MPI_TOPO_TEST(3)

🎀 NAME 🎀

MPI_Topo_test — bestie, this one tells you what kind of topology (if any 💀) your communicator is out here repping. It's from the Open MPI manual, page MPI_TOPO_TEST(3).

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✨ SYNTAX ✨

🍓 C Syntax

#include <mpi.h>

int MPI_Topo_test(MPI_Comm comm, int *top_type)

🍓 Fortran Syntax

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

🍓 Fortran 2008 Syntax

USE mpi_f08
MPI_Topo_test(comm, status, ierror)
     TYPE(MPI_Comm), INTENT(IN) :: comm
     INTEGER, INTENT(OUT) :: status
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
             DOUBLE PRECISION MPI_Wtick()
             DOUBLE PRECISION MPI_Wtime()

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💜 INPUT PARAMETER 💜

• comm — the communicator, aka a handle. That's the one and only input, slay.

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🌈 OUTPUT PARAMETERS 🌈

• top_type — the topology type of the communicator comm, and it's a choice. Yes queen, you get options.
• ierror — Fortran only: error status (integer). C girlies, this one isn't for you.

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👑 DESCRIPTION 👑

The function MPI_Topo_test returns the type of topology that is assigned to a communicator. That's it, that's the whole job, and honestly? Iconic. 💅

The output value top_type is one of the following:

• MPI_GRAPH — graph topology 🌸
• MPI_CART — Cartesian topology 🦋
• MPI_DIST_GRAPH — distributed graph topology ⭐
• MPI_UNDEFINED — no topology at all 💀 (vibe check: empty, no cap)

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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. Keep track of which one you're in, bestie, this matters.

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. So dramatic, and yet so final. 🫶
• 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. So like... don't just yolo past it, okay 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_Graph_create
• MPI_Cart_create

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🦋 COPYRIGHT 🦋

2003-2026, The Open MPI Community

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And that's the whole page, fr fr 💖 this was MPI_TOPO_TEST(3) from Open MPI, dated Sep 10, 2026 — go forth and topology-test your communicators, you absolute main character. 🧚👑🌸