MPI_COMM_ACCEPT(3)

💖 MPI_COMM_ACCEPT(3) 💖

okay bestie, welcome to the Open MPI manual, page MPI_COMM_ACCEPT(3). this is the one where you make friends with a client. it's giving ✨networking✨ but make it MPI.

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🌸 NAME 🌸

MPI_Comm_accept — establishes communication with a client. that's it, that's the whole vibe. it's the "yes hello i will take your call" of MPI 🫶

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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

no cap, that's three whole dialects of the same call. pick your fighter 💅

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📥 INPUT PARAMETERS 📥

• port_name — the port name. it's a string, and it's used only on root. so like, nobody else needs to know about it, it's root's little secret 🤫
• info — options given by root for the accept. it's a handle</color>... wait, no, it's a handle, and it's used only on root. also: no options are currently supported. so it's giving "we made a parameter and it does nothing yet" 🙈
• root — the rank in comm of the root node. it's an integer. this is the main character of this whole operation 👑
• comm — the intracommunicator over which this call is collective. it's a handle. everybody on this communicator is in on it together, fr fr 🤝

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📤 OUTPUT PARAMETERS 📤

• newcomm — an intercommunicator with the client as the remote group. it's a handle. this is your shiny new connection to the client 🦋
• ierror — Fortran only: error status. it's an integer. Fortran besties get their errors in the last argument, that's just how it is 💜

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🌈 DESCRIPTION 🌈

MPI_Comm_accept establishes communication with a client. periodt.

it is collective over the calling communicator — meaning everyone on comm has to show up, no ghosting 👻

it returns an intercommunicator that lets you communicate with the client, after the client has connected using MPI_Comm_connect. so the client calls MPI_Comm_connect, you call MPI_Comm_accept, and then it's a whole thing. it takes two, okay 😭

and the port_name? that must have been established through a call to MPI_Open_port on the root. no port, no party. the port has to come from root via MPI_Open_port, that's the rule 🎀

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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). so like. bestie. launch it with mpirun/mpiexec or it might just hang forever and you'll be staring at your terminal like 💀

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:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. yeah, everybody. it's a total shutdown, no survivors 😭
• 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. so it's context-dependent, iykyk.
• MPI_ERRORS_RETURN — returns an error code to the application. the chill one. it just hands you the error and lets you deal with 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

build your own, main character energy 🔥

Note that MPI does not guarantee that an MPI program can continue past an error. like, it might just be over. don't count on recovery 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_Comm_connect

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📜 Copyright

2003-2026, The Open MPI Community

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and that's the whole page babes 🎀 this was Open MPI's MPI_COMM_ACCEPT(3), last touched Sep 10, 2026. go accept some clients, you absolute icon 👑✨💖