MPI_COMM_ACCEPT(3)

💅 MPI_Comm_accept 💅

okay so we're deep in the Open MPI manual bestie, and this one is genuinely iconic — it's the " answer the phone" half of the whole client/server situation 🎀

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🌸 NAME 🌸

MPI_Comm_accept — Establishes communication with a client.

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✨ SYNTAX ✨

🩵 C Syntax

#include <mpi.h>

int MPI_Comm_accept(const char *port_name, MPI_Info info, int root, MPI_Comm comm, MPI_Comm *newcomm)

💜 Fortran Syntax

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

MPI_COMM_ACCEPT(PORT_NAME, INFO, ROOT, COMM, NEWCOMM, IERROR)
    CHARACTER*(*)   PORT_NAME
    INTEGER     INFO, ROOT, COMM, NEWCOMM, IERROR

🦋 Fortran 2008 Syntax

USE mpi_f08

MPI_Comm_accept(port_name, info, root, comm, newcomm, ierror)
    CHARACTER(LEN=*), INTENT(IN) :: port_name
    TYPE(MPI_Info), INTENT(IN) :: info
    INTEGER, INTENT(IN) :: root
    TYPE(MPI_Comm), INTENT(IN) :: comm
    TYPE(MPI_Comm), INTENT(OUT) :: newcomm
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🌈 INPUT PARAMETERS 🌈

• port_name : the port name (string, used only on root) — it's the little name tag your client is gonna dial, so keep it cute
• info : options given by root for the accept (handle, used only on root). ngl there are no options currently supported, so it's giving decorative
• root : rank in comm of the root node (integer) — this is the main character who actually does the accepting
• comm : intracommunicator over which the call is collective (handle) — everybody in it has to show up, no ghosting 🫶

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💖 OUTPUT PARAMETERS 💖

• newcomm : intercommunicator with client as remote group (handle) 🔥
• ierror : Fortran only: error status (integer).

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👑 DESCRIPTION 👑

MPI_Comm_accept establishes communication with a client. It is collective over the calling communicator — so like, everyone in comm, we're all doing this together periodt. It returns an intercommunicator that allows communication with the client, after the client has connected with the MPI_Comm_accept function using the MPI_Comm_connect function. And the port_name must have been established through a call to MPI_Open_port on the root — like you can't just make up a port name bestie, it has to have been opened first 💅

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💀 ERRORS 💀

Important 🚨 In Open MPI, this function only works properly when the MPI job is launched via mpirun / mpiexec. Using this function in other run-time environments is currently unsupported, and may result in undefined behavior (e.g., the MPI job may hang). yes literally hang. do not test this fr fr 😭

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 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 — collect all three, they're lowkey essential:

• MPI_ERRORS_ARE_FATAL — Causes the program to abort all connected MPI processes. everyone. gone. dramatic but fair 💀
• 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.
• MPI_ERRORS_RETURN — Returns an error code to the application.

MPI applications can also implement their own error handlers by calling — build-your-own, we love a DIY era ✨

• 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. like, it might just be over 😭

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 other half of this whole situation, go read it iykyk

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🎀 COPYRIGHT 🎀

2003-2026, The Open MPI Community

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okay and for the cute sign-off: this whole masterpiece was dated Sep 11, 2026 and lives on the MPI_COMM_ACCEPT(3) page of the Open MPI manual — go forth and accept those connections bestie, slay, no cap 💖🌸🫶