MPI_COMM_CREATE_ERRHANDLER(3)

💅 MPI_COMM_CREATE_ERRHANDLER(3) — like, the Open MPI girlies' guide to making your own error handler ✨

okay bestie, welcome to MPI_COMM_CREATE_ERRHANDLER, a page straight out of Open MPI's manual (third section, obvs), and it does exactly one iconic thing: it creates an error handler that you can then attach to communicators. that's the whole vibe. let's get into it 🫶

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🌸 SYNTAX 🌸

✨ C Syntax

#include <mpi.h>

int MPI_Comm_create_errhandler(MPI_Comm_errhandler_function *function,
    MPI_Errhandler *errhandler)

🎀 Fortran Syntax

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

MPI_COMM_CREATE_ERRHANDLER(FUNCTION, ERRHANDLER, IERROR)
    EXTERNAL    FUNCTION
    INTEGER ERRHANDLER, IERROR

🦋 Fortran 2008 Syntax

USE mpi_f08

MPI_Comm_create_errhandler(comm_errhandler_fn, errhandler, ierror)
    PROCEDURE(MPI_Comm_errhandler_function) :: comm_errhandler_fn
    TYPE(MPI_Errhandler), INTENT(OUT) :: errhandler
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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💀 DEPRECATED TYPE NAME NOTE 💀

so history lesson real quick: MPI-2.2 deprecated the MPI_Comm_errhandler_fn type in favor of MPI_Comm_errhandler_function. and Open MPI supports both names — fr fr, the _fn names are literally just typedefs to the _function names. so if you see the old one floating around, she's not cancelled, she's just legacy 💅

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🍓 INPUT PARAMETER 🍓

• function — your user-defined error handling procedure (a function). it's your moment to shine, main character energy ✨

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👑 OUTPUT PARAMETERS 👑

• errhandler — the MPI error handler (a handle). this is the thing you just birthed, go attach her to a communicator 💖
• ierror — Fortran only: the error status (integer). classic Fortran, always gotta have the last word 🙈

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🌈 DESCRIPTION 🌈

MPI_Comm_create_errhandler creates an error handler that can be attached to communicators. and get this — it's identical to MPI_Errhandler_create, whose use is deprecated (so like, don't @ her, she's old news).

in C, your user routine should be a function of type MPI_Comm_errhandler_function, which is defined as:

typedef void MPI_Comm_errhandler_function(MPI_Comm *, int *, ...);

break it down 🧚:

• the first argument is the communicator in use.
• the second argument is the error code to be returned by the MPI routine that raised the error.

and this typedef replaces MPI_Handler_function, whose use is deprecated (again, deprecated, we don't stan).

in Fortran, your user routine should be of this form:

SUBROUTINE COMM_ERRHANDLER_FUNCTION(COMM, ERROR_CODE, ...)
   INTEGER COMM, ERROR_CODE

slay, that's it, that's the shape of it 🎀

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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. iykyk 😌

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. that 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. 💀
• 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.
• MPI_ERRORS_RETURN — returns an error code to the application.

🌸 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. like, no cap, that's a real caveat, bestie. 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 page, babe — official Open MPI documentation, dated Sep 11, 2026, manual section 3, MPI_COMM_CREATE_ERRHANDLER. go forth and handle your errors iconically 👑✨🦋