MPI_FINALIZE(3)

📦
version 5.0.10 · 7 versions
, in ubuntu stonking

💖 NAME 💖

MPI_Finalize — it terminates the MPI world model. that's it, that's the job, and it does it flawlessly 👑

✨ SYNTAX ✨

🌸 C Syntax

#include <mpi.h>

int MPI_Finalize()

🌸 Fortran Syntax

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

MPI_FINALIZE(IERROR)
    INTEGER IERROR

🌸 Fortran 2008 Syntax

USE mpi_f08

MPI_Finalize(ierror)
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

🎀 OUTPUT PARAMETER 🎀

  • ierror — Fortran besties only: the error status, and it's an integer. that's the whole vibe 💖

🦋 DESCRIPTION 🦋

okay so. this routine finalizes the MPI world model. If the MPI world model was initialized in your MPI process, then it must be finalized exactly once by invoking this routine somewhere during the lifetime of that process. once. not twice. not zero times. we are not doing that today. 🫶

and that is different from the MPI session model, which can be initialized and finalized multiple times inside one MPI process. See MPI_Session_init and MPI_Session_finalize for that whole other situation ✨

Unless there's been a call to MPI_Abort, you have to make sure that all pending communications in the MPI world model that involve a process are complete before that process calls MPI_Finalize. If the call returns, each process can either keep doing local computations or just exit, without participating in any further communication with other processes in the MPI world model. And here's the moment of truth: at the moment when the last process calls MPI_Finalize, all pending sends in the MPI world model must be matched by a receive, and all pending receives in the MPI world model must be matched by a send. no loose ends, periodt 💅

See MPI-5.0:11.4.1 for a list of MPI functionality that is available (e.g., even when the MPI world model hasn't been initialized yet, or has already been finalized). lowkey iconic that some things just keep working 🌈

MPI_Finalize is collective over all connected processes. If no processes were spawned, accepted, or connected, then that means it's collective over MPI_COMM_WORLD. Otherwise, it's collective over the union of all processes that have been and continue to be connected. the whole group chat has to show up, fr fr 😭

💜 NOTES 💜

The MPI session model is different from the MPI world model, and it has different scopes of availability for MPI functionality. See MPI_Session_init and MPI_Session_finalize. two models, two vibes, don't mix them up 🧚

All processes that initialized the MPI world model must call this routine before exiting. All processes will still exist, but they may not make any further MPI calls in the MPI world model. MPI_Finalize guarantees that all local actions required by communications in the MPI world model that the user has completed will, in fact, occur before it returns. However — and this is the part everyone ignores — MPI_Finalize guarantees nothing about pending communications in the MPI world model that have not been completed. completion is only ensured by the MPI_Wait and MPI_Test variants, or by MPI_Request_free combined with some other verification of completion. so like. don't assume. 🙈

For example: a successful return from a blocking communication operation, or from one of the MPI_Wait or MPI_Test variants, means the communication is completed by the user and the buffer can be reused — but it does not guarantee that the local process has no more work to do. Similarly, a successful return from MPI_Request_free with a request handle generated by an MPI_Isend nullifies the handle but does not guarantee that the operation has completed. The MPI_Isend is complete only when a matching receive has completed. read that one again, bestie, it's giving "subtle but important" 💀

If you'd like to cause actions to happen when a process finalizes the MPI world model, attach an attribute to MPI_COMM_SELF with a callback function. Then, when MPI_Finalize is called, it will first execute the equivalent of an MPI_Comm_free on MPI_COMM_SELF. This will cause the delete callback function to be executed on all keys associated with MPI_COMM_SELF in an arbitrary order. If no key has been attached to MPI_COMM_SELF, then no callback is invoked. This freeing of MPI_COMM_SELF happens before any other parts of the MPI world model are affected. Calling MPI_Finalized will thus return false in any of these callback functions. And once you've done this with MPI_COMM_SELF, the results of MPI_Finalize are not specified — so like, tread carefully, that's undefined behaviour territory ⚠️

🚨 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.

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 the 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. yeah. everyone. the whole server. 💀
  • 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. only the local one, slay 🌈
  • MPI_ERRORS_RETURN — Returns an error code to the application. polite behaviour, we love to see it 🎀

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. it just doesn't, bestie 😭

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.

See also:

  • MPI_Finalized
  • MPI_Init
  • MPI_Initialized
  • MPI_Session_init
  • MPI_Session_finalize

Copyright 2003-2026, The Open MPI Community.

and that's the tea, bestie 💖 you just read MPI_Finalize(3) from the Open MPI manual, dated Sep 10, 2026, and the copyright is held by The Open MPI Community, 2003-2026. go forth and finalize responsibly, and remember: exactly once. i'm so serious. ✨👑💅

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