(KIND=MPI_ADDRESS_KIND) ATTRIBUTE_VAL

Fortran 2008 Syntax

USE mpi_f08
MPI_Comm_set_attr(comm, comm_keyval, attribute_val, ierror)
     TYPE(MPI_Comm), INTENT(IN) :: comm
     INTEGER, INTENT(IN) :: comm_keyval
     INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: attribute_val
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🫶 INPUT/OUTPUT PARAMETER 🫶

• comm — the communicator the attribute is getting attached to (a handle). the main character of the operation, honestly 💜

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🎀 INPUT PARAMETERS 🎀

• comm_keyval — the key value (an integer). your little lookup ticket 🔑
• attribute_val — the attribute value itself. the payload. the moment. 💅

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🌈 OUTPUT PARAMETER 🌈

• ierror — Fortran only: the error status (an integer). yes only Fortran, don't come for me 😭

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💖 DESCRIPTION 💖

okay so MPI_Comm_set_attr stores the stipulated attribute value attribute_val so that it can be retrieved later by MPI_Comm_get_attr. set it now, get it later, iconic behavior honestly.

if the value is already present? then the outcome is as if MPI_Comm_delete_attr was first called to delete the previous value — and yes, the callback function delete_fn was executed — and then a new value was stored. out with the old, in with the new, periodt. 🔥

the call is erroneous if there is no key with value comm_keyval; in particular MPI_KEYVAL_INVALID is an erroneous key value. so like… don't do that. 🙈 and the call will fail if the delete_fn function returned an error code other than MPI_SUCCESS.

this function replaces MPI_Attr_put, whose use is deprecated ⚠️ (respectfully, retire it). the C binding is identical. the Fortran binding differs in that attribute_val is an address-sized integer.

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🦋 NOTES 🦋

values of the permanent attributes MPI_TAG_UB, MPI_HOST, MPI_IO, and MPI_WTIME_IS_GLOBAL may not be changed. those ones are locked in, no edits, no notes, no cap 💀

the type of the attribute value depends on whether C or Fortran is being used. in C, an attribute value is a pointer (void *); in Fortran, it is a single, address-size integer system for which a pointer does not fit in an integer. iykyk 🧚

if an attribute is already present, the delete function (specified when the corresponding keyval was created) will be called. it's giving cleanup crew energy, we love her.

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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. so like, check it, bestie.

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. dramatic, but make it functional 🫠
• 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 "it depends on the context" of it all 💅
• MPI_ERRORS_RETURN — returns an error code to the application. the chill 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… plan accordingly 😭

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.

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👑 COPYRIGHT 👑

2003-2026, The Open MPI Community

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and that's the whole page, bestie 🫶 this drop is brought to you by Open MPI, dated Sep 11, 2026, and the page footer badge is MPI_COMM_SET_ATTR(3) — wear it with pride 💖✨