MPI_TYPE_COMMIT(3)

🎀 MPI_Type_commit 🎀

okay bestie, welcome to the Open MPI manual page for MPI_Type_commit — this is literally the moment your fancy custom datatype goes from "cute idea" to "actually usable" 💅✨

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✨ SYNTAX ✨

💜 C Syntax

#include <mpi.h>

int MPI_Type_commit(MPI_Datatype *datatype)

💜 Fortran Syntax

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

💜 Fortran 2008 Syntax

USE mpi_f08
MPI_Type_commit(datatype, ierror)
     TYPE(MPI_Datatype), INTENT(INOUT) :: datatype
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🌸 INPUT PARAMETER 🌸

• datatype — your datatype handle, aka the little guy you built and now want to make official 🫶

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🦋 OUTPUT PARAMETER 🦋

• ierror — Fortran only: the error status, as an integer. slay, Fortran stays keeping receipts 📝

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👑 DESCRIPTION 👑

so the commit operation commits the data type, which is the whole point. and here's the vibe check you need to internalize: a data type is the formal description of a communication buffer, NOT the content of that buffer. like, it's the blueprint, not the house 🏠✨

once a data type has been committed, you can reuse it over and over again — to communicate the changing content of a buffer, or honestly the content of completely different buffers with different starting addresses. it's giving reusable tote bag energy, no cap ♻️

Example: the following Fortran code fragment gives examples of using MPI_Type_commit.

INTEGER :: type1, type2
CALL MPI_TYPE_CONTIGUOUS(5, MPI_REAL, type1, ierr)
              ! new type object created
CALL MPI_TYPE_COMMIT(type1, ierr)
              ! now type1 can be used for communication

and the iconique little detail: if the data type specified in datatype is already committed, it's equivalent to a no-op. literally nothing happens. it's fine. go off 💀

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💀 ERRORS 💀

almost all MPI routines return an error value — the C routines hand it back as the return result of the function, and the Fortran routines put it in the last argument. iykyk 🔥

before that error value gets returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. and if there's no communication object associated with the MPI call? then the call is considered attached to MPI_COMM_SELF and it'll 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. phew, still with me? 🫠

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. them's the rules ⭐

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? yes. effective? also yes 💀
• 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. versatile queen 👑
• 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. no cap, fr fr — 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 — you're officially certified to commit datatypes 💖 this was the Open MPI MPI_TYPE_COMMIT(3) manual page, dated Sep 11, 2026, brought to you by The Open MPI Community (copyright 2003-2026). go forth and communicate 🧚‍♀️✨🍓