MPI_Comm_accept(3OpenMPI)

💖 MPI_Comm_accept — the Open MPI glow-up edition 💖

okay bestie, welcome to MPI_Comm_accept(3OpenMPI), straight outta the Open MPI fam. this is the page where your root node sits by the phone waiting for a client to hit it up, and honestly? it's giving "waiting for your situationship to text back" but make it parallel computing. ✨

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🌸 NAME 🌸

MPI_Comm_accept — establishes communication with a client. that's it, that's the whole job. 🫶

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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

🎀 C++ Syntax

#include <mpi.h>
MPI::Intercomm MPI::Intracomm::Accept(const char* port_name,
     const MPI::Info& info, int root) const

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🌈 INPUT PARAMETERS 🌈

• port_name — the port name, bestie. it's a string, and heads up: it's used only on root. so everybody else in comm can just vibe, this one's on the root node.
• info — options that root is passing in for the accept. it's a handle, and again, used only on root. and the tea? no options are currently supported. it's giving "we built the field but left it empty" 😭
• root — the rank in comm of the root node. an integer. this is your main character for this call. 👑
• comm — the intracommunicator that this whole call is collective over. a handle. everybody in it is in on this together, no solo acts. 💅

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💜 OUTPUT PARAMETERS 💜

• newcomm — an intercommunicator where the client is the remote group. a handle. this is the little connection y'all just made. 🦋
• IERROR — Fortran only: the error status, as an integer. the "did it work tho" report card. 📝

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🧚 DESCRIPTION 🧚

so like, MPI_Comm_accept establishes communication with a client. that's the whole vibe. it's collective over the calling communicator — meaning every process in comm has to show up, no ghosting, no "sorry I was busy."

it hands you back an intercommunicator that lets you talk to the client. and when does the client show up? after the client has connected with the MPI_Comm_accept function using the MPI_Comm_connect function. yes bestie, connect on one side, accept on the other. it's a two-way thing, like any good friendship. 🫶

the port_name? it must have been established through a call to MPI_Open_port on the root. so you can't just make up a port name out of thin air, that's not how this works, that's not how any of this works. 💀

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😭 ERRORS 😭

almost all MPI routines return an error value, okay? here's the breakdown so you're not caught off guard:

• C routines: the error value is the return value of the function.
• Fortran routines: it lands in the last argument.
• C++ functions: they do not return errors. periodt.

and if the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object. so C++ besties, get ready to catch. 🙈

before the error value is returned, the current MPI error handler gets called. by default, this error handler aborts the MPI job — except for I/O function errors, those get a pass. the error handler may be changed with MPI_Comm_set_errhandler, and the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. so like, if you don't want the whole job to just perish, MPI_ERRORS_RETURN is your girl. 💅

see the MPI man page for a full list of MPI error codes. iykyk. 📖

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🔥 SEE ALSO 🔥

• MPI_Comm_connect
• MPI_Open_port

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and that's the page, bestie! 🎀 this whole thing is Open MPI version 4.1.6, dated Sep 30, 2023, and yes it's the MPI_Comm_accept(3OpenMPI) manual page, iconic as ever. now go accept that connection — you got this, no cap. 💖✨🦋👑