MPI_COMM_DISCONNECT(3)

💅 MPI_COMM_DISCONNECT(3) — an Open MPI moment ✨

okay so bestie, welcome to MPI_COMM_DISCONNECT(3) from the Open MPI girlies 🫶 this one's literally about yeeting a communicator into the void and setting its handle to MPI_COMM_NULL, and it's so iconic of it honestly.

🌸 NAME 🌸

MPI_Comm_disconnect — deallocates a communicator object and sets the handle to MPI_COMM_NULL. that's it. that's the whole vibe. 💅

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✨ SYNTAX ✨

🎀 C Syntax

#include <mpi.h>

int MPI_Comm_disconnect(MPI_Comm *comm)

🦋 Fortran Syntax

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

MPI_COMM_DISCONNECT(COMM, IERROR)
    INTEGER COMM, IERROR

🌈 Fortran 2008 Syntax

USE mpi_f08

MPI_Comm_disconnect(comm, ierror)
    TYPE(MPI_Comm), INTENT(INOUT) :: comm
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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💖 INPUT/OUTPUT PARAMETER 💖

• comm — the communicator, aka the handle. that's the one getting disconnected, no cap.

🍓 OUTPUT PARAMETER 🍓

• ierror — Fortran only bestie: the error status, and it's an integer. ✨

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🔥 DESCRIPTION 🔥

so what does MPI_Comm_disconnect actually do? it waits for all pending communication on comm to complete internally, then deallocates the communicator object, and then sets the handle to MPI_COMM_NULL. three steps, all slay, all in that order. 👑

it is a collective operation. meaning everybody's in on it, group-chat style, no lurking.

⚠️ heads up: it may not be called with the communicator MPI_COMM_WORLD or MPI_COMM_SELF. those two are not the vibe for this, fr fr.

MPI_Comm_disconnect may be called only if all communication is complete and matched, so that buffered data can be delivered to its destination. this requirement is literally the same as for MPI_Finalize. so like, don't be messy about it. 😭

and here's the tea: MPI_Comm_disconnect has the same action as MPI_Comm_free, except that it waits for pending communication to finish internally AND enables the guarantee about the behavior of disconnected processes. so it's MPI_Comm_free but with extra steps and also extra guarantees. highkey the upgrade. ⭐

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🧚 NOTES 🧚

to disconnect two processes, you may need to call MPI_Comm_disconnect, MPI_Win_free, and MPI_File_close to remove all communication paths between the two processes. all of them. every last one. 🫶

note that it may be necessary to disconnect several communicators (or to free several windows or files) before two processes are completely independent. like, sometimes you gotta do the whole cleanup arc before anyone's actually free. main character energy is doing the work. 💜

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💀 ERRORS 💀

almost all MPI routines return an error value, bestie. C routines as the return result of the function, and Fortran routines in the last argument. both valid, both documented, we respect both.

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 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. dramatic but make it fatal. 💀
• 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. it's giving versatile. 🔥
• 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. so like, plan accordingly. no cap.

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_connect

the one and only cross-reference, and she ate. 💅

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🎀 COPYRIGHT 🎀

2003-2026, The Open MPI Community

and that's the whole page bestie!! 🌈🦋🍓 this was MPI_COMM_DISCONNECT(3) from Open MPI, dated Sep 11, 2026 — go disconnect something responsibly, ily, bye 💖✨🎀