MPI_OP_FREE(3)

✨ NAME ✨

MPI_Op_free — ok so this one frees a user-defined combination function handle 💖 like it's the lil cleanup bestie for your custom reduction ops. (This is page MPI_OP_FREE(3) from the Open MPI manual, bestie 🫶)

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🌸 SYNTAX 🌸

🎀 C Syntax

#include <mpi.h>

int MPI_Op_free(MPI_Op *op)

🎀 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_OP_FREE(OP, IERROR)
     INTEGER OP, IERROR

🎀 Fortran 2008 Syntax

USE mpi_f08
MPI_Op_free(op, ierror)
     TYPE(MPI_Op), INTENT(INOUT) :: op
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🦋 INPUT/OUTPUT PARAMETER 🦋

• op — the operation handle, and yeah it's input and output because it comes in as your op and leaves as... not that bestie 💀 (see below, it's giving glow-down to MPI_OP_NULL)

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⭐ OUTPUT PARAMETER ⭐

• ierror — Fortran only, and it's the error status (an integer, obviously 💅)

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👑 DESCRIPTION 👑

So basically: it marks a user-defined reduction operation for deallocation, and then it sets op to MPI_OP_NULL. That's it. That's the whole vibe. Cleanup era 🧹✨

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🔥 ERRORS 🔥

Okay bestie, sit with me for a sec because this part is long but it's important 🌈

Almost all MPI routines return an error value, yeah? And where it shows up depends on the language:

• C routines: it's the return result of the function itself
• Fortran routines: it's in the last argument

Now — before that error value even gets handed back to you, the current MPI error handler associated with the communication object (think: 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 it'll call the associated MPI error handler instead.

And here's the plot twist 😭 — when MPI_COMM_SELF is not initialized (which is: 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. You can change that initial error handler by:

• calling MPI_Comm_set_errhandler on MPI_COMM_SELF when you're 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

And 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. No cap.

💜 The Three Predefined Error Handlers 💜

Open MPI ships three of these, and they're iconic:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. Dramatic? Yes. Effective? Also yes 💀
• MPI_ERRORS_ABORT — an error handler that can be invoked on a communicator, window, file, or session. When it's called on a communicator, it acts as if MPI_Abort was called on that communicator. If it's 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. And if it's called on a session, it aborts only the local process 🫶
• MPI_ERRORS_RETURN — returns an error code to the application. Chill vibes, no chaos 🌸

🧚 Make Your Own, Bestie 🧚

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

🚨 Real talk though: note that MPI does not guarantee that an MPI program can continue past an error. Like, that's a genuine caveat, not me being cute. Plan accordingly 🙈

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 info 📚

🍓 See Also 🍓

• MPI_Op_create
• MPI_Reduce
• MPI_Allreduce
• MPI_Reduce_scatter
• MPI_Scan

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🎀 Copyright 🎀

2003-2026, The Open MPI Community

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k that's the whole page bestie, you're officially an MPI_Op_free girlie now 💅 This was MPI_OP_FREE(3) from the Open MPI manual, dated Sep 10, 2026, and it's all © 2003-2026, The Open MPI Community. Free your ops, free yourself 🦋✨