MPI_COMM_REMOTE_SIZE(3)

💖 MPI_COMM_REMOTE_SIZE(3) 💖

okay bestie, welcome to the Open MPI manual, and today's main character is MPI_Comm_remote_size — the lil function that tells you how big the remote group of an intercommunicator is. yes queen, we're counting processes across the gap 👑

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✨ NAME ✨

MPI_Comm_remote_size — Determines the size of the remote group associated with an intercommunicator.

like it literally just checks how many friends are on the other side of the intercomm 🫶

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✨ SYNTAX ✨

🌸 C Syntax

#include <mpi.h>

int MPI_Comm_remote_size(MPI_Comm comm, int *size)

🌸 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_COMM_REMOTE_SIZE(COMM, SIZE, IERROR)
     INTEGER COMM, SIZE, IERROR

🌸 Fortran 2008 Syntax

USE mpi_f08
MPI_Comm_remote_size(comm, size, ierror)
     TYPE(MPI_Comm), INTENT(IN) :: comm
     INTEGER, INTENT(OUT) :: size
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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✨ INPUT PARAMETER ✨

• comm — Communicator (handle). the vibes container, if you will 🎀

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✨ OUTPUT PARAMETERS ✨

• size — Number of processes in the remote group of comm (integer). that's the headcount, bestie 🔥
• ierror — Fortran only: Error status (integer). Fortran girlies get a whole extra slot for the drama 💅

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✨ DESCRIPTION ✨

MPI_Comm_remote_size determines the size of the remote group associated with an intercommunicator. periodt. that's the whole job and she does it flawlessly 💖

The intercommunicator accessors (MPI_Comm_test_inter, MPI_Comm_remote_size, MPI_Comm_remote_group) are all local operations. like, no cap, they're local — no network chatter, no waiting on anybody, they just know ✨

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✨ ERRORS ✨

Almost all MPI routines return an error value; C routines as the return result of the function and Fortran routines in the last argument. iykyk 🙈

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. it's giving nuclear option 💀
• 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. the polite one, she hands you the receipt 🧾

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 just keep going and hope bestie, fr fr 😭

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_test_inter
• MPI_Comm_remote_group
• MPI_Intercomm_create
• MPI_Intercomm_merge

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✨ Copyright ✨

2003-2026, The Open MPI Community 👑

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and that's the whole page, bestie!! 💜 this was pulled straight from Open MPI's docs, dated Sep 10, 2026 — the manual page for MPI_COMM_REMOTE_SIZE(3), which is exactly what it says on the tin. go forth and count your remote processes, you icon 🦋🌸💅