MPI_COMM_CONNECT(3)

💖 MPI_COMM_CONNECT(3) 💖

okay bestie, welcome to the Open MPI corner of the manual, page MPI_COMM_CONNECT(3) — she's the one who slides into the server's DMs and sets up a whole relationship. let's get into it ✨

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🌸 NAME 🌸

MPI_Comm_connect — Establishes communication with a server.

no cap, that's literally the whole vibe: you wanna talk to a server, this is the call that makes it happen 🫶

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✨ SYNTAX ✨

🎀 C Syntax

#include <mpi.h>

int MPI_Comm_connect(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_CONNECT(PORT_NAME, INFO, ROOT, COMM, NEWCOMM, IERROR)
    CHARACTER*(*)   PORT_NAME
    INTEGER     INFO, ROOT, COMM, NEWCOMM, IERROR

🎀 Fortran 2008 Syntax

USE mpi_f08

MPI_Comm_connect(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 — Port name (string, used only on root). this is the server's address bestie, and only the root process needs to know it 👑
• info — Options given by root for the connect (handle, used only on root). No options currently supported. yeah she's giving empty-handed but we respect her 💅
• root — Rank in comm of root node (integer).
• comm — Intracommunicator over which call is collective (handle). it's a group effort, everybody shows up 🫶

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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 🦋

So the tea is: MPI_Comm_connect establishes communication with a server specified by port_name. It is collective over the calling communicator and returns an intercommunicator in which the remote group participated in an MPI_Comm_accept.

and listen, the timing matters, periodt — the MPI_Comm_connect call must only be called after the MPI_Comm_accept call has been made by the MPI job acting as the server. like, you can't text first if they haven't even opened the chat 😭

If the named port does not exist (or has been closed), MPI_Comm_connect raises an error of class MPI_ERR_PORT. 💀

MPI provides no guarantee of fairness in servicing connection attempts. That is, connection attempts are not necessarily satisfied in the order in which they were initiated, and competition from other connection attempts may prevent a particular connection attempt from being satisfied. so it's lowkey a chaotic group chat, not a queue, iykyk 🙈

The port_name parameter is the address of the server. It must be the same as the name returned by MPI_Open_port on the server. same name, no improvising, fr fr 🌟

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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). like bestie she needs her launch environment or she's just gonna sit there and stare at you 😭

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. 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.
• MPI_ERRORS_RETURN — Returns an error code to the application.

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. like, no promises 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_accept

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👑 Copyright 👑

2003-2026, The Open MPI Community

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and that's the whole page, bestie!! shoutout to the Open MPI girlies who wrote this one, dated Sep 10, 2026, filed under MPI_COMM_CONNECT(3) — go connect with your servers responsibly, mwah 🎀💖✨