MPI_COMM_DELETE_ATTR(3)

💖 MPI_COMM_DELETE_ATTR 💖

okay bestie, so this one is from the Open MPI manual, section 3 (that's the library-calls girlies, not the commands). Let's get into it 🫶

✨ NAME ✨

MPI_Comm_delete_attr — literally deletes the attribute value that's associated with a key. bye bye attribute 💅

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✨ SYNTAX ✨

🌸 C Syntax 🌸

#include <mpi.h>

int MPI_Comm_delete_attr(MPI_Comm comm, int comm_keyval)

🌸 Fortran Syntax 🌸

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

MPI_COMM_DELETE_ATTR(COMM, COMM_KEYVAL, IERROR)
    INTEGER COMM, COMM_KEYVAL, IERROR

🌸 Fortran 2008 Syntax 🌸

USE mpi_f08

MPI_Comm_delete_attr(comm, comm_keyval, ierror)
    TYPE(MPI_Comm), INTENT(IN) :: comm
    INTEGER, INTENT(IN) :: comm_keyval
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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✨ PARAMETERS ✨

🌈 INPUT/OUTPUT PARAMETER 🌈

• comm — the communicator you're deleting the attribute from (it's a handle, bestie).

🌈 INPUT PARAMETER 🌈

• comm_keyval — the key value, and it's an integer.

🌈 OUTPUT PARAMETER 🌈

• ierror — Fortran only: your error status (integer).

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✨ DESCRIPTION ✨

So MPI_Comm_delete_attr deletes an attribute out of the cache, by key. ✨ And here's the part that matters: this function invokes the attribute delete function delete_fn that you specified back when the comm_keyval was created. And if that delete_fn returns an error code that isn't MPI_SUCCESS? The call fails. no cap 😭

Whenever a communicator gets replicated using MPI_Comm_dup, all the callback copy functions for attributes that are currently set get invoked (in arbitrary order, so don't come for the ordering, it's not promised). And whenever a communicator is deleted using MPI_Comm_free, all the callback delete functions for attributes that are currently set get invoked.

This function is the same as MPI_Attr_delete, but it's needed so everything matches the communicator-specific functions that the MPI-2 standard introduced. Also: using MPI_Attr_delete is deprecated, so pls don't 👑 The MPI_Attr_delete of it all is giving 2002, periodt.

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✨ NOTES ✨

Heads up bestie: the MPI standard does not define what happens if the delete_fn callback invokes other MPI functions. Undefined behaviour, truly iconic in a terrifying way 💀

In Open MPI specifically, it is not valid for delete_fn callbacks (or any of their children) to add or delete attributes on the same object that the delete_fn callback is being invoked on. just don't 🚫

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✨ ERRORS ✨

Almost all MPI routines return an error value. C routines give it back as the return result of the function, Fortran routines put it in the last argument. classic 💅

Before that error value gets returned, the current MPI error handler associated with the communication object (like a communicator, window, or file) is called. And if there's no communication object associated with the MPI call, then the call counts as attached to MPI_COMM_SELF and will call the associated MPI error handler. But when MPI_COMM_SELF isn't initialized (like, 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 instead 🌱

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 via the mpi_initial_errhandler CLI argument to mpiexec, or via an info key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. And 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.

🦋 The three predefined error handlers 🦋

Open MPI ships three of them, ready to go:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. dramatic AND effective 💀
• MPI_ERRORS_ABORT — an error handler you can invoke 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. the chill one 🫶

🦋 DIY error handlers 🦋

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. so like. 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 information 📚

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✨ COPYRIGHT ✨

2003-2026, The Open MPI Community

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and that's the whole page, bestie!! 🎀 this Open MPI page is dated Sep 10, 2026 and it slid into your terminal courtesy of the Open MPI girlies — go delete those attributes responsibly, mwah 💖🦋✨