MPI_COMM_CONNECT(3)

💫 MPI_Comm_connect — Open MPI manual page, bestie edition 💫

okay so this is the MPI_COMM_CONNECT(3) page from the Open MPI manual set, and honestly? it's giving "networking but make it MPI." let's get into it 🫶

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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 — the port name, a string, and it's only used on root. that's the address of the server, bestie.
• info — options that root hands over for the connect, a handle, also only used on root. heads up: no options are currently supported 🙈
• root — the rank in comm of the root node, an integer.
• comm — the intracommunicator that this whole call is collective over, a handle.

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💅 OUTPUT PARAMETERS 💅

• newcomm — an intercommunicator where the client is the remote group, a handle. this is the new bestie connection ✨
• ierror — Fortran only: the error status, an integer.

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🎀 DESCRIPTION 🎀

so MPI_Comm_connect literally establishes communication with a server that you point at with port_name. iconic. it's collective over the calling communicator, and it returns an intercommunicator where the remote group participated in an MPI_Comm_accept. periodt.

🚨 important ordering tea: 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. don't jump the queue, bestie.

if the named port doesn't exist (or has already been closed), MPI_Comm_connect raises an error of class MPI_ERR_PORT 😭

and ngl, MPI provides no guarantee of fairness in servicing connection attempts. meaning: 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. it's giving rush hour at the port, fr fr 💀

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. match it exactly, no improvising 👑

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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). we're so serious about this one 🫠

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. okay that was a lot, but it all matters 💖

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 effective 💀
• 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, it 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, it aborts only the local process. choose your fighter ✨
• 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, don't assume you can just walk it off 😭

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_accept — the other half of this whole handshake situation, iykyk 👑

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📜 COPYRIGHT 📜

2003-2026, The Open MPI Community

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and that's the page, bestie! slay 💖 this was the MPI_COMM_CONNECT(3) page, dated Sep 11, 2026, from the Open MPI crew — go connect to something iconic 🎀✨