MPI_ERRHANDLER_SET(3)

💖 MPI_Errhandler_set 💖

okay so bestie, welcome to the Open MPI manual, section 3, and yes we are starting with a ⚠️ deprecation warning because this one is old old. MPI_Errhandler_set sets the error handler for a communicator — and it's deprecated in favor of MPI_Comm_set_errhandler. She's giving legacy MC energy but we still gotta learn her, so let's go 🫶

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🌸 SYNTAX 🌸

💻 C Syntax

#include <mpi.h>

int MPI_Errhandler_set(MPI_Comm comm, MPI_Errhandler errhandler)

🧚 Fortran Syntax

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

MPI_ERRHANDLER_SET(COMM, ERRHANDLER, IERROR)
     INTEGER COMM, ERRHANDLER, IERROR

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📥 INPUT PARAMETERS 📥

• comm — the communicator you're setting the error handler for. it's a handle bestie, a little handle ✨
• errhandler — the new MPI error handler for that communicator. also a handle 🎀

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📤 OUTPUT PARAMETER 📤

• ierror — Fortran only: the error status, and it's an integer. C girlies stay unbothered, y'all get the return value instead 💅

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📝 DESCRIPTION 📝

heads up: using this routine is deprecated as of MPI-2. please, for the love of everything, use MPI_Comm_set_errhandler instead 🙏

What she actually does: she associates the new error handler errhandler with communicator comm at the calling process. And here's the lil fact that lives rent free in my head — an error handler is always associated with the communicator. always. she's never not got one 🦋

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💀 ERRORS 💀

Almost every single MPI routine returns an error value, and the delivery method is giving "depends on your language":

• C routines → it comes back as the return result of the function.
• Fortran routines → it lands in the last argument.

Before that error value ever gets returned, the current MPI error handler associated with the communication object is called — and that object could be a communicator, a window, or a file, iykyk.

But what if there's no communication object attached to the MPI call? Then the call is considered attached to MPI_COMM_SELF and it'll call the associated MPI error handler. 🫠

And when MPI_COMM_SELF is not initialized — meaning 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
• the info key to MPI_Comm_spawn / MPI_Comm_spawn_multiple.

If no other appropriate error handler has been set, then:

• MPI_ERRORS_RETURN gets called for MPI I/O functions, and
• MPI_ERRORS_ABORT gets called for all other MPI functions.

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👑 the three predefined error handlers Open MPI ships with 👑

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. not a drill, not one process, all of them 💀
• 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.
• MPI_ERRORS_RETURN — returns an error code to the application. the chill one, the respectful one, the queen of handing you the receipt 🧾

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✨ make your own error handler ✨

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

very important, no cap: MPI does not guarantee that an MPI program can continue past an error. like, at all. 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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🦋 SEE ALSO 🦋

• MPI_Comm_create_errhandler
• MPI_Comm_get_errhandler
• MPI_Comm_set_errhandler

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📜 Copyright

2003-2026, The Open MPI Community

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and that's the whole page bestie, you ate it up 💅✨ this absolute classic is from the Open MPI manual, dated Sep 10, 2026, and she's filed as MPI_ERRHANDLER_SET(3) — go forth and use MPI_Comm_set_errhandler instead, mwah 🫶💖